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This paper describes a model of hydrogen blowdown dynamics for storage tanks needed for hydrogen safety engineering to accurately represent incident scenarios. Heat transfer through a tank and pipe walls affects the temperature and pressure transients inside the storage vessel and at the nozzle exit, and thus the characteristics of the resulting hydrogen jet in the case of loss of containment. Current non-adiabatic blowdown models are validated against experiments performed with hydrogen storage tanks at only ambient temperature. The effect of heat transfer for cryo-compressed hydrogen is more significant due to a larger difference of temperature between the stored hydrogen and the surrounding atmosphere, especially in case of equipment insulation failure during an incident. Our previous work demonstrated that the heat transfer through a discharge pipe wall can significantly affect the mass flow rate of cryogenic hydrogen releases. Thoroughly validated models of non-adiabatic blowdown dynamics for cryo-compressed hydrogen are missing at the moment. This work develops further the non-adiabatic blowdown model at ambient temperature using the under-expanded jet theory developed at Ulster University, to expand it to cryo-compressed hydrogen storage tanks. The non-ideal behaviour of cryo-compressed hydrogen due to low temperatures is taken into account through the high-accuracy Helmholtz energy formulations. The developed model includes effect of heat transfer at both the tank and the discharge pipe walls. The model is thoroughly validated against sixteen tests on blowdown of hydrogen storage tanks with initial pressure 0.6–20 MPa ab and temperature 80–310 K, through release nozzle of diameter in the range 0.5–4.0 mm, performed within the PRESLHY project. The model well reproduces the experimental pressure and temperature recordings in the storage tank during the entire blowdown duration for the whole set of sixteen tests. In conjunction with the volumetric source model, explained in detail, the physical model allows to perform CFD simulations accurately reproducing the temperature distribution in time and space for the cryogenic hydrogen jet experiment. • Physical model of blowdown dynamics for cryo-compressed hydrogen storage tanks. • The model accounts for heat transfer at both the tank and the discharge pipe walls. • The model employs the high-accuracy Helmholtz energy formulations. • Validation against tests with pressure 0.6–20 MPa and temperature 80–310 K. [ABSTRACT FROM AUTHOR]

• The double two-phase thermosyphon loops (DTPTLs) used for low temperature Stirling refrigerator is developed. • The characterization of heat transfer and pressure drop in the DTPTLs is investigated by theoretical calculation for various working refrigerants. • The basic structure of the DTPTLs is modified and improved for dragging and moving convenience. • The no-load cooling temperature could reach −80 °C, and the maximum temperature difference all inside the refrigerator container is less than 5 °C during steady-state operation. With the growing of demand for the low temperature pharmaceutical cold chain, the Stirling cooler has been attractive for years. However, the heat transfer inside the refrigerator could be ineffective by natural convection due to the small area of the plug-in Stirling cold finger. In this paper, the double two-phase thermosyphon loops (DTPTLs) used for low temperature Stirling refrigerator is developed. The characterization of heat transfer and pressure drop in the DTPTLs is investigated by theoretical calculation for various working refrigerants. Then the basic structure of the DTPTLs is modified and improved for dragging and moving convenience. Moreover, the comparison of the temperature distribution inside the refrigerator container between the DTPTLs and the plug-in cold finger methods is demonstrated by numerical simulation. The simulation result indicates that a well temperature distribution inside the container can be obtained by using DTPTLs. In the end, an experimental test is conducted at room temperature. It's shown that the no-load cooling temperature could reach −80 °C in a few minutes. Over steady-state operation, the maximum temperature difference all inside the container is less than 5 °C, which proved the positive heat transfer effect of the DTPTLs on the cooling performance of the low temperature Stirling refrigerator system. [ABSTRACT FROM AUTHOR]

• Flow boiling heat transfer and pressure drop data for R513A. • HTC shows both nucleative and convective behavior with operating conditions. • Pressure drop increases with mass flux and decreases with saturation temperature. • New composite prediction method (MAPE = 25.3%) for heat transfer coefficient. • Frictional pressure gradients well predicted by Friedel correlation (MAPE = 13.8%). This paper presents two-phase heat transfer coefficient and pressure drop data of refrigerant R513A, a new azeotropic mixture conceived as possible alternative to R134a for medium temperature small-size refrigeration systems. All the experiments were performed in a commercial horizontal stainless-steel tube having an internal diameter of 6.0 mm and an outer diameter of 8.0 mm. The channel heating was obtained through DC current and Joule effect. The effect of the main operating parameters in terms of mass flux (from 150 to 500 kg/m2s), heat flux (from 5.0 to 40 kW/m2), saturation temperature (from 30 to 50 °C) and vapor quality (from the onset of boiling up to the dry-out occurrence) was analyzed and discussed for the heat transfer coefficient values, finding that both convective and nucleate boiling were significant contributions. The same ranges of mass flux and saturation temperature were also applied to frictional pressure gradient trends with vapor quality, taken in adiabatic conditions. The thermo-hydraulic performances were then compared with those of R134a, obtaining lower heat transfer coefficients and very similar pressure gradients. Finally, the collected experiments were assessed with values predicted from the most quoted correlations available in literature. A new composite method for nucleate-dominant or convective-dominant mechanisms was proposed for the evaluation of the heat transfer coefficient, with a mean absolute error of 25.3%, whereas the frictional pressure gradient values were well predicted with the Friedel correlation, that provides a mean absolute error of 13.8%. [ABSTRACT FROM AUTHOR]

• Time-varying buckling and post-buckling of tapered columns in fire. • Temperature-dependent material properties. • The convective–radiative condition. • Geometric nonlinearity and yield strength. • Effects of transient localised fire on the tapered column. This paper presents time-varying flexural buckling and post-buckling responses of tapered columns under a transient fire of which the temperature is non-uniform along the length. First, the transient temperature field within the column is determined by solving a dimensionally reduced transient heat transfer problem considering the convection-radiation boundary conditions and temperature-dependent (TD) material properties. Subsequently, the von Kármán geometric nonlinear theory is applied to obtain the nonlinear equilibrium equation. The nonlinear heat transfer and equilibrium equations are solved by the differential quadrature (DQ) method. According to a yield criterion, the ultimate load at which the material failure occurs is predicted. The influences of a transient localised fire on the temperatures, buckling and post-buckling responses of tapered steel tubular columns are discussed. [ABSTRACT FROM AUTHOR]

The goal of the current paper is to create a novel model for the two-dimensional flow (TDF) of a second-grade fluid and the transfer of heat due to free convection. The second-grade fluid travels through the porous media and is electrically conducted. The governing equation for fluid velocity and temperature is formulated as a set of partial differential equations jointly. The model is developed in fractional form by applying the Caputo-Fabrizio (CF) fractional derivative approach. The two-dimensional flow problem is modeled in terms of one-sided coupled fractional partial differential equations with corresponding physical conditions imposed on the fluid flow and temperature. The problem is initially converted to a dimensionless form and then solved for the exact solutions by applying joint Fourier and Laplace transforms. Exact solutions are examined for fluid velocity and temperature and then in limiting cases are reduced to some well-known fluid motions. Some special cases are also obtained from the general solutions. For the numerical results, Mathcad-15 software is used and the results are plotted in various graphs. The temperature, and velocity profiles are discussed and highlighted for embedded flow parameters. The model obtained in this work is new and can be extended for other fluid models hence this article provides a base for future research. [ABSTRACT FROM AUTHOR]

High inter-laboratory reproducibility is required for conducting collaborative experiments among several laboratories. The primary aim of our evaluation of the physical stability of amorphous drugs, conducted in co-operation with eight laboratories, was to establish a protocol for isothermal storage tests to obtain data of the same quality from all the participating laboratories. Sharing a protocol that contained the same level of detail as the experimental section of general papers was insufficient for high inter-laboratory reproducibility. We investigated the causes of variations in the data from the various laboratories and restricted the protocol step-by-step to achieve high inter-laboratory reproducibility. The various experimentalists had very different levels of awareness regarding how to control the temperature of a sample as the samples were transferred into and out of thermostatic chambers. Specific instructions on how to conduct this operation, such as regarding the time required for the transfer and thermal protection of the container during the transfer, helped to reduce variation. Improved inter-laboratory reproducibility revealed that the physical stabilities of amorphous drugs differed when samples were prepared in differently shaped aluminum pans designed for various differential scanning calorimeters. [ABSTRACT FROM AUTHOR]

The vast significance and applications in various industrial works such as heat and cooling process, chemical reactors, food storage systems and several medical works motivated the author to conduct this type of study. The aim of this paper is to inspect the two-dimensional incompressible magnetohydrodynamic flow of Williamson fluid through a stretching sheet. The Cattaneo-Christov temperature and concentration flow is considered with the effects of double stratification and viscous dissipation. The leading nonlinear partial differential equations of flow are transformed into ordinary differential equations by means of renowned similarity transformations and the solutions of flow problem are obtained by means of bvp4c method on MATLAB software. The Williamson fluid parameter depending on time relaxation and declines the fluid motion. The motion of fluid slowed down due to Hartman number. The mass and heat flow is noted to be decline due to thermal and solutal relaxation parameters. The rises in stratification coefficient reduce the mass and heat transferal rate. [ABSTRACT FROM AUTHOR]

The present paper investigates the flow field and heat transfer in a microchannel with incorporating surface hydrophobicity and considering its thickness. The microchannel is under partial magnetic field (MF), which is applied to the top thermal-insulated wall in Hartmann numbers 0 to 30. The results show that at Ha = 0, viscous dissipation (VD) and heat transfer decrease with increasing slip coefficient. Also, raising the Hartmann number (Ha) increases the friction coefficient. The Nusselt number (Nu) reaches its highest value at Ha = 20 for all cases, but then, as the Ha increases, the average Nu reduces. [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]

A two-phase thermosyphon loop is an ideal heat transfer device to achieve compact and efficient cooling with low energy consumption. In this paper, a two-phase thermosyphon loop with a horizontal parallel tube evaporator for multiple heat source cooling is proposed. The effect of the filling ratio on the transient response of temperature and pressure, heat transfer characteristics, instability issues, as well as flow regimes under different heat loads are investigated experimentally and visually. The filling ratios are divided into three groups according to their unique heat transfer and instability characteristics. The research results show that a too low or too high filling ratio is not conducive to the safe and stable operation of the system. At medium and high filling ratios, temperature and pressure overshoot are prone to occur, threatening the safe operation of the system; geyser boiling is another unstable phenomenon that can be inhibited as the heat load increases. Gravity will lead to uneven distribution of working fluid in the evaporator and further affect the temperature uniformity and heat transfer capability. From the perspective of temperature control performance and heat transfer capability, 30% is the optimal filling ratio in this study, with a minimum thermal resistance of 0.12 ℃ ⋅W-1 and a maximum heat transfer coefficient of 1345.36 W⋅m−2⋅℃−1. This paper provides a basis for designing and applying a two-phase thermosyphon loop for multiple heat source cooling in confined spaces. [ABSTRACT FROM AUTHOR]

Absorption machines are frequently used for cooling and heating. However, they must be improved to achieve high performance at a lower cost. Being a key component of these machines, this paper focuses on the absorber and specifically on falling film absorber configuration due to its compactness and simple geometry. This paper reviews the different analytical and numerical approaches used to analyze the thermal, mass and hydrodynamic phenomena occurring in falling films for both smooth and wavy-laminar regimes. It shows the significant progress made since 2000 in terms of mathematical models developed and coupling effect resolution. Research using thermodynamics to identify, locate and quantify the entropy generation sources in falling film absorbers is also presented. [ABSTRACT FROM AUTHOR]

Deaerator is one of the most important equipment for steady state and dynamic operation of power plants. The deaerator energy storage utilization process is one of the most essential ways to enhance the variable load rate of power plants. The purpose of this study is to improve the dynamic simulation performance of the deaerator during unit load changes by constructing a more reasonable deaerator model, aiming to provide guidance for practical operations. In this paper, a thermal mass microelement algorithm is proposed for the heat transfer between droplets and steam in the deaerator, followed by segmental modeling of the deaerator. By comparing with the operation data of a power plant, the steady state operation error of the deaerator model is within 0.6 %. Subsequently, the unit load variation process is simulated and the dynamic variation accuracy of the model proposed in this paper is enhanced by 1–2 % compared to the lumped parameter model. The dynamic characteristics of the deaerator are obtained by simulating the step and ramp changes of the deaerator boundary conditions and the deaerator start-up process. In addition, during the simulation of condensate throttling, the maximum power of the unit using the deaerator model in this paper is 0.2–1.5 MW larger than that of the lumped parameter model. • A thermal mass microelement algorithm for heat exchange between droplets and steam in deaerator is proposed. • A more rational deaerator model is established. • Compared to the lumped parameter model, the proposed model enhances the accuracy of the dynamic simulation by 1–2 %. • The maximum power in the proposed model during condensate throttling is 0.2–1.5 MW greater than that in the lumped model. [ABSTRACT FROM AUTHOR]

• Neutron physics, thermal–hydraulic and water chemistry are coupled to predict corrosion product growth and CIPS risk. • Boron hideout mass shows a parabolic tendency as CRUD depositions thicken and bulk coolant boron concentration decreases. • Power tends to shift to 0 % axial offset at EOC after the most negative axial offset of −5.07 % with 5.03 mg boron hideout. CRUD depositions on fuel cladding are the main cause of power shift and localized corrosion in nuclear power plants. This paper is the third of a three-part study concerning the prediction of CIPS risks during fuel burnup. In this paper, based on the coupling modules of CRUD growth and internal heat and mass transfer in Part 2, a multi-physics coupling method for high-fidelity simulation of CRUD growth and CIPS phenomenon is developed to better understand coupled physics and respective feedback mechanisms. Based on OpenMC, Fluent and self-developed CRUD-related code, this coupling method considers nuclide depletion, coolant flow, heat transfer and water chemistry, in which fine radial CRUD mesh in neutronic module and influences of CRUD surface characteristics on heat transfer in thermal–hydraulic module are introduced. The coupling method is applied to predict CIPS risk during a 360-day cycle depletion process reaching burnup of 22.04 MWd/kgHM. Corrosion products deposit on cladding to thicken CRUD, while flow erosion gets enhanced washing away more particles on CRUD surfaces, resulting in a slow-down net CRUD growth rate, reaching maximum values of 8.60 g in mass and 37.10 μm in thickness at EOC. As CRUD depositions thicken, boron hideout mass increases, while subsequently bulk coolant boron concentration decreases and boron diffuses out of CRUD depositions causing a decrease in boron hideout mass. The highest boron hideout mass and most negative AO both occur near MOC time. At EOC, net mass reduction of boron hideout and bottom-favored nuclide depletion contribute toward pushing power distribution closer to 0 % axial offset. The results of this study provide a precise method for understanding CIPS risk and its influencing factors to further predict and alleviate CRUD-related safety issues. [ABSTRACT FROM AUTHOR]

• Typical CRUD depositions are obtained via accerlated deposition method in rod array channels. • Effective CRUD thermal conductivity decreases as heat flux increases with 1.3866 W/(m × K) on average. • CRUD growth process is a combination of soluble precipitation and particulate aggregation. • Fouling resistance of corrosion product deposition behavior has been experimentally measured. CRUD depositions on fuel cladding are the main cause of power shift and localized corrosion in nuclear power plants. This paper is the first of a three-part study concerning the formation mechanism of CRUD depositions and its related heat transfer issues. In this paper, CRUD depositions are obtained under subcooled boiling conditions in 2 × 2 rod array channels via accelerated deposition method to explore corrosion product deposition and its feedback on heat transfer. Imbalance of deposition and erosion at initial stage causes fouling resistance to increase first and then decrease. CRUD growth is proposed as a relatively pure fouling process combining soluble precipitation and particulate aggregation. Through high-resolution characterizations, boiling chimney diameters span from 3 μm to a dozen microns. Principal components are nickel ferrite and nickel elemental with Fe/Ni ratio of 1.9:1. Static contact angle decreases to less than 30°. Effective CRUD thermal conductivity decreases with the increase of heat flux with 1.3866 W/(m × K) on average. The results of this study provide a precise method for understanding corrosion product deposition and its impact on heat transfer to further establish accurate CRUD-related models and predict CRUD-related safety issues. [ABSTRACT FROM AUTHOR]

• Decay of swirling flow and heat transfer parameters in a long straight pipe (l/d = 150) is experimentally studied. • Eight blade-type swirl generators with central body are tested. • Flow and heat transfer parameters are summarised and correlated using the swirl flow number. • Conclusions are made regarding transition from swirling to axial flow in terms of the energy loss reduction and heat transfer decay. • Heat transfer demonstrates the earliest transition to axial flow conditions. This paper describes an experimental study of heat transfer, local and total swirl flow parameters in the pipe 80 mm in a diameter and 150 diameters long. The pipe consists of 12 separate pipes of different length, connected to each other using 20 mm ring spacers. These spacers were also used to provide the flow and heat transfer measurements. Overall, eight blade-type swirl generators with central body and profiled according to the power low, are installed at the pipe inlet. The actual swirl intensity S of swirl generators is ranged from 0.38 to 1.29. The profiles of mean axial and tangential velocity, surface heat flux, swirl flow angle, static and total pressure, flow and surface temperature are measured. A few novel scientific results and equations are obtained, including the axial and tangential speed maximum, axial and tangential momentum flux, swirl number decay and energy loss transformation. The common link between the local and total swirl parameters, one-valued correlation between tangential and axial velocity were obtained. The results, presented in the paper led to the conclusion that transition from swirling to axial flow occurs at S ≈ 0.19 in terms of the heat transfer decrease, but at S ≈ 0.10 – in terms of the energy loss reduction. [ABSTRACT FROM AUTHOR]

Unlike ordinary nuclear power reactors, the floating nuclear power plants are constantly affected by sea waves and are often under inclined condition. The flow and heat transfer characteristics in the rod bundle channel for inclined condition is crucial for the design and operation of floating nuclear power plants. This paper experimentally investigates the flow resistance and heat transfer in an inclined 3 × 3 rod bundle channel at 10∼15 MPa in a natural circulation system and the inclination angle is 10°–30°. The mass flux becomes smaller as the experimental loop is inclined due to the decrease of the natural circulation driving force. As the system inclination angle becomes larger, the mass flux decreases more. Re and the outlet mass quality also affect the mass flux decreasing amplitude for inclined condition. For single phase flow, the friction coefficient correlation in a rod bundle channel is developed and the MAE (mean absolute error) is 2.82 %. The friction coefficients when the channel is inclined are larger than the friction coefficients when the channel is vertical. Correlations for Nu in the static vertical rod bundle channel are also developed and the MAE is less than 2 %. The heat transfer coefficient is enhanced for inclined condition if the effect of mass flux change is eliminated. For flow boiling, inclination has little effect on the number and size of the bubbles for highly subcooled boiling, while inclination has large influence on the flow pattern for saturated boiling. When the inclination angle becomes larger, the two phase multiplier increases. As the outlet mass quality increases, the increasing amplitude of two phase multiplier will become even larger when the inclination angle is larger. The heat transfer coefficient of flow boiling increases when the channel is inclined, and the enhancement is larger when the mass flux is smaller. When the inclination angle is 30°, the boiling heat transfer coefficient could increase by 25.7 % at a low mass flux. The paper reveals the quantitive influence of inclination on both single phase flow and flow boiling in the rod bundle channel. The working pressure and temperature have reached the operating conditions of the floating nuclear power plants, and the results can be applied to the design of nuclear power floating plants and pressurized water reactor using rod bundle fuel assembly. [ABSTRACT FROM AUTHOR]

An efficient thermal regulation strategy is of great significance in ensuring the safe operation of electric vehicles (EVs). However, the commonly used thermal management systems suffer from the problem of not being able to accurately and uniformly control the temperature distribution of lithium-ion batteries (LIBs), which poses great risks to the thermal safety control of batteries. In this paper, an advanced thermal management system for LIBs based on thermoelectric cooler (TEC) was designed to overcome the above problems. First, a temperature regulation mechanism model for LIB was constructed. Then, a novel temperature distribution modeling method for TEC was developed by using spectral method. This modeling process took into account the unsteady heat transfer characteristics, which can achieve high modeling accuracy. Next, a state space model of temperature control was constructed by combining a differential model of LIB with the proposed cooler model. On this basis, a temperature control strategy for LIB using nonlinear model predictive control (NMPC) method was proposed to optimize the cooling process because of its superior processing ability to constraints and nonlinearity. A various of experiments and verifications demonstrated that the presented thermal regulation strategy was effective and feasible. • An advanced thermal regulation system for lithium-ion battery based on thermoelectric cooler is designed. • A novel temperature distribution modeling method for TEC is proposed. • A regulation strategy is developed to control the uniformity of temperature distribution. • The paper provides a good guidance for the application and further study of advanced thermal management system in electric vehicle. [ABSTRACT FROM AUTHOR]

Power system flexibility can be improved effectively, if the advantages of the peak shaving ability of molten salt solar tower power (STP) plant can be developed and utilized. In this paper, the heat transport and load response characteristics of the molten salt STP plant in the regulation process are studied, aiming at serving the development of the regulation method in the rapid peak regulation process. The steam generation system and turbine system models of a 50 MW STP station are established. Two load regulation methods and operation modes are used to investigate the inertia and delay effects of heat transfer and evaporation, as well as load response characteristics during the actual regulation operation, including steam generation system following (SF), turbine following (TF), constant pressure operation (CP), and sliding pressure operation (SP). The results show that when the plant load is reduced by 10% Pe at the rate of 3% Pe /min, the heat transfer of salt/water and the evaporation process of water in the whole regulation process have a 250 s delay compared with the load. The larger heat storage characteristics of the plant help to improve the load response speed. The load response speed of the plant is faster in SF mode. TF mode is beneficial to the safe operation of the plant. Considering the operational safety of thick-wall component, the recommended running mode is the collocation of SF and SP mode, TF and CP mode. The results show that the load change rate of 10% Pe /min is permittable under TF and CP modes. The conclusion of this paper lays a foundation for the formulation of a peak regulation strategy for molten salt STPs. • Dynamic model for STP plant as participated in grid peak-shaving is established. • Transient response characteristics of STP plant during real load regulation are analyzed. • Influences of load changing rate on SPT plant under SGS following control mode are compared. • Recommended operation mode and load adjusting rate of the 50MW el STP plant are given. [ABSTRACT FROM AUTHOR]

• A comprehensive review on numerical simulations of boiling heat transfer from atomistic to mesoscopic and macroscopic scales is presented. • Critical issues related to nanoscale bubble nucleation mechanisms, pool boiling, and flow boiling are highlighted. • Potential solutions and future research in the field of boiling heat transfer using the MDS, LB and CFD methods are proposed. Boiling is an efficient heat transfer mode with significant potential for thermal management in high-power electronic equipment. However, a comprehensive understanding of the boiling process, which encompasses bubble nucleation, growth, coalescence, slipping, and detachment across various scales, remains challenging. Molecular dynamics simulation, lattice Boltzmann, and computational fluid dynamics methods are popular and powerful tools for investigating boiling heat transfer phenomena at microscopic, mesoscopic, and macroscopic scales. These methods enable researchers to uncover the underlying boiling mechanisms and propose heat transfer enhancement techniques. Therefore, this paper provides a comprehensive review of boiling heat transfer, spanning from atomistic to mesoscopic and macroscopic scales, utilizing these three numerical methods. It addresses critical issues related to nanoscale bubble nucleation mechanisms, pool boiling, and flow boiling, and proposes potential solutions and future researches, supplementing our previous review [Some advances in numerical simulations of multiscale heat transfer problems and particularly for boiling heat transfer, Annu. Rev. Heat Transf., 6 (2022) 217–269]. Besides, by shedding light on the characteristics of these numerical methods in studying boiling heat transfer, this paper aims to foster their development and advance enhanced heat transfer technologies. [ABSTRACT FROM AUTHOR]

Efficiently and actively dissipating accumulated heat within asphalt pavement is crucial for reducing pavement distress and improving subgrade stability. This paper proposed a novel inverted "T" shaped heat induced structure (IT-HIS) that facilitates the rapid transfer of heat from the pavement to the subgrade and shoulders. The IT-HIS consists of two components: a vertical gradient thermal conductivity structure utilizing steel slag, and a horizontal oriented carbon fiber heat induced structure. The heat transfer behavior of the IT-HIS was analyzed using a finite element heat transfer model created in ABAQUS, and the results were validated through indoor irradiation experiments. The findings demonstrated that the IT-HIS enhanced heat flow and promoted secondary aggregation in the vertical direction, while facilitated lateral heat dissipation. Compared to the ordinary group (OG), the heat flux of IT-HIS at depths of 5 cm and 6.5 cm increased by 19.8 % and 64.6 %, respectively. The indoor irradiation experiment results indicated that during the heat absorption period, the IT-HIS reduced temperatures at depths of 0 cm, 2 cm, and 5 cm by 1.5 ℃, 1.7 ℃, and 1.1 ℃, respectively. During the heat dissipation period, the IT-HIS reduced temperatures at depths of 0 cm, 5 cm, and 10 cm by 0.9 ℃, 0.7 ℃, and 1.8 ℃, respectively. The IT-HIS enhanced the cooling effect during daytime and inhibited heat upward during nighttime based on the gradient thermal conductivity structure. The proposal and validation of this structure provide a fundamental approach to forming large-scale high-speed microchannel heat dissipation within asphalt pavements, and is expected to provide experimental and theoretical foundations for the development of directional active cooling technologies. • In order to reduce heat accumulation within asphalt pavement, this paper proposed a novel inverted "T" shaped heat induced structure (IT-HIS). • IT-HIS enhanced heat flow and promoted secondary aggregation in the vertical direction, while facilitated lateral heat dissipation. • IT-HIS enhanced the cooling effect during daytime and inhibited heat upward during nighttime. [ABSTRACT FROM AUTHOR]

Surfactant aids boiling enhancement, but the related mechanism is not yet comprehensively understood. For mechanism investigation on surfactant molecule, most of existing studies focused on its hydrophobic part, while research on hydrophilic part is scarce. In this paper, a group of non-ionic Triton surfactants with same functional group but different hydrophilic chain lengths were experimentally tested for pool boiling on flat copper. At critical micelle concentration (CMC), long-chain Tx-405 exhibited higher heat transfer coefficient (97.4 kW/(m2·K)) than Tx-100 (77.1 kW/(m2·K)) and Tx-114 (77.4 kW/(m2·K)). Long-term test indicated a gradually deteriorating trend of heat transfer performance from days on. Solution properties and bubble dynamics were measured. At low concentration, surfactant with shorter hydrophilic chain has better heat transfer performance due to greater surface tension reduction. The increase of hydrophilic chain length improves water affinity of surfactant and thus leads to higher CMC. If there is no restriction for surfactant concentration, a longer hydrophilic chain is favorable for higher heat transfer coefficient at CMC. The results in this paper provide insights for mechanism investigation on surfactant, promote further design of new surfactant, and contribute to the prediction of heat transfer enhancement effect. • Nucleate pool boiling of Triton surfactant solutions on flat copper was experimented. • Bubble behaviors during boiling and related solution properties were measured. • At CMC, Tx-405 with longer hydrophilic chain showed higher HTC of 97.37 kW/(m2·K). • At low concentration, Tx-114 with shorter hydrophilic chain was favorable. • Heat transfer enhancement mechanism regarding hydrophilic chain length was discussed. [ABSTRACT FROM AUTHOR]

With the highly integrated development of electronic components, higher requirements are put forward for heat transfer components, there is an urgent need for high-performance heat transfer components. Oscillating heat pipe (OHP) is novel types of heat pipe with excellent heat transfer capability. However, the heat transfer limit hinders their operation and application. This paper proposes an OHP under trans-critical conditions with the working fluid of R218 and explores its operating characteristics and heat transfer capability. Visualization experiments and pressure monitoring were conducted to analyze the state changes within the OHP under trans-critical conditions. After evaporation section temperature surpassing the critical temperature of R218, the pressure increases with the temperature, once the pressure reached near the critical pressure, OHP can transcend the limitation of the critical temperature and realize efficient oscillating operation under trans-critical conditions. With stable operation, the working fluid velocity can reach up to 1.49 m/s, and the OHP under trans-critical conditions presented excellent heat transfer performance with the thermal resistance of 0.22 °C/W. This paper proves the feasibility of the OHP under trans-critical conditions and provides a basis for further research. [ABSTRACT FROM AUTHOR]

• A 3D thermal lattice Boltzmann model for simulating melt flow and heat transfer in CZ single crystal growth has been constructed. • The coordinate system transformation is adopted to extend the application of LBM on 3D cylindrical cavities. • The critical Reynolds numbers are increased by introducing a transverse magnetic field. A three-dimensional (3D) thermal lattice Boltzmann model of crystal growth is presented to study the magneto-hydrodynamics (MHD) mixed convection in the melt of Czochralski silicon single crystal growth in this paper. In order to solve the problem of lattice Boltzmann method's difficulty in solving the flow of 3D cylindrical cavity, the 3D physical model of crystal growth is transformed from the Cartesian coordinate system to the Curvilinear coordinate system. And the irregular grids in the Cartesian coordinate system are transformed into regular grids in the Curvilinear coordinate system to facilitate the establishment of the Lattice Boltzmann model. Under the above operations, two coupled distribution functions are established to solve the governing equations. Two D3Q19 models are adopted to solve the melt velocity and temperature. And the 3D lattice Boltzmann modeling of crystal growth with cylinder boundary is realized by interpolation in Curvilinear coordinate system. The comparison with the experiment and other references proves that the proposed model and boundary treatment scheme is correct and it proposes a new way for studying the 3D crystal growth or other similar 3D cylindrical cavity simulations. Furthermore, the unstable melt flow for two cases are also simulated in this paper and the critical Reynolds number are also obtained. Results show that the introduction of the transverse magnetic field enhances the stability of the crystal growth system and increases the adjustable range of crystal rotation parameter. The obtained conclusion has an important reference for adjusting the process parameters during the CZ crystal growth. [ABSTRACT FROM AUTHOR]

Micro fins on the internal surface of the tube improves its heat transfer ability. This paper investigates the thermal performance of tube flow numerically by adding axial straight micro fins (ASMF) on internal tube surfaces. The numerical method is experimentally validated using a tube featuring ASMF. The effects of fin height e , fin number N f , and fin shape of the tube with ASMF on the thermal performance are numerically studied within the range of Reynolds number (Re) from 1280 to 7687. Compared to a smooth tube, the Nusselt number (Nu) for tube with ASMF is reduced over the entire range of Re. In order to assess the performance of heat transfer, the ratio of the heat transfer coefficient (h) multiplying the heat transfer area (F) of ASMF tube (hF) to that of the smooth tube (h s F s) is utilized. Parametric studies were performed. The optimal fin height, fin number are found to be 0.0429 and 32. The optimal fin profile is found to be quadratic function profile. By combining the optimal fin height, fin number and fin profile, the maximum value of hF /(h s F s) can reach 1.32. Besides, the heat transfer enhancement mechanism induced by ASMF is also disclosed in this paper. [ABSTRACT FROM AUTHOR]

Porous surfaces are a common modified surface used to enhance boiling heat transfer. In this paper, a method for preparing gradient porous surfaces is presented, that is, magnetic stirring is added to the electrolyte and the cathode surface to be deposited is placed vertically downward. Within the Cl ion concentration range of 30–140 mg/L, increasing the Cl ion concentration results in lager pore sizes. When the Cl concentration was greater than 120 mg/L, the average pore size of the surface gradually increased from the center to the edge, and the number of pores gradually decreased from the center to the edge. All surfaces showed superhydrophilicity. The critical heat flux of Sample#3 is 158.72 W/cm2, which is 67% higher than the smooth surface. The wall superheat of Sample#3 was only 15 °C in the critical state. This porous surface has plenty of nucleation sites. These nucleation sites are gradually activated when the heat flux increases. At low heat fluxes, heat transfer on these porous surfaces presents a disadvantage because the nucleation sites are not fully activated. At high heat fluxes, these porous surfaces show a decrease in wall temperature. Consequently, the porous surface prepared in this paper has good boiling heat transfer at high heat flux. [Display omitted] • An inverted deposition method was designed to prepare gradient porous surfaces. • The gradient porous surface is superhydrophilic and provides a large number of nucleation sites. • An appropriate increase in Cl-ion concentration increases the pore size and pore wall thickness. [ABSTRACT FROM AUTHOR]

The distributed energy supply system provides a good scheme for energy supply. The micro gas turbine with a recuperator is a common power device in distributed energy supply systems. In recent years, several achievements have been made in the development of micro gas turbine recuperators. Plate-fin and primary surface recuperators have been used in mature applications. Moreover, the thermodynamic properties of the heat transfer channel have been studied in detail. Among them, the cross wavy primary surface recuperator developed by Capston Company is one of the important achievements. This paper reviews the technical development of thermodynamic performance of micro gas turbine recuperator in recent years. The micro gas turbine recuperators are divided into plate-fin and primary surface recuperators commonly. In this paper, the correlation formula, heat exchange enhancement, optimum design and the influence of recuperator on the overall machine performance are reviewed. It has been found that the plate-fin recuperators have been sufficiently studied by scholars, and the results are more comprehensive. As for the primary surface recuperators, which have just become popular in recent years, the research results are less comprehensive due to their unique structure. In the future development of micro gas turbine recuperators, this will be the future research and development trend due to the high heat exchange efficiency and the lack of comprehensive research on primary surface recuperators. [ABSTRACT FROM AUTHOR]

Passive radiative coating (PRC) is a technique that lowers the temperature and increases the efficiency of solar cells by emitting thermal radiation to the sky without consuming any energy. This paper reviews the fundamentals, the recent progress, and the future challenges of PRC integrated with solar cells. The review covers the state-of-the-art progress on material synthesis, system designs, and practical implementations of PRC. The authors critically evaluate the different methodologies and research techniques that have been used to analyse and evaluate the cooling performance of PRC-cooled solar cells. The paper concludes by identifying the major challenges that require future research and development in the field of PRC-cooled solar cells. The authors emphasize the need for a better understanding of the fundamental mechanisms of heat transfer in PRC, as well as the development of more efficient and cost-effective PRC materials and system designs. Overall, this review provides valuable insights into the current state-of-the-art of PRC-cooled solar cells and highlights the key challenges that need to be addressed to further advance. [ABSTRACT FROM AUTHOR]

• Heat transfer correlations robustness is assessed against experimental data. • Predictions of experimental data by 1D Thermal-Hydraulics models is performed. • Common problems and possible lines of improvement for HTC evaluation are discussed. The paper addresses the present engineering predictive capabilities for heat transfer at supercritical pressures, with main reference to the studies in support to the design of supercritical water nuclear reactors. The work that was made in the frame of the EU ECC-SMART Project by participants, in assessing existing correlations in front of different experimental data sets by a variety of means, is taken as a basis for discussing the adequacy of some of the available formulations. In particular, previously proposed correlations have been assessed in a stand-alone fashion or by the use of in-house and existing system codes. Specific computer programs have been also set up to try optimising the parameters of classical correlation forms when applied to selected experimental data sets. The obtained results show the present difficulties in predicting specific heat transfer regimes of interest for supercritical reactors, with main reference to deteriorated heat transfer, though some correlations have been found to represent at least qualitatively the increase of wall temperature observed in some tube or rod bundle experiments, providing hope of a reasonable quantitative description. A reflection on the different forms in which deteriorated heat transfer is observed in experiments and suggestions for possible improvements of the adopted modelling strategy are also provided in the paper, trying to investigate possibly promising lines of future research. [ABSTRACT FROM AUTHOR]

This paper formulates quadrilateral elements for the NURBS-enhanced finite element method (NEFEM). The objective is to extend the application of NEFEM to problems where the use of quadrilateral elements is preferred. By leveraging a mapping, between reference and physical spaces, that encapsulates the exact boundary representation of the domain, a tight integration with computer aided design (CAD) systems is achieved. The contribution of this work is an enhanced quadrilateral finite element that incorporates the exact CAD geometry purely from the boundary representation (B-rep) from CAD and without the need for a whole volume representation (V-rep) as a NURBS entity. Numerical examples involving heat transfer and linear elastic problems are used to numerically demonstrate the optimal convergence properties of the method under mesh refinement. [Display omitted] • This paper aims to reduce the gap between CAD and analysis. • A new NEFEM bilinear superparametric element is presented. • The shape functions are redesigned and solely reside in the parametric space. • Heat transfer and elasticity problems show that NEFEM achieves higher accuracy. [ABSTRACT FROM AUTHOR]

This paper is the second of a two-part series that presents experimental data and analysis on the liquid nitrogen quenching heat transfer process of a stainless-steel tube with an inner surface low-thermal conductivity thin-film coating. This paper focuses on the effects of different flow directions and two tube wall thicknesses. Additionally, this paper also provides an analysis on the chilldown thermal efficiency of the quenching process. Three flow directions with four different inner surface coating modifications, and three tube wall thicknesses were examined. The experimental data covers the Reynolds numbers ranging from 3500 to 140,000. The chilldown efficiency, along with chilldown time and LN 2 (liquid nitrogen) mass consumption were analyzed to assess the overall performance of the LN 2 line chilldown process. For thin tube wall cases, the chilldown efficiencies cover a range between 3% and 41%, and the maximum chilldown efficiency value is found for the tube with 3 L coating at Re = 5278 in the vertical up flow direction. For thick wall tube cases, the efficiencies cover a range between 4% and 52%, and the maximum chilldown efficiency value was found for the tube with 4 L coating at Re = 5308 in the vertical up flow direction. [ABSTRACT FROM AUTHOR]

Pressurizer is widely used in the industrial systems, which can maintain the pressure of the system in a certain range. Especially, as the system pressure rises, the spray droplets interacts with the saturated steam in pressurizer to reduce system pressure. In this paper, a heat and mass transfer model of droplet and steam in pressurizer is established through the lattice Boltzmann method (LBM), and the characteristics of moving droplet in steam space with different Reynolds numbers are analyzed. In this paper, these results show that the flow fields on both sides of the droplet have obvious symmetry at low Reynolds number. As the Reynolds number increasing, the wake region of flow field for moving droplets gradually loses symmetry. When the Reynolds number reaches 103 orders of magnitude, the droplet motion begins to appear horizontal deviation. The growth of droplet condensation radius is inhibited with the increase of Reynolds number. When Reynolds number reaches 2600 and Fo = 0.2, the growth of droplet radius stops and then decreases. Due to the influence of inertia force generated by internal circulation flow and droplet movement, as the Reynolds number increasing, the droplet heat transfer rate decreases at first, but begins increasing when Reynolds number raises to about 2000. The calculation results have reference value for the development of spray droplet model of pressurizer. • A heat and mass transfer model of droplet and steam in pressurizer is established. • The characteristics of moving droplet in steam under different Re are analyzed. • With the increase of Re , the growth of droplet condensation is inhibited. • Heat transfer rate decreases first and then increases with the increase of Re. [ABSTRACT FROM AUTHOR]

• First overview of the flow characteristics of CO 2 -lubricant mixtures in gas coolers. • Presents multiple factors affecting the flow characteristics of CO 2 -lubricant mixtures. • Reviews the analysis models of the flow and heat transfer of CO 2 -lubricant mixtures. • Comments on pressure drop correlations of CO 2 -lubricant mixtures. • Recommendations for future studies on the CO 2 -lubricant mixture flow characteristics. With the recent advancements in designs and optimization of gas coolers in CO 2 transcritical refrigeration and heat pump systems, the impact of the lubricant on the performance of gas coolers has been gaining increasing attention. The existing literature reviews focus on examining the lubricant effect on the heat transfer performance of gas coolers. However, the studies do not present a detailed discussion and a systematic summary of the flow characteristics. The present paper aims to offer an overall review of the lubricant impact on the flow characteristics of CO 2 in gas coolers. The authors hope it will help researchers conduct additional research about practically designing and optimizing gas coolers. This paper reveals the flow mechanism by providing critical discussions on how temperature, lubricant type, lubricant concentration, mass flux, operational pressure, tube diameter, and tube configuration influences the flow characteristics of the CO 2 -lubricant mixture. Then, the paper summarizes and evaluates the latest developments related to CO 2 -lubricant mixture in the flow and heat transfer analysis models and pressure drop correlations. Moreover, the current research gap is summarized, and the study proposes development directions. These include measuring thermo-physical properties of CO 2 -lubricant mixture, examining pressure drop characteristics under different tube configurations, developing universal pressure drop correlations, and studying flow characteristics in vertical tubes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lewis number deviates from one in the entrance length. • The catalyst activity do not modify the initial Nu and Sh inside of the channels. • Re modifies the thermal entrance length because of the reduction of the flow area. This paper is devoted to the multi-scale model of the heat and mass transfer inside of a honeycomb monolith substrate. Due to computational limitations, monoliths are modelled as a continuum in full-scale catalytic reactors models. That makes it necessary to use correlations or sub-models derived from channel scale results to account for a physically consistent heat and mass transfer inside of the substrate. In this paper detailed computational models at a channel and reactor scales are analyzed. Catalytic oxidation of CO is used as a reaction and the fluid properties are considered to be temperature-dependent. First, a channel scale model is used to analyze Nusselt, Sherwood, Lewis, and Damköhler numbers inside of the monolith channels. Secondly, sub-models obtained at a channel level are implemented in a full-scale reactor model using the continuum approach, to evaluate the impact of using detailed vs. highly simplified correlations for heat and mass transfer. The reactor scale model accounts for the transitions of the flow regime, entrance length effects, an-isotropic substrate thermal conductivity and temperature-dependent fluid properties. According to the results, the Lewis number can deviate significantly from one in the entrance length, however, it approaches asymptotically to unity as the flow develops. Regarding Nusselt and Sherwood, current interpolating methodologies are not able to predict the correct value in the entrance region when Damköhler is low, nonetheless, are reasonably accurate for the asymptotic one. [ABSTRACT FROM AUTHOR]

Abstract: Process integration methods aim at identifying options for heat recovery and optimal energy conversion in industrial processes. This paper introduces a targeting method, which includes heat exchange restrictions between process sub-systems. The problem is formulated as a MILP (mixed integer linear programming) problem, which considers not only restricted matches but also the optimal integration of intermediate heat transfer units and the energy conversion system, like heat pumping and combined heat and power production. Moreover a new mathematical formulation is presented to chose optimal heat transfer technologies. For solutions avoiding the energy penalty, the composite curves of optimal heat transfer units have to be embedded between the new generated hot and cold envelope composite curves. The application of the method is illustrated through an industrial example from the pulp and paper industry. [Copyright &y& Elsevier]

There is great interest in predicting flow condensation heat transfer for lower global warming potential (GWP) fluids. This paper analyzes the efficacy of common flow condensation correlations developed for particular fluids in order to identify their suitability to predict heat transfer performance of low GWP fluids. Condensation heat transfer data were extracted from the literature, including 19 papers and 1,473 data points for natural refrigerants [ i.e. , ammonia (R717), CO 2 (R744), propane (R290), isobutane (R600a)] and 35 papers and 5,030 data points for synthetic refrigerants [ i.e. , R12, R1234yf, R1234ze(E), R1234ze(Z), R22, R32, R41, R123, R125, R134a, R142b, R152a, R161, R404A, R410A, R448A, R449A, R450A, R452B, R454C, R455A, R513A] encompassing tube diameters of 0.1–11.5 mm, mass fluxes of 55–1200 kg/m2s, and saturation temperatures of -25 °C–65 °C. Correlations analyzed included (Akers et al., 1959; Cavallini et al., 2006; 2011; Kim and Mudawar, 2013; Macdonald and Garimella, 2016; Shah, 1979, 2009, 2013, 2016) and (Traviss et al., 1973) for smooth tubes and (Chamra et al., 2005) and (Kedzierski and Goncalves, 1999) for enhanced tubes. Since most studies did not report wall temperature, correlations which relied on wall temperature directly or indirectly were excluded from the analysis. For synthetic refrigerants, mean average error (MAE) ranged from 6% to 257%, and (Cavallini et al., 2011) and (Kim and Mudawar, 2013) were the best predictors for emerging synthetic refrigerants. The (Kim and Mudawar, 2013) correlation was found to best predict the heat transfer performance for propane and R600a data, but most correlations did not accurately predict ammonia and CO 2 flow condensation. [ABSTRACT FROM AUTHOR]

The Nusselt number variations of supercritical carbon dioxide during in-tube cooling are presented and discussed. Using data presented in this paper as well as prior publications, a new correlation to predict the heat transfer coefficient of supercritical carbon dioxide during in-tube cooling has been developed. The new correlation is presented in this paper. It is based on mean Nusselt numbers that are calculated using the thermophysical properties at the wall and the bulk temperatures, respectively. It is seen that the majority of the numerical and experimental values are within ±20% of the values predicted by the new correlation. [Copyright &y& Elsevier]

The continuous ortho-para hydrogen conversion technology represented by the plate-fin heat exchanger filled with catalyst (PFHEFC) is one of the key technologies for the breakthrough of large-scale hydrogen liquefaction system. An appropriate numerical model of the PFHEFC can provide reference and guidance for its design. The thermal-hydraulic behaviors of the catalyst filled layer (CFL) are essential for the model development of the PFHEFC. In this paper, the thermal-hydraulic correlations of the high-pressure and low-temperature hydrogen in the CFL are investigated by the numerical simulation and then used to improve the existing numerical models of the PFHEFC. The results show that the simulation results of the face centered cubic (FCC) packing structure are close to the results of some classical correlations of the CFL with most relative deviations within ±10% and can be used to approximate the actual CFL. And taking 40 K as the dividing point, the new thermal-hydraulic correlations of the high-pressure and low-temperature hydrogen in the CFL are obtained with the relative deviations within ±10%. Further, the New model of the PFHEFC is developed with the new thermal-hydraulic correlations. The New model has some margin in the heat transfer performance, considers the special thermal-hydraulic performances of the high-pressure and low-temperature hydrogen in the CFL, and is consistent with the existing numerical models in the ortho-para hydrogen conversion performance. It shows the New model is more suitable for the PFHEFC and can provide more accurate results for the design of the PFHEFC than the existing numerical models. • Assumption of the FCC approximating the actual CFL is reasonable and enforceable. • Thermal-hydraulic behaviors of high-pressure hydrogen at 30–80 K in the CFL are analyzed. • Porosity is a nonnegligible parameter affecting the thermal-hydraulic performances of the CFL. • New thermal-hydraulic correlations of high-pressure hydrogen at 30–80 K are obtained. • New model of the PFHEFC is proposed and is better than the existing numerical models. [ABSTRACT FROM AUTHOR]

This paper studies fast fueling of gaseous hydrogen into large hydrogen (H2) tanks suitable for maritime applications. Three modeling methods have been developed and evaluated: (1) Two-dimensional computational fluid dynamic (CFD) modeling, (2) One-dimensional wall discretized modeling, and (3) Zero-dimensional modeling. A detailed 2D CFD simulation of a small H2-tank was performed and validated with data from literature and then used to simulate a large H2-tank. Results from the 2D-model show non-uniform temperature distribution inside the large tank, but not in the small H2-tank. The 1D-model can predict the mean temperature in small H2-tanks, but not the inhomogeneous temperature field in large H2-tanks. The 0D-model is suitable as a screening tool to obtain rough estimates. Results from the modeling of the large H2-tank show that the heat transfer to the wall during fast filling is inhibited by heat conduction in the wall which leads to an unacceptably high mean hydrogen temperature. • Modeling of gas temperature development inside hydrogen tanks during pressurization. • Inhomogeneous gas temperature distribution occurs inside large hydrogen tanks. • Important to understand how heat transfer in tank wall affects heating of the gas. • Monitoring of the gas temperature at the end of large tanks is recommended. [ABSTRACT FROM AUTHOR]

Modeling and optimization of liquid hydrogen (LH 2) pumps require accurate in-cylinder heat transfer correlations. However, the applicability of existing correlations based on gas mediums to LH 2 remains to be verified. In this paper, the unsteady heat transfer and fluid flow in a closed LH 2 pump cylinder are numerically studied by adopting the gas spring model. The phase shifts and temperature distribution in the closed pump cylinder are investigated. LH 2 is less affected by in-cylinder heat transfer and has a more uniform temperature distribution compared to nitrogen gas, while a low-temperature zone appears near the piston face at 120 rpm. Finally, the validity of Lekic's correlation in predicting the heat flux of the LH 2 compression process in the closed pump cylinder is verified, and the efficiency decrement versus rotational speed is analyzed based on the correlation. This work would be useful for selecting a proper in-cylinder heat transfer model for predicting the thermodynamic process in reciprocating LH 2 pumps. [Display omitted] • Gas spring model is applied for unsteady heat transfer process of LH2 compression. • Low-temperature zone appears near piston surface at 120 rpm due to LH2 properties. • Heat flux on piston surface with rotational speed differs from that of other walls. • Lekic's correlation predict heat flux on cylinder wall well excluding piston face. • Rotational speed has a notable effect on efficiency decrement from 0 to 200 rpm. [ABSTRACT FROM AUTHOR]

In cooling towers and condensers, accurate measurement of the void fraction in gas-liquid two-phase flow can help optimize heat transfer efficiency. By monitoring the void fraction, operational parameters can be adjusted to maximize heat exchange effectiveness. As such, the development of a technique for measuring void fraction in high-temperature and opaque containers is necessary. This paper presents a method for measuring the void fraction of the section during direct contact heat transfer using electromagnetic tomography. In order to enhance the magnetic field, a certain amount of nanofluid is introduced into the direct contact evaporator. With the aid of a self-developed EMT system, the gas and liquid phases are differentiated, ultimately yielding the section void fraction value. The final results are qualitatively consistent with three classical models for void fraction calculation. This is the first report on measuring cross-sectional void fraction in direct contact heat transfer processes using the EMT system. The findings demonstrate the feasibility of the measurement method based on EMT and provide a reference for research on high-precision and automated measurement techniques of void fraction in gas-liquid two-phase flow. [Display omitted] • The EMT technique is suitable for flow pattern detection of direct contact heat transfer processes. • The void fraction rate of EMT data has the highest correlation with the drift flow model trend. • The void fraction measured by EMT method has a consistent trend with the results calculated by three classic models. [ABSTRACT FROM AUTHOR]

The distribution of ground thermal conductivity (λ s) is a significant consideration for the design of ground source heat pump systems. This paper proposed a new method to estimate the layered λ s for U-tube borehole heat exchanger (BHE) using particle swarm optimization (PSO) and distributed thermal response test (DTRT) data. Firstly, a quasi-3D heat transfer model considering geothermal gradient for U-tube BHE had been built to simulate fluid temperature profiles. And the experiment in DTRT was performed using a 45 m sandbox. Then, the layered λ s were estimated through PSO and DTRT data based on the established model. The results showed that the convergent λ s distribution could be reliably obtained by short-term DTRT. Furthermore, the estimation results are independent of the number of layers and data points. The mean difference in λ s distribution between 9 layers and 45 layers is 0.007 W/(m∙K) and the layered λ s also could be obtained when the number of layers is more than the number of temperature data points, and the root mean square error between 30 and 220 points is less than 0.3 W/(m∙K). • Quasi-3D heat transfer model for U-tube BHE is built to estimate layered λ s. • Sensitivity analyses were conducted to investigate parameter impacts. • Novel estimation of layered λ s is presented by using DTRT data and PSO. • Short-term DTRT data is efficient to estimate the layered λ s. • Estimation is independent with layered conditions and number of test points. [ABSTRACT FROM AUTHOR]

• A dynamic performance model is developed and experimentally investigated for a domestic freezer under varying conditions. • Numerous heat and mass transfer parameters are investigated through repeated multiple experiments. • A semi-empirical door opening scheme is considered in the present dynamic model. • A close agreement is obtained between the model predictions and experimental measurements for temperature, pressure, humidity, power and energy consumption. This paper performs a comprehensive experimental and modelling study to examine the dynamic behaviour of an upright freezer with adjustable shelving under periodic door opening conditions with different temperature, pressure and relative humidity values. An uncertainty analysis is carried out for the experimentally measured data. Additionally, the dynamic model is developed with crucial sub-components, such as discretized upright cabinet, frosted evaporator and semi-empirical door opening mechanism using an object-orientated programming language called Modelica. The present model is the validated with experimental data employing the values of the airflow from ambient into the cabinet along with the average cabinet air flowrate and back wall temperatures, transient evaporation and condensation pressures, cabinet average relative humidity change, compressor operation time and power consumption, and finally total energy consumption of refrigerator for both 85%RH and 65% RH conditions at 32 °C ambient. The results show that the model predictions have a similar trendline with the experimental findings within ±3 K error bands regarding average cabinet air and back wall temperature. In contrast, the dynamic cyclic trend before and after door opening is closer to the experiments within ±1 K. The current model predictions for the low and high pressures are found to be within ±3% and ±5% error bands, respectively, whereas the average relative humidity level of the cabinet is captured within ±10% deviation. Furthermore, transient compressor power is well predicted with deviations, but not exceeding 4.5%, and the total energy consumption level is compatible with 6% error bands during the entire experimental period. [ABSTRACT FROM AUTHOR]

This paper mainly analyzes the heat transfer of Carreau fluid over an infinite rotating disk, and two models with variable thermal conductivity are considered. Firstly, the governing partial differential equations (PDEs) are transformed into ordinary differential equations (ODEs) by similarity transformation. Then, the boundary value problem is solved by improved bvp4c method, which reduced sensitivity to the initial values. For shear-thinning and shear-thickening fluids, the effects of Carreau fluid index n and Prandtl number Pr on velocity and temperature fields are shown and analyzed when 0.5 ≤ n ≤ 1.5 , 1 ≤ P r ≤ 10. Furthermore, the thermal conductivity is computed under two cases. [ABSTRACT FROM AUTHOR]

• Two CO 2 air conditioning systems based on liquid cooled gas cooler (LCGC) were developed. • The cooling performances of direct and secondary loop systems were experimentally compared. • The effects of refrigerant charge, CO 2 cycle parameters, and air-side parameters were investigated. • Exergy analysis revealed the enhancing potentials of the Chiller and evaporator. As a natural refrigerant, CO 2 is considered one of next generation refrigerants of electric vehicle (EV) applications for excellent environmental and heating performance. The integration and safety performance of CO 2 systems could be enhanced by secondary loop configuration, which is highly valuable for practical applications. This paper investigates the cooling performance characteristics of direct (DAC) and secondary loop (SLAC) transcritical CO 2 air conditioning systems based on liquid cooled gas coolers (LCGC). A series of steady-state experiments were carried out for both systems to study the effects of compressor speed, EXV opening, outdoor air velocity, and indoor air flow rate on the cooling performances. Furthermore, the exergy destruction of each component and the exergy efficiency of both systems were analyzed based on the experimental results, showing that the evaporator needs to be better designed to balance heat transfer performance with pressure loss performance. The results showed that the cooling capacity and COP of SLAC system were reduced by up to 9.1% and 10.8% under the same compressor speed, compared with the DAC system. This study presents experimental references for further research and practical extension of the CO 2 mobile air conditioner. [ABSTRACT FROM AUTHOR]

• Vacant heating core in cooling mode was first utilized for evaporation. • A series cross-parallel dual-evaporator configuration was recommended. • An automotive CO 2 air conditioner with the recommended configuration was tested. • COP was improved by 6∼12% without additional cost. Inefficient performance of CO 2 refrigerant in hot climates has become a major obstacle to its wide application in electric vehicles. In this paper, the vacant heating core in cooling mode was exploited to increase the heat transfer area of evaporator and improve system performance. With the aid of a validated evaporator model and an experimental test rig, performance improvements brought by this added area were evaluated. Results indicated that this area is not suggested to be directly added to cooling core. This necessitates a dual-evaporator (D-E) configuration. For case I (small CO 2 pressure drop), the growth rate in heat transfer rate brought by D -E configuration is 19∼20% and less sensitive to parallel or series operation. Nevertheless, this growth rate for case II (large CO 2 pressure drop) is greatly affected, 30.6∼32.6% for parallel operation and 7.5∼17.6% for series operation. Specifically, it is around 17.5% and 7.5∼13.6% for series cross-parallel and cross-counter arrangements, respectively. By comprehensive consideration, the cross-parallel arrangement is recommended to be adopted. Experimental results indicated that the cross-parallel D -E configuration greatly increases the evaporation temperature and exhibits a slight impact on optimum high pressure within the transcritical cycle. The enhancement in COP brought by this configuration is around 6∼12% without additional cost, and it rises with the decreased air flowrate through evaporator and air velocity through gas cooler and the increased ambient temperature. This indicates that this configuration is an effective and economical technology to alleviate the efficiency degradation issue of transcritical CO 2 automotive air-conditioners. [ABSTRACT FROM AUTHOR]

• A new model-based approach was presented for the evaluation of the heat transfer coefficient in large-scale freeze-dryers using a small-scale freeze-dryer. • Results in a small-scale freeze-dryer (MicroFD®) and in a large-scale one (REVO®) were compared, pointing out the robustness and the accuracy of the developed model. • The resistance to vapor flow was also calculated and the two model parameters were used for in-silico simulations to calculate the drying time and the product temperature profiles in a different unit. This paper presents a model-based approach for the design of the primary drying stage of a freeze-drying process using a small-scale freeze-dryer (MicroFD® by Millrock Technology Inc.). Gravimetric tests, coupled with a model of the heat transfer to the product in the vials that account also for the heat exchange between the edge vials and the central vials, are used to infer the heat transfer coefficient from the shelf to the product in the vial (K v), that is expected to be (almost) the same in different freeze-dryers. Differently from other approaches previously proposed, the operating conditions in MicroFD® are not chosen to mimic the dynamics of another freeze-dryer: this allows saving time and resources as no experiments are needed in the large-scale unit, and no additional tests in the small-scale unit, apart from the three gravimetric tests usually needed to assess the effect of chamber pressure on K v. With respect to the other model parameter, R p , the resistance of the dried cake to mass transfer, it is not influenced by the equipment and, thus values obtained in a freeze-dryer may be used to simulate the drying in a different unit, provided the same filling conditions are used, as well as the same operating conditions in the freezing stage, and cake collapse (or shrinkage) is avoided. The method was validated considering ice sublimation in two types of vials (2R and 6R) and at different operating conditions (6.7, 13.3 and 26.7 Pa), with the freeze-drying of a 5% w/w sucrose solution as a test case. An accurate estimate for both K v and R p was obtained with respect to the values obtained in a pilot-scale equipment, determined through independent tests for validation purposes. Simulation of the product temperature and drying time in a different unit was then possible, and results were validated experimentally. [Display omitted] [ABSTRACT FROM AUTHOR]

Carbon monoxide selective methanation (CO-SMET) is one of the most efficient technologies for hydrogen purification and CO deep removal. This paper applies the field synergy principle for a deep understanding on the chemically reactive flow in a CO-SMET tubular reactor. The variation of CO conversion rate under different operating conditions is interpreted, at the first time, as relevant to the variation of the synergy angle between temperature and gas concentration fields. Sensitive analyses of the bed pressure, CO/CO 2 ratio, heat exchange modes, etc., are studied to obtain the profile of field synergy angle in the inlet gas temperature range of 373 K – 873 K. It is found that the region with synergy angles between 0° and 70° enhances the heat transfer between mass transfer and contributes the main output of CO conversion. This work provides a fundamental basis on the future optimal design of CO–SMET reactors. [Display omitted] • Field synergy principle with CO selective methanation reaction. • Simulation of CO selective methanation by kinetic equation and CFD. • Synergy angle distribution influence on heat and mass transfer. • Uniform explanation of change of CO conversion rate by field synergy principle. [ABSTRACT FROM AUTHOR]