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Highlights • Gas injection increases a maximal velocity within the boundary layer. • Gas suction decreases an overshoot phenomenon till his absolute vanishing. • Separation of thermal boundary layer at gas injection. • Conventional point of thermal boundary layer separation is proposed. Abstract The paper reports on numerical simulation of an accelerated laminar boundary layer over the heated permeable wall. Xenon was used as a working gas. The finite difference method was applied to solve the system of laminar boundary layer equations with variable gas properties. It has been shown that the gas injection in the mentioned conditions increases maximal velocity within the boundary layer and decreases skin-friction coefficient and thermal Stanton number. On the contrary, gas suction decreases an overshoot phenomenon down to its vanishing and increases skin-friction coefficient and thermal Stanton number up to the value at asymptotic suction. The paper considers a separation of thermal boundary layer at gas injection. The proposed conventional point of this separation is situated farther from the leading edge than the separation point of the dynamic boundary layer. [ABSTRACT FROM AUTHOR]

Highlights • CFD analyses of heat transfer to supercritical carbon dioxide are performed. • AHFM is adopted as a valid tool for modelling the turbulent heat flux. • Phenomena reported in the experimental data were reproduced by the adopted model. Abstract The present paper reports the results of analyses concerning heat transfer to supercritical pressure fluids, performed by adopting a k − ε turbulence model modified in association with the AHFM model, here used for calculating both buoyancy effects and the turbulent heat flux. The promising capabilities of this approach were already highlighted in past studies and the present paper represents a further step in this line of research. Experimental data concerning supercritical carbon dioxide flowing in tubes are here considered, with operating conditions involving both high and low mass flux values and spanning from relatively low inlet temperatures to values higher than the pseudocritical threshold. Some of the interesting features appearing in the experimental data are correctly reproduced by the model, which manages to predict reliable wall temperature trends, both qualitatively and quantitatively. The performed analyses, though reporting successes in a sufficiently wide range of operating conditions, suggest that some parameters of the proposed model should be varied in accordance with the boundary conditions, e.g. considering the mass flux, in order to improve predictions in the most challenging situations. [ABSTRACT FROM AUTHOR]

Highlights • A steam injection physical simulation experimental device is designed independently. • Wellbore stock liquid is taken into consideration to study variable mass flow in horizontal wells. • A novel model is proposed to predict the thermophysical properties of steam along the horizontal wellbore. • The influence of parameters on the thermophysical properties distribution of steam is analyzed in detail. Abstract In this paper, a novel model is proposed to study the variable mass flow process in a long horizontal well and to predict the distribution of thermophysical properties along the horizontal wellbore. First, a physical simulation device is designed to carry out a steam-injection experiment. Second, considering both the uneven distribution of steam and the effect of wellbore stock liquid, a steam-absorption model and a pressure drop model are proposed to predict the distribution of steam and pressure along the horizontal wellbore. Third, the effects of different parameters on steam distribution are analyzed in detail. The results indicate that: (1) an uneven employment phenomenon exists along the wellbore; (2) the pressure distribution along the wellbore is higher when wellbore stock liquid is taken into consideration; (3) the length of the unemployed section along the wellbore increases with an increase in the wellbore stock liquid viscosity; (4) the length of the unemployed section along the wellbore decreases with an increase in the steam injection rate; and (5) the reasonable wellbore length can prevent an unemployed section along the wellbore. This paper presents a basic reference for engineering for parameter optimization as well as for the prediction of steam distribution along the horizontal wellbore. [ABSTRACT FROM AUTHOR]

Highlights • The leading edge film cooling of a rotating twist turbine blade is studied with TLC. • The mainstream Re and DR can affect the leading edge film cooling effectiveness. • Influence of M on the leading edge film cooling effectiveness is also studied. • A new photo testing technology in rotating state is introduced in this paper. Abstract This paper reports on an experimental investigation of the influences of mainstream Reynolds number and coolant density on film cooling characteristics on the leading edge of a twisted turbine blade under rotational conditions. The experiments were carried out at a test facility with a 1-stage turbine using the thermochromic liquid crystal (TLC) technique. The mainstream Reynolds number varied from 4.4201 × 104 to 7.1797 × 104. All tests were carried out at three rotational speeds of 400 r/min, 500 r/min and 650 r/min to fix the rotation number at 0.0018. The coolant-to-mainstream density ratios were fixed at 1.04 and 1.56 with N 2 and CO 2 as coolants, respectively. The blowing ratio effect was also considered. The results showed that under the same blowing ratio, the averaged film cooling effectiveness on the measurement area increased with increasing mainstream Reynolds number for both coolant gases. Under the same Reynolds number, the span-wise averaged film cooling effectiveness increased as the blowing ratio increased for both coolant gases. Under the same Reynolds number and blowing ratio, higher-density coolant jets (CO 2) provided higher averaged film cooling effectiveness than lower-density coolant jets (N 2) on the measurement area. Overall, mainstream Reynolds number, blowing ratio and coolant density played significant roles in the film cooling characteristics of the leading edge under rotational conditions. [ABSTRACT FROM AUTHOR]

Graphical abstract This paper presents an experimental investigation of heat transfer performances including heat transfer coefficient along flowing direction, log-mean temperature difference and differential pressure of pure R123 and four volume concentrations 20 nm Al 2 O 3 -R123 nanorefrigerants with various volume concentrations 0.03%, 0.13%, 0.18%, 0.23% flowing inside a double-tube counter flow heat exchanger of an organic Rankine cycle system under the conditions of various heat source temperatures and flow rates. A comparison has been made between pure R123 and four kinds of nanorefrigerants to find out the influences of different nanoparticles volume concentrations on local heat transfer coefficient and variation tendency (straight lines) along flowing direction in evaporator. By using polynomial fitting where polynomial order is 3, the polynomial fitting curves (dash lines) and the optimum of volume concentration has been acquired, which indicates the loading carrying capacity in each operation condition. Highlights • Effect of Al 2 O 3 nanoparticles on R123 heat transfer performances. • Variation tendency along flowing direction in evaporator of ORC. • Polynomial fitting curve. • Comparison of differential pressure and log-mean temperature difference of R123 and nanorefrigerants. Abstract This paper presents an experimental investigation of variation tendency of heat transfer coefficient, log-mean temperature difference and differential pressure of pure R123 and 20 nm Al 2 O 3 -R123 nanorefrigerants with four various volume concentrations, 0.03%, 0.13%, 0.18%, 0.23% flowing inside the evaporator of organic Rankine cycle system under the conditions of various heat source temperatures and flow rates. Heat source temperatures are in the range of 50–90 °C at an interval of 10 °C, and heat source flow rates are 0.7 m3/h, 1.3 m3/h and 1.8 m3/h. Results show an increment of heat transfer coefficient along flowing direction for both pure R123 and four Al 2 O 3 -R123 nanorefrigerants with the increment of heat source temperature and flow rate, and that of four nanorefrigerants are higher than that of pure R123. There is no optimum value of heat transfer coefficient when operation condition is changed for the loading carrying capacity increasing with the increasing intensity of operation condition. Meanwhile, suspending nanoparticles and increasing heat source temperature can change the variation tendency of heat transfer coefficient along flowing direction except pure R123 and 0.18 vol% nanorefrigerant. In addition, 0.13 vol% as a whole is the optimum volume concentration for both log-mean temperature difference and differential pressure. [ABSTRACT FROM AUTHOR]

Highlights • A novel method of stabilization of levitating droplet clusters is suggested. • Experiments showed that modulation of the laser heating power is effective. • An optimal period of laser power variation is determined. • Heat conduction calculations give reliable estimates of water temperature. Abstract The relatively stable clusters of regularly positioned small droplets formed over the locally heated water surface have been studied starting from the early paper by the first author. The life of a cluster appeared to be not long because of growing of droplets due to condensation of steam and the final coalescence of large droplets with the substrate layer of water. However, further laboratory studies of biochemical processes in single droplets will be possible only in the case of their longer life. One way to stabilize the cluster suggested recently by the authors is an external infrared heating which prevents growing of droplets. The present paper is focused on another way to stabilize the cluster. This is an expected rebuilding of droplet clusters at periodic changes in power of the heating laser beam. The frequency of these oscillations is more important than their amplitude because of the resonance nature of the phenomenon. The experiments showed that in the simplest variant of alternating constant power values with the same duration of heating, the droplet growth rate is approximately twice reduced with a power modulation period of about 0.9 s. It means that such a “rejuvenescence” procedure can be used at laboratory conditions to prolong the life of levitating droplet clusters. [ABSTRACT FROM AUTHOR]

Highlights • The force balance approach and correlation approach are conducted to predict bubble departure diameter. • A new semi-empirical correlation for bubble departure diameter is proposed in this paper. • The effects of dimensionless parameters on bubble departure diameters are analyzed. Abstract According to the force balance analysis on a bubble, the bubble departure diameter in horizontal subcooled flow boiling is mainly influenced by quasi-steady drag force, surface tension force and bubble growth force while an additional force, buoyancy force, plays an important role in vertical flow boiling. In this paper, the effects of these forces can be concluded by a series of dimensionless parameters including density ratio of vapor and liquid, Prandtl number, Jacob number and bubble Reynolds number. Based on the different forces, two different characteristic lengths are adopted to non-dimensionlize bubble departure diameters in horizontal flow boiling and vertical flow boiling, respectively. Finally, the semi-empirical correlations for bubble departure diameters in both horizontal and vertical subcooled flow boiling are proposed in this paper based on the force balance analysis and available experimental data from literature. The predicted results using the present correlations agree fairly well with the experimentally measured values with a mean relative error of 19.72%. [ABSTRACT FROM AUTHOR]

Highlights • Effect of external magnetic field on convection heat transfer of ferrofluid flow is investigated. • Magnetic field changes the streamline patterns and enhances the heat transfer. • Increasing magnetic field strength would not necessarily improve the heat transfer. • Magnetic field strength should be large enough to create large circulation zones inside the duct. • Adding line dipoles on high-temperature regions closer to the duct inlet is beneficial. Abstract In this paper, a numerical method is developed to simulate the effect of an external magnetic field on convection heat transfer of a ferrofluid flow inside a rectangular duct. This model is two-dimensional, steady-state, laminar and incompressible. Simple finite volume method is used to couple and solve continuity, momentum and energy equations. In the first part of this paper, it is observed that ferrofluid particles movement along the magnetic field of a line dipole changes the streamline patterns and enhances heat transfer. In the second part of this paper, a sensitivity analysis is performed to investigate the effects of Reynolds number, magnetic field strength, location, and number of line dipoles on the convection heat transfer. It is observed that cooling rate is higher at larger Reynolds numbers while increasing magnetic field strength would not necessarily result in noticeable improvement in heat transfer. It is also noticed that magnetic field strength should be large enough to merge small vortexes and to create large circulation zones inside the duct. Our simulation also revealed that heat transfer could be augmented by adding line dipoles on high-temperature regions closer to the duct inlet. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A numerical modeling framework for thermo-fluids is applied to investigate liquid hydrogen. • Dynamic evolution of liquid hydrogen cavitating flow is numerically investigated. • Thermal transition process and transition temperature in liquid hydrogen are presented. • A modified C -factor is proposed to evaluate and predict thermal transition in thermos-fluids. Abstract The objectives of this paper are to (1) validate the present numerical modeling framework for liquid hydrogen cavitating flow, (2) investigate the dynamic evolution of liquid hydrogen cavitating flows in a wide range of free-stream conditions and (3) propose a thermal parameter to evaluate and predict the transition process of two typical cavitation dynamics in thermo-fluids. The dynamic evolutions of liquid hydrogen cavitating flows in a wide range of free-stream conditions (T ∞ = 14–33 K, U ∞ = 63.9 m/s, 90 m/s, σ ∞ = 0.38, 0.8, 1.2) are numerically investigated. General agreements are obtained between the numerical results and the experimental measurements, including the pressure distribution, temperature drop as well as the cavity structures. The results show that the cavitation behaviors near the triple point are similar to cavitating flows without thermodynamic effects. Two typical cavitation dynamics named the quasi-isothermal mode and the thermo-sensitive mode in liquid hydrogen are observed under the same cavitation number and flow velocity. When the free-stream T ∞ is below 30 K (T N ≤ 0.85), as the temperature increases, the cavity area increases to the maximum around the thermal transition temperature and then decreases when the cavitation dynamics transits from the quasi-isothermal mode to the thermo-sensitive mode. Further analysis indicates that the thermal transition temperature for liquid hydrogen is approximately at T ∞ = 17 K and the transition temperature slightly increases with the increasing free-stream velocity and cavitation number. When the free-stream T ∞ is above 30 K (T N > 0.85), the thermodynamic effects significantly decrease due to the suddenly changed physical properties. And then, the cavitation dynamics turns from the thermo-sensitive mode to the quasi-isothermal mode with the increasing temperature. The modified C -factor including both the thermodynamic effects and the effects of turbulent pressure fluctuations proposed in this paper could quantitatively evaluate and predict dynamics transition from the quasi-isothermal mode to the thermo-sensitive mode in thermos-fluids cavitating flows. It could be utilized as a parameter to design the operating conditions for thermos-fluids apparatus or system to avoid the maximum cavitation aggressiveness around the thermal transition temperature. [ABSTRACT FROM AUTHOR]

Highlights • Condensation heat transfer is studied inside a 4.0 mm OD microfin tube. • Heat transfer coefficients and pressure drops are analyzed at different conditions. • Experimental values are compared against values predicted by empirical correlations. Abstract Small sized microfin tubes are a smart option to keep the refrigerant charge under the stricter and stricter values depicted by the new environmental laws. Despite of the large number of papers dedicated to phase change phenomena inside traditional microfin tubes with diameters larger than 5 mm, small sized microfin tubes are still a topic which deserves further studies. In this context, this paper proposes experimental results of heat transfer coefficients and frictional pressure drops collected during condensation of R1234ze(E) and R134a inside a small sized microfin tube with an outer diameter of 4.0 mm. Experimental tests were carried out for mass velocities from 100 to 1000 kg m−2 s−1, vapor qualities from 0.1 to 0.99, at saturation temperatures at the inlet of the test section of 30 °C and 40 °C. The range of working conditions permitted to better understand how each operative parameter affects the thermal and hydraulic behavior of the microfin tube during condensation heat transfer. The experimental results of heat transfer coefficient and frictional pressure drop were finally compared against values predicted by empirical correlations available in the open literature. [ABSTRACT FROM AUTHOR]

Highlights • We establish a more reasonable vortex cooling model for gas turbine blade leading edge. • Experiments and numerical simulations are conducted. • Influential mechanisms of temperature ratios are revealed more deeply. • This paper provides a guideline for the gas turbine blade leading edge cooling. Abstract Based on combined Infrared Thermography and numerical simulations, the heat transfer and flow performance in a vortex cooling configuration with 5 nozzles were investigated at various Reynolds numbers and temperature ratios. Validation was conducted between experiment and numerical simulation and results showed that the k - ω turbulence model has the best accuracy to predict the vortex cooling behavior. High Nusselt number regions appear under each nozzle in all cases, but air from downstream nozzles is easily impacted because of the “anti-cross flow” ability. Along the axial direction, targeting surface has a fluctuant heat transfer coefficient distribution, while along the circumferential direction, the heat transfer coefficient decreases linearly. Overall heat transfer coefficient increases with increasing Reynolds number and decreasing temperature ratio. Especially, the influence of temperature ratio under 3 setting methods is compared and discussed in detail, revealing the fundamental impact of temperature ratios. A globally-averaged Nusselt number correlation is presented over 22,000 < Re D < 39,000, 0.88 < TR < 0.94, and results in this paper are compared with other vortex cooling systems. [ABSTRACT FROM AUTHOR]

Highlights • Numerically investigated the heat transfer and pressure drop in a three-dimensional surface roughness nuclear fuel rod. • Heat transfer coefficient enhanced by 86% at Re = 4.18 × 10 5 compared to the smooth surface. • Pressure drop increased by 15.75% within Re ranging 4.50 × 10 4 - 1.07 × 10 5 . Abstract The paper focuses on the numerical studies of heat transfer and pressure drop in a simulated nuclear fuel rod with three-dimensional surface roughness. Two-dimensional numerical simulations utilizing SST k - ω turbulent model were performed to evaluate heat transfer and pressure drop on the smooth and rough section of the heater rod. The numerical results were compared with experimental data obtained from a heater element which simulates a single Inconel-Nickel fuel rod for pressurized water reactor (PWR). The length of the rod was 2152.6 mm, and an outer diameter 9.5 mm, of which the outer surface of a 304.8 mm long section of the Inconel fuel rod was modified with three-dimensional (Diamond-shaped blocks) surface roughness. The angle of corrugation for each diamond block was 45°, and the length of each side of the diamond block was 1 mm. The numerically computed local heat transfer coefficient, overall Nusselt number, and pressure drop across the test rod shows good agreement with the corresponding experimental results. For the simulated rough surface, heat transfer coefficient was enhanced by 86% at Re = 4.18 × 10 5 as compared to the smooth surface, and pressure drop was found to increase by 15.75% within Re range of 4.50 × 10 4 - 1.07 × 10 5 . Plausible reason of the heat transfer enhancement of the three-dimensional surface roughness was discussed in the paper. [ABSTRACT FROM AUTHOR]

Highlights • High alcohol surfactant has a significant effect on spray cooling. • Each surfactant has optimal concentration value to have the best performance. • Effect of surfactant on physical properties is mainly on surface tension. • Effect of surfactant on spray characteristics is mainly on droplet number. • Correlations to predict droplet diameter and droplet velocity are proposed. Abstract The addition of surfactant is considered as an important method for heat transfer enhancement in spray cooling based on numerous advantages such as less demand, significant effect and stable performance. Recent studies have found that high alcohol surfactant has a significant effect on the heat transfer in spray cooling. In this study, the effect of four kinds of high alcohol surfactants, 1-heptanol, 1-octanol, isooctanol and n-decanol, on spray cooling heat transfer using water as the working medium was studied experimentally. It was found that there exists an optimal concentration for each surfactant to achieve the best heat transfer performance. Under the experimental conditions, the optimal value of 1-heptanol was 0.3‰, heat dissipation flux reached 180.9 W/cm2, and the heat transfer increased by 20.9%; the best value of 1-octanol was 0.3‰, heat dissipation flux reached 200.8 W/cm2, and the heat transfer increased by 34.2%; the best value of isooctanol was 0.5‰, heat dissipation flux reached 185 W/cm2, and the heat transfer increased by 23.7%; the best value of n-decanol was 0.1‰, heat dissipation flux reached 180.7 W/cm2, and the heat transfer increased by 20.8%. To further analyze the enhancement mechanism, this paper also studied the influence of surfactant concentration on physical properties of working fluid and the spray characteristics. The experimental results showed that the effect of surfactant on saturated vapor pressure was small, and the change became obvious at higher temperature. The tension changed obviously with the surfactant concentration, and the surface tension decreased rapidly at lower concentration. The dynamic viscosity did not vary much with the type and concentration of the surfactant. The relationship between physical properties and concentration was also obtained in experiments. After adding surfactant, droplet number was lower than that of water, the distribution of droplets at different heights was more even. Droplet diameter reduced in certain area, however it increased in the edge of the area due to local impact and fusion. The change of droplet velocity was not obvious. This paper also put forward relations between the physical properties of different working fluids and their concentration and correlations which can predict diameter and velocity of spray droplet. [ABSTRACT FROM AUTHOR]

Highlights • A novel truncated cone helix energy pile (CoHEP) was proposed. • A 3-D numerical model considering the dynamic surface condition was developed. • The heat flux per pipe length of 20° cone angle is 6.16% larger than that of 0°. • The whole pipe of CoHEP can be divided into four stages along the flow direction. • The heat flux per pipe length of CoHEP increases linearly as cone angle increases. Abstract As for the cylinder helix energy pile (CyHEP), in order to reduce thermal interference and improve heat transfer efficiency, a novel truncated cone helix energy pile (CoHEP) was proposed in this paper. A 3-D numerical model both considering the dynamic surface condition and the initial soil temperature distribution was developed to investigate its thermal performance, and three main influencing factors (inlet water temperature, water flow rate, cone angle) were studied by the established model. In addition, the laboratory investigation was carried out to verify the accuracy of the numerical model. The results indicate that the heat flux per unit pipe length of the 20° cone angle CoHEP is 6.16% larger than the traditional CyHEP. The whole pipe of CoHEP can be divided into four stages along the flow direction of the pipe length: the entrance stage → the thermal short circuit stage → the small temperature difference stage → the exit stage. During the design of CoHEP, the proportion of the thermal short circuit stage and the small temperature difference stage should be reduced to ensure the overall heat transfer capability. Heat flux per unit pipe length of the CoHEP increases linearly with the inlet water temperature. Increasing the water flow rate can increase the heat flux per unit pipe length of the CoHEP, but it can also reduce the flow time in the pipe, resulting in insufficient heat exchange. As for the cone angle, increasing the cone angle can effectively reduce the radial thermal interference at the upper part of CoHEP and the axial thermal interference. When the system running time is 12 h, as the cone angle increases from 0° to 10° to 20°, the growth rates of heat flux per unit pipe length are 2.54% and 3.53% respectively. Moreover, there must be an allowable maximum cone angle considering the minimum spiral radius of PE pipe, for example, the allowable optimal cone angle is 21° for the model built in the paper. [ABSTRACT FROM AUTHOR]

Highlights • A critical review addresses issues in one-group interfacial area transport models. • A critical review addresses future directions of interfacial area modeling. • 1D interfacial area models of turbulent diffusion & lateral migration are derived. • A preliminary interfacial area model for high-pressure conditions is developed. Abstract This paper provides the state-of-the-art critical review on the modeled source and sink terms of the one-group interfacial area transport equation. The reviewed source and sink terms include models developed by Wu et al., Hibiki and Ishii, Hibiki et al., Yao and Morel, Park et al., Hibiki et al., Kataoka et al., Nguyen et al., Shen and Hibiki and Hazuku et al. The present critical review assesses major issues in modeling the one-group source and sink terms. Important conclusions are that the existing source and sink terms are not well-validated for developing and transient flows and the applicability of the source and sink terms to high pressure conditions such as prototypic nuclear reactor conditions has not been well-discussed. In view of these, coefficients of the source and sink terms in Hibiki and Ishii’s model have been modified for their application to prototypic nuclear reactor conditions. In addition, approximated area-averaged source and sink terms due to turbulent diffusion and lateral migration are derived by area-averaging local source and sink terms due to turbulent diffusion and lateral migration developed by Kataoka et al. The role of the area-averaged source and sink terms due to turbulent diffusion and lateral migration on the interfacial area transport should be tested in a future study. This paper also overviews important model validation challenges to be addressed in a future study. The challenging model validation should address the model performance for various test sections and flow conditions. They are (1) the effect of channel size (small (or micro/mini)-to-large channels) on the interfacial area transport, (2) the scalability of the interfacial area transport equation to prototypic nuclear reactor conditions, (3) the effect of covariance due to phase distribution on the interfacial area transport, (4) the effect of inlet conditions on the interfacial area transport, (5) the applicability of the interfacial area transport equation to transient and developing flow conditions, and (6) the applicability of the interfacial area transport equation to various flow channels including a rod bundle. [ABSTRACT FROM AUTHOR]

Nitrogen-assisted cyclic steam stimulation (NCSS, i.e. huff and puff) is an important alternative to recover heavy oil reservoirs. In order to forecast the production performance accurately and rapidly, a novel model is developed for heated radius calculation and production prediction of NCSS wells. The underlying assumption in this paper is different from the Marx-Langenheim isothermal model, the heated area is assumed to be non-isothermal and the temperature decreases exponentially. A new heated radius calculation equation is then established and solved by the Newton iteration method. Afterwards, an analytical model for production prediction is derived with pseudo-steady state percolation method by considering the variation of temperature, pressure, relative permeability, etc. during the different periods of the huff-n-puff process. After verification by numerical simulation runs, a sensitivity analysis is performed with the consideration of multiple factors, such as injection rate, injection temperature, fluid component and threshold pressure gradient (TPG). The results indicate that the increase of injection rate, injection temperature and nitrogen-steam ratio, or the decrease of TPG will lead to an increase in oil production. This paper provided a reference for heated radius evaluation and productivity estimation in NCSS processes for heavy oil. [ABSTRACT FROM AUTHOR]

The labyrinth seal with a honeycomb land is one of the most typical sealing solutions used in gas turbines. The paper presents an analysis of a straight-through seal with two fins. Such seals are used in places with limited space and where design and tribological constraints are of great importance. At a small number of the labyrinth fins, an improvement in the labyrinth performance can bring notable operating benefits. The paper presents optimisation of the seal labyrinth with different geometrical land configurations. The first part describes the labyrinth seal geometry and individual land types. The analysis covers seals with a honeycomb land, a squeezed-honeycomb land, a rhomboid land and a smooth land. The seal computational model and the optimisation task algorithm are presented. The objective function is minimization of the discharge coefficient, and the parameters are the labyrinth geometrical quantities: the fin height, the fin position, the fin thickness and the fin inclination angle. The optimisation task is solved for each land type. The results of individual optimisation tasks are presented and discussed, and the potential for improvement in the seal efficiency by means of appropriate selection of both the labyrinth parameters and the type of the land is pointed out. The obtained values of the reduction in the discharge coefficient reach 18% compared to the reference labyrinth configuration. However, taking account of both the labyrinth and the land shape, the benefit of 22.4% is achieved in comparison to the reference configuration with a honeycomb land. [ABSTRACT FROM AUTHOR]

This paper is the first in a series of papers describing the temperature fields created by a circular area heat source (CHS) in various situations. In this paper, the derivation of the solution of the 3D transient heat flow from an embedded finite CHS supplying heat to an infinite medium is shown by employing different methods. The different adopted techniques include Laplace, Hankel and Fourier Cosine transforms, and solutions are based on first principles with minimum assumptions. Both isotropic and orthotropic infinite media are considered. Finite element simulations performed in COMSOL Multiphysics are provided and compared with the analytical solutions, with deviations between analytical solution and simulation of <1 mK for a typical temperature rise of 1 K. Fitting of the numerical results with the analytical solutions is performed to extract the thermal transport properties of the media, which are found to deviate by a maximum of 1.7% for all considered cases. [ABSTRACT FROM AUTHOR]

In this paper, an analytical and numerical study of species separation in binary mixtures taking account of the presence of bounding plates for the cell is presented. A rectangular horizontal porous cavity saturated by a binary mixture and heated from below is considered. This cavity is bounded by thin plates of uniform thickness, the outer surfaces of which are subjected to a constant heat flux. The transition from the equilibrium solution to the convective one, either stationary or oscillatory, was previously studied by Ouattara et al. (2012). Thus in the first part of this paper, the critical parameters associated with the onset of long wavelength disturbances, obtained analytically, are recalled. Then the hypothesis of parallel flow is used to determine an analytical solution which describes the unicellular flow which may appear in the case of a large aspect ratio cell for a given range of separation ratio, ψ , Rayleigh number, Ra , Lewis number, Le, the ratio of the plate to the porous layer thickness, δ, and their thermal conductivity ratio, d . The analytical results are corroborated by direct numerical simulations. We verify that if d goes to infinity, the walls become infinitely conductive and we find the results obtained by Charrier-Mojtabi et al. (2007). When d tends to 0, the walls become infinitely thin the results obtained by Yacine et al. (2016) are recovered. A linear stability analysis of the unicellular flow is also presented. The eigenvalue problem resulting from the temporal stability analysis is solved by a Tau spectral method. The optimal Rayleigh number leading to an optimal value of the separation horizontal gradient is determined for different values of physical parameters. We show that the species separation depends sensitively on the ratio of the plate to the porous layer thickness, and the ratio of their thermal conductivities. Furthermore, we have shown that in the stationary state and for a given value of the thermal conductivity ratio ( d  = 29), the maximum separation is almost equal for walls of the same thickness than the one of porous cavity or for the case of porous cell delimited by the infinitely thin walls. [ABSTRACT FROM AUTHOR]

The theoretical basis for the calculation of shell side condensation of the spiral coil heat exchanger is weak. In order to solve the problem of pure steam film condensation heat transfer of the shell side of the spiral coil heat exchanger, the theoretical model of the homogeneous flow was established. Considering the centrifugal force, two different mathematical models were established and the heat transfer characteristics were studied. The solution formula of the heat transfer coefficient and thickness of first layer liquid film, meanwhile, was obtained. The theoretical formula of the membrane-like condensation heat transfer of the heat exchanger was worked out, based on the calculation model of the heat transfer coefficient of one-component working fluid outside the tube bundle, considering the effect of tube bundle. The two calculated results in this paper and the theoretical result of Bays and McAdams were compared with experimental values respectively. The results show that the relative error between the calculated values obtained by the two theoretical models and experimental values is 7.48% (ignoring centrifugal force), 3.05% (considering centrifugal force), while the relative error between Bays and McAdams’s result and the experimental value is 61.3%. The correctness of the theoretical models proposed in this paper are verified. The theoretical models can be used to calculate the film condensation heat transfer of the spiral coil heat exchanger. [ABSTRACT FROM AUTHOR]

Multiphase flow pattern identification is of utmost importance to the energy industry, given that thermohydraulic operating conditions are drastically affected by flow and heat transfer regimes. In industrial boilers and nuclear reactors, for instance, the heat transfer coefficient – and hence the heater temperature – is significantly affected by the boiling regime, where the onset of film boiling can be catastrophic to the equipment and cause irreparable damage. In this paper, it is shown that a machine can learn from visualization and successfully classify and separate natural convection, nucleate boiling and film boiling regimes using low speed and low resolution image frames acquired from visualization of an on-wire pool boiling experimental setup (direct visualization) even when only the departed, ascending bubbles are considered – i.e., the heater is suppressed from the image (indirect visualization). While not the main objective of this paper, principal component analysis of the frames is shown to provide information regarding bubble dynamics and hence is used for dimensionality reduction. Two types of classifiers, namely support vector machines and neural networks, are shown to be able to classify pool boiling frames with over 93% accuracy sufficiently fast, possibly enabling real-time execution and classification, even during indirect visualization and, hence, providing a non-intrusive and low-cost pool boiling regime identification. [ABSTRACT FROM AUTHOR]

The paper addresses the problem of coupled heat and moisture transfer in porous materials with the time-periodic boundary conditions applied. The solution of Luikov equations [1] , which describe coupled heat and moisture transfer, is presented. Laplace transform is used, where some terms of the inverse Laplace transform ought to be solved by Gaussian quadrature, meaning that the solution is semi-analytical. The time-periodic boundary conditions are applied to simulate the humidity and temperature oscillations of natural environment. Therefore, the proposed solution is appropriate to evaluate the distribution of moisture and temperature within the porous material exposed to everyday natural cycles. The paper presents convergence tests, validation of semi-analytical solution and application to different building materials are presented in the paper. [ABSTRACT FROM AUTHOR]

The discharging process causes the multiple physical field coupling problem, which make it complicated to analyze the heat effect of discharging arc. The heat effect of the arc can be divided two parts including the heat effect of the arc column and the heat effect on the cathode surface. Therefore, this paper proposes an equivalent heat source to be equivalent to the two parts heat effect of the arc and simplifies the process for thermal analysis of the arc. Firstly, this paper analyzes the heat source characteristics of the arc based on MHD model. According to the heat source characteristics of the arc, this paper proposes respectively using ellipsoid heat source and Gaussian surface heat source to be equivalent to the two parts of the heat effect of the arc. Then the equivalent heat source is used to calculate the temperature distribution of tip-plane electrode under discharging. Comparing with the numerical results in MHD model, the error between the two models is within 0.5%, which proofs that the equivalent heat source can be used to equivalent to the heat effect of the arc. Moreover, this paper discusses the method to determine the parameters of the equivalent heat source. Finally, an experiment is carried out to verify the accuracy of the MHD model and the equivalent heat source of the arc. [ABSTRACT FROM AUTHOR]

This paper presents a comparative study of a counter-cross flow plate heat recovery exchanger, which operates as an indirect evaporative air cooler in cooling conditions. In the study, thermal performance of this exchanger with different placement modes (vertical and horizontal) was investigated by numerical simulation based on original mathematical model. To validate the numerical model, vertically and horizontally positioned prototypes with the same exchangers were made and tested on the test rig. According to the test results, the numerical model has a satisfactory accuracy. For these two types of prototypes, influence of supply and exhaust air inlet parameters (temperature and relative humidity) on the thermal performance of the two prototypes in both constant inlet airflow rate and variable inlet air flow rate was researched. The results show that, under conditions of constant airflow rate with variable supply air parameters, the outlet supply air temperature of the exchanger set vertically is 1.41–2.40 °C lower than that of exchanger set horizontally, meanwhile, 24–44% more cooling capacity is obtained by the vertical exchanger. It indicates that placement mode has important effects on thermal performance of the exchangers and the exchanger set vertically always shows a better performance. The main reason is considered to be the existence of larger dry areas in exhaust air channels of the horizontal exchanger that reduce the heat transfer between supply air and exhaust air. Therefore, characteristics of the heat transfer in horizontal exchangers was especially studied in this paper. [ABSTRACT FROM AUTHOR]

In a magnetic hyperthermia treatment, malignant cells are ablated by the heat produced by power dissipation of magnetic nanoparticles (MNPs) under an alternating magnetic field. MNPs need to be placed inside the tumor region and a prominent method for doing this is to inject magnetic fluid directly into tumor. When this alternative is used, the efficiency of a magnetic hyperthermia treatment depends on factors such as the infusion rate and diffusion duration, since they affect the shape of MNP distribution inside tumor, which affects the temperature distribution during treatment. This paper analyzes the impact of different shapes of MNP distribution, caused by different infusion rates, on mass diffusion and treatment temperature field during magnetic hyperthermia. Three different shapes of MNP distribution were assumed based on images of experiments presented in literature, which used an agarose gel with different concentrations to represent different tissues. In addition, the distribution for a very low infusion rate, obtained from a model proposed in this paper, is used for comparison purposes. A proposed geometric model is used to numerically evaluate the impact of injection and diffusion parameters on a liver tumor considering the four different shapes of MNPs produced by different infusion rates. The simulation results demonstrate that the longer the diffusion duration and the larger the infusion rate are, the better the therapeutic effects are when a proper power dissipation of MNPs is used to control the maximum temperature reached during hyperthermia. To further improve the effective therapeutic area inside tumor, two alternative methods are also evaluated using the model proposed in this paper: multi-site injection and low Curie temperature MNPs. The results show that both of them can significantly improve the tumor area which is subjected to the therapeutic temperature, especially the latter one. [ABSTRACT FROM AUTHOR]

The enthalpy-porosity method is widely used in solving solid-liquid phase change problems that involve convection in the melt; however the influence of the required mushy zone parameter on the melting process has been largely overlooked. In this paper, further investigation of the mushy zone parameter is presented. The enthalpy-porosity method is the default model in Fluent for melting simulations. A comprehensive discussion of previously reported mushy zone parameter values is presented with a comparison to numerical and experimental results. In this paper, based on experimental validations of melting times, it is found that mushy zone parameters can be optimized based on relevant driving temperature differences. And despite the fact that the model cannot capture bulk solid sinking behaviors, numerical solid sinking behaviors by Fluent are still widely reported in the literature. Explanations and supporting numerical analysis are given for this seeming contradiction. Finally, an analytic solution for unconstrained sinking is developed. With the introduction of a tuning parameter to modify the viscosity of the mushy region in the bottom liquid layer, good agreement between the analytical model and experimental results is achieved. A linear correlation for the tuning parameter based on driving temperature differences is given. [ABSTRACT FROM AUTHOR]

A porous medium with separated paths for liquid and vapor flows does not fail even after part of the porous medium is dried out. Instead, a vapor film resides within the porous medium, and it grows very slowly. This heat transfer regime was named as “confined film-boiling regime” in this study, and a heat transfer model for this regime was suggested in this paper. Especially, this paper mainly focuses on heat transfer of a CRUD (Chalk River Unidentified Deposit), which is a naturally occurring porous medium found in nuclear reactors. In the present model, the balance between capillary pressure and pressure drops of liquid and vapor flows determined thickness of the vapor film. In addition, we assumed that capillary pressure was changed with applied heat flux. This assumption was validated with a planar heat pipe case: the root-mean-square-error (RMSE) was 16% for the model with the heat flux dependent capillary pressure, while one for a model with the constant capillary pressure was 790%. Furthermore, this approach also turned out to be valid for the case of the CRUD: the model predicted the wall superheat during the film boiling of the CRUD, and its relative error was only within 20% when it was compared with the measured wall superheats. Finally, sensitivity analysis for CRUD parameters found that the heat transfer performance of the CRUD is largely sensitive to chimney density and pore size. [ABSTRACT FROM AUTHOR]

This paper presents an evaluation of the weighted-sum-of-gray-gases (WSGG) model in the computation of the radiative heat transfer in an axisymmetric gas system composed of H 2 O, CO 2 and soot by comparison with line-by-line (LBL) integration. The test cases consider temperature and species concentrations fields that are representative of a laminar diffusion jet flame of ethylene diluted with H 2 O. Different approaches are considered in the application of the WSGG model, including the use of WSGG coefficients obtained for different ratios between the mole concentrations of H 2 O and CO 2 , and the superposition between the coefficients of H 2 O/CO 2 and soot. The WSGG coefficients for H 2 O and CO 2 are based on HITEMP2010 database, while for soot they are based on the consideration of linear spectral dependence of its absorption coefficient. The spatial integration of the radiative transfer equation is carried out with the discrete ordinates method. The results in the paper show that, although the ratio between the mole concentrations of H 2 O and CO 2 varies locally in the flame, using WSGG coefficients for a constant ratio, but equivalent to the global average ratio in the flame, can provide satisfactory solutions in comparison to the LBL integration. Moreover, the superposition method between the WSGG coefficients of combined H 2 O/CO 2 and of soot proved accurate considering both moderate and high concentrations of soot. The paper provides algebraic relations for the temperature and concentration fields, which can be used for the evaluation of other gas models in future studies. [ABSTRACT FROM AUTHOR]

In this paper, we experimentally investigated the effect of turbulent intensity on heat transfer in a square rotating channel. The grid generated turbulence is measured by hot-wire, and the heat transfer coefficient is measured by TLCs. In the experiment, the Reynolds number, based on the channel hydraulic diameter ( D = 80 mm ) and the bulk mean velocity ( V m = 1.82 m / s ), is 10,000, and the rotation number ranges from 0 to 0.52. The mean density ratio ( d . r . = ( T w - T b ) / T w ) is about 0.1 in the current work using transparent heater glass (Indium Tin Oxide) to provide uniform heat flux. Two different turbulent intensity of inlet air (0.6% and 5.5%) are taken into consideration to investigate the heat transfer distribution on the leading and trailing side. The results show that turbulent intensity has an effect on heat transfer on both leading and trailing side, especially at rotating conditions. At static conditions, the effect of turbulent intensity on heat transfer is not obvious. However, with the increase of rotation number, in case B with a medium turbulent intensity (Tu) of 5.5%, the Nu/Nu 0 is about 10% higher than that in the case A with low turbulent intensity of 0.6% with the rotation number of 0.52 at X/D = 2 on trailing side. The enhancement of case B decreases along X/D directions. On the leading side, the turbulent intensity has same effect on heat transfer with that on trailing side, but not as prominent as that on the trailing side. In current work, the turbulent intensities at different X/D directions are also presented to explain the phenomenon of heat transfer in the channel. More detail of results will be presented in this paper. [ABSTRACT FROM AUTHOR]

In light water reactor, melting of nuclear fuel rod (NFR) is critical. Therefore, this issue needs to be simulated and analyzed with different accidental conditions. In this paper, one-dimensional model is build and used to simulate the melting process of NFR in nuclear core. The numerical model includes three regions; these are Uranium dioxide fuel pellet, Helium layer and Zirconium alloy cladding. Due to huge temperature gradient in radial direction of NFR, material properties which include specific heat, thermal conductivity and density are non-linear and depends on temperature. In addition to this the convection and radiation heat transfer are also considered in the Helium layer region. To solve the enthalpy formulation of melting process, the Half Boundary Method (HBM) is used in this paper. The HBM is accurate, efficient and save calculational memory. The melting process of fuel rod is simulated during Reactivity-Initiated Accidents (RIAs) and Loss-Of-Coolant Accidents (LOCAs). The results showed us that if RIA happens melting will first take place at the center of pellet and in case of LOCA, melting will begin inside cladding. [ABSTRACT FROM AUTHOR]

The liquid desiccant cooling system (LDCS) is a promising alternative for the conventional vapor compression system due to its high energy efficiency. To enhance the mass transfer between the regeneration air and liquid desiccant in the regenerator, the paper firstly introduced a kind of surfactant called polyvinyl pyrrolidone (PVP-K30) which was added into the LiCl solution for better desiccant regeneration performance. The falling film characteristics and regeneration performance were investigated and compared with and without surfactant. The results indicated that the contact angle of desiccant solution on plate decreased from 58.5° to 28.0° by adding surfactant with 0.4% of concentration. The average wetting area increased from 0.174 m 2 to 0.209 m 2 with a relative increment of 20.1% with the addition of surfactant. Correspondingly, the film thickness had a reduction of 0.103 mm from 0.696 mm to 0.593 mm averagely. The regeneration rate had an average enhancement of 26.3% under the same working conditions, resulting from the decrement of solution contact angle with the addition of the surfactant. Finally, correlations to predict the mass transfer coefficient were proposed with and without surfactant and the mean absolute relative deviation between the results of correlations and the experiments were kept within 8%. The results and findings of present paper could be applied to guide the design of compact regenerator for higher regeneration performance. [ABSTRACT FROM AUTHOR]

Overheating of power electronic devices has become a significant issue due to their continued miniaturization and increased heat flux that needs to be dissipated. Ferrofluids (magnetic nanofluids) have been shown to have higher thermal conductivity than their base aqueous or oil based fluids due to the solid magnetic nanoparticles that make up the ferrofluid. This allows higher convective heat transfer rates and, importantly, the ability to externally effect the flow using a magnetic field. In this paper, we focus on material characterization of ferrofluids and measurement of heat transfer rates for single-phase ferrofluidic forced convective flow in microchannels. We show that heat transfer properties of the flow are enhanced with the use of ferrofluids and that the material make-up of the ferrofluid affects these properties. In this paper, we argue that generally, convective heat transfer rates for ferrofluids are increased by increasing the solid volume concentration of magnetic particles (∼0.2–0.4%). Interestingly, increasing magnetic flux was shown to decrease heat transfer enhancement. This was due to a reduction in the thermal conductivity of the bulk fluid caused by magnetic nanoparticles being drawn out of the isotropic mixture and becoming pinned to the channel wall in the region of strongest magnetic field. We show that there is good correlation between both theory and experimental visualization of this phenomenon. [ABSTRACT FROM AUTHOR]

Hydrothermal jet is an alternative drilling method for the exploitation of oil and geothermal energy in deep hard formations. For the application of this novel technology, the successful generation of hydrothermal jet is very important. This paper focuses on investigating applications of different reaction, turbulence and radiation models to the supercritical water oxidation process in downhole reaction chamber of hydrothermal jet drilling. The objective is to identify the pros and cons of each model and determine a set of models that are the most appropriate for the reaction. Simulation models are tested and optimized through two different operating conditions. Simulation results are compared with experimental data. Results show that the entire space of the reaction chamber is in a high temperature state using the laminar finite rate model. The finite rate model is suitable for the simulation compared with other reaction models discussed. The Magnussen constant A and B in the finite rate model can be modified to be 7 and 0.5 to further reduce the error. In addition, the high temperature areas in k-omega model and SAS model are more concentrated, while they are more uniform in RNG k-epsilon model and standard k-epsilon model. The RNG k-epsilon model and DO or DTRM are the most appropriate turbulence and radiation models through comparison. Results in this paper can provide implications for the reaction simulation of hydrothermal jet drilling. [ABSTRACT FROM AUTHOR]

In the current paper it is presented and tested an innovative method for estimating internal heat transfer coefficients in ducts adopting only thermal measurements acquired on the external wall surface. This approach is based on the reciprocity functional analysis, which is a powerful non-intrusive inverse problem technique. The adoption of this technique is promising since it avoids intrusive measurements, it is fully non-iterative and the computational time and cost are very limited. In this paper, it is presented an extension of the classical reciprocity functional methodology in the sense that a fully analytical expression, obtained by the integral transform technique, is developed for estimating the internal heat transfer coefficient in a three-dimensional problem. Such methodology, avoiding the solution of linear systems, reduces the computational costs that are massive when the traditional approaches are applied to three dimensional problems. The proposed procedure is first validated adopting synthetic temperature data and then tested using real temperature measurements acquired by an infrared camera. The results highlight that the methodology is able to recover the unknown functions in a very short computational time with a good accuracy. [ABSTRACT FROM AUTHOR]

With the increasing demand for oil storage, storage tanks are developing towards large-scale tanks better adaptability to extreme working conditions. The variation law of the oil temperature field and the flow field inside the tank should be accurately understood to guarantee safe and economical operation of an oil depot. Aimed at understanding the periodic variation in the ambient environment of the tank’s location and the physical properties of the crude oil, the theoretical model of unsteady heat transfer flow in a large floating roof tank was established by using the relative heat transfer theory in this paper. The numerical solution technique for the crude oil temperature field and the flow field was studied. This paper thoroughly analyzed the effect of heat transfer and flow coupling characteristics on the tank static storage process under the influences of the atmospheric temperature, solar radiation, etc. The results show that according to the variation law of the temperature field, the static storage cooling process was divided into a partial rapid cooling stage, overall rapid cooling stage, condensate reservoir growth stage and overall low-speed cooling stage. The heating process was divided into a partial low-speed heating stage and partial rapid heating stage. The solar radiation has a great influence on the temperature fluctuation, and the atmospheric temperature has a great influence on the rate of temperature decrease. The results can provide theoretical support for optimizing the design of the storage process and managing the manufacturing of a large floating roof tank. [ABSTRACT FROM AUTHOR]

• The influence of temperature gradient on the diffusion and dissolution process of CH 4 is expounded. • Temperature gradient could drive CH 4 to diffuse from low concentration position to high. • Soret and thermal diffusion coefficients of dissolved CH 4 in the range of 1 ∼ 200 MPa and 273.15 ∼ 600 K are calculated. • The influence of Soret effect on CH 4 diffusion in geological fluid is discussed in detail. This paper has investigated the mass transfer process of methane (CH 4) in aqueous solution under the effect of temperature gradient using quantitative Raman spectroscopy. At 20 MPa and 473.15 K, it was observed that CH 4 diffuses from low concentration position to high driven by temperature gradient, indicating that thermodynamic factors play a dominant role. According to the assumption that the saturated concentration of CH 4 is treated as steady concentration profile, Soret and thermal diffusion coefficients of dissolved CH 4 in the range of 1 ∼ 200 MPa and 273.15 ∼ 600 K are calculated. Based on the temperature gradient distribution calculated by thermal model in the Ashizuri section of the Nankai Trough, this paper estimates the CH 4 solubility distribution in this section and provides a new perspective to reveal a possible formation mechanism of CH 4 accumulation, leakage and related geological disasters in the geological body. [ABSTRACT FROM AUTHOR]

• Near-field thermal diode based on 2D gratings is proposed to improve rectification performance. • The rectification mechanism of the 2D gratings-based near-field thermal diode is studied. • The effects of structural grating parameters are discussed in detail. • The validity of effective medium theory is investigated. • The longitudinal asymmetric structure is proposed to further improve rectification ratio. This paper proposes a near-field thermal diode (NFTD) based on VO 2 and cBN 2D gratings to improve the rectification ratio. Different from previous studies, this paper is the first to verify the positive effect of 2D gratings on NFTD. The exact calculations are based on rigorous coupled wave analysis (RCWA). After optimization, the rectification ratio of the 2D grating-based NFTD reaches the maximum R = 29.5 at filling factor f = 0.04 and gap distance d = 100 nm, which is nearly four times larger than the optimal result of the plain-based one. The reason for the improvement of rectification ratio is that the reverse spectral heat flux is weakened by more than an order of magnitude in nearly the whole spectrum, while the forward spectral heat flux is influenced little in the hyperbolic regions. Besides, the lattice period P = 100 nm and grating height h = 1 μm are feasible solutions for symmetric configurations. The validity of effective medium theory (EMT) for calculating 2D grating-based NFTD is also investigated. The EMT is consistent with RCWA in predicting the optimal filling factor and grating height at d = 100 nm, but is invalid in predicting the optimal gap distance and the maximum rectification ratio. The longitudinal asymmetric configuration is further proposed by changing the structural parameters. When the size ratios of cBN grating and VO 2 grating are selected as 0.6 and 0.1, respectively, the rectification ratio is better than the symmetric configuration due to the broadening of the hyperbolic region during forward bias. After optimizing grating height, the rectification ratio further reaches 54. Our study deepens the understanding of the rectification mechanism of 2D grating-based thermal diodes and paves the way for potential applications of thermal diodes. [ABSTRACT FROM AUTHOR]

• Adiabatic self-heating phenomenon was clarified and characterized. • A novel 3D methodology to determine adiabatic self-heating is presented. • Advanced measurements techniques such as DIC or IR were used. • The methodology accurately considers all possible thermal losses which could occur. • The relevance of a proper thermal control in material characterization was proved. Nowadays, numerical models are one of the most widely used techniques to predict material performance subjected to different manufacturing processes. However, to obtain accurate predictions, these models require reliable input data from thermomechanical tests. Nevertheless, during the test performance the material is self-heated due to a phenomenon known as adiabatic self-heating. Despite the proven relevance of a proper characterization, adiabatic self-heating is not properly taken into account during thermomechanical tests. In addition, in the literature, two different definitions were found under the umbrella of adiabatic-self heating. On the one hand, it could be defined as the ratio between the heat spent to heat the sample to the plastic work, value commonly taken as 0.9. On the other hand, many authors define the adiabatic heating as the ratio between the heat experimentally measured to the total plastic work. This second approach, although seems easier, is neglecting heat losses. These two different approaches could lead to misunderstandings once this parameter is implemented in the models. This paper aims to clarify this issue. Moreover, the techniques found in literature aiming to measure this parameter are usually based on 2D approaches at low temperatures. In this paper, a 3D methodology to measure adiabatic self-heating is presented which considers all possible heat losses (conduction, convection, radiation and mass flux) through infrared measurements and Digital Image Correlation (DIC) technique. The adiabatic self-heating was measured for a widely used alloy (Ti6Al4V) obtaining promising results. [ABSTRACT FROM AUTHOR]

• Application of porous materials to heat dissipation of LFR-PV system. • A new metal foam porous-wall mini-channel is proposed. • The MFP-channel increases the heat transfer coefficient by 35%. This paper takes the heat dissipation problem of linear Fresnel concentrating photovoltaic devices as the research background, this paper conducts an experimental investigation on the boiling flow characteristics of the dielectric liquid R141b, and discusses the enhancement effect of the electric field on the foam metal porous wall microchannel heat sink. In this paper, the effects of electric field strength (applied voltage) on wall temperature, heat transfer coefficient and critical heat flux (CHF) of mini-channel heat sink are investigated. The bubble departure diameter and incipience location in the mini-channel heat sink under different electric field strengths are recorded using a high-speed camera. Combined with the theory of electrohydrodynamic (EHD), the behavior of bubbles appearing in mini-channel heat sink under the action of electric field is analyzed. It is observed by visualization that the number of bubbles in the channel increases and the volume of bubbles becomes smaller under the electric field force. Research shows that when the voltage is 200V, the heat transfer coefficient of the mini-channel heat sink increases by a maximum of 178%, and the critical heat flux can be increased by a maximum of 123%. As the applied voltage increases, the wall temperature decreases. [ABSTRACT FROM AUTHOR]

• A multiphase model of heat and mass transfer in porous media was established, and the thermal desorption characteristics of mixed adsorbate in spent activated carbon were studied, reflecting the existence of residual adsorbate. • The fluid flow within the sample is dominated by vapor flow and supplemented by liquid flow, with 90% of the vapor flow being viscous and the liquid flow being driven by Darcy friction. • It was found that both the heat area and the uniformity of the temperature distribution of the sample affect the time required for thermal regeneration of spent activated carbon, and the mechanisms involved were investigated. • In terms of practical application, this paper designs and compares column and barrel shaped regeneration samples, which can save up to 24.4% of the thermal regeneration time of spent activated carbon at the same external temperature. In the thermal regeneration of spent activated carbon, the thermal desorption of the adsorbate is the key process. In the actual desorption process, traditional models lead to inaccurate simulation results due to the presence of residual adsorbent. In this paper, a multi-phase porous media heat and mass transfer model is developed, which can calculate the thermal desorption characteristics of mixed adsorbates in spent activated carbon and reflect the presence of residual adsorbates, with a significant improvement in accuracy compared to the traditional model. The feasibility of the application of the model is verified by comparing the computational simulation results with the experimental results. Based on the simulations and theoretical analysis, it was concluded that the temperature rise and liquid phase content of the spent activated carbon samples under constant heating conditions were characterized by "fast-slow-fast" and "slow-fast-slow", respectively; the fluid flow inside the thermally regenerated samples was dominated by vapor flow The fluid flow within the thermally regenerated samples is dominated by vapor flow, with 90% of the vapor flow being viscous and the liquid flow being driven mainly by Darcy friction. In addition, the design and comparison of column and barrel shaped regeneration samples resulted in savings of up to 24.4% in thermal regeneration time for spent activated carbon at the same external temperature. [ABSTRACT FROM AUTHOR]

• The heat transfer process of NH 4 Cl fouling was studied experimentally. • The local heat transfer characteristics around tube wall was analyzed. • The effects of flow rates and temperature on heat transfer process were investigated. • The fouling resistance and average fouling thickness on the HET wall were obtained. The crystallization fouling of ammonium chloride (NH 4 Cl) often occurs on heat exchange tube bundles in petroleum refining equipment, which seriously reduces the heat transfer and operational efficiency of the equipment. In this paper, the heat transfer characteristics of heat exchange tube (HET) with NH 4 Cl crystallization fouling was studied experimentally. The effects of velocity, temperature and mass flow rate of hot and cold fluids on the overall and local heat transfer characteristics were analyzed. The results indicate that the local heat transfer coefficient around the tube wall decreases first and then increases with the increase of the circumferential angle (θ) under clean condition. At the position of 0°-45°, the local heat transfer coefficient is the largest. At 90°-135°, the local heat transfer coefficient is the smallest. Under fouling condition, the local heat transfer coefficient increases with the increase of circumferential angle. In the region of 0°-45°, the local heat transfer coefficient is the smallest. The region with the largest local heat transfer coefficient is 135°-180° The heat transfer coefficient (h), fouling resistance (R f) and average fouling thickness increase with the increase of Reynolds number (Re), temperature of hot fluid (T h) and mass flow rate of cold fluid (q m,c), but decrease with the increase of temperature of cold fluid (T c). [Display omitted] [ABSTRACT FROM AUTHOR]

• Two magnetic flux forms suitable for RPECT and the supporting devices are proposed. • The effect of the magnetic parameters, the external cooling and the initial roll temperature on the energy efficiency and control ability of RPECT is analyzed. • The energy efficiency intersection of TMF and LMF is studied. Roll profile electromagnetic control technology (RPECT), which has the flexible control ability of the roll profile, is a new roll gap control technology that can be applied in the cold rolling process. The electromagnetic stick (ES) is generally used as the main bulging driving to adjust the roll profile. However, the ES structure can be changed with the variation of the electromagnetic flux forms, which further results in the difference of the energy efficiency and control ability. In this paper, the transverse magnetic flux form (TMF) and longitudinal magnetic flux form (LMF) of RPECT are proposed, and the principles of TMF and LMF are analyzed, and their advantages in the heat transfer paths are discussed. To conduct the parameterized impact analysis, the electromagnetic-thermal-structural coupled model matching the two electromagnetic flux forms are established and verified. Through the analysis of the current density, the current frequency, the external cooling and the initial roll temperature, the results show that the variation of the current densities, the current frequencies or the initial roll temperatures can change the control ability of RPECT, while changing the external cooling can not affect that of RPECT. The energy efficiency intersection of TMF and LMF can be achieved by changing the current density or current frequency separately. However, compared with changing the current frequency, increasing the current density of TMF to two times of LMF at different initial roll temperatures can realize the energy efficiency intersection of TMF and LMF, which is the best way to achieve this goal. [ABSTRACT FROM AUTHOR]

• The pressure drop through polyurethane foams was studied. • A correlation for friction factor based on fiber diameter and permeability in polyurethane foams was obtained. • A correlation for Nusselt number based on fiber diameter in polyurethane foams was obtained. • Comparison of heat transfer and friction factor in polyurethane foams with metal foams was made. Foam-like materials have a large specific surface area and complex structure that promotes flow turbulence, which makes them useful for heat transfer. In the literature, heat transfer in metal foams (MF) with high thermal conductivity is mainly considered. In the present paper, an experimental study of the hydraulic and heat transfer characteristics of a rectangular channel filled with polyurethane foam (PUF) inserts with a thermal conductivity of 0.2 W⋅m−1⋅K−1 in the air flow was carried out. The open-cell PUF samples had 20 and 80 pores per inch (PPI), 0.97 and 0.98 porosity, 269 µm and 60 µm fiber diameter, respectively. The Reynolds number, based on the fiber diameter ranged from 0.04 to 50. From the results of hydraulic tests, friction coefficients were determined based on the fiber diameter and permeability. The Forchheimer coefficient was 0.198 and 0.318 for 20 and 80 PPI samples, respectively. The permeability was 1.889 10−7 ⋅m2 and 7.535 10−9 ⋅m2 for 20 and 80 PPI samples, respectively. The Nusselt number for both tested PUF samples was correlated with the Reynolds number based on the fiber diameter in a power law with the Reynolds number exponent and constant equal to 0.61 and 0.037 respectively. The intensity of heat transfer in the PUF samples was 7–12 times lower than that in MF. However, a significant heat transfer enhancement is still possible compared to the empty channel up to 7 times. The heat transfer performance of PUF was higher compared to the empty channel, but the thermal performance factor was lower than one. Nevertheless, in practical situations where the mass or cost of the heat exchanger is preferable, PUF can be considered as a heat transfer intensifier. [Display omitted] [ABSTRACT FROM AUTHOR]

• Validation of numerical models is presented by comparison with experimental results. • Influence of turbulence Prandtl number model and turbulence model is analyzed. • Effects of structural parameter on thermal hydraulic performances are discussed. • Effects of flow parameter on thermal hydraulic performances are analyzed. Sodium-cooled fast reactor coupled with supercritical CO 2 Brayton cycle has broad development prospects owing to the high thermal efficiency, smaller components and compact footprint. As one of the key components, sodium-supercritical CO 2 compact heat exchanger plays a vital role in improving the operation performance of coupled power systems. In this paper, a numerical model for coupling heat transfer of sodium-supercritical CO 2 in a straight-channel compact heat exchange channel is established and the prediction accuracy of the model is verified with experimental results. The influence of structural parameters and flow parameters on the resistance characteristics and heat transfer performance of cold and hot channels is systematically analyzed. The results show that the structure of semi-circular cross-section with an ABAB layout performs best in heat transfer performance. For the sodium channel, performance evaluation criteria gradually grow with the increase of sodium inlet velocity and slowly decline with the supercritical CO 2 inlet velocity. For the supercritical CO 2 channel, performance evaluation criteria decrease with the increase of sodium inlet velocity and increase with the supercritical CO 2 inlet velocity. Reducing the supercritical CO 2 inlet temperature could effectively improve the thermal hydraulic performance of the sodium-supercritical CO 2 compact heat exchange channel. [ABSTRACT FROM AUTHOR]

• Optimizing Permanent Magnets for Ferrofluid Cooling Breakthroughs. • Ferrofluid Cooling with Permanent Magnet Configurations for Efficient Thermal Management. • Unravelling the Impact of Permanent Magnet Configurations on Ferrofluid Cooling Efficiency. • Optimizing Magnet Configurations for Ultra-Efficient Heat Transfer in Ferrofluids. Many industries, such as microelectronics and power electronics, face challenges in removing large amounts of heat from small areas to prevent overheating. Recent research has shown that microchannel flow of ferrofluids driven by an external magnetic field (MF) has the potential to deliver efficient cooling systems for modern electronics. Despite this potential, robust optimisation of the MF has not been undertaken. This paper addresses this shortcoming by reporting the effect of the MF produced by three permanent magnets in various configurations on the heat transfer of ferrofluids undergoing laminar flow through a microchannel under constant heat flux boundary conditions at Peclét number Pe=73. Observations from numerical simulation show that the rate of convective heat transfer varies strongly with position and orientation of the magnets. We show that for the optimum magnet configuration, the maximum and average Nusselt numbers increase by more than 146% and 51% over the unperturbed flow, some of the highest values reported in the literature. These results show that significantly accelerated heat transfer is possible in magnetically driven ferrofluids, with potential for further enhancement with more rigorous optimisation. [ABSTRACT FROM AUTHOR]

• A hybrid heat exchanger which enables sole air or liquid cooling as well their combination simultaneously is proposed. • The performance of the proposed heat exchanger is documented experimentally. • Hybrid heat exchanger keeps the battery cell temperature below 30°C for continuous 3C discharge rate. • Hybrid cooling increases temperature uniformity and the maximum temperature difference is 2.7°C. • The applicability of the proposed heat exchanger for electronic cooling is validated experimentally with resistance heaters. The temperature of cells varies greatly during dis/charge while their performance and lifetime are greatly affected by this fluctuation. Elevated temperatures may yield battery fire due to thermal runaway as well they accelerate ageing and capacity fade of cells. Thermal management systems are a necessity for electric vehicles to extend the lifetime of battery cells and eliminate any fire risks, especially for fast dis/charging applications. Here, we document a hybrid cold plate with a working fluid(s) of sole air or liquid as well as both of them. Hybridization of air and liquid cooling promises to minimize energy consumption requirements during a charge/discharge cycle by combining the benefits of both thermal management strategies if energy management is controlled accordingly. The temperature of each cell can be kept below 30°C with the proposed hybrid cooling heat exchanger, and the temperature difference between the cells is reduced by 30 % relative to liquid cooling. The maximum temperatures are decreased by 18 % and 3 % in hybrid cooling when compared to air and water cooling, respectively. Furthermore, a step function combining various discharge rates (1C and 3C) was employed in experiments to mimic a realistic situation, i.e. variable C-rate rather than constant. The results show that the temperature of the battery cells can be kept below 30°C with air cooling for variable discharge rate and the effect of contact resistance should not be overlooked for liquid cooling. Furthermore, the possible use of the proposed hybrid cold plates is surveyed in the cooling of electronic devices which produce more and continuous heat than cells. Therefore, three resistance heaters with a capacity of 50W are used in experiments as well. The results show that the proposed cold plates could be used in both electronics cooling and battery thermal management with a control algorithm to switch between sole working fluid and combination modes which could be developed based on the results of this paper. [ABSTRACT FROM AUTHOR]

• A fully visualized experimental facility combined with PIV system was designed to study the reverse flow phenomenon in the EHDPHRS. • Single-phase reverse flow velocity is proportional to heating power and inversely proportional to subcooled-water temperature. • Two-phase reverse flow velocity increases first and then decreases with heating power. • Buoyancy lift induced by density difference and pressure difference induced by direct contact condensation are the driving force for reverse flow. • Flow inertia force caused by forward flow is the restraining force for reverse flow. The equal-height-difference passive heat removal system (EHDPHRS) has a large potential in floating nuclear power plants (FNPPs) due to its ability to fully utilize the marine environment to achieve residual heat removal. However, the horizontal connection between the heat sink and the heat source could easily lead to the subcooled-water reverses flow and thus trigger serious flow instabilities. In the present paper, a fully visualized experimental set was built, combined with a particle image velocity (PIV) system to investigate the subcooled-water reverses flow in the EHDPHRS. First, PIV observations clearly highlighted five flow stages during a complete natural circulation, including the reverse flow occurred in the single-phase and two-phase flow. Then, it was shown that the single-phase reverse velocity is proportional to heating power and inversely proportional to subcooled-water temperature. While, the two-phase reverse velocity increases first and then decreases with the increase in heating power. Moreover, the two-phase reverse flow phenomenon shows obvious periodicity. Finally, the buoyancy force (F b) caused by the density contrast, and the pressure difference (F Δ P) caused by the direct contact condensation (DCC) are the triggering forces for the reverse flow, while the flow inertia force (F i) caused by the forward flow represents the restraining force. [ABSTRACT FROM AUTHOR]

• Poorer cooling leads to a higher likelihood of thermal runaway. • Voltage platforms vary in different environments. • Overcharge increases R s , R SEI , R ct , and reduces lithium-ion diffusion coefficient. • Transition metals Ni, Co, Mn appear at the anode. Lithium-ion batteries (LIBs) are widely used, but there are few studies on their behaviour under different heat dissipation conditions. This paper comparatively investigates the electro-thermal behaviour of LIBs in air, quasi-adiabatic, and adiabatic environments during thermal runaway caused by overcharging. Our study reveals the internal mechanism of overcharging that leads to battery degradation. We find that the battery is more prone to thermal runaway under deteriorating heat dissipation conditions or with an increase in charging rate, but the state of charge (SOC) at the time of thermal runaway is not necessarily correlated with it. Regardless of the conditions, the battery develops a voltage plateau, and the temperature rises during this phase due to the decomposition reaction of the solid electrolyte interface (SEI) film or the electrolyte's reaction with the intercalated lithium. Inconsistent airflow and temperature can affect the battery's temperature and voltage during overcharging. Increased impedance, cathode destruction-including an increase in particle distance, dissolution and deposition of transition metals on the anode, and lithium precipitation on the anode's surface are significant reasons for the battery's degradation due to overcharge. These observations play a crucial role in the storage, transportation and use of LIBs in different environments. [Display omitted] [ABSTRACT FROM AUTHOR]

• The retention angle models are modified considering the flow vicious effect. • Convection mechanism is adopted at high heat flux. • The new model has satisfactory predictions for liquid film profile and heat transfer coefficient. • Flow and heat transfer characteristics at high heat flux and low temperature are analyzed. In this paper, a new analytical model is developed for the condensation of refrigerants outside low-finned tubes. It is based on the flow and heat transfer characteristics at low saturation temperatures and high heat flux, such as those in the LNG intermediate fluid vaporizer (IFV). Due to the increase of viscous effect at lower saturation temperature and higher heat flux, the previous condensate retention angle models are modified by adding the viscous term. At high heat flux and condensate rate, the condensate profile at the fin root is simplified to be arc-shaped and obtained directly by force analysis. Furthermore, considering the heat transfer enhancement caused by the circumferential flow at high heat flux, the convective mechanism is included for the heat transfer through the thick liquid film between the fins. The distributions of liquid film and fin surface temperature are also predicted. The present analytical model is in good agreement with different experimental and numerical results, while most deviations are within 10% for predicting the heat transfer coefficients at high heat flux. Because of the increased flow viscosity and surface tension, the optimal fin spacing and fin height increase as the heat flux increases and the saturation temperature decreases. [ABSTRACT FROM AUTHOR]

On the basis of numerous experimental studies the Guyer–Krumhansl heat conductivity model can be considered as one of the most promising theoretical models to simulate the low temperature processes and the thermal behavior of such complex structures as materials with inhomogeneities and interfaces, as well as porous materials. However, the classical h -version finite element methods do not provide convergent and accurate results for the solution of the Guyer–Krumhansl heat conductivity model. In recent paper, a new three-field variational formulation is derived treating the temperature, the heat flow and its current density as independent variables. Both the temperature- and the heat flow boundary condition are weakly imposed, i.e., built in the variational form. Based on this variational background, a new, hp -version mixed finite element method is constructed. The h - and p -convergence behaviors of the temperature and the heat flow are analyzed on the transient region for two representative model problems: (i) a rapid heating process with exponentially changing rate and (ii) a ramp-type heating process. The relative and absolute errors are measured in maximum norm. From the computational experiments it follows that the mixed hp -finite element method gives reliable, robust (uniformly stable) results not only for the h - but also for the p -approximation in the case of both the temperature and the heat flow. • Three-field variational formulation is derived for the Guyer–Krumhansl heat conduction model. • The boundary conditions are weakly imposed. • Mixed hp -finite element method is presented for modeling the transient behavior. • The temperature, the heat flow and its current density are approximated as independent variables. • Fast h - and p -convergence and high accuracy are experienced for the temperature and heat flow computations. [ABSTRACT FROM AUTHOR]