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Abstract: Effects of suction pressure and permeability on the steam heating characteristics of the wet paper are studied. Experimental results show that suction pressure enhances the energy absorption in the wet paper and effects of suction pressure strongly appear in the high-permeability paper, and also absorbed energy rate is decreased with increasing in heating time. From the numerical simulation results it is found that increase in moisture content and decrease of pressure gradient reduce the absorbed energy rate. Dimensionless numbers are derived from the basic equations to summarize the experimental and numerical simulation results. [Copyright &y& Elsevier]

• The outdoor air relative humidity also has an impact on the threshold temperature of frost accumulation. • Under certain conditions, higher efficiency of heat recovery may be safer in terms of frost risk. • The largest ' frost ' accumulation area is formed for the middle values of the return air relative humidity (in analyzed case RH 2 i =38.5 %). In this paper, a process of frost accumulation inside the non-hygroscopic rotary heat exchanger depending on operating conditions is investigated. The study was based on the results of the numerical simulations conducted in the original computer program. The analysis considers both the threshold conditions of frost accumulation and the conditions of frost layer growth. For this purpose, three indicators related to frost accumulation were distinguished: a frost accumulation limit temperature, a surface of the matrix covered with the accumulated frost layer, a maximum thickness of the accumulated frost layer. The analyzes assessed the influence of operating parameters on these indicators, focusing on the return air relative humidity. It was revealed that the highest values of this parameter cause the greater thickness of the frost layer. However, the largest ' frost ' accumulation area was created in the range of average return air relative humidity values – in the analyzed cases it was RH 2 i =38.5 %. The paper also includes a detailed analysis of the threshold temperature of frost accumulation. These limits of outdoor air temperature were determined for a wide range of operating parameters' values: both airstream relative humidity and nominal temperature effectiveness. Additionally, eight probable configurations of active heat and mass transfer areas within rotary heat exchanger channels were revealed, which are related to the initiation of frost accumulation. Consequently, the locations of the initial ' frost ' accumulation area were predicted. It was also found that the greatest impact on the frost accumulation threshold temperature has the return air relative humidity RH 2 i , although this influence is not unequivocal. The most unfavorable conditions regarding nominal temperature effectiveness in terms of frost accumulation are also unclear. In some cases, it was even demonstrated that an increase in the effectiveness can eliminate the ' frost ' accumulation area. [ABSTRACT FROM AUTHOR]

• LaplacianFoam in OpenFOAM® solves the scalar diffusion equation. • Thermal diffusivity may be often incorrectly used in heat conduction problems. • It is tempting to make just a little change from a constant to a scalar field. • To correctly model heat conduction in heterogeneous media, ρ , c p and λ is needed. In the paper "Numerical study with OpenFOAM on heat conduction problems in heterogeneous media" by K. Zhang, C.-A. Wang, J.-Y. Tan, International Journal of Heat and Mass Transfer, Vol. 124 (2018) 1156–1162 the authors modify laplacianFoam from open-source CFD package OpenFOAM® to solve heat conduction problems in heterogeneous media by changing the diffusion coefficient from a constant value to a scalar field. Their paper clearly demonstrates a fundamental, overlooked, and common mistake in rearranging the heat conduction equation, which cannot be replaced with the temperature diffusion equation. In this comment, we provide clear evidence through mathematical derivations and numerical examples calculated in OpenFOAM®. [ABSTRACT FROM AUTHOR]

• Some ambiguities in experimental test results. • Some ambiguities in the simulation results. • Lack of definition of some symbols. This paper presents some comments on "Chen, Bo, et al. "DPM-LES investigation on flow field dynamic and acoustic characteristics of a twin-fluid nozzle by multi-field coupling method." International Journal of Heat and Mass Transfer 192 (2022): 122927. "We thank the authors for conducting this valuable research. However, some points should be noted to improve their paper. In general, there are some serious concerns about the accuracy and validity of experimental and simulation results. In addition, some less important things such as the lack of definition of some symbols in their paper should be corrected. Details are mentioned below in comments 1-8. [ABSTRACT FROM AUTHOR]

• A theoretical framework is proposed to consider non-equilibrium configurations at the macroscopic scale. • The new formulation is validated using a full dual-scale model of coupled heat and mass transfer. • With the new model, a very good accuracy is obtained with a huge reduction of CPU time. • Dual-scale diffusion and molecular relaxation can be considered additively in the modified macroscopic formulation. • This framework can be applied to other configurations, such as coupled transfer in packedbeds. This paper proposes a macroscopic formulation of coupled heat and mass transfer that can consider non-local equilibrium often encountered in biosourced building materials (wood- and plant-fiber based materials). Transferring dual-scale effects and molecular relaxation at the macroscopic level involves a kernel function acting in a convolution product. To ease the computational solution of the set of equations, the memory function is decomposed as a series of exponential functions. Each function yields an internal variable that obeys a simple ordinary differential equation (ODE). This paper first describes the macroscopic and dual-scale formulations used as reference solutions. Subsequently, the modified macroscopic formulation of coupled transfer and its computational solution are presented in detail. The major outcomes of the present study, validated against reference solutions obtained with a comprehensive dual-scale model, are as follows: • Dual-scale diffusion can be approached accurately by two exponential functions, • Even though the dual-scale phenomenon and molecular relaxation do not occur at the same scale, both can be considered in the modified macroscopic formulation of coupled transfer additively, • The new macroscopic formulation, together with the computational procedure proposed in this study, can be applied to various configurations, namely coupled heat and mass transfer in packed beds. [ABSTRACT FROM AUTHOR]

• Algorithm for PLIC-based interfacial area concentration on 3D non-orthogonal grids. • Thermal phase change model with geometrical basis and free of empirical input. • Oscillating behavior of GOX jet plume in LOX crossflow is reproduced in simulation. • Imbalance between the mass transfer rate and the supply causes the oscillation. • Methodology developed is verified by the Stefan problem and the bubble experiment. In order to enhance the physical basis of the mass transfer model in numerical simulation of gas-liquid direct contact condensation and improve the fidelity, a set of methods and models are developed. Based on the concept of the piecewise-linear interface calculation (PLIC), an interface reconstruction algorithm is proposed to calculate the interfacial area concentration in three-dimensional non-orthogonal structured grids. The actual interface in the cell is replaced by a plane, whose position is determined iteratively to satisfy the local volume fraction and orientation of the actual interface. The area of the polygonal cut by the plane is taken as the interfacial area in the cell. The proposed algorithm is validated by calculating the surface area of a series of basic geometries. Obvious superiority of the proposed algorithm over the traditional models (gradient model and algebraic model) is seen. Then, the reconstructed area is used to determine the interfacial area concentration in the thermal phase change model. The process is implemented by ANSYS Fluent user-defined functions. The Stefan problem and steam bubble condensation experiment are used to test the performance of the developed methods and models. The simulation results agree well with the theoretical and experimental results with the quantitative relative errors no more than 4.3 % and 15 %, respectively. The oxygen jets condensation experiments are also used as test cases. The primary dominant frequencies predicted by the simulations are 163.01 Hz and 131.65 Hz, which agree well with the 139.72 Hz and 125.75 Hz in the experiments. The relative errors are only 17 % and 4.7 %. The unstable flow pattern of oxygen jet in liquid oxygen crossflow is explained based on the dynamic characteristics of turbulence, heat and mass transfer. The periodic variation of mass transfer rate is considered as the cause of condensation oscillation. The method for calculating the interfacial area proposed in this paper can serve as an optional and practical improvement to the numerical simulation of direct contact condensation. [ABSTRACT FROM AUTHOR]

• A Reference-Standard-Volume optimization method is proposed to improve CESPB. • The best aspect ratio of CESPB is 2–4 considering efficiencies and pressure drop. • The volume multiple is given at 1.1 with the highest exergy efficiency of 63.72 %. • The thermal and exergy efficiencies are increased by 2.03 % and 3.65 %, respectively. Cryogenic liquids (e.g., liquid air, liquid hydrogen, liquid carbon dioxide) have gained popularity in electricity storage due to their high energy density, no geographical constraints, and environmental friendliness. The cryogenic energy storage packed bed (CESPB) is widely employed as a cold recovery device to enhance the round-trip efficiency of cryogenic energy storage systems. Nonetheless, the cycle efficiencies of CESPB remain relatively low, with limited research investigating efficient methods for determining the design parameters. To address this, a novel optimization method named as the Reference-Standard-Volume (RSV) approach is introduced to enhance the thermodynamic performance of CESPB. In this paper, the complete optimization process of CESPB is illustrated, presenting the optimization outcomes in the view of heat and mass transfer. The findings reveal that a larger aspect ratio leads to the higher efficiencies but increased pressure drops. An optimal aspect ratio of 3 and a volume multiple of 1.1 is identified, achieving the highest exergy efficiency of 63.72 %. Meanwhile, increasing charging/discharging time enhances heat transfer in CESPB, however, it leads to an increase in external cold dissipation, which gives an optimal charging/discharging time of 3/3 h. By implementing the RSV optimization method, the percentage increase of discharging efficiency, thermal efficiency, and exergy efficiency of CESPB is 2.08 %, 2.03 %, and 3.65 %, respectively. These research outcomes offer valuable reference and guidance for future CESPB design and research. [ABSTRACT FROM AUTHOR]

• The process of melting-reconsolidation of the frost layer is considered. • Improvement of the existing Eulerian multiphase flow model of frost formation. • The whole process of frost layer growth under prolonged periods of time was studied. • Changes of ice-phase volume fraction and melt-reconsolidation region with time are discussed. Frost growth is a complex heat and mass transfer process, which involves the vapor-liquid-solid three-phase interconversion problem, and the investigation of the frost growth process helps to understand the mechanism of frost growth. In this paper, frost model is considered, taking into account the role of the frost layer melting-reconsolidation. The aim is to improve the existing Eulerian multiphase flow model. Using the improved frost model, the whole process of the frost layer growth is simulated. In addition, an investigation is presented dealing with, the frost layer growth in various stages of the ice phase volume fraction and melting-reconsolidation area, considering the change and the proportion of the situation. The results showed that the volume fraction of the ice phase increased with time. Additionally, the melting-reconsolidation process starts from the front area of the frost layer surface and then gradually spreads to the whole surface. Moreover, it is shown that the proportion of the melting area increases and then decreases with time before attaining a constant value. On the other hand, the proportion of the solidifying area increases with time and finally tends to 0. [ABSTRACT FROM AUTHOR]

Highlights • A new periodical solution with reverse-central-symmetrical-structure has been discovered. • The flow is divided into seven stages by ten critical buoyancy ratios. • Dynamical behavior, flow patterns and heat and mass transfer efficiencies in each stage are investigated. • The governing equations are discrete by using high-order high-resolution schemes. Abstract The paper investigates numerical results of double-diffusive convection in a slim rectangular enclosure with horizontal temperature and concentration gradients. The case with the thermal Rayleigh number, Ra T = 10 5 , the Prandtl number, Pr = 1 , the Lewis number, Le = 2 and height-to-width aspect ratio, A = 4 is considered. Effects of the buoyancy ratio of composition to temperature, N , on dynamical behavior, flow structure and heat and mass transfer efficiency are investigated carefully. The present results suggest that with the buoyancy ratio N increasing from 1 to 2, the flow of transition is a complex series of changes from the periodic to quasi-periodic, chaotic, periodic, and finally to laminar with concentration dominated. There are three types of periodic flows, the first one is simple periodic flow with single fundamental frequency (FF), the second one is periodic flow with FF and its integer multiple of frequencies (INTMF), the last one is the more complex periodic flow with FF, INTMF and its sub-harmonic frequency multiple (SFM). A new type periodical solution with reverse central symmetrical structure is captured in the present paper. Multi cells structures traversing between two vertical walls will produce salt figure phenomenon and benefit to enhance heat and mass transfer efficiency. [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]

In this paper, we present a theoretical study aimed at investigating the rate-limiting factors in thin-film evaporative heat transfer processes, considering the finite-rate evaporation kinetics. The problems of evaporation of a flat thin-film in either pure vapours or vapour-inert-gas mixtures are analysed based on the non-dimensionalised macroscopic transport equations for continuum fluids, coupled with out-of-equilibrium kinetic boundary conditions. Both the full numerical solutions and asymptotic analytical solutions at slow evaporation limit are provided and applied to analyse thin water film evaporation. Existing solutions, assuming negligible heat transfer in the gas domain, or negligible temperature jump across the non-equilibrium kinetic layer, or more boldly a thermodynamically equilibrial interface (i.e. its temperature is at the saturation temperature), can be fully recovered from the more general solutions presented here. Our results show that while these assumptions hold in special cases, they can lead to significant errors in many conditions, especially when the film thickness δ is reduced to a few micrometers or thinner. We show that the conventional views that the rate-limiting factors in thin-film evaporative heat transfer is either the heat diffusion through the liquid film or the mass transfer in the gas domain only apply to thick film (i.e. δ ≫ λ where λ is the mean free path in the vapour phase). As δ decreases to a few micrometer or smaller (more precisely when the Knudsen number Kn increases beyond O (1) in an pure vapour environment or when the kinetic Peclet number Pe is reduced below O (1) in inert gases), the interfacial thermal resistance due to the evaporation kinetics can be on the same orders of magnitude as the thermal resistance in the liquid film. The analysis also allow us to compare the heat transfer processes during the evaporation of a thin-film in pure vapours to those in inert gases, providing deeper insight into the effectiveness of various strategies for exploring the evaporation process in practical thermal management. • Analysis of thin-film evaporation counting for finite-rate evaporation kinetics. • Provision of both dimensionless numerical and analytical asymptotic solutions. • Significant thermal resistance due to kinetics observed in micrometers or thinner films. • Limitations and conditions for existing assumptions to hold are identified. [ABSTRACT FROM AUTHOR]

• The v shape pressure reflects interaction relations among 3 thermodynamic mechanisms. • FFC reflect the intensity and rate of progress of flash at unique start stage. • The factors influencing flash rate and intensity are analyzed. • FFC rises with initial temperature and valve opening degree at unique start stage. • Expanders with larger outlet area or higher working temperature have larger flash intensity. Our experiments showed that a V shape pressure drop appeared at start stage of non-equilibrium flash. V shape pressure drop firstly denoted the generating of superheat degree, which should be the starting force driving the non-equilibrium flash. Then evaporated vapor made up the pressure drop. Finally, a dynamic equilibrium was reached between the flash rate and the outflow rate, and the pressure behaved decreasing gradually. However, few published references focus on this start stage of the non-equilibrium flash. In this paper, experiments of the flash were conducted to investigate the heat and mass characteristics during V shape start stage. Dimensionless flash conversion coefficient (FCC) was proposed to normalize the flash with different initial liquid mass at start stage. The effects of initial temperature and the valve opening degree on the heat and mass characteristics of flash during the V drop start stage were studied. The results showed that the pressure of the working fluid changed dramatically during the V drop start stage. The peak of instant liquid superheat was proportional to the opening degree of the valve, which controlled the outflow rate. The flash rate increased with increasing initial temperature and valve opening degree, which had an approximately linear relationship with the flash time. FCC increased with valve opening degree. It could be deduced that flash intensity or flash rate would be higher for an expander with larger outlet area or higher working temperature. [ABSTRACT FROM AUTHOR]

• Heat and mass transfer model of pyrolysis gases in a confined space was developed. • Growth rates of pyrolysis product concentrations were determined. • Synergistic effects were identified for different fire hazard sources. • Role of ventilation in the growth of pyrolysis gases concentrations was defined. • Correlation of room sizes with concentrations of pyrolysis gases was established. Numerical research findings are presented on the patterns of spread of thermal decomposition products of wood-based materials in confined spaces isolated from the external environment. Based on the experimental data, a physical problem statement was formulated and a mathematical model of heat and mass transfer was developed for rooms with the most typical sources of fire hazard. The experimental and numerical research findings were obtained for the conditions corresponding to compartments isolated from the external environment (e.g., rooms at dedicated facilities, like ships, small and medium-sized rooms) and to underventilated rooms. The performed experiments and calculations revealed satisfactory agreement in the findings and demonstrated the validity of the proposed model of heat and mass transfer. Wood was used as the main material in fires. A comparative analysis was also carried out for paper of different quality. The modeling was performed for the most frequent causes of fires: careless handling of fire, unsafe operation of heating equipment and electrical short circuits. The rates of growth of thermal decomposition product concentrations were determined for different distances from the material. The impact of a number of factors on the characteristics under study was determined. These are the fire and room sizes, fire cause, supply and exhaust ventilation. The data were extrapolated to the conditions corresponding to business, warehouse and residential premises. [Display omitted] [ABSTRACT FROM AUTHOR]

• A correct formulation of average Nusselt number for the case of linearly heated wall is derived. • Thermal balance analysis provides the verification of the correct formulation. • Comparison of the existing and the correct formulation is included. The comment below addresses an inaccurate formulation in the calculation of the Nusselt number for linear heating as presented in the paper titled "Steady natural convection flows in a square cavity with linearly heated side wall(s)" by M. Sathiyamoorthy, T. Basak, S. Roy, and I. Pop, Int. J. Heat Mass Transfer 50 (2007) 766–775. Consequently, this analysis provides a mathematical reformulation for the local and mean Nusselt numbers of a linearly heated side wall. It regenerates a few quantitative results for a specific case solely intended for comparative purposes. [ABSTRACT FROM AUTHOR]

• RBF-DG was a novel prediction for absorption process in falling film and membrane based absorbers. • RBF-DG method provided excellent solutions. • Comparison with analytical solutions and experiments provided good agreements. • It becomes possible to predict accurately the absorption rate of falling film and membrane. The present investigation is intended to develop an understanding of how the vapor pressure and inlet temperature of the solution affect the absorption rate, which is helpful for the design of absorption heat pump systems. Many conjugated heat and mass transfer processes in falling film and membrane during lithium bromide (LiBr) absorption have not been well addressed. This paper proposes combining the meshless Radial Basis Function (RBF) and Discontinuous Galerkin (DG) methods to solve the conjugated heat and mass transfer in falling film and membrane-based absorption problems. The derivatives in the transverse direction are discretized using the RBF method. Owing to the parabolic nature of the governing equations, the DG methods can be used to discretize the derivatives in the streamwise direction. The efficacy of the proposed method is shown by comparing its results with analytical solutions and experimental data available in the literature. Furthermore, the proposed method is used to evaluate the analytical solutions of the heat and mass transfer problem in a membrane-based absorber. The previous published works simplified the problem to obtain the analytical solutions by providing the mean temperature and concentration values as the boundary conditions at the membrane-solution interface. The comparison of the RBF-DG method and the analytical solutions reveals that there are minor changes in temperature and local concentration values along the streamwise direction, but the profiles and trends are relatively similar across the film. A comparison of mass absorption rate calculations shows that RBF-DG and analytical solutions are compatible. The advantage of the numerical method is that various types of boundary conditions can be handled easily without any simplifications. Moreover, the numerical results of the proposed method are compared with experimental data, and they present good agreement. As a results, the absorption rate of falling film and membrane becomes capable of being accurately predicted. [ABSTRACT FROM AUTHOR]

Smoke and Heat Exhaust Ventilation Systems (SHEVS) are technical solutions used to limit the consequences of a fire in a building, related to the spread of the smoke. Currently, the design methodologies follow an assumption, that if a system constantly exhausts amount of the smoke estimated with a calculation method based on an onerous steady-state fire scenario, the building should be safe. This paper introduces a different approach to optimal system design, based on the transient characteristic of the fire. The main idea is that a system can adapt to the momentary density of the removed smoke, to benefit from the thermal expansion of gases in the fire. As the fire grows, the temperature does rise, and the pressure within installation falls down, and so do the forces acting on ducts, dampers and other elements. This behaviour is observed in high-temperature furnace tests of exhaust fans, during which the change of pressure and power-supply requirement in changing temperature can be measured. The author presents results of 9 high-temperature tests that are a proof of the concept. The practical implementation of the idea presented in this paper could mean, that a system designed with an existing methodology for ambient conditions, could work with a higher capacity in high-temperature, without additional strain on the elements of the system. This shift in thinking allows using higher capacity systems, in place of currently used, by artificially limiting the capacity of an oversized fan in ambient conditions and increasing it, following the measurements of the temperature of the exhausted air or pressure in the shafts. Beside the theoretical introduction to a new concept, the paper presents results of 8 numerical analysis (CFD) of airflow in an enclosed car park during a fire, performed in ANSYS® Fluent® solver. The author created an User Defined Function (UDF) to automate the transient change of the fan boundary condition, dependant on the exhausted smoke temperature – following the assumptions of the adaptive solution presented in the paper. Four CFD analysis were performed for each traditional and new solution, and their results were compared in with qualitative and quantitative approach. Results of the CFD analysis show a possible gain of 25–41% of system capacity, using the same ductwork and reaching the same design goal, as contemporary SHEVS. The pressure within the ductwork and at fans is almost constant in the adaptive analysis. The paper is closed with a discussion of legal aspects, possible limitations in the design and the further research necessary to establish the new method of the design. [ABSTRACT FROM AUTHOR]

Abstract: For industrial paper drying, the entropy production from heat and mass transfer irreversibilities was determined by combining principles of irreversible thermodynamics with information from a dryer simulator. Transport irreversibilities depend on sheet and dryer characteristics. Entropy production for multi-cylinder paper dryer sections was compared for 5 paper machines, producing 3 grades of linerboard, 2 of newsprint. The three major contributions to entropy production were evaluated: entropy production for evaporation of water, for convective heat transfer between the sheet and ambient air, and for cylinder-to-sheet heat conduction. Effects on entropy production from paper basis weight and drying cylinder steam pressure were examined. [Copyright &y& Elsevier]

Highlights • Effect of wellbore stock liquid should be re-studied. • The wellbore stock liquid can be divided into two regions. • Effect of temperature distribution in heated oil region should be considered. Abstract This paper presents some comments on "Heat and mass transfer characteristics of steam in a horizontal wellbore with multi-point injection technique considering wellbore stock liquid" that was recently published on [International Journal of Heat and Mass Transfer 127 (2018) 949–958]. Overall, the paper deserves to be published on International Journal of Heat and Mass Transfer. However, some points should be noted to improve the paper. The model presented in their model neglected the heat conduction process, which can lead to a mis-understanding of behaviors of wellbore stock liquid during the steam injection process. In fact, the wellbore stock liquid can be divided into two regions: the heated oil region (region ①) and the cold region (region ②). The oil in region ① will be injected into reservoir, while the oil in region ② cannot flow. However, they assumed that oil in both regions can flow in the horizontal direction. Their purpose of making such an assumption is to build a model. However, this assumption is unreasonable and should be questioned. Their model can be improved by taking the temperature distribution in region ① into consideration. [ABSTRACT FROM AUTHOR]

• Propose composite adsorbent with improved heat and mass transfer. • Establish the effect of three types of composite adsorbent on the adsorption refrigeration. • Clarify the impacts of operation parameters on the system with composite adsorbent. Adsorption refrigeration is a typical environmental protection and energy-saving waste heat utilization refrigeration technology. However, improving the heat and mass transfer performance of adsorption beds is crucial to the wide-spread applications of adsorption refrigeration systems. In this paper, three types of composite adsorbents are proposed: adsorbents with improved heat transfer, improved mass transfer, and simultaneously improved heat and mass transfer. Both characteristics of adsorption and heat transfer are tested and compared. Based on the experimental results, the use of these three types of composite adsorbents in the adsorption refrigeration system is further examined. The results indicate that the silica gel (SG)/MIL-100/CF (SGMC) composite outputs the highest cooling capacity and exhibits a coefficient of performance (COP) comparable to that of a composite adsorbent with improved mass transfer. The cooling capacity and COP of the proposed SGMC system compared with those of the traditional SG–water system increase by 22% and 12.8%, respectively, and the refrigeration cycle time is shortened by 16.7%. Based on the optimal SGMC system, the impact of operation parameters is further investigated, and optimum parameters are selected to enhance the overall system performance. [ABSTRACT FROM AUTHOR]

In this note, consideration is given to a generalization of the previous paper entitled, "A symple analytic formula for the effective thermal conductivity of dilute dispersion of hollow and floating hollow spheres" in which now the spherical core is not empty and the filling material is of no negligible thermal conductivity. [ABSTRACT FROM AUTHOR]

• A parallel mini-channel heat sink with bionic structure is proposed • Using BPM-channel heat sink to cool the LFR-PV system. • The influence of the rotation angle on the liquid filling characteristics of the BPM-channel is studied. • Study the heat transfer characteristics of BPM-channel heat sink. • Study the dynamic characteristics of BPM-channel heat sink. This paper proposes a parallel mini-channel with bionic structure (BPM-channel) heat sink for linear Fresnel reflector photovoltaic systems (LFR-PV system), which can be rotated axially to trace the solar ray. In this paper, the design of rectangular channel as well as a mini-channel with a bionic structure is optimized. The thermal enhancement factor of the horizontally placed BPM-channel and the rectangular channel, the influence of the rotation angles on the channel flow characteristics and liquid filling are investigated. The research results show that the thermal enhancement factor of the BPM-channel can be increased by up to 50%. The rotation angle has little effect on the inlet pressure, and the pressure change range is within 4%. Within the current operating condition (volume flow rate 70mL/min-190mL/min, the rotation angle ±45°), the smallest flow resistance can be found when the characteristic dimension of the bottom structure is 1mm (D r =1mm) in the BPM-channel. The BPM-channel with D r =2mm has the best liquid filling performance. [ABSTRACT FROM AUTHOR]

A heat and mass transfer process for solid–gas reactors in a disc-shaped body is investigated in this paper. Radial- and branched-pattern integrated collectors are embedded in the body to enhance heat and mass transfers. The distributions of the integrated collectors in the two pattern discs are optimized using constructal theory and entransy theory. The results indicate that the optimal elemental volume fractions obtained by the minimizations of entransy dissipation rate and entropy generation rate are evidently different. There exists a critical radius, which decides whether the radial- or branched-pattern design is used. The decrease in the thermal conductivity ratio and increase in the first order volume fraction of the integrated collector lead to a better performance of the solid–gas reactor. The model with pure heat conduction or mass transfer is special case of the model in this paper. The results obtained in this paper can provide some design guidelines for the solid–gas reactors. [ABSTRACT FROM AUTHOR]

In this study, we investigated the heat and mass transfer characteristics of a desiccant-coated fin-tube heat exchanger (DCHE), in which the desiccant was coated on the surface of a conventional fin-tube heat exchanger. It differs from desiccant wheels in which the desiccant is cooled or heated by the fluid inside the tube during the adsorption or desorption process, and from conventional heat exchangers, in which moisture transfer occurs and the latent heat transfer is caused by phase change of the adsorbed moisture. Firstly, the heat and mass-transfer model for the DCHE was presented in this paper, whereupon the influences of air velocity, desiccant temperature and moisture content on the overall mass-transfer coefficient were separately analyzed for desorption and adsorption processes. It emerged that the overall mass-transfer coefficient rose with increasing air velocity. The moisture content of the desiccant significantly impacted on the overall mass-transfer coefficient. Higher desiccant temperature resulted in lower overall mass-transfer coefficient. Finally, the heat transfer model given in this paper was applied to calculate the DCHE heat transfer rate and the values obtained by calculation were observed to correlate well with the experimental results. [ABSTRACT FROM AUTHOR]

• A mathematical model based on non-equilibrium formulation was established. • The simulation results show better accordance with the experimental results compared with the model based on equilibrium formulation. • The heat and mass transfer during the drying stage were analyzed. • The effects of different operating parameters on the drying time were investigated. Spray freeze drying has been expanding its influence in many fields. However, the long duration dramatically hinders its further development. A model established based on non-equilibrium formulation was established in this paper. The accuracy of the model proposed with that established based on equilibrium formulation was compared. And the history of temperature, vapor concentration and ice saturation were then investigated. Lastly, the effects of product thickness, particle diameter on the drying time were investigated. The simulation results reproduce well with the experimental data, and show a better agreement with the increase rate of experimentally measured temperature curve than that based on equilibrium formulation. In addition, the temperature increases from the bottom to the top region while the vapor concentration distribution presents the opposite trend. The ice saturation first obtains a slight increase and then decreases. Lastly, the drying time decreases as: (i) the product thickness decreases, (ii) the packing porosity increases and (iii) the chamber temperature increases. The mathematical model proposed in this paper could offer better understanding of the process and guide the design and optimization for the process. [ABSTRACT FROM AUTHOR]

• Study the Buoyancy-Marangoni convection in a porous cubic cavity with complex surface. • The Weierstrass–Mandelbrot (W-M) function is applied to simulate the shape of the complex upper surface. • Find the effects of fractal dimension on fluid flow, heat and mass transfer. • Simulate the 3D convection with the high order accurate compact finite volume method. In this paper, a convection and heat transfer problem of power-law fluid in a three-dimensional porous media with complex surface is studied. The Buoyancy-Marangoni convection for non-Newtonian power-law fluids in porous media is solved using a compact high-order finite volume method. For this single-phase model, the left wall is kept at high temperature and high concentration, the right wall is affected by lower temperature and lower concentration, the upper wall is a complex surface, and the remaining walls are considered to be adiabatic and impermeable. The Weierstrass–Mandelbrot function is used to simulate the shape of the upper surface. The fluid in the porous cavity is a power-law nanofluids containing copper oxide nanoparticles. The solid material of the porous medium is aluminum foam. Numerical simulations can be used to determine the power law exponent, Marangoni number, Rayleigh number, and aspect ratio on the flow, heat transfer, and mass transfer rate. [ABSTRACT FROM AUTHOR]

• The increases in Darcy number changes the size and shape of the unyielded section. • Heat and mass transfer augments gradually as the porosity increases. • The unyielded region is decreased by the augmentation of the buoyancy ratio. In this paper, thermosolutal natural convection in an open porous cavity filled with Bingham fluids has been simulated numerically. Fluid flow, heat and mass transfer, and yielded/unyielded parts have been conducted for certain pertinent parameters of Rayleigh number (Ra = 10 4 – 10 6 ), Darcy number (Da = 10 - 2 – 10 - 6 ), porosity (∊ = 0.1–0.9), Lewis number (Le = 2.5–100), the Buoyancy ratio (N = 0.1–20), and Prandtl number (Pr = 1–100). Moreover, the Bingham number (Bn) is studied in a wide range of different studied parameters. Results indicate that the heat and mass transfer increases and the unyielded section diminishes as Rayleigh number rises. For specific Rayleigh and Darcy numbers, the increase in the Bingham number decreases the heat and mass transfer. However, the decreases in heat and mass transfer due to Bingham number becomes stronger as Darcy number drops from Da = 10 - 2 to 10 - 6 . The growth of the Bingham number expands the unyielded sections in the cavity generally in different Darcy numbers and porosities. The increases in Darcy number changes the size and shape of the unyielded section while heat and mass transfer drop gradually. For fixed Rayleigh, Darcy and Bingham numbers, the unyielded region is decreased by the augmentation of the porosity. In addition, heat and mass transfer augments gradually as the porosity increases. The enhancement of buoyancy ratio increases heat and mass transfer for the studied parameter. The rise of Lewis number has a marginal effect on heat transfer, but the mass transfer rises considerably. [ABSTRACT FROM AUTHOR]

• Oscillatory surface is proposed to enhance direct contact heat transfer. • Influence of oscillation parameters on heat transfer are analyzed. • The reasons for enhancement of heat transfer are demonstrated. Direct contact heat transfer between stratified immiscible fluids is commonly encountered in solar salt industry, desalination, petrochemical engineering, etc. Usually, the mutual mixing and penetration between stratified flows are weak, and hence the heat and mass transfer rates are quite limited and act as an obstacle in their wider applications. Considering the fact there is always clear surface (interface) between immiscible fluids, this study proposes to stimulate interface oscillations artificially to reinforce the mixing between fluids and thus enhance the transfer processes. The artificial oscillations employed in this paper are sinusoidal wave and their amplitude, period and wave length on the direct contact heat transfer between stratified airstream and water surface are investigated respectively. Heat transfer was found to be enhanced to a great extent by artificial oscillations, ranging from one to three times higher than that without oscillations. With the amplitude, period and wave length covered in this study ranging from 1 mm to 4 mm, 0.1 s to 2 s, and 40 mm to 100 mm, respectively, the heat transfer enhancement effect was found to increase with increase of oscillation amplitude and decrease of wave length, and this effect became more distinct at higher airstream velocity. However, the change of oscillation periods covered in this study shows minor difference on the heat transfer enhancement. Without using special solid inserts or alternation to the heat exchanger structure, artificial oscillation of phasic interface can be a simple and efficient technique to enhance transfer process between stratified flows. [ABSTRACT FROM AUTHOR]

• Experimental study was performed for the internally heated corium pool with high Rayleigh numbers. • Transient model was developed for the high-Rayleigh-number corium pool with heat and mass transfer. • The component diffusion at interface will influence the corresponding liquidus temperature and transient heat transfer. The natural convection heat transfer driven by internal decay heat and the diffusive mass transfer at the crust interface are the critical problems in study of thermal behaviors in volumetrically heated reactor corium pools. In this paper, experiment and transient code were developed to analyze the heat and mass transfer characteristics in the high-Rayleigh-number corium pool. The COPRA experiment was carried out in seven tests with different heights and heating powers. The near-wall modified low-Reynolds-number k - ε turbulence model was used for the natural convection simulation in the whole flow region. Both the heat transfer with phase change and the diffusive mass transfer at crust interface boundary were taken into consideration. In addition, the heat conduction in the crust and wall, as well as the heat radiation in top space were included. The validation was performed for the developed code with transient simulation of COPRA experimental tests. The calculation results agreed well with experimental data for the pool temperature, heat flux and crust distributions, proving the reliability of the transient analysis code for the corium pool simulation with heat and mass transfer. [ABSTRACT FROM AUTHOR]

• Critical ambient temperatures are established for hydrate granule ignition. • Ignition delay times are determined for gas hydrate granules in air. • The influence of neighboring hydrate granules is established on their ignition in a chamber. • A model is developed for predicting the hydrate granule ignition conditions. • A process scheme is proposed for the use of granulated hydrate for power production. This paper details the heat and mass transfer at the ignition patterns of single (methane) and double (methane-isopropanol) granulated hydrates in a heated air. The experiments were performed in a laboratory-scale combustion chamber in the form of an oblong reactor with free-falling powder of the gas hydrate granules. The air in the combustion chamber was heated by the walls with ceramic plate heaters. The variation ranges of the input parameters were chosen to match the capacities of modern energy generation systems. We established the ignition delay times of the gas hydrate granules, combustion regimes, and sizes of the flame zone behind moving granules. We also analyzed the joint influence of the gas hydrate granules on their ignition behavior. A model was developed to estimate the threshold boundary conditions of gas hydrate ignition in different-sized chambers, with variable hydrate component composition granule size. Gas hydrate dissociation rates were determined in different sections of the laboratory-scale combustion chamber. Thermal conditions were predicted in which gas hydrates consistently ignite in combustion chambers with minimum cooling of the chamber walls and minimum unburnt fuel. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: A thermal model of chemical vapor deposition of titanium nitride (TiN) on the spherical particle surface under irradiation by a nanosecond laser pulse is presented in this paper. Heat and mass transfer on a single spherical metal powder particle surface subjected to temporal Gaussian heat flux is investigated analytically. The chemical reaction on the particle surface and the mass transfer in the gas phase are also considered. The surface temperature, thermal penetration depth, and deposited film thickness under different laser fluence, pulse width, initial particle temperature, and particle radius are investigated. The effect of total pressure in the reaction chamber on deposition rate is studied as well. The particle-level model presented in this paper is an important step toward development of multiscale model of LCVI. [Copyright &y& Elsevier]

Abstract: A mathematical model of heat and mass transfer in activated carbon (AC) tank for hydrogen storage is proposed based on a set of partial differential equations (PDEs) controlling the balances or conservations of mass, momentum and energy in the tank. These PDEs are numerically solved by means of the finite element method using Comsol MultiphysicsTM. The objective of this paper is to establish a correct set of PDEs describing the physical system and appropriate parameters for simulating the hydrogen storage process. In this paper, we establish an axisymmetric model of hydrogen storage by adsorption on activated carbon, considering heat and mass transfer of hydrogen in storage tank during the charging process at room temperature (295K) and the pressure of 10MPa. To simulate the hydrogen storage process accurately, the heat capacity of adsorbed phase, the contact thermal resistance between the AC bed and the steel wall and the inertial resistance of high speed charging hydrogen gas are all taken into account in the model. The governing equations describing the hydrogen storage process by adsorption are solved to obtain the pressure changes, temperature distributions and adsorption dynamics in the storage tank. The pressure reaches a maximum value of 10MPa at about 240s. A small downward trend appears in the later stage of the charging process, which lasts 700s. The temperature distribution is highest in the center of the tank. The temperature history exhibits a rapid increase initially, followed by a steady decline. A modified Dubinin–Astakhov (D–A) model is used to represent the hydrogen adsorption isotherms. The highest hydrogen uptake is 10molH2/kg AC, at the entrance of hydrogen storage tank, where the temperature is lowest. The adsorption distribution at a given time is mainly determined by the temperature distribution, because the pressure is almost uniform in the tank. The adsorption history, however, is dominated by the pressure history because the pressure change is much larger than temperature change during the charging process of hydrogen storage. [Copyright &y& Elsevier]

Abstract: The current paper presents experimental investigation of nucleate pool boiling of R-134a and R-123 on enhanced and smooth tubes. The enhanced tubes used were TBIIHP and TBIILP for R-134a and R-123, respectively. Pool boiling data were taken for smooth and enhanced tubes in a single tube test section. Data were taken at a saturation temperature of 4.44°C. Each test tube had an outside diameter of 19.05mm and a length of 1m. The test section was water heated with an insert in the water passage. The insert allowed measurement of local water temperatures down the length of the test tube. Utilizing this instrumentation, local heat transfer coefficients were determined at five locations along the test tube. The heat flux range was 2.5–157.5kW/m2 for the TBIIHP tube and 3.1–73.2kW/m2 for the TBIILP tube. The resulting heat transfer coefficient range was 4146–23255W/m2.°C and 5331–25950W/m2.°C for both tubes, respectively. For smooth tube testing, the heat flux ranges were 7.3–130.7kW/m2 and 7.5–60.7kW/m2 for R-134a and R-123, respectively; with resulting heat transfer coefficient ranges of 1798.9–11,379W/m2.°C and 535.4–3181.8W/m2.°C. The study provided one of the widest heat flux ranges ever examined for these types of tubes and showed significant structure to the pool boiling curve that had not been traditionally observed. Additionally, this paper presented an investigation of enhanced tubes pool boiling models. [Copyright &y& Elsevier]

Abstract: Transient heat or mass transfer to a spherical drop of a dielectric fluid suspended in another dielectric fluid in the presence of steady and time periodic electric fields (both uniform and non-uniform) is investigated in this paper. The internal problem or the heat (mass) transfer limit that corresponds to the bulk of the resistance being in the dispersed phase is addressed. Using a finite volume formulation, the energy conservation equation is solved to obtain the transient temperature distribution and the overall Nusselt number for the drop Peclet numbers from 0 to 10,000 and the dimensionless frequency (ω ∗) from 0 to 50,000 using a fully implicit method. Application of steady and time-periodic fields leads to fluid circulation in the drop which provides an increase in the heat (mass) transfer rate. At first glance one might expect that the time-periodic field, which gives rise to a continuously varying flow field, might provide better mixing and improved heat (mass) transfer enhancement compared to time invariant one which gives rise to a steady flow field. However results show that for low to moderate Peclet numbers, the steady electric field is more effective in heat transfer enhancement compared to non-uniform time periodic field which in turn is more effective than the uniform time-periodic field. This counterintuitive heat (mass) transfer behavior is explained in detail in the paper. On the other hand, at high Peclet numbers, the non-uniform time periodic field provides significant improvement in heat (mass) transfer relative to steady uniform electric field. We show that at high Peclet numbers the maximum heat (mass) transfer enhancement is obtained when the dimensionless electric field frequency is of the order of Peclet number or ω ∗ ∼O(Pe). By tracking Lagrangian fluid particles, it is revealed that application of non-uniform unsteady electric field results in chaotic advection at high Pe whereas steady and unsteady uniform electric fields do not. [Copyright &y& Elsevier]

Graphical abstract Highlights • The heterogeneous fractal surfaces possess obvious heat transfer enhancement. • Bubble behaviors are observed to explain the CHF trigger mechanism. • The smooth region affects the liquid supply and results in different CHF. • The condensation effect of subcooling can increase CHF by decrease bubble size. Abstract Heterogeneous surfaces can offer superior heat transfer performance by using characteristics of different structures compared with the homogeneous surfaces. The micro-pin-finned structure facilitating bubble nucleation and the smooth area as a good liquid supply pathway constitute a heterogeneous surface for further enhancing boiling heat transfer. Inspired by the fractal geometry's enhancement for the heat and mass transfer in nature, the created surface is designed into a fractal pattern. In this paper, five fractal structures F0–F4 with the same micro-pin-finned area ratio of 49% were designed. The smooth surface S and homogeneous micro-pin–fin surface PF30-60 were also used as comparisons. Pool boiling experiments using FC-72 were conducted under different subcoolings of 0 K, 15 K, 25 K and bubble behaviors were observed with a high-speed camera. The results indicated that under saturated conditions, the critical heat flux (CHF) of fractal surfaces increases first, and then decreases with the increase of fractal dimension. Besides, with the increase of subcooling, the fractal dimension with the highest CHF surface also increases. These results are explained from the liquid supply and the dry spots on the heating surface based on the bubble behaviors. There exists an optimal fractal dimension that can effectively impede the bubble coalescence and promote the liquid supply to achieve the highest CHF. The subcooling has also influence on CHF by affecting the bubble size. [ABSTRACT FROM AUTHOR]

Highlights • A model with optimized anode-side prediction was developed for PEM-based dehumidification. • Optimal anode-side exchange current density and heat/mass transfer coefficient were derived by the multi-parameter fitting. • The model showed a close trend to experiments, especially in the current prediction. • At higher airflow rates or larger electrical fields, the prediction deviation could be reduced by more than 50%. • The electrical field has the largest influence on anode-side electrochemical process. Abstract Electrolytic dehumidification based on a polymer electrolyte membrane (PEM) is promising due to the fast humidity control, safe operation and ultra-compactness. However, predictions with existing methods deviated widely, mainly due to the inaccurate calculations of the anode-side over-potential and heat/mass transfer. In this paper, an improved theoretical model was developed, by optimizing the anode-side prediction using newly developed equations for the exchange current density and heat/mass transfer coefficient. The equations were derived by the multi-parameter fitting, with a database obtained by making the simulation results as close as possible to the experimental data under various operating conditions. Compared to the results of previous models, the developed model showed a data trend that was much closer to the experimental data. The overall errors for the moisture removal rate and operating current under most conditions were less than 15% with acceptable average errors of 10.4% and 7.1%, respectively. Particularly, this model showed much higher accuracy at higher air flow rates or larger electrical fields, especially for the current prediction. When the air Reynolds number was above 2 or the applied voltage was above 3 V, the deviation of the prediction could reduce by more than 50% with the new model. And the common problem of overestimation for current prediction (up to 4–5 times) in existing models could be solved. In addition, the parameter analysis of the optimal exchange current density and heat/mass transfer coefficient was conducted. It could be found that the applied voltage during dehumidification had the largest influence. The influences of the anode air inlet temperature, flow rates and inlet relative humidity were also significant. But the effects of cathode air temperature and flow rates were slight. This research significantly improves the prediction accuracy and provides a good guidance for the performance optimization of electrolytic dehumidification systems. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Design of a LIB pack with 3 LiFePO 4 prismatic batteries arranged in series with 4 mini channels cooling plates. • Experiments of the pack under distinctive currents and different ambient temperatures. • Examination of LIB cells/pack with respect to the temperature and voltage profile. • Buildup of a modified polynomial model and approval with testing information. Abstract Li-ion batteries (LIBs) are found to be deep spots in the Electric Vehicles (EVs) as well as Hybrid Electric Vehicles (HEVs) application. Combination of such high capacity LIBs in large serial-parallel configurations have been wrapped up with serious problems such as safety, durability, cost, and uniformity, which are imposing limitations on this broad application. A narrow area of these limitations, in which LIBs should operate safely and reliably, is the essential requirement of an effective control-thermal management scenario. In this paper, we examined the heat and mass transfer (temperature and mass flow rate of water) field as well as voltage profiles for a 20 Ah Graphite/LiFePO 4 LIB pack at low currents of 20 A (1 C) and 40 A (2 C) with the selected ambient conditions using unique water-cooling methods with 35 °C, 25 °C, 15 °C, and 5 °C. This gives significant data information for the thermal behavior of LIB packs to design the temperature control (or thermal management) systems and develop an empirical voltage-thermal estimation model. In such manner, 3 prismatic LIBs with 20 Ah nominal capacity are arranged in a series with 4 micro-channel cooling plates placed within cells. There are six evenly placed thermocouples on the surface of each of these 3 battery cells used to extract time dependent temperatures. To make the data compatible for EV/HEV application, we developed a modified exponential-polynomial equivalent circuit model to simulate the temperature and voltage field. Outputs of the simulations are compared with the test data with specified C-rates and ambient conditions. The results demonstrate that increasing discharge currents and ambient conditions result in an increased surface temperature at 3 spots; close to the −ve electrode, close to the +ve electrode, and near the middle part of the LIB cell. [ABSTRACT FROM AUTHOR]

Highlights • Mars investigations, space vehicle in Mars atmosphere. • System of supersonic jets of vehicle brake motors. • Heat and mass transfer in flow field of jets. Abstract The paper simulates a structure and processes of heat and mass transfer in the system of exhaust jets of space vehicle brake motors during descent in the atmosphere of Mars. It is taken into account that the jet system is a chemically reacting gas medium formed by exhaust gases and atmosphere of the planet at sufficiently high temperatures and is characterized by developed turbulence. For realistic conditions the calculated fields of the complete set of parameters of the medium formed by the system of interacting supersonic exhaust jets of brake motors of the descent vehicle in the atmosphere of the planet are obtained. The parameters of the flow field in the most characteristic areas of the system of interacting jets are presented. [ABSTRACT FROM AUTHOR]

Highlights • Optimal architecture of tree-shaped heat sinks is studied. • Y-assemblies of tubes and Y-assemblies of tubes filled with a packing material are studied. • Optimal size ratios and optimal angles of branching under different size constraints are determined. Abstract Losses due to irreversible processes accompanying the heat and fluid flows. This paper addresses the fundamental question of what the shape of parent and offspring branches should be, to minimize the total irreversibility. I explore how the delivery of fluid and heat influences both the optimal size of Y-assemblies of tubes and Y-shaped junctions of tubes filled with a packing material, that are used as an elemental unit to construct tree-shaped flow networks. The geometric features of these constructs are obtained from the global minimization of expenditure of power associated to fluid flow and heat transfer. The optimal step factors for tube diameters and for tube lengths, and the optimal angle between the branches are obtained under different size-limiting constraints (surface area and volume). Among other results, I show that the geometrical features of the construct may be influenced by the heat flux. Besides, it is crucial to include the size-limiting requirements in agreement with goal of the system. For similar geometries, the heat and mass transfer correlations are analogous. Then, optimal size ratios and optimal angles of branching obtained here are also valid for mass flux by replacing the heat transfer dimensionless numbers by the equivalent mass transfer numbers. The analytical expressions obtained here provide fundamental information for designers assemble the inserts that formed a tree-shaped flow network. [ABSTRACT FROM AUTHOR]

Highlights • Counter- and cross-flow configuration of the indirect evaporative cooler was compared. • Numerical simulations considering condensation from product airflow were performed. • Exchangers performance was compared under different operating parameters. Abstract Following paper presents a comparative study of the indirect evaporative exchangers operating as heat recovery units, arranged in the counter- and cross-flow configuration. Presented analyses are carried out with particular emphasis on the condensation process that occurs in the product air channels of the exchangers. Several aspects related to the water vapor condensation are address. Those aspects include the identification of factors that influence the condensation process and analyzing those factors impact on different IEC exchanger configuration. Another issue is a performance comparison of the counter- and cross-flow exchanger for various inlet parameters and operating conditions. Performed analyses are based on the numerical simulations conducted with mathematical ε–NTU model of the heat and mass transfer. Presented model is validated against experimental data and the measurements taken at the test station. Achieved results showed that the counter-flow configuration has higher sensible and latent cooling potential than the cross-flow unit. Nonetheless, due to the technical limitation of the counter-flow configuration, the cross-flow exchanger achieved higher Energy Efficiency Ratio and is characterized by lower investment cost. [ABSTRACT FROM AUTHOR]

Highlights • Neglecting the phase change effects leads to an erroneous design of the insulation. • Mass transfer is negligible for predicting the temperature and water content. • Using granular soil (sand) as backfill is more critical than clay. • The Nelder-Mead algorithm is effective to determine the optimum design. Abstract Frost action in soils can cause detrimental damage to buried utilities, such as water and gas pipes. One of the promising approaches to protect buried utilities against frost damage and reduce the excavation cost is to install thermal insulation over and around the pipe. This paper considers two different conductive heat transfer models, with and without the effect of soil pore-water phase change, as well as a heat and mass transfer model for freezing soils to investigate the effectiveness of insulation systems for frost protection of buried pipes. It was found that the latent heat released during the phase change significantly affects the heat transfer process and that the impact of phase change on insulation design should not be overlooked. Furthermore, by comparing numerical results to field measurement data, it is found that the mass transfer has an insignificant effect on the temperature and unfrozen water content distribution in the frost-susceptible foundation soil. A parametric study was carried out to assess the effects of different factors such as the backfill materials, geometry, total length, thickness of insulation, distance between pipe and insulation as well as the burial depth of pipe on the thermal performance of insulation. Finally, the Nelder-Mead algorithm was implemented to determine the optimum insulation design so that the overall cost is minimized while the pipe is protected from freezing. [ABSTRACT FROM AUTHOR]

Highlights • Constructal design of a disc-shaped heat exchanger is implemented. • Maximum thermal efficiency is taken as optimization objective. • Total tube volume is taken as constraint. • Optimal tube lengths are obtained. • Effect of mass flow rate on its optimal construct is analyzed. Abstract Constructal design of a disc-shaped heat exchanger (DSHE) is implemented in this paper. Maximum thermal efficiency and total tube volume are taken as the optimization objective and constraint, respectively. Optimal tube lengths of the DSHE are obtained, and the effect of mass flow rate on its optimal construct is analyzed. The results show that for the first order DSHE, its thermal efficiency has the maximum and the elemental tube angle has the corresponding optimal value. For the higher order DSHEs, the optimal constructs of the DSHEs are not varied when their mass flow rates are small and large enough, and the DSHE structure is simplified into the structure of the last order DSHE when the mass flow rate is large enough. For the same tube volume and area of the DSHEs with 4 central tubes and a large mass flow rate, the thermal efficiency of the third order DSHE is increased by 7.33% than that of the first order DSHE. Therefore, the performance of the DSHE is increased when its structure becomes complex in this case. The obtained results can offer some instructions for the optimal designs of various thermal systems, such as power, refrigeration and heat pump plants. [ABSTRACT FROM AUTHOR]

Highlights • Review summarizes constructal optimizations about engineering problem in China. • Six classes of objects are included performed over the past decade. • Multi-disciplinary, multi-objective and multi-scale constructal optimizations. • A model of generalized transfer process based on various transfer processes. Abstract Constructal theory has been widely used in performance optimizations of various problems. Among these problems, engineering problem is a hot topic for constructal theory. The developments of constructal theory about engineering problem in China over the past decade are reviewed in this paper. Multi-disciplinary, multi-objective and multi-scale constructal optimizations of various transfer processes in engineering, such as heat conduction and thermal insulation processes, fluid flow processes, convective heat transfer processes of fins, heat sources, cavities, cooling channels, vascular networks and heat exchangers, mass transfer processes of porous mediums, heat and mass transfer processes of solid-gas reactors and solid oxide fuel cells, iron and steel production processes and generalized transfer processes, have been conducted since 2006. Performance improvements are realized, new design requirements are satisfied, and more practical and generalized results are obtained after new research objects, model improvements, optimization objectives, boundary conditions, constraint conditions and transfer extensions are considered. It shows that the developments of constructal theory are still being made in China, which will provide more design guidelines not only for engineering problem, but also for natural and social problems. [ABSTRACT FROM AUTHOR]

Highlights • Falling film flows with natural and forced disturbances are simulated. • Velocity vector in a wave is obtained by LBM. • Dimensionalization to actual absorption by a velocity ratio. • Compare wave flow with laminar one on falling film absorption. Abstract The investigations on heat and mass transfer in the form of falling film flow were mainly focused on the simulation of heat and mass coupling adopting the continuity hypothesis of Navier-Stokes equations. Most of the previous works were done with laminar flow assumptions, or just deal with a very short smooth laminar section beyond the falling film entrance. In this paper, a study investigating the effects of wavy flow on stream absorption by falling liquid film is presented in the perspective of sorption refrigeration process. A multi-phase model lattice Boltzmann method is adopted to simulate the wavy falling liquid film flow, and the absorption process takes place in this flow field region. Absorption simulation was carried out using the laminar flow assumption with the semi-parabolic velocity distribution and the fluctuation results in the LBM simulation. When the overall simulation section is 1 m in length, with initial velocity 0.1 m/s for lithium bromide solution falling film flow, results show that the wave flow has apparent enhancement on heat and mass transfer. Local dimensionless numbers for mass (Sh) and heat (Nu) transfer with waves increase 4 times and 2 times, respectively, compared with the laminar flow. [ABSTRACT FROM AUTHOR]

Highlights • Analytical model of drop pair evaporation with variable gas density is developed. • The dependence of gas mixture density on temperature/composition is considered. • Analytical solution to conservation equations in bi-spherical coordinate system. • Effect of drop interaction for any Lewis number is analytically quantified. • Comparison with constant gas density solutions and experimental results. Abstract The paper reports an analytical approach to model heat and mass transfer from neighbouring spherical drops accounting for the dependence of the gas mixture density on temperature and composition. The conservation equations for single-component non-identical spherical drops evaporating in gaseous quiescent environment are analytically solved in a bi-spherical coordinate system. Analytical expressions for the local heat and mass fluxes on drop surfaces and for the evaporation and the sensible heat rates are reported. The effect of relieving the commonly adopted assumption of constant gas density is quantified by comparison with existing constant density solutions for different evaporating species and operating conditions. The model applies to any value of Lewis number. Comparison with analogous results for single isolated drops allows to quantify the screening effect on vapour and heat fluxes and evaporation and heat rates. [ABSTRACT FROM AUTHOR]

Highlights • Diffuse-interface simulation of bubble dynamics in a binary mixture is performed. • Local accumulation of gas with the bubble is critical to continuous bubble growth. • Strong thermocapillary flow peaks before bubble pinch-off from the biphilic surface. Abstract In this paper, we numerically study pool boiling of a binary (water and nitrogen) mixture on a surface endowed with a combination of hydrophobicity and hydrophilicity (i.e., the so called biphilic surface). Here we adopt a numerical approach based on the phase field theory, where the vapor-liquid interface is assumed to be of a finite thickness (hence diffusive in nature) and requires no explicit tracking schemes. The theoretical modeling of two-phase heat and mass transfer in water diluted with nitrogen demonstrates the significant impact of impurities on bubble dynamics. The simulations show that locally high concentrations of nitrogen gas within the vapor bubble is essential to weakening the condensation effect, which results in sustained bubble growth and ultimately (partial) departure from the surface under the artificially enlarged gravity. Simply increasing the solubility of nitrogen in water, however, turns out to be counterproductive because possible re-dissolution of the aggregated nitrogen by the bulk water could deprive the bubble of vital gas contents, leading instead to continuous bubble shrinkage and collapse. Additionally, it is found that with the significant accumulation of nitrogen, the bubble interface is increasingly dominated by a strong interfacial thermocapillary flow due to the Marangoni effect. [ABSTRACT FROM AUTHOR]

Graphical abstract Temperature and moisture profiles inside the PEM-based element during the dehumidification. Highlights • A 2D theoretical model for PEM-based electrolytic dehumidifier was developed. • The inside heat/mass transfer mechanisms of five-layer elements can be disclosed. • The model predictive results showed good agreement with experimental ones. • The largest moisture gradient occurred inside the PEM during dehumidification. • Increasing PEM water content can significantly improve the system performance. Abstract In this paper, a two-dimensional steady-state theoretical model was established, to model the internal transport phenomena in a polymeric electrolyte membrane-based (PEM-based) air dehumidification element. The influences of electrochemical reactions, activation and concentration over-potentials, and Ohmic and electro-osmotic effects were considered. The model was solved by the finite difference method with conjugate boundary conditions. So, with this model, the heat, mass and current transfer through the five layers of the element (diffusion layers, catalyst layers and a PEM) could be described theoretically, as well as the convective heat and mass exchange with adjacent airflows. Compared with the results from previous models, this model showed a much closer trend to the experimental data. The overall error was less than 15%, with an acceptable average error of 8.6%. However, greater deviations were observed under larger airflow conditions, probably due to the assumption of laminar airflow and steady-state heat conduction. Furthermore, by the performance analysis, the maximum moisture gradient was found inside the PEM, so the PEM’s parameters could largely affect the system performance. With the increase in PEM water content, the dehumidification was significantly enhanced, especially when the air humidity was high. If the PEM water content was doubled, the dehumidification rate was increased by 42%. Then, decreasing the PEM thickness also improved the performance. However, the effect became minor if the thickness was less than 100 μm. It was also helpful by increasing the PEM conductivity, although the effect of this variable was relatively small. This study provided theoretical guidance for further system improvement and material preparation for PEM-based dehumidification systems. [ABSTRACT FROM AUTHOR]

Performance estimation of heat exchanger apparatuses requires a proper knowledge of the thermo-fluid dynamic interaction between fluid and device. One of the aspects to take into account is related to the estimation of the internal convective heat transfer coefficient. This requires the knowledge of the internal temperature and the internal wall heat flux, although these quantities are complicated to be measured. Therefore, the use of inverse problem techniques may be very useful for estimating these quantities. This approach deals with the estimation of the local internal properties, given some external temperature measurements, possibly by means of contactless experimental methodologies (i.e. infrared camera imaging). The solution strategy here presented, for a 2D model, is based on the Reciprocity Functional approach (RF), which requires the solution of two auxiliary problems that are solved, in this paper, by means of the Classical Integral Transform Technique (CITT). The RF approach coupled with CITT, presents some advantages over other techniques since its solution is completely analytical and therefore computationally fast, and it does not require any numerical simulation. Moreover, it deals with the noise content of the experimental data, filtering it and overcoming the documented limits of the classical RF approach. This original method, named Filtered Reciprocity Functional (FRF) approach, was applied to different test cases using simulated measurements, and the results were compared to both the exact and the reconstruct solutions obtained by the Truncated Singular Value Decomposition (TSVD) method, showing a good agreement. Finally, the FRF approach was applied to an experimental case in order to test its robustness when dealing with real data. [ABSTRACT FROM AUTHOR]

R32, namely the main component of R410A, is thought to be a kind of transitional alternative refrigerant in developing countries. In this paper, a set of experimental apparatus of the flow boiling heat transfer of R32 in horizontal tubes was built up. Effects of mass flux, heat flux, boiling temperature, tube sizes, vapor quality, channel geometry of heat transfer tubes on flow boiling heat transfer coefficient of R32 were investigated. The results demonstrate that flow boiling heat transfer coefficients increase with mass flux, saturated evaporating temperature and heat flux. Besides, the flow boiling heat transfer coefficients of R32 in the micro-fin tubes with tube diameters of 5 mm and 7 mm are 1.19 and 1.23 times, respectively, as large as that in the smooth tubes. Vapor quality seems to have a complicated influence on the boiling heat transfer coefficients of R32 due to the emerging dry-out point, the vapor quality of which are experimentally tested to range from 0.41 to 0.57. The change of mass flux and heat flux have influence on the vapor quality of the dry-out point. Furthermore, the experimental data in smooth and micro-fin tubes are respectively compared with the predictive values of semi-empirical correlations. It should be necessary for researchers to explore the flow boiling heat transfer characteristics of R32 in horizontal tubes, which will be of great benefit to further optimization research and applications on heat exchangers of R32. [ABSTRACT FROM AUTHOR]

Air dehumidification is of vital importance in building air conditioning and production safety. Semi-permeable membrane module is a novel heat and mass exchanger, which separates the air and liquid desiccant to overcome desiccant droplet carry-over problem in traditional direct-contact systems. Recently, some research works have been carried out in mathematical modelling and experimental testing of membrane-based liquid desiccant dehumidification technology. Compared with the experimental testing, the mathematical modelling has advantages of significant time and cost reductions, practically unlimited level of detail, more profound understanding of physical mechanism and better investigation of critical situation without any risks. This paper presents a comprehensive review of various modelling methods for two types of membrane-based liquid desiccant modules: flat plate and hollow fiber. [ABSTRACT FROM AUTHOR]

The reflow soldering process of large size components was always problematic in microelectronics manufacturing due to the possibility of component displacement failures after soldering; like tombstone formation or skewing, which can be traced back to the different heating of the opposite component sides. During vapour phase soldering, the efficiency of heat transfer highly depends on the thickness of the condensate layer. In this paper, the inhomogeneity of condensate layer formation and its effects were investigated at large size components during vapour phase soldering by numerical simulations. For this purpose, a 3D computational fluid dynamic model was established. According to the condensate layer formation in different cases, the onset differences in the melting of the solder alloy at the opposite leads of the component were calculated. By the results, the risk of the component displacement during reflow soldering was analysed. It was found, that the congestion of the condensate layer around the large size components can cause considerable differences in the onset of the solder alloy melting, which can yield in component displacement failures after soldering. The extent of difference in the onset of melting depends on the location of the component on the board and on the applied soak temperature. Keep-out zones on the board were suggested to reduce the possibility of the component displacement failures during the vapour phase soldering process. [ABSTRACT FROM AUTHOR]