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Heat is generated as a byproduct of the electrochemical reactions of a polymer electrolyte membrane fuel cell. This heat raises the temperature of the system, and if it is not properly removed from the cell, it can cause membrane damage and overheating. Thermal management is thus critical for PEM fuel cell stability, efficiency, and safety. This paper investigates the potential use of NiFe 2 O 4 -water nanofluid as a novel coolant for PEM fuel cells. To determine the nanofluid thermophysical properties, an experimental study for different mass% concentrations of NiFe 2 O 4 -water nanofluid is first performed. Then, a three-dimensional CFD model is built to demonstrate the effect of nanofluid use on the thermal performance of a cooling plate. Simulation results show that replacing water with 0.5% NiFe 2 O 4 nanofluid improves temperature uniformity by 11.97%. Furthermore, nanofluid cooling reduces maximum surface temperature by up to 0.75 °C while increasing pressure drop by 5.6%, implying higher pumping power. [Display omitted] • A novel nanofluid (NiFe 2 O 4 -water) as a coolant for PEM fuel cells. • Thermophysical properties of nanofluid obtained experimentally for CFD analysis. • Variable heat flux was applied to represent PEM fuel cell heat generation. • Increased temperature uniformity by 11.97%. [ABSTRACT FROM AUTHOR]

A load-type supersonic fluidic oscillator has potential application for introducing small oscillations in the chamber of a superplastic forming process to improve performance. This paper presents a study of a special bi-stable load-type supersonic fluidic oscillator capable of simultaneously producing self-sustained oscillations in two gas pressure chambers during their filling at high-pressure. The experimental portion of the work verifies the robust nature of the device performance. Distinct differences, however, are observed compared to those previously shown for a similar prototype supplying pressure fluctuations to a single chamber at low pressure. It is also found that a three-dimensional computational fluid dynamics model is required to accurately simulate the transient filling process of the current oscillator facility, unlike the previous case. This leads to an unaffordable computational cost. To address this issue, a low-order fluid circuit model is developed. This simplified approach is based on a quasi-steady assumption and is of the same form as the one which accurately predicts the performance of the previous prototype. The model is "numerically empirical" in that the model parameters are determined using steady state 3D-CFD analysis rather than physical experiments. The circuit model combined with a lumped parameter numerical model of tank filling with realistic heat transfer to the surroundings provides an accurate and rapid prediction of the transient performance of the device. Also, the usefulness of the circuit model as an industrial design tool is demonstrated by predicting the effect of two design changes. • Experimental data for pulsatile pressurization of a chamber using a supersonic fluidic oscillator. • Transient 3D CFD solution is used along with experimental results to explain the supersonic fluidic oscillator performance. • A lumped-parameter model using steady 3D CFD generated parameters accurately describes the transient filling process. • Lumped-parameter model is used to investigate oscillator design modifications. [ABSTRACT FROM AUTHOR]

Slurry bubble columns (SBCs) are used industrially in various applications because of their advantages. In spite of the simple construction of the SBCs, their scale-up analyses are complex due to the effect of various parameters on the hydrodynamic and heat transfer rates in these columns. In SBCs, Direct Contact Heat Transfer (DCHT) includes a highly complicated process of the gas flow through the slurry. In this paper, the slurry and gas temperature profiles of the DCHT process in a SBC with a high temperature gas, is investigated by using Computational Fluid Dynamics (CFD) simulations. The case study that is examined in this paper, is injecting a helium gas at 363 K through a slurry of water liquid and alumina solid particles at 295 K. The CFD simulations of the temperature distributions are performed for churn-turbulent flow regime only. In this paper, different factors that can affect the temperature profiles of the slurry and gas are studied, such as: the superficial gas velocity (U gs), static liquid height (H), and solid particles concentration (C s). From the results of this paper, it is found that the average slurry temperature decreases by decreasing U g s and increases by decreasing H and/or C s at any given U gs. In addition, it is noted that the decrease rate of the slurry temperature with increasing the solid concentration is insignificant. The results also show that the gas temperature decreases significantly near the bottom of the column, and the effects of U gs , H and C s on gas temperature are negligible. • CFD analyses were performed to study the DCHT in a SBCR for a churn-turbulent flow regime. • The average slurry temperature and gas temperature profiles were calculated. • The effect of solid concentration on slurry temperature is negligible. • The gas temperature decreases rapidly in the region immediately above the sparger. • The effect of superficial gas velocity on gas temperature is negligible. [ABSTRACT FROM AUTHOR]

The working principle for the energy separation observed in a Ranque–Hilsch Vortex Tube (RHVT) is a matter that is widely debated and unsettled. It is, however, indisputable that modifications to the tube geometry can substantially affect the performance of the tube. In this paper, a three-dimensional computational fluid dynamic study is performed to investigate the enhanced performance of a geometrically modified vortex tube by studying the flow structure, heat transfer, and energy separation. The novel vortex tube is modeled in ANSYS FLUENT, similar to the original device: 3D Steady-state flow analysis using the standard k- ϵ turbulence model on a hybrid mesh. The results acquired are compared and found to demonstrate the increase in the observed energy separation in the novel geometry. The total increase in thermal separation for the novel design is observed to be 15.1 K at 0.9 Cold Mass Fraction, with an increase of 10 W in overall energy transfer. Compared to the nominal design, a maximum of 13.74 percent improvement in thermal separation. Furthermore, the flow structures are compared to understand the reason behind the increased performance. It is found that the factors responsible for the extent of separation of energy in the tube are: Higher Radial Pressure Gradient, Higher Circumferential, and Axial Shear Work, and Conductive Heat Transfer. Finally, an energy balance is carried out on the peripheral hot control volume to study the fundamental modes of energy transfer. The energy balance verifies that these factors are the prominent factors responsible for the observed increase in separation. • Effect of right-angled ribs on energy separation in an RHVT was analyzed in detail. • Recirculation zones promote the transfer of energy through shearing. • Net radial potential difference plays a governing role in the final flow structure. • An improvement in thermal separation was achieved in the presence of ribs. [ABSTRACT FROM AUTHOR]

Scaling-up a lyophilization cycle to the manufacturing scale successfully at the first pass is of crucial importance to the bio-pharmaceutical community in order to save expensive and sparsely available drug products for clinical and industrial manufacturing. The constraints on time, cost and energy consumption during process development are prohibitive to performing multiple experimental studies at the manufacturing scale. Most process analytical techniques to obtain cycle data are often not available at the manufacturing scale due to sterility concerns with intrusive tools and experimental uncertainties at industrial manufacturing scales. Modeling techniques offer an attractive alternative solution under these circumstances to gain knowledge about the manufacturing scale equipment limitations and predict the probability of success prior to performing experimental trials in order to minimize the risk associated with scale-up. In this paper, we present a detailed characterization of equipment capability curves for lyophilizers across laboratory, pilot and manufacturing scales using Computational Fluid Dynamics (CFD) modeling and highlight the flow features in manufacturing-scale equipment with different geometric attributes. We present the equipment, process and product parameters which determine the outcome of the cycle and develop guidelines for robust scale-up practices from the laboratory and pilot scales to the manufacturing scale using vial heat and mass transfer modeling. We present examples of cycles which would seem to scale-up to the manufacturing-scale successfully using a deterministic model but would have a high probability of failure when process excursions, deviations, and input uncertainties are accounted for by applying a Monte-Carlo based probabilistic model. We demonstrate the method to reduce the failure probability and de-risk the scale-up of such processes. We also present the significant reduction in primary drying time that can be achieved by implementing a lyophilization recipe with varying setpoints of chamber pressure and shelf temperature for the primary drying stage in a manufacturing-scale lyophilizer. All the observations from our modeling analyses and example studies indicate that CFD simulations in combination with deterministic and Monte-Carlo based probabilistic vial heat and mass transfer modeling would significantly improve the success of scale-up to industrial lyophilized drug manufacturing. • Lyophilization or Freeze drying. • Scale-up and Tech Transfer. • Pharmaceutical Manufacturing. • Computational Modeling. • Process Optimization. [ABSTRACT FROM AUTHOR]

To solve the problem of the lightweight design of metal fins and strengthen the heat transfer between phase change material (PCM) and lithium batteries, the synergistic design of fins and phase change material-battery thermal management system (PCM-BTMS) is particularly important. In this paper, 9 new branch fin design schemes were proposed based on the conventional straight fin. The reliability of the computational fluid dynamics model was verified through the heat transfer experiments at different discharge rates. Firstly, the thermal performances of 9 new fins and the conventional straight fin under 5C discharge rate were compared and analyzed, and the optimal model was selected. Secondly, the effects of transverse fin coverage area, number, arc length, thickness, and arc length of inner and outer arc fins on the thermal performance were analyzed considering the effects of different heat transfer coefficients. The results show that the preferred fins have less effect on the heat transfer coefficient enhanced thermal performance compared with the conventional fins; the average cell temperature is reduced by 3.14 K and 3.92 K respectively by increasing the fin coverage area and the number of transverse fins to increase the contact area with PCM to enhance heat dissipation; the average cell temperature changes more significantly with the inner arc fins, and the cell temperature of Case H6 was reduced by 7.2 K; while the transverse fin arc length extension reduced the thermal performance of the system in high temperature cases. The volume of system remained the same, and the thickness of the transverse fins decreased the heat storage capacity of the system when the thickness of the transverse fins was larger. The optimal fins could keep the average cell temperature within 318.15 K. The heat transfer capability was improved by 14.98%, the operating time was extended by 131.5%, and the system weight was reduced by 10.28%. [Display omitted] • 9 new branch metal fins are proposed to enhance the thermal performance of PCM. • The new branch fin structure can effectively reduce the cell temperature. • Coverage area, number, arc length, and thickness are key indices of transverse fins. • The inner and outer arc angles of fins greatly affect the heat transfer ability. • The new optimized branch fin structure better meets the lightweight design. [ABSTRACT FROM AUTHOR]

• SST k–ω model combined with low- Re model can simulate the change of wall temperature and surface heat transfer coefficient in critical state best. • Low- Re method performed better than wall function method with more refined near-wall grids. • The simulation results computed by RNG k–ω model with wall function method at supercritical region are also acceptable due to the low computational consumption. • k–ω model fits the low Re method better than the wall function method, and k–ω model fit the wall function method better than the low Re method. Computational fluid dynamics is increasingly applied to reactor safety analysis, and the applicability evaluation of turbulence model can effectively improve the calculation accuracy. In this paper, the applicability of six turbulence models and two near wall models is compared for simulation of flow and heat transfer of supercritical carbon dioxide in wire wrapped rod bundle. According to experimental data under various conditions, the applicability of turbulence models and near wall models is respectively evaluated from wall temperature and surface heat transfer coefficient. The results show that SST k–ω model combined with low- Re model can simulate the change of wall temperature and surface heat transfer coefficient in critical state best, and the average relative error (T w and h) is 6.88% and 13.17%. When CO 2 is heated into supercritical state in the latter 900 mm of wire wrapped rod bundle, the relative error (T w and h) calculated by RNG k–ω model is 5.94% and 18.02%. The grids number of low Re method is nearly double of the grids number of wall function method. Therefore, the simulation results computed by wall function method at supercritical region are also acceptable due to the low computational consumption. This paper researches the applicability of turbulence model and near wall model to enhance the accuracy of simulation of flow and heat transfer in supercritical CO 2 reactor rod bundle. [ABSTRACT FROM AUTHOR]

Under severe accident conditions, in addition to steam and air, there may also be hydrogen produced by the reaction of zirconium alloys and steam, CO 2 produced by the molten corium concrete interaction (MCCI) and other gases in the containment. These gases, whose properties are quite different from air, can significantly affect the steam condensation process outside the tube bundle. This paper aims to investigate the effects of non-condensable gas mixtures with varying component concentrations on the steam condensation process outside a 3 × 5 tube bundle using computational fluid dynamics (CFD) methods. The thermal conditions studied are set to a pressure of 0.4 MPa, a subcooling of 40 K, and a molar concentration of steam of 0.66. The results show that CO 2 has an acceleration effect on the flow field outside the tube bundle, which promotes the diffusion of steam to the inside of the bundle, thus increasing the condensation heat transfer coefficient (CHTC) of the bundle and decreasing the difference in CHTC between different heat transfer tubes inside the bundle. Hydrogen, on the other hand, inhibits the downward flow of the gas mixture, causing a decrease in CHTC. However, at high hydrogen concentration (X H2 >0.1), the gas mixture will form a buoyant flow upward, and then the CHTC of the tube bundle will be significantly increased by up to 177%. When the two gases act together, they will weaken each other's influence on the flow field, thus reducing the CHTC of the tube bundle. [ABSTRACT FROM AUTHOR]

In this paper, we present a comprehensive study on the heat transfer in the spiral coiled tubes, employing both numerical simulations and experimental analysis. The investigation includes an exploration of water flow at different mass flow rates, ranging from 0.025 to 0.11 kg / s , to capture a wide range of operating conditions. The numerical simulations were conducted using advanced computational fluid dynamics (CFD) techniques, providing detailed insights into the heat transfer behavior within the spiral tube. Concurrently, experimental tests were performed to validate the numerical results and compare them with existing findings from previous studies. The primary aim of our study is to establish correlations for calculating the Nusselt number and friction coefficient in the spiral coiled tubes. These correlations serve as essential tools for engineers and researchers in predicting heat transfer characteristics and pressure drop, thus facilitating the design and optimization of heat exchangers and heat recovery systems that incorporate spiral coiled tubes. Overall, the results obtained from this investigation enhance our understanding of heat transfer in spiral tubes and contribute to the development of reliable predictive models. The proposed correlations offer practical and efficient means of assessing heat transfer performance, making significant strides towards achieving more energy-efficient and sustainable industrial processes. • Fluid flow and heat transfer in a spiral coiled tube were studied. • Effects of mass flow rate of water on heat transfer in a spiral coiled tube were investigated. • Correlations for calculation of Nusselt number and friction coefficient for water flow in a spiral coiled tube were developed. [ABSTRACT FROM AUTHOR]

• A new wall boiling heat transfer model is developed to offer a fresh approach for CFD simulations within the Eulerian two-fluid framework. • Each parameter within the new model is calculated based on local physical properties and macroscopic parameters at cell level. • The new model reasonably predicts the wall temperature in flow boiling cases. • The sensitivity of the coefficients introduced in the proposed model are analyzed. Accurate prediction of flow boiling heat transfer is prominently dependent on the modeling of wall heat flux partitioning. In this paper, a new wall boiling heat transfer model was developed for three-dimensional Computational Fluid Dynamics (CFD) code to predict the wall heat flux and wall temperature. The proposed model partitioned the wall heat flux into convective heat flux and nucleate boiling heat flux, which were further modified by two correction factors. The key feature is that the new wall boiling heat transfer model was derived from bubble growth mechanism, incorporating reasonable assumptions, and each parameter within the model was calculated based on local physical properties and macroscopic parameters at the cell level. On this basis, the new wall boiling heat transfer model was coupled into ANSYS-Fluent and validated against various public experiments as well as the KIMOF experiments conducted under different conditions. Simulation results indicated that the proposed model could predict reasonable results for wall temperature and cross-section average void fraction. Finally, a comprehensive investigation was carried out to assess the sensitivity of the computational grids and the coefficients introduced in the new model. [ABSTRACT FROM AUTHOR]

• The mathematical model of fluid–solid coupling is used for numerical calculation. • The distribution of the parameters of the annular fuel element with double-sided cooling is studied. • Analysis of flow heat transfer parameters for the annular fuel element flow channel. • Suitability analysis for existing empirical flow and heat transfer equations. • Development of new empirical relations for the friction factor and Nusselt number for the annular fuel element. Compared with conventional rod fuel elements, ring fuel elements have the advantage of high core power density and low fuel temperature. The study of their thermal and hydraulic characteristics is of significant importance. In this paper, computational fluid dynamics (CFD) is used to simulate the flow boiling in the annular fuel element based on the mathematical model of fluid–solid coupling. Parameters such as velocity field, temperature field and heat transfer coefficient of the flow channel were analyzed. The results show that the surface temperature of the solid fuel rod varies in a 90° cycle at the same position in the axial direction along the circumference. The heat transfer coefficient shows regular fluctuations along the flow direction. A new empirical equation for the heat transfer in the flow of the annular fuel element is also proposed, and the error of the predicted data is controlled within ± 3 %. [ABSTRACT FROM AUTHOR]

The existing Chinese solar greenhouse (CSG) had different spatial structure types, which spatial structure can make the greenhouse fully utilize solar energy and obtain the best thermal performance effect is worthy of further research. This paper took the CSG in the Shenyang area as the research object. A mathematical model was established to simulate the three-dimensional dynamic thermal environment of CSG at the crop level by combining experimental and computational fluid dynamics (CFD) numerical simulation. The model can well describe the heat transfer process in the greenhouse. Based on this model, the effects of variation of multiple structural parameters on the temperature distribution, solar energy interception, heat storage and release performance of CSG were quantitatively specified. The simulation results demonstrated that for the CSG with a span of 10 m in the Shenyang area, the optimal ridge height was 6.2 m, the optimal north wall height was 4.4 m and the optimal horizontal projection length of the north roof was 2.0 m. Furthermore, the spatial structure parameters of CSG with an 8 m–12 m span were obtained for the Shenyang area. This paper can provide theoretical guidance for the design and optimization of spatial structure parameters of CSG in the Shenyang area. • A CFD model was established to simulate the thermal environment of crop level in CSG. • The CFD model can accurately depict the dynamic heat and mass exchange process in CSG. • The effect of structural parameters on the thermal environment of CSG was expounded. • The structural parameters of CSG with 8 m–12 m span were obtained for the Shenyang area. [ABSTRACT FROM AUTHOR]

• Physics-Informed neural networks (PINNs) are used for single and two-phase flows. • The study investigates the rising bubble problem with and without heat transfer. • The pertinent physics of wake interaction and thermal boundary layer are discussed. • Physics-Informed neural networks are agnostic to geometry and fluid properties. • The maximum error in the position of the centre of mass by PINN is less than 2.8 %. This paper presents data-driven simulations of two-phase fluid processes with heat transfer. A Physics-Informed Neural Network (PINN) was applied to capture the behaviour of phase interfaces in two-phase flows and model the hydrodynamics and heat transfer of flow configurations representative of established numerical test cases. The developed PINN approach was trained on simulation data derived from physically based Computational Fluid Dynamics (CFD) simulations with interface capturing. The present study considers fundamental problems, including tracking the rise of a single gas bubble in a denser fluid and exploring the heat transfer in the wake of a bubble rising close to a heated wall. Tracking of a rising bubble phase interface of fluids with disparate properties was performed, revealing a maximum error of only 5.2% at the interface edge and a maximum error of 2.8% at the position of the centre of mass. Inferred (hidden variable) flows are studied in addition to a purely extrapolative inverse isothermal bubble case. When no velocity data was supplied, velocity field predictions remained accurate. Rise of an inferred isothermal bubble with unseen fluid properties was found to produce a maximum mean-squared error of 0.28 and centre of mass error of 1.25%. For the case of the rising bubble with a hot wall, the maximum error in the temperature domain using specified boundary conditions was 6.8%, while the bubble position analysis reveals a maximum positional error of 3.6%. These results demonstrate that PINN is agnostic to geometry and fluid properties when studying the combined effects of convection and buoyancy on two-phase flows for the first time. This work serves as a starting point for PINN in multiphase cases involving heat transfer over a range of geometries. Eventually, PINN will be used in such cases to provide solutions for forward, inverse, and extrapolative cases. Each of which represent a dramatic saving in computational cost compared to traditional CFD. Contours of volume fraction (α) and temperature (T*) predicted by the CFD (Top) and PINN (Bottom) for the evolution of flow showing how the rising bubble influences the thermal boundary layer on the wall. [Display omitted] [ABSTRACT FROM AUTHOR]

To determine the safe boundary of fuel assembly operation and improve the heat transfer performance of fuel assembly, it is necessary to accurately calculate the thermohydraulic characteristics and the critical heat flux (CHF) in rod bundles. The Eulerian two-phase model coupled with extended wall boiling model was used to numerically investigate the 5 × 5 fuel rod bundle flows with four sets of mixing vane spacer grids. A wide range of working conditions were analyzed to validate the numerical method. The results indicate that the current numerical model can not only accurately calculate the CHF values but also predict the location of heat transfer crisis. Based on CFD (Computational Fluid Dynamics) results, the detailed two-phase flow distributions were provided to analyze the CHF performance under special structures, such as bowed rod and spacer backward shift. The quantitative results were obtained on the analyses of spacer position influence on CHF and the penalty effect of bowed rod. Furthermore, the prediction of present numerical model under low inlet subcooling conditions and cold rod CHF were discussed. The research of this paper provides support for the design and optimization of fuel assemblies. [ABSTRACT FROM AUTHOR]

In this paper, a novel gradient porosity transpiration cooling plate structure (GP-TCPS) is proposed to address the heat transfer deterioration phenomenon owing to non-uniform local temperature distribution in transpiration cooling plate structure (TCPS). The flow and heat transfer (FAHT) of the GP-TCPS were analyzed qualitatively and quantitatively by computational fluid dynamics (CFD) and response surface method (RSM). The effects of various parameters on the injection pressure (P c) and average cooling efficiency (η ave) of the GP-TCPS were investigated, ultimately identifying optimal structural parameters. The results show that the GP-TCPS significantly improves the temperature uniformity by 20.58–23.78 % compared to uniform porosity transpiration cooling plate structure (UP-TCPS) at low coolant mass flow rates. Compared with the UP-TCPS, the P c of the GP-TCPS decreases by 84.5–86.2 %, and the deviation of the η ave is 1.3–2.4 %. The RSM indicates that the most important parameters affecting the P c and η ave of the GP-TCPS are average particle diameter and the thickness of porous media, respectively. The P c of the optimized structure is reduced by 57.19–77.39 %, the η ave is increased by 7.72–9.42 %, and the temperature uniformity is increased by 52.33–66.14 %. The results provide valuable insights into the mechanism of TCPS and offer promising solutions to mitigate heat transfer deterioration. [ABSTRACT FROM AUTHOR]

· The sheet-network and solid-network TPMS structures considering porosity and other parameters are constructed. · The solid-network TPMS structures with larger through-hole and skeleton concentration ratio have higher overall performance. · Under the same pressure drop, the heat transfer performance of TPMS with D-type sheet structure is better. Triply periodic minimal surface (TPMS) structures are widely used in the field of flow and heat transfer. In this paper, four TPMS structures, Schwartz Diamond-sheet (D-sheet), Schwartz Diamond-solid (D-solid), Schoen IWP-sheet (IWP-sheet), and Schoen IWP-solid (IWP-solid), are designed based on two structure generation strategies. The above structures all are manufactured through additive manufacturing, and the material is AlSi10Mg. The samples were characterized by X-ray scanning. The flow and heat transfer performance of different TPMS structures was studied by computational fluid dynamics (CFD) and experimental methods. The results show that the pressure drop of sheet-network is larger than that of solid-network for the same TPMS type. With the same structure generation strategy, the pressure drop of Schwartz Diamond (D-type) is greater than that of Schoen IWP (IWP-type). The heat transfer performance of the TPMS structure shows the same results as the pressure drop. The performance enhancement criterion (PEC) of the solid-network TPMS is better than that of the sheet-network structure, and the D-type TPMS structure is better than the IWP-type structure. The average PEC of D-solid and IWP-solid is 31 % and 44 % larger than that of D-sheet and IWP-sheet, respectively. The average PEC of D-sheet and D-solid is 11.8 % and 1.7 % larger than that of IWP-sheet and IWP-solid, respectively. The mechanism of the higher PEC of the solid-network structure is the low pressure drop caused by the high through-hole ratio and relatively concentrated skeleton. Under the same pressure drop, the heat transfer performance of TPMS with D-type sheet structure is better. The research content of the article is mainly applied to fin-enhancement, which can replace fins in traditional heat exchangers. In actual engineering applications, the TPMS structures type is reasonably selected according to the requirements. [ABSTRACT FROM AUTHOR]

In this paper, the experimental and numerical investigations of both swirling hybrid rocket motors without and with the design of regenerative cooling (RC hereafter), using 90%-wt H 2 O 2 and polypropylene (PP) as the liquid oxidizer and the solid fuel, respectively, were performed and compared. We implemented a new design of regenerative cooling using the oxidizer to transfer the heat generated from combustion. A series of ground horizontal hot-fire tests, which include the catalytic-bed only and the motor without/with RC were performed to measure the propulsion performance related parameters. The resulting C* efficiency of the RC design with catalytic-bed only remained in comparison with the one without RC. With a similar initial combustion chamber geometry, the RC implementation resulted in a better engine Isp efficiency from 96.3 to 98.6 with a lower O/F ratio from 6.49 to 5.94. In addition, the topologies of the burned fuel grain surface were optically measured by a 3D laser scanner. The resulting variation of regression rates between the upstream and downstream fuel for the chamber with the RC was smaller than case without the RC. Moreover, a simplified semi-empirical computational fluid dynamics (CFD) model based on the measured regression rates was constructed for investigating the physical phenomenon inside the hybrid rocket combustion chamber. The simulations show that a higher swirling number in the later portion of the port was found for the RC case. By concerning about the different O/F ratios and port size of the burned fuel, a series of simplified numerical CFD investigation with a fixed O/F and a fixed port size varying the regression rates from upstream to downstream fuel systematically with the same average region rate was performed to complement the semi-empirical CFD simulations. The results showed that there were two distinct regions including an upstream non-classical region dominated by the gas impingement of gas and a downstream classical region caused by the swirling effect of gases. In the non-classical region, the calculated distributions of the swirling numbers of the former are essentially the same for all the cases no matter what the magnitude of the regression rate is, while in the classical region higher swirling numbers are found for the case of more uniform distribution of regression rates. Heat generated near the upstream of the fuel grain was transferred more efficiently through the design of RC, which makes the resulting fuel regression more uniform than that without RC. The resulting swirling efficiency in the RC case was higher than that without RC. The HRM with RC hence had a better engine Isp efficiency with a lower O/F ratio. • Hybrid rocket motors with the design of regenerative cooling improves the propulsion efficiency. • Optical 3D scanner precisely measures the solid fuel topology. • The results of the proposed numerical model for hybrid rocket combustion are in good agreement with experiments. [ABSTRACT FROM AUTHOR]

• A cross-scale real-time coupling analysis model is established to simulate the full-regime flow boiling with coupled heat transfer in sodium-cooled fast reactor OTSG. The independent coupling of each heat transfer tube of the water side in OTSG with the 3D fluid domain of sodium side is realized. • The cross-scale coupling simulation method has significant advantages in solving efficiency, convergence and stability since it avoids the use of a three-dimensional multiphase model. • A three-dimensional refined numerical analysis model of a seven-tube OTSG prototype model was established, and the full-regime boiling heat transfer of the tube side and the coupled heat transfer of the shell- and tube-sides were simulated based on the cross-scale coupling method. • The cross-scale coupling method has the potential to be applied to practical engineering OTSG containing large-scale heat transfer tube bundles. The once-through steam generators (OTSG) in sodium-cooled fast reactor (SFR) are characterized by full-regime flow boiling heat transfer, coupled heat transfer on both sides and complex structure with a large dimensional span. This makes the computational fluid dynamics (CFD) and 3D refinement modeling methods to analyze the 3D temperature field of OTSG containing large-scale heat transfer tube bundles generally face the problems of high computational difficulty, low solution efficiency and poor solution stability. In this paper, based on the full-regime flow boiling heat transfer model and the flow pattern discrimination model, a one-dimensional full-regime flow boiling heat transfer model from subcooled water to superheated steam on the water side (tube side) and its cross-scale coupling solution model with the three-dimensional refined CFD model on the sodium side (shell side) are established. The effectiveness of the coupling analysis model was verified by comparative analysis with experimental data of the Indian 19-tube Steam Generator Test Facility (SGTF). The independent coupling of the water side of each heat transfer tube in the OTSG with the sodium side 3D fluid domain is realized. The results show that the cross-scale coupling method using the one-dimensional full-regime flow boiling heat transfer model for the water side and the three-dimensional CFD model for the sodium side can accurately predict the temperature distribution, the main heat transfer characteristic points on the full height of each heat transfer tube, and can obtain the temperature difference between different heat transfer tubes and tube walls. The maximum error between the calculated results and experimental data for the distribution of sodium temperature along the axial direction of the tubes is less than 3%. The cross-scale coupled solution method avoids the direct adoption of the three-dimensional multiphase flow model, which significantly improves the efficiency and stability of the solution of the three-dimensional temperature field of OTSG. This study provides an efficient 3D refinement numerical analysis method for the design and safety verification of OTSG. [ABSTRACT FROM AUTHOR]

The increase demand in liquefied natural gas (LNG) leads to an increase in the import and export of LNG cargo using LNG carriers with composite insulation and double-hull structures for membrane-type storage tanks. Therefore, the transient characteristics of cryogenic heat transfer in LNG cargo containment systems have become important for understanding the physics when LNG vaporizes into the gas phase to minimize the cargo loss of boil-off gas (BOG). However, public papers on fundamental research on long-term computational fluid dynamics (CFD) simulations are still lacking. In the present study, the transient flow behaviors of LNG fluids and the heat transfer characteristics were numerically studied by applying the simplified single-layer insulation in an LNG cargo containment system, based on an initial temperature of T LNG,0 = 110.5 K and saturation temperature of T LNG,sat = 111.5 K in the boundary condition of IGC code. The proposed analysis procedure can serve as a reference for relative comparison of predicted BOG difference in LNG cargo holds. Consequently, the heat transfer mode between the two-phase methane and the solid insulation could be typically classified into two different regimes: (1) a subcooled regime before reaching the saturation temperature from the initial temperature, and (2) a boiling regime after reaching the saturation temperature. In the subcooled regime, the subcooled liquid exhibited bulk flow motion induced by natural convection. The loss rate of LNG mass per time interval was extracted from the best-fit correlations as −0.0448 kg/s at 1 d (105 s) to cool down the insulation system and −0.0072 kg/s at 5 d (5 × 105 s) to reach the LNG saturation temperature. When the predicted value of the loss rate of LNG mass by the CFD simulation was regarded as the generation rate of boil-off gas, it was smaller than the designed value of the boil-off gas of 0.464 kg/s corresponded to boil-off rate (BOR) about 0.2 %/day. In the boiling regime and under sufficiently cooled conditions, the loss rate of LNG mass per time interval did not consistently exceed the BOR value. The liquid flow exhibited a turbulent-like motion despite the relatively low velocity at 10 d (106 s). Especially, the increase in the effective thermal conductivity was a good indicator for distinguishing between the boiling and subcooled regimes. • A novel boil-off gas analysis procedure using long-term simulation • A full-scale membrane-type LNG storage tank was applied. • Differences in boil-off gas and heat flux characteristics between 1-D and 3-D results. • Boil-off gas generation characteristics distinguished by two heat transfer modes. • Thermofluid behaviors inside the LNG cargo were investigated. [ABSTRACT FROM AUTHOR]

Convection/conduction simulations have been performed to determine flow and heat transfer phenomena in steady-state, for a plate carrying few embedded discrete heaters, exposed to by a turbulent offset cooling jet. This configuration is relevant, for example, in thermal design of vehicle body segments in aerodynamics conditions: when realized in certain alloys, their configuration will be determined based their discrete structural state prompted by supplied electrical heating. In order to approach an appropriate thermal design of the plate and obtain their precise state, the space of geometric and operating variables needs to be explored by a thorough parametric study based on the governing momentum and energy equations. In this paper, the interaction between the impinging boundary layer and the conductive effects produced by such discrete heaters is explored, giving rise to a conjugate heat transfer situation. With a flexible notation for discretized heating and temperature-dependent conduction, dimensionless heat transfer is discussed spanning the entire range of design parameters. Results report considerable variation in heat transfer: as an example, air jet over polypropylene plates brings about peak Nusselt numbers between 2000 and 4000 for an inclined configuration at Re ≈ 1 × 10 6 based on nozzle width, with related strong temperature gradients that must be addressed during design, depending on discrete heaters' configuration and properties; whereas for alumina plates the peak Nusselt numbers fall down between 600 and 750, featuring much smoother temperature variations and consequent more stable structural states. • Addressing heat transfer from finite plate thickness with discrete streamwise heating sectors for Shape Memory Alloy morphing. • Study employs a coupled steady-state dimensionless model with sensitivity analysis for solid/fluid/thermal interactions. • Analyzed local Nusselt number and heat transfer dependency on design parameters; heated sectors temperature range varies considerably. • Thermal variations may lead to operation faults as stringent thermal regimes are required for Shape Memory Alloy morphing. • Study reveals nonlinearities in discretely-source heated plate thermal regimes, laying the foundation for rational design. [ABSTRACT FROM AUTHOR]

Nowadays, a bio-inspired heat exchanger incorporating a triply periodic minimal surface (TPMS) structure has demonstrated great potential in the fields of new energy research and aerospace, which necessitates achieving a balance between low volume and high heat transfer efficiency while maintaining low pressure drop. In this paper, the adjustable heat efficiency of the heat exchanger with TPMS in gradient thicknesses is specially designed. A steady-state conjugate heat transfer (CHT) model is coupled with computational fluid dynamics (CFD) analysis. In addition, the temperature profile and velocity streamline are also checked to analyze the fluid flow behavior of the radiator. The results show that the convective heat transfer coefficient of the Gyroid with gradient level set values is 26.02–60.10% higher than that of the uniform Gyroid model, and the pressure drop is decreased by 9.66–18.05%. Both high heat transfer efficiency and low pressure drop can be achieved when the thickness is 0.2–0.3 mm and Re is 100–125. The heat exchangers with a TPMS thickness gradient in the ratio of 2:4:6 demonstrate a remarkable enhancement in overall heat transfer efficiency, achieving a 30.22% improvement compared to those with a TPMS thickness gradient in 6:4:2. [ABSTRACT FROM AUTHOR]

Accurately representing the time dependent heat release rate of fuels is critical to performance-based design in fire safety applications. Existing simplified models either use average pyrolysis rates at different heat fluxes or do not account for the change in burning behavior at higher heat transfer rates. This paper presents the theoretical basis of a scaling-based pyrolysis model, S-Pyro. The model is based on the concept of maintaining the shape of a reference heat release rate per unit area curve but scaling the magnitude and time based on a dynamic thermal exposure. The model has been implemented in the computational fluid dynamics software Fire Dynamics Simulator (FDS). The model is validated with solid-phase only and multi-phase simulations of cone calorimeter experiments. The solid-phase simulations evaluated the capability of the model to predict the heat release rate per unit area of 149 materials tested at heat fluxes other than the reference flux. Multi-phase simulations of bench-scale fire experiments with a single material, Canada Pine and Spruce plywood, were used to evaluate the performance of the pyrolysis model in FDS. The model uncertainty was lower for high heat release rate materials, with the model uncertainty approaching the experimental uncertainty at higher burning rates. • Developed a scaling-based model to dynamically scale cone calorimeter data. • Validated the model using experimental measurements from 149 different materials. • Implemented pyrolysis model as an option in Fire Dynamics Simulator (FDS). • Evaluated the impact of the model on burning behavior in FDS simulations. [ABSTRACT FROM AUTHOR]

• Subcooled flow boiling sequences in microchannels at high aspect ratios are explored. • Effects of aspect ratio, hydraulic diameter and subcooled degree on thermal- fluid characteristics are studied. • Increasing aspect ratio and inlet subcooled temperature realize better cooling performance. • A decrease in hydraulic diameter can augment thermal/frictional outcomes. • Channel with an aspect ratio of 5.0 achieve coefficient of performance up to 116277.8. With the fast progress of new technologies applied to cloud computing, artificial intelligence, and fifth generation communication, the researches on the heat dissipation of high-power electronic devices have concentrated on the two-phase flows in the microchannel, with the phase change used to achieve excellent cooling efficiency. The objective of this paper is to conduct the computational and experimental studies for investigating the thermal-fluid behaviors of subcooled flow boiling in microchannels. In the computational fluid dynamics (CFD) model, the numerical solver is built in ANSYS/Fluent® implementing the multiphase formulation with the full consideration of the effects of turbulence, surface tension, and phase change to appropriately imitate the interfacial movements between liquid water and vapor for probing the subcooled boiling and bubble nucleation processes over the microchannel. In the experimental investigation, a syringe pump and a programmable DC power supply is employed to regulate the heat flux and subcooled temperature for determining the heat transfer and pressure drop outcomes across the microchannel at varied aspect ratios and hydraulic diameters. In addition, this study sets up a high-speed camera with a LED fiber optical light source to acquire the close-up observation images over the complex flow boiling phenomena. The accuracy of CFD predictions is assessed by comparison against both the measured heat transfer coefficients and pressure drops as well as the photo-captured interfacial behaviors. The numerical simulations are then conducted to resolve the temperature gradients on the heating wall surface due to intense disturbances incited by the confined bubbly flow and sweeping flow at high aspect ratios, enhancing the cooling performance over the microchannels. The experimental measurements show that a reduction in inlet subcooling from 65 to 50 °C tends to enlarge the average heat transfer coefficient and pressure drop by 21.5 and 17.1%, respectively. The design impact study also reveals the average heat transfer coefficient and pressure drop at an aspect ratio of 5 greater than those at an aspect ratio of 2 by up to 41.1 and 27.2%, respectively. In contrast, increasing hydraulic diameter from 0.92 to 1.38 mm can strengthen the thermal and frictional outcomes by 17.2 and 20.3%. The microchannel design having an aspect ratio of 5.0 can realize the estimated coefficient of performance (COP) up to 116,277.8, achieving the satisfactory overall thermal and frictional outcomes. [ABSTRACT FROM AUTHOR]

• A magnetic field changes the ferrofluid droplet-surface interaction and cooling performance. • Ferrofluid cooling with a magnet is from 28% to 263% higher than that without it. • A silicon substrate under a magnetic field shows the best heat transfer performance. • Superhydrophobic surfaces do not foul after ferrofluid droplet impact and evaporation. [Display omitted] This paper documents the spreading characteristics and heat transfer of a single ferrofluid droplet impinging onto dry solid surfaces with and without a magnetic field. Three surfaces were investigated: a pure silicon substrate, a silicon substrate with a thin titanium film, and a superhydrophobic coating. Fluid dynamics and cooling results of a ferrofluid droplet were compared to that of pure water and water-surfactant droplets for the same Weber number (We = 61) and initial surface temperature (T 0 = 95 ∘ C). Our results show that the magnetic field (magnetic Bond number Bo m = 2186) increased the droplet spreading diameter up to 12% and suppressed droplet rebound, thus improving the cooling performance of a ferrofluid droplet. The highest heat transfer rates were measured for the pure silicon substrate under a magnetic field with an average value of 14 W. The lowest cooling performance was observed for the superhydrophobic surface without a magnetic field with a peak value of 0.82 W. However, using the magnetic field, the superhydrophobic surface achieved 263% higher heat transfer rate than the non-magnetic case because of the suppression of droplet rebound. Moreover, the surface did not foul from ferrofluid deposition, an advantage for spray cooling applications when using any nanofluid. [ABSTRACT FROM AUTHOR]

The thermal load heterogeneity will lead to inhomogeneous local heat flux and thermal stress, extremely detrimental to the operational stability of heat exchangers with multi-assembly structure. In this paper, a full-scale analysis method for the helical coil steam generator in industry was developed and implemented. The validation was performed against flow boiling heat transfer experiment of helical tube. The simulation of single assembly and full-scale helical coil steam generator in high temperature gas-cooled reactor was performed, and the distributions of thermal-hydraulic parameters in heat exchange region were obtained. The results show that the nonuniform helium flow distribution with the inhomogeneous factor D m value of 34.83% has a significant influence on the heat transfer characteristics. The peak heat transfer power of central assembly increases by 33.76% against design condition, introducing large thermal load heterogeneity with the inhomogeneous factor D p value of 30.45%, even threating the structural integrity of helical tube in long-term operation circumstances. The structural elements design in the superior compartment should be optimized to increase the helium mass flow rate of the assemblies below the nozzle and behind the helium baffle, improving flow distribution uniformity and reducing the peak value of local heat flux and thermal stress. • A full-scale analysis method of helical coil steam generator in HTGR was developed. • The flow distribution in multiple heat exchange assemblies was obtained. • The thermal load heterogeneity was quantificationally investigated. • The optimization suggestion of superior compartment elements was provided. [ABSTRACT FROM AUTHOR]

• PCM melting in a finned cold thermal energy storage tank is studied. • Geometric structures of fins can significantly affect the melting process. • Increasing fin height is more effective than increasing fin number to reduce melt time. • Mean power with new stratified fin design is 156.3% higher than that without fins. Cold thermal energy storage (CTES) is of great importance for the enduring decrease in fossil fuel energy consumption. Moreover, CTES with phase change materials (PCMs) can be an effective measure to accumulate the heat or cooling energy for overcoming the mismatch between the supply and demand of air conditioning loads, augmenting system dependability and flexibility in operations of power grids. This paper numerically and experimentally examines the melting characteristics of PCM inside a CTES tank with the installation of interior fins. The computational fluid dynamics (CFD) software ANSYS/Fluent® is applied to predict the time sequences of liquid fraction contours and temperatures in comparison with the photographed images of ice-liquid water interface and measurement data in the CTES tank to verify the accuracy of CFD predictions. The simulations by the validated CFD model are extended to evaluate the influences of fin height and total number of longitudinal fins on the heat transfer outcomes in the storage tank. The present study further proposes a novel design adopting stratified fins to enhance the melting performance of the CTES device. The estimated mean power with the new stratified fin design is notably greater than that without fins by 156.3%, achieving the effectively liquefaction enhancement of ice for guiding the development of finned cold thermal energy storage. [ABSTRACT FROM AUTHOR]

Vertical louvers are a widely used external shading system to control natural lighting and solar heat gain for buildings. However, when installed on a building façade, they can disrupt the flow field around the façade and affect the external convective heat transfer process of building's exterior surfaces. To this end, this paper conducted CFD simulations to clarify the forced convective heat transfer patterns in a vertical louver-facade system based on the k-ω SST model with a detailed verification. The extended Newton's cooling equation is used to describe the heat exchange process between louvers, building façade, and air, which generates four heat transfer coefficients: h wa , h wb , h ba, and h bw. Then the impacts of dimensionless temperature difference (θ), louver angle (φ), louver slat width (B), and installation distance (W) on the heat transfer coefficients are investigated. The results show that θ does not affect the average heat transfer coefficients. h wa reaches a minimum value and h ba reaches a maximum value when φ = 75o. In addition, h wa increases by 55.3% and h ba decreases by 21.9% as B increases from 0.3 m to 1 m. When W increases from 0.25 m to 1 m, h wa decreases by 5.6% and h ba increases by 39.6%. The variation in the heat transfer coefficients (h wb and h bw) between the louvers and building façade is also explained. Finally, new correlations of paired heat transfer coefficients are established as a function of φ , B , W , and wind velocity (U 10). The accuracy of these correlations is evaluated by comparing calculated values with simulated results. • Impact of vertical louvers on convective heat transfer at façades is investigated. • Using the extended Newton's cooling equation to describe the heat exchange process. • Taking into account the effects of louver geometry and temperature differences. • Paired CHTC correlations for windward building facades and louver surfaces. • Accuracy evaluation for CHTC correlations. [ABSTRACT FROM AUTHOR]

• A new pattern bundle with a smaller wire diameter of peripheral rods was proposed. • The comparative study between the new bundle and the conventional one was carried out by RANS-based CFD simulation. • The better flow and heat transfer performance was obtained for the new pattern bundle. In this paper, a new pattern bundle with a smaller wire diameter of peripheral rods was proposed. By decreasing the wire diameter of peripheral rods, the flow area of peripheral sub-channels is reduced diverting more coolant towards the central sub-channels. This would lead to a more uniform sub-channel temperatures distribution. To analyze the flow and heat transfer performance of the new bundle, the comparative study between the new bundle and conventional one was carried out by RANS-based CFD simulation. It was found that decreasing the partial wire diameters, the uniformity of coolant flow distribution is improved, resulting in a more homogeneous temperature distribution. The local transverse pressure difference characterizing global swirl motion is smaller, resulting in a weaker sweeping flow in peripheral sub-channels. Moreover, the obvious sweeping flow also could be observed in inter-connected sub-channels due to the smaller wire diameter of peripheral rods. At last, Nusselt number and friction factor are the parameters targeted for the investigation, and the results show that the thermal-hydraulics performance of the new bundle has been significantly improved. Through the research of this paper, the qualitative understanding of fuel assembly structure optimization could be provided for the core design in future. [ABSTRACT FROM AUTHOR]

In this paper, a 2D computational fluid dynamics (CFD) approach combined with 3D discrete element method (DEM) is extended by incorporating heat, mass transfers, and drying kinetic models to study the drying of ellipsoidal particles with equivalent volumes in fluidized beds. The validity of the proposed model is tested in terms of hydrodynamic and mass transfer behaviors. It is shown that the simulation results are in well-agreement with existing correlation or data. Finally, the effects of aspect ratio on heat and mass transfer behaviors at the same superficial gas velocity are then analyzed to improve the fundamental understanding of the system. It is demonstrated that the spherical particle has the highest drying rate compared to other ellipsoidal particles due to its highest average Reynold number of individual particles. The obtained results should be useful to the development of the fundamental understanding and optimization of fluidized bed dryers. [Display omitted] • CFD-DEM approach for the drying process of ellipsoidal particles in fluidized beds is developed. • The proposed model is validated. • The statistical behaviors of heat and mass transfer are analyzed. • The different drying rates for different aspect ratios are explained. [ABSTRACT FROM AUTHOR]

• The effect of continuous pressure waves on heat transfer of pipe bundle was studied. • Continuous pressure waves were stimulated by vibrating membrane in CFD models. • A larger affected space was observed in the presence of continuous pressure waves. • The heat transfer is enhanced by 7.01% to 156.22% at the frequency of 20–160 Hz. • Continuous pressure waves have the great potential in enhancing the heat transfer. This paper presents a numerical study of the heat transfer enhancement outside the pipe bundle under the effect of continuous pressure waves (PW) stimulated by a vibrating membrane as a PW generator. Model 1 and 2 made of one and two rows of pipe bundles were investigated, respectively. An oscillating wall boundary condition was applied to the vibrating membrane. Based on the RNG k-ε turbulent model and full cavitation model, the computational fluid dynamics (CFD) model was developed. The prediction results of the model were in good agreement with the experimental data of other researchers. The validity of PW was investigated from the viewpoint of the affected scale by comparing the flow and heat transfer with ultrasound and PW. The effect of the frequency and amplitude of the membrane on the heat transfer enhancement was analyzed. The result shows that the continuous PW had significantly larger affected scale than ultrasonic waves, which can cover the whole pipe bundle space and increase the velocity amplitude of the fluid around the bundle. While the affected scale of ultrasonic waves was limited to the center place of the pipe bundle because of the acoustic stream. In addition, the effect of continuous PW on the convective heat transfer increased with increasing the frequency and amplitude of the membrane. The heat transfer was enhanced by 7.01% to 156.22% at a frequency of 20–160 Hz and an amplitude of 2 mm. Considering the benefits and the energy consumed of PW, the optimal frequencies of models 1 and 2 were 110 and 120 Hz, and the heat transfer coefficient were increased by 119.19% and 150.36% compared to the steady-state flow. The results confirm continuous PW has the great potential in enhancing the heat transfer of large-space pipe bundles. [ABSTRACT FROM AUTHOR]

• A two-equation model is used to reproduce the LBE-cooled flow and the Reynolds analogy hypothesis is applied to predict the heat transfer of S-CO 2 far from the pseudo-critical region. • The inlet Reynolds number of S-CO 2 is identified as the main factor affecting heat transfer. • The effects of inlet flow rates and inlet temperature on the detailed thermal–hydraulic behavior of a PCHE straight channel are quantitatively analyzed. • The relevant research results of this paper can provide a reference for optimizing CFD conjugate heat transfer model between LBE and S-CO 2. The Printed Circuit Heat Exchanger (PCHE) is the optimal heat transfer structure of the fourth-generation advanced Lead–Bismuth Eutectic (LBE) cooled fast reactor coupling with the supercritical carbon dioxide (S-CO 2) Brayton cycle system. It is of great significance to study the conjugate heat transfer characteristics between LBE with low Prandtl number turbulent heat transfer characteristics and S-CO 2 with supercritical convective heat transfer characteristics. However, the conventional Reynolds analogy assumption will affect the numerical heat transfer precision of LBE and, thus, the accuracy of the coupled heat transfer of LBE and S-CO 2. In the present work, an advanced two-equation turbulent heat transfer model, which can effectively correct the numerical heat transfer process of LBE, is introduced into the conjugate heat transfer solver of the open-source Computational Fluid Dynamics (CFD) program OpenFOAM, where the Reynolds analogy assumption is retained to reproduced the heat transfer of S-CO 2 flow away from the pseudo-critical region. The currently developed model and numerical method are compared with the experimental data of an LBE-cooled pipe and the simulation data of conjugated heat transfer of S-CO 2 and S-CO 2 in a PCHE straight channel. The results show that the calculation method in this study can improve the numerical conjugate heat transfer accuracy of LBE compared with the Reynolds analogy assumption model and can reproduce the flow and heat transfer process of S-CO 2 in a PCHE straight channel. Then, the conjugate heat transfer characteristics between LBE and S-CO 2 in a PCHE straight channel are studied. The effects of inlet Reynolds number and inlet temperature are focused on to study the conjugate heat transfer law of LBE coupling S-CO 2. [ABSTRACT FROM AUTHOR]

Semicircular spacers are creatively introduced into the micro vacuum membrane distillation (VMD) modules for the purpose of modifying flowing field, decreasing mass transfer resistance and enhancing water production. A two-dimensional computational fluid dynamics model is developed to conduct the performance evaluation of rectangular micro-VMD modules. Calculated results indicate that novel VMD modules obtain remarkable improvement in terms of transmembrane mass flow rate. Local velocity and vorticity magnitude around the semicircular spacers increase with augment of the dimension of semicircular spacers as revealed in flow performance evaluation. Thermal performance displays that temperature distribution evolves into uniform when the semicircular spacers are introduced and noticeable improvement can be observed in transmembrane heat flux rate, local temperature and temperature polarization coefficient (TPC) performance. Whereas, Nu number varies in a certain range depending on the configuration of semicircular spacers. This paper further discloses the effect of operating parameters on the mass transfer, heat transfer and TPC performance. It is theoretically found that performance of proposed VMD modules is more sensitive to feed inlet temperature rather than feed inlet velocity. In conclusion, semicircular spacers are believed to be effective strategies to enhance performance of micro-VMD modules, with remarkable improvement to flow field, heat and mass transfer. [Display omitted] • A feasibly numerical model of micro-VMD with semicircular spacers is developed. • The flow and thermal performance of micro-VMD modules are revealed. • Structural analysis elaborates effect of various parameters on module performance. • Semicircular spacers enable to boost transmembrane performance with improved TPC. • Production of micro-VMD is more sensitive to feed inlet temperature than velocity. [ABSTRACT FROM AUTHOR]

• Hybrid heat source considered the vapor heat influence and laser-material interaction was developed. • Molten pool evolutions and keyhole dynamics during keyhole, transition and conduction modes were analyzed. • Reflections of laser rays in the keyhole and the energy absorptions were predicted. • Penetration spiking defect influenced by keyhole stability was studied. Melting modes have significant effects on the heat transfer and fluid flow in laser beam oscillating welding (LBOW), which in turn affects the welding quality and solidification microstructure. In this paper, a computational fluid dynamics (CFD) model for LBOW of 2219 aluminum alloy is developed to study the melting/solidification, fluid flow pattern, keyhole dynamics and energy absorption under different welding modes: keyhole, transition and conduction mode. A hybrid heat source model is developed to describe the influence of the vapor heat and multiple reflections of the laser rays on the keyhole surface. The predicted molten pool dimensions and weld profiles are in good agreement with the experimental results. By increasing the oscillating frequency, the line energy density significantly decreases due to a higher scanning speed that results in a shallower keyhole with wider opening. The laser rays are more likely to leak out after 2-3 reflections which reduces the energy absorption. Thus, the melting mode will transfer from keyhole to conduction mode. With further increase of the oscillating frequency, the heat transfer will be dominated by heat conduction when the energy density is below the threshold for keyhole formation. Our work lay the foundations for optimizing the LBOW process to obtain sound joints. [ABSTRACT FROM AUTHOR]

[Display omitted] • Improving building performance simulations with the help of finite-element method simulations. • Comparison of convection, radiation and heat transmission through walls with different simulation methods. • Added value for thermal bridges and internal convection in comparison to conventional building performance simulations. • Building physics simulation methods. This paper presents a method to improve building-performance simulations (BPS) by the comparison and analysis of different approaches based on finite-element method (FEM) models. The lumped parameter method (LPM) is used in several BPS programs and tools. It has the advantage of fast computing times and comparably good accuracy for thermal and energy loads. With the help of detailed FEM simulations, it is possible to further improve the degree of detail and accuracy while maintaining the high simulation speed. In this work, we compare time-dependent results for local temperatures in a generic reference room within a given periode of time. In a second step, the differences between the models with respect to various physical effects are analyzed and used to introduce additional equations into the LPM model in order to improve its accuracy. Thus, we discuss potentials for improvement for BPS and demonstrate a method of a practical implementation. The results show minor differences of less than 0.1 K for radiation and heat transfer, so their level of detail in BPS is appropriate. In these terms, no improvements were pursued within the work. However, the FEM simulation is capable of calculating the internal convective heat transfer and thermal bridges more accurately due to the use of computational fluid dynamics (CFD) and the geometrically precise representation of the FEM model. Here, deviations of up to 1 K in room temperature (convective heat transfer) and up to 0.5 K in wall temperatures (thermal bridges) were pointed out. By improving the LPM with equations obtained from the FEM, these deviations can be reduced to less than 0.2 K, which is a considerable improvement in accuracy. [ABSTRACT FROM AUTHOR]

• Impingement heat transfer for venting of Li-ion cells was considered. • Infrared thermography provides spatially resolved heat transfer distribution. • Peak heat transfer occurs near stagnation point for each jet emerging from the vent. • Asymmetric heat transfer distribution was caused by complex safety vent geometry. • Local and area-averaged heat transfer correlations were developed. During thermal runaway of Li-ion battery cells, high-temperature gas jets may impinge onto nearby surfaces and may increase the risk of a propagating failure. In this paper, heat transfer rates of jets emerging from a cylindrical Li-ion cell and impinging on a flat surface were measured experimentally and empirical correlations were developed based on the resulting data. Experiments used compressed air as the working fluid, which issued from the isolated safety vent and impinged on a target plate. Infrared thermography was used to obtain the spatially-resolved, convective heat transfer distribution on the target plate. While heat transfer distributions showed local maxima at the site of jet impingement, complex geometric features within the vent resulted in variation in the convection rate when comparing the multiple impinging jets emerging from a single Li-ion cell. Heat transfer correlations were developed in the form of Nusselt number as a function of Reynolds number and may be used in thermal runaway models which seek to include the effects of venting and combustion as an alternative to resolving the impingement heat transfer rates with expensive 3-D computational fluid dynamics simulations. [ABSTRACT FROM AUTHOR]

Inter-wrapper flow (IWF) is a typical thermal hydraulic phenomenon that exists in narrow gaps among the adjacent assemblies of a liquid metal fast reactor (LMFR) that can dissipate heat from assemblies and transfer heat among adjacent assemblies. Moreover, when blocked or reduced flow accidents occur, the IWF has a significant effect on reactor safety, especially reducing the peak cladding temperature. In this study, a computational fluid dynamics (CFD) model of the Karlsruhe liquid metal laboratory IWF experimental setup (called MYRRHA design) is built. The model contains three fuel assemblies with seven rods using lead–bismuth eutectic as working fluid. The new mesh generation method, correlation of turbulence model, and fluid–solid coupling heat transfer were considered in the CFD model. The established model was initially validated, and the simulation results were found to be in good agreement with experimental data. The influence of IWF on the thermal hydraulic characteristics within the rod bundle was revealed. The results indicated that the IWF rate can affect the heat transfer capability of the bundle under. The amount of heat removed increased by up to 10% with the IWF rate in a single bundle. The occurrence of IWF reduces the wall surface temperature and appropriately balances the temperature of adjacent bundles; however, it cannot effectively reduce the peak temperature of the cladding. The complex heat transfer characteristics and flow mechanism under the influence of IWF and wire mixing were revealed. The work presented in this paper represents an important step toward the IWF research on blocked flow scenarios. • A CFD model of a typical three bundles with IWF in LFR is developed. • The three dimensional flow and heat transfer features of the IWF is investigated. • The IWF effects the distribution of coolant temperature and velocity in the bundles. • The heat dissipation capacity increases as the IWF rate increases in LFR. [ABSTRACT FROM AUTHOR]

• Streamlined structures - new promising 3D printed catalytic carrier. • New catalytic carriers, the walls of which are modelled like airfoil profiles. • Influence of the streamlined walls shape on the flow resistance, Nu number and fluid velocity distribution. The paper presents the research on the new structured catalytic carriers, called streamlined structures. The innovative structures are composed of short triangular channels, the walls of which are similar to an airfoil profile. The structures were made using additive manufacturing method – selective laser melting (SLM) - in three different lengths. The study includes flow resistance and heat transfer, both realized using Computational Fluid Dynamics (CFD) modeling and experimentally. Flow resistance was measured by precise micromanometer over a wide range of gas velocities. During heat transfer experiments, electric current flowing through the metal structures heated them (Joule effect). The experimental results are in acceptable agreement with the CFD taking into account the accuracy of the structures' manufactured. The novel structures display improved heat transfer properties compared to monoliths and satisfactory low pressure drop. The flow patterns modelled using CFD prove that the inlet vortex has completely disappeared and the outlet vortex is significantly reduced compared to classic monolithic structures. The novel structure studied here is a promising prospect for the development of catalytic reactors. [ABSTRACT FROM AUTHOR]

• Five ML models have been developed to predict thermal-hydraulic performance of MFHS. • MF porosity, pore density, D h , and R e have been considered as input feature. • N u and f have been considered as output parameters. • A database of 1000 data points has been generated using CFD/HT model. • SVR and ANN predict independent test datasets with a M A P E of less than 3.1%. Metal foam heat sinks (MFHSs) are often used for electronic cooling because of their high specific heat transfer surface area, fluid mixing capability, and lightweight. Thermal-hydraulic performance of MFHS is known to be related to the morphological parameters of the metal foam (MF), physical dimensions of the heat sink, and coolant flow condition. Moreover, the highly random and complex geometrical nature of MFHS makes full-scale numerical simulation and experimental analysis expensive. In this paper, we have utilized machine learning (ML) methods to predict the thermal-hydraulic performance of MFHS, considering MF morphology, heat sink dimension, and coolant flow condition as input features. Considering local thermal non-equilibrium conditions for MFHS, a database of 1000 data points is generated utilizing a validated high-fidelity computational fluid dynamics/heat transfer (CFD/HT) model. The data sets consist of two non-dimensional descriptors, i.e., Nusselt number (N u) and friction factor (f) , along with the four input features such as MF morphological parameters, i.e., porosity and pore density, heat sink geometrical dimensions, i.e., hydraulic diameter (D h) and flow condition, i.e., Reynolds number (R e). Five different ML-based regression models, namely k-nearest neighbor (KNN), random forest (RF), extreme gradient boosting (XGBoost), support vector regressor (SVR), and artificial neural networks (ANN), have been developed. Hyper-parameters of each ML model have been systematically optimized, and optimized model's performance have been compared using statistical score metrics and considering the initialization effect. Additionally, in order to demonstrate the robustness of the developed ML models, individual model performance has been evaluated by independent datasets. Results indicate that for testing datasets, all ML algorithms, except KNN, can predict the thermal-hydraulic performance of MFHS reasonably well, with a mean absolute percent error (M A P E) of about 4.59% and a 1.24 standard deviation (SD). However, SVR and ANN outperform other models for independent datasets with a M A P E of less than 3.1%. [ABSTRACT FROM AUTHOR]

• Experimental test is employed to investigate the effects of adding array impingement and area ratio on overall cooling effectiveness and temperature uniformity. • Adding array impingement can bring more than 20% overall cooling effectiveness increment and more than 24% temperature uniformity increment. • Increasing the area ratio from 1 to 4 can bring more than 80% overall cooling effectiveness increment and more than 40% temperature uniformity increment. • Increasing the area ratio can maximize the cooling potential of impingement/effusion scheme, resulting in a high and uniform temperature distribution, thereby increasing the reliability and durability of afterburner heat shields. • The experimental results of DCH with various area ratios at different momentum flux ratios can be used to predict the temperature distribution in real engine conditions. Considering that the jet impingement cooling method applied to the combustion chamber and turbine blade has a beneficial effect on the cooling performance, the impingement/effusion cooling was applied in the afterburner heat shield (DCH) to improve the reliability and durability of the afterburner cylinder. Although the impingement/effusion cooling scheme has been numerously investigated on the internal heat transfer, its investigation of conjugated heat transfer characteristics is limited as applying in the afterburner heat shield. This paper aims to investigate the effects of adding array impingement and area ratio on the conjugate heat transfer of afterburner heat shield. The surface temperatures on the mainstream side of DCH in the upstream (UR), midstream (MR), and downstream (DR) regions were measured using IR thermography under a high-temperature ratio between mainstream and coolant (T g /T c = 2). The overall cooling effectiveness (ϕ) and temperature uniformity (RSD) were plenty compared with the single-layer effusion cooling heat shield (ECH) at three momentum flux ratios (I = 0.02,0.22,0.50). Moreover, the area ratio of film to impingement holes (A f /A i) was enlarged from 1 to 4 to obtain high cooling effectiveness and low-temperature gradient. The results indicate that when I is larger than 0.22, the area-averaged ϕ of DCH compared with ECH can be improved by about 16% over the whole measured regions, and 20% in the UR with the lowest ϕ. In addition, the drop coefficient of the RSD of DCH can reach 18%. In comparison with the DCH at A f /A i = 1, the DCH with an area ratio of 4 can achieve gains of 80% and 45% on ϕ and RSD , respectively. Therefore, adding array impingement on the coolant side of DCH and increasing A f /A i cannot only effectively reduce the surface temperature of the heat shield and form efficient cooling in the UR, but also increase the temperature uniformity over the entire heat shield, thereby improving the reliability and durability of the afterburner cylinder. Furthermore, the comprehensive and new database can be used to evaluate the computational fluid dynamics simulations in related coupled and decoupled research. [ABSTRACT FROM AUTHOR]

• An optimization method using the conjugate heat transfer CFD and the cGAN model is developed for the arrangement of film holes on turbine blades. • The optimized scattered arrangements of film holes can improve the uniformity of wall temperature under heterogeneous thermal loads. • Sampling principles of cGAN model are suggested for the prediction of complex phenomena including backflow. Cooling design optimization with complex nonuniform heat loads is a typical challenge in the development of new generation gas turbines. Combined inlet hot streaks and swirls caused by lean-burn combustor force film cooling to attenuate uneven heat loads on the blade surface, especially in the spanwise direction. Besides, the complex coupling relationship among hundreds of design variables of film cooling arrangement hinders the development of the optimal design. The deep learning model shows a strong fitting ability when dealing with high-dimensional nonlinear problems, which could fit the mapping relationship between design variables and the temperature field. In this paper, a turbine cooling design optimization methodology based on conjugate heat transfer (CHT) simulation and conditional generative adversarial network (cGAN) is developed, and the film cooling design of the 1st stage turbine vanes is optimized through the multi-objective genetic algorithm (MOGA). An initial sample containing 96 cases is constructed by CHT computational fluid dynamics (CFD) simulation with inlet hot streaks and swirls. Based on the initial sample, a cGAN model that predicts the temperature distribution of the vane surface is trained and tested. The film hole arrangement of the vane surface is described by a 276-bit binary optimization variable. The 5% maximum temperature predicted by cGAN and the regressed coolant mass flow is used as the dual optimization objectives. The optimal film hole arrangements in rows and the scattered film hole arrangements found by MOGA are compared, which shows that the optimal scattered arrangements perform better due to well adaptability to the nonuniform thermal load in the spanwise direction. The impact of sample size and sample selection on the performance of the cGAN model is discussed. The retrained cGAN model indicates that a proper abundance of specific samples can improve the prediction of complex coupling phenomena such as backflow. [ABSTRACT FROM AUTHOR]

• Replication is used to fabricate open-cell aluminum foams with bimodal cell size. • Coarse (C – 7 mm) and fine (F – 1 mm) cells are combined in different proportions. • The foam containing 67%C-33%F (C67F33) has a remarkable total porosity of 76%. • C67F33 exhibits the highest heat transfer coefficient and the lowest pressure drop. • C67F33 shows excellent thermal efficiency and great potential in thermal management. Recent advances in cellular materials for active thermal management applications involve the integral design of their porous structure. In this work, open-cell aluminum foams with porosities in the range of 0.60–0.76 are developed, containing pores with spherical geometry and a bimodal pore size distribution. The fabrication strategy involves the use of the replication method by infiltration with liquid aluminum of porous preforms formed by packing NaCl spheres of two largely different sizes (7 mm and 1 mm average diameter), which are then removed by water dissolution. The paper describes cellular materials with different proportions of coarse and fine pores. Their detailed characterization by pore volume fraction, pressure drop, permeability, thermal conductivity and heat transfer coefficient is supported by analytical schemes. In addition, these materials were characterized under realistic operating conditions using computational fluid dynamics simulations. The material with 67 percent coarse pores and 33 percent fine pores, which has the highest porosity (and thus permeability), has the most appealing heat dissipation properties with the lowest pressure drops, making it an excellent candidate for emerging thermal management applications in electronic systems. [Display omitted] [ABSTRACT FROM AUTHOR]

• The effect of pulsating flow on heat transfer efficiency of ice slurry is studied. • The cycle-averaged heat transfer coefficient can be increased by 34%. • Heat transfer is more efficient for large particles and high ice volume fraction. • The prediction correlation for the time-averaged nusselt number is proposed. In this paper, the heat transfer enhancement of ice slurry in a horizontal pipe with constant heat flux has been investigated numerically. The model is validated with the experimental results from the literature. Then the axial distribution of the heat transfer coefficient, the bulk and wall temperature and the ice volume fraction are obtained. The factors that affect the heat transfer coefficient are analyzed. Furthermore, the heat transfer efficiency of ice slurry in pulsating flow is compared with that in steady state. It is found that the heat transfer efficiency of ice slurry can be significantly improved by pulsating flow. The maximum increment of cycle-averaged heat transfer coefficient reaches 34.32%. Moreover, the degrees of heat transfer enhancement increase with increasing pulsating frequency, relative amplitude of velocity, ice particle diameter and ice volume fraction, and decrease with increasing cycle-averaged velocity. And the heat transfer is more efficient to ice slurry with large particles and ice volume fraction under the pulsating flow conditions. The pulsating frequency is suggested to be not more than 10π Hz. Finally, the correlation for predicting cycle-averaged Nusselt number of ice slurry in pulsating flow is established, and obtaining the reasonably good prediction results. [ABSTRACT FROM AUTHOR]

The impingement cooling is used to protect turbine components under high thermal load. This paper conducts a numerical study of heat transfer characteristics of turbine leading edge with lamilloy cooling structure. Target surface curvature and jet-to-surface spacing under various crossflow Reynolds number conditions are considered. Meanwhile, the target surface is dimpled to enhance heat transfer capability. Besides, staggered film holes are considered in the computational domain. The results show that the crossflow induces a counter rotating vortex pair that greatly increase the near wall turbulence and local heat transfer. The vortex pair forms the bound for a U-shaped high heat transfer region caused by the jet impingement. The target surface curvature tends to enlarge the relative area of the U-shaped region. The increased crossflow strength weakens the jet cooling effect, the total heat transfer performance is therefore decreased. Large jet-to-surface spacing enhances the impingement cooling when crossflow is weak but the total heat transfer will not recover as crossflow Reynolds number get higher compared with small and medium spacing cases. • Computational fluid dynamics (CFD) models used to simulate turbine leading edge internal heat transfer. • Impingement cooling configured with dimpled surface and film holes. • Compound influence of jet-to-surface spacing, surface curvature under crossflow. [ABSTRACT FROM AUTHOR]

The paper presents comprehensive experimental and numerical study to evaluate thermo-hydraulic performance of 30° and 60° chevron plate geometries using multi walled carbon nanotubes (MWCNT)/distilled water nanofluid as coolants. The experimentation using distilled water and MWCNT nanofluid on cold side was conducted by varying flow rate and concentration, keeping hot side at constant flow. The three dimensional computational models geometrically similar to actual plates were developed. The numerical analysis was done using Ansys 15.0 (Fluent) solver. The correlations based on experimental data are proposed to evaluate Nusselt number and friction factor of both chevron geometries having coefficient of determination 0.996–9998. The thermo-hydraulic performance parameters were numerically evaluated and validated with experiments. The results deviate by <1.5%. The heat transfer increases by 9.25% for 60° plates compared to 30° using distilled water. However, maximum heat transfer of 13.64% and 17.27% was found for 30° and 60° plates respectively using 1 vol% nanofluid. [Display omitted] • MWCNT nanofluid as coolant on thermo-hydraulic performance of PHEs are reported. • Effect of concentration, flow rate, chevron angles are studied. • Correlation for Nusselt number and friction factor for both PHEs are proposed. • Maximum Q avg of 13.64% & 17.27% is reported for 30° & 60° PHEs at 1 vol%. • Temperature and flow distribution inside 60° plate is best. [ABSTRACT FROM AUTHOR]

Heat pipe reactor relies on heat pipes to transfer the fission energy generated in the core to the secondary loop or thermoelectric conversion system. In our group's design, thermoelectric generators (TEGs) are selected to convert fission energy to electricity. In this paper, we established a heat pipe reactor experimental device with TEGs. To verify the heat transfer performance of the heat pipes and the thermoelectric conversion efficiency of TEGs, steady-state experiments were carried out. The minimum temperature drop between the evaporator and condenser sections of heat pipes can reach 6.4 °C. The maximum output power of TEGs can go 74.4 W. The thermoelectric conversion efficiency is about 8.0%. The Computational Fluid Dynamics (CFD) method is used to simulate the steady-state operation of the experimental device. After comparing the simulation results with the experimental data, the temperature error of the heat pipes is less than 26.8 °C, and the temperature error of the TEGs is less than 17.3 °C. A CFD simulation method for heat pipe reactor steady-state operation is presented based on the verification and validation. [ABSTRACT FROM AUTHOR]

• A combined RANS/URANS study on the natural draft and heat transfer of a thermal chimney consisting one row or two rows of horizontally-aligned cylinders in multiple columns is presented. • The effect of horizontal pitch on thermal chimney performance is balanced by two counteracting mechanisms: the chimney effect and the blockage effect. • At a fixed horizontal pitch of intermediate value, a minor modification of the vertical pitch could change the flow pattern substantially from a plume-dominant mode to a chimney-dominant one, leading to significant enhancement of natural draft strength and heat transfer for the thermal chimney system. To address the scarcity of natural convection research for the tube array with three or more columns of horizontally-aligned cylinders, this paper conducts RANS/URANS simulations for multiple cylinder columns in one or two rows, validated by particle-image velocimetry and heat transfer measurements. Parametric study with varying horizontal and vertical pitches is implemented by RANS with transition SST model. Key findings are then substantiated and examined by URANS. It is found that the horizontal pitch influences the balance between the chimney effect and the blockage effect, thus has an optimum with respect to the natural draft velocity. For all the vertical distances computed in the two-row thermal chimney model, the flow pattern stays in a plume-dominant mode at the large horizontal pitch and a chimney-dominant mode at the small horizontal pitch. Interestingly, at the intermediate horizontal pitch (pitch/diameter≈2.5), the flow pattern switches from plume-dominant to chimney-dominant over a minor increase of the vertical pitch (from 4.5 to 6 diameters), leading to significant augmentation in natural draft velocity and heat transfer on cylinder surfaces. This distinct thermo-flow behavior, identified for the first time to the authors' knowledge, may be harnessed to improve the performance of passive heat exchangers. [ABSTRACT FROM AUTHOR]

• A set of experiments of LBE heat transfer in a circular tube were carried out. • CFD simulations of LBE heat transfer in a circular tube were carried out using different turbulent model and Pr-t model. • Evaluation of the applicability of the numerical models was carried out combing simulation results and experiment results. The understanding of flow and heat transfer characteristics of liquid lead–bismuth eutectic (LBE) is essential for nuclear applications. In this paper, a corresponding experimental facility was established and a set of experiments of heat transfer of lead–bismuth eutectic flow in a circular tube was carried out, and a new heat transfer correlation was obtained through the experimental data to study the flow and heat transfer characteristics and evaluate a suitable computational fluid dynamics (CFD) model for LBE flow. The correlation fits well to the experimental data and the deviation of the correlation is smaller than 15%. At the same time, a CFD program was employed to evaluated the applicability of various turbulent models (standard k- ∊ , standard k- ω , SST k- ω) and turbulent Prandtl number models for LBE flows in the circular tube. Among the turbulence models, SST k- ω model shows the best agreements, the relative deviation of the simulation result from the experimental data is −3.0%∼34.7%. Among the turbulent Prandtl number models, Cheng-Tak model shows the best agreement, the relative deviation is 0.18%∼24.7%. This work provides valuable experimental data and CFD simulation method for liquid metal flow and heat transfer analysis. [ABSTRACT FROM AUTHOR]

• Two different immersed surfaces are studied: a sphere and a vertical cylinder • CPFD properly predicts low heat transfer rates in defluidized regions • TFM approach over predicts heat transfer rate up to 77 % compared to CPFD • Different local heat transfer mechanisms are observed on the heat transfer surface This paper presents a 2-D numerical simulation of a freely bubbling fluidized bed with immersed surfaces, using the Computational Particle Fluid Dynamics (C P F D) model implemented in the Barracuda commercial software. The heat transfer coefficients obtained are compared with an experimental study available in the open literature and numerical simulations based on the two-fluid model approach performed by other authors. Two different immersed surfaces, representing spherical and cylindrical geometries were studied. The simulations results show different heat transfer mechanisms, depending on the angular position in the two immersed surface geometries studied. The time average heat transfer coefficient around the whole heat transfer surface were 25 % and 38 % lower than the experimental study, for the cylindrical and spherical surfaces, respectively. These differences are lower than the results obtained with the two-fluid model approach reported in the open literature. The numerical results indicate that CPFD-Barracuda is able to properly simulate the heat transfer and the dynamics of the bed in defluidized regions, such as on the top of an immersed surface, where the two-fluid model fails and overpredicts the heat transfer rate. [ABSTRACT FROM AUTHOR]

A solid oxide fuel cell (SOFC) is an energy converter device that directly converts the fuel's chemical energy into thermal and electrical energies. However, the performance of a SOFC is sensitive to the operating conditions, which indicates the need to control the operating parameters such as the operating temperature and inlet gas physical and chemical properties. In this paper, a three-dimensional (3- D) computational fluid dynamics (CFD) model of a button SOFC has been developed based on fluid flow, mass and heat transfer, and current and potential transport to study the performance of the button SOFC at different operating temperatures and flow rates. The results of all the investigated operating conditions have been validated with an in-house button SOFC. The results showed that the current density of the button SOFC increased significantly, to about 108.5% at average cell voltage 0.6 V and at oxygen flow rate of 1.8 L min−1 and hydrogen flow rate of 0.6 L min−1, when the operating temperature increased from 973 to 1023 K. However, less sensitivity has been found at the same average voltage of 0.6 V and an operating temperature of 973 K, the increase in the current density was about 9.7% when the flow rate of the oxygen increased from 0.4 to 0.6 L min−1, and the hydrogen flow rate increased from 1.2 to 1.8 L min−1, respectively; this was in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

• External subroutine for the GOTHIC code Critical Heat Flux heat transfer. • Subroutine qualification for In-Vessel-Retention Critical Heat Flux. • Atucha-1 NPP containment safety analysis for IVR, for two scenarios, LBLOCA and SBO. GOTHIC is an integrated, general purpose thermal hydraulic software package for design, licensing, safety and operating analysis of Nuclear Power Plant containments, confinement buildings and system components. It bridges the gap between the lumped parameter codes frequently used for containment analysis (such as MELCOR, MAAP, COCOSYS, ASTEC codes) and Computational Fluid Dynamics codes. Within a single model, GOTHIC can include regions treated in conventional lumped parameter mode and regions with three-dimensional flows in complex geometries. The heat transfer correlations built into GOTHIC cover the portion of the boiling curve which spans single phase heat transfer up to pre-Critical Heat Flux (CHF) heat transfer. The implemented boiling curve is truncated to exclude post-CHF heat transfer as it has not been adequately verified and was considered by the developers to have little application in general containment analysis. As such, one area that the code is not currently qualified for is post-CHF heat transfer, which could occur for example in the case of In-Vessel Corium Retention, where cooling water enters in contact with the high temperature of the Reactor Pressure Vessel wall. The presented research focuses on creating an external subroutine that solves this limitation, enabling the GOTHIC code to account for CHF phenomena. The modeling of CHF would be very useful in order to enable the code to simulate the external Reactor Pressure Vessel (RPV) Cooling , as well as other types of severe accidents or analyses where post-CHF simulation is required. Several subroutine function switches were implemented in order to facilitate its usage for different types of heat structures and correlations. The subroutine determines the CHF values based on either: the 2006 Groeneveld Look-up Tables, Lookup Tables for Large Diameter Vertical Tubes, Look-up Tables for Large Diameter Horizontal Tubes, or the correlation used by the MELCOR code for critical heat flux situations. It shall be noted that the developed subroutine and its implementation were performed without the need to have access to the GOTHIC source code. In a previous paper, the GOTHIC code was used to perform a containment safety analysis for the Atucha-I NPP (CNA-I) for an in-vessel retention type of analysis. Highly conservative vapour generating boundary conditions were used in order to simulate the boiling between the cavity water and the RPV surface, and to bypass the GOTHIC limitation. The newly developed subroutine was used for the analysis of two postulated Atucha-I in-vessel retention scenarios, a Large Break Loss Of Coolant Accident (LBLOCA) and a Station Black-Out (SBO), with the simulation of heat transfer between RPV and cavity water. Specifically for in-vessel retention situations, a separate user selectable option for the subroutine was developed, in which the Critical Heat Flux is determined based on experiments performed at the ULPU facility from the University of California, Santa Barbara, USA, which were combined with the 2006 Groeneveld Look-up Tables primarily in order to have a pressure dependence. This was performed because for the Atucha-I analysis, the pressure was higher than in the ULPU facility. [ABSTRACT FROM AUTHOR]