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Abstract: In this work we present a mathematical model describing the coupled heat and moisture transport in paper. The model is solved numerically and the numerical solution is used to study the interdependency of the moisture and temperature distribution in paper. The results show that variation with temperature of the saturated water vapor concentration and the sorption isotherm parameters are both important for inducing moisture desorption. It is also found that for steep relative humidity ramps moisture sorption generates temperature increments that slow down the sorption process itself. The model is also used to study the moisture gradients in a paper sheet inside a printer from Océ Technologies, which contains a warm print surface. The results predict changes in moisture content of only 0.2%, which suggests that no deformations are induced on the printed sheet. [Copyright &y& Elsevier]

A mathematical model describing the heat and mass transfer in the dryer section of a paper machine has been applied to the production data from four paper machines. Model predictions for the machine speed are compared to actual machine speeds for a total of 163 data sets. The mathematical model assumes that the temperature and moisture content remain homogeneous in the thickness direction of the sheet. For three paper machines producing paper with basis weights ranging from 0.056 to 0.159 kg d.s./m2 the model predictions are adequate. For the paper machine producing the heaviest grades with basis weights ranging from 0.189 to 0.390 kg d.s./m2 the model predictions are flawed by a systematic error. For low machine velocities/high basis weights the machine velocity is over-predicted and for high machine velocities/low basis weights the machine velocity is under-predicted. This systematic error is caused by the assumption of homogeneous moisture content and temperature within the sheet being severely in error for thick sheets. [Copyright &y& Elsevier]

The present study investigates two models—two limiting cases—for the internal heat and mass transfer in a multicylinder dryer: the first model assumes that complete redistribution of heat and moisture in the thickness direction occurs instantaneously. The second model assumes that moisture transfer occurs only by vapor diffusion and that heat transfer takes place by conduction and condensation. The two models are written in dimensionless form, and applied for the same set of standard paper machine data. For basis weights below approximately 0.05 kg d.s./m2 the results are so close that the first, simple model is sufficient. A higher limiting basis weight—approximately 0.16 kg d.s./m2—was previously indicated by comparison of model predictions, assuming the simple model, to extensive sets of machine data from four different paper machines. [Copyright &y& Elsevier]

This paper describes an accurate model of the Electrical Power Subsystem (EPS) of the Thermal Analysis Support and Environment Characterization Laboratory (TASEC-Lab), a university experiment developed for using in high-altitude balloon missions to measure and analyze the convection heat transfer. A Li-ion battery and two high efficient DC–DC converters have been characterized through laboratory tests and fitting to the experimental results. The developed mathematical models described in this paper are used to carry out accurate EPS simulations and are validated by comparison with the experimental data. • Design and modeling of the electrical power subsystem of a stratospheric balloon experiment. • New Li-lion battery discharging model that describes the three main parts: initial decay, linear, and exponential decay. • Formulation of a new DC/DC converter efficiency model. • Simulation and model validation of the electrical power subsystem. [ABSTRACT FROM AUTHOR]

In order to make full use of the advantages of superheated steam (SHS), SHS injection in multi-point injection wells (MPIW) is proposed in this paper. Firstly, a mathematical model comprised of SHS flow model in inner tubing (IT) or long tubing (LT) and annulus, transient heat transfer model in oil layer is established. Secondly, type curves of SHS flow in MPIW is obtained by finite difference method on space and the iteration technique. Then, the effect of injection temperature on distributions of thermophysical properties of SHS in MPIW is discussed in detail. Results show that: (a) When the heat exchange between IT and annulus is taken into consideration. SHS temperature in IT has a decrease while SHS temperature in annulus has an increase. (b) With the help of MPIW, heating effect at both heel and toe points of the horizontal wellbores can be enhanced. (c) While the increase of SHS temperature certainly benefits the formation heating effect through the increase of both SHS temperature and superheat degree, the following decrease of SHS pressure in annulus will lead to the decrease of SHS absorption rate. This paper unravels some intrinsic flow characteristics of SHS in MPIW, which has a significant impact on the optimization of SHS injection parameters and analysis of heat transfer law in MPIW. [ABSTRACT FROM AUTHOR]

The numerical modelling of the internal heat generation in passenger vehicle tyres using finite element analysis is a well-known numerical approach. However, this application is rather uncommon for earthmover tyres. This paper describes the development of a finite element model of a 23.5R25 earthmover tyre for the numerical modelling of the temperature distribution in the tyre cross-section at steady-state heat transfer conditions using an uncoupled analysis procedure. Considering the non-linear behaviour of the rubber compounds used for the manufacturing of these tyres, as well as the complexity associated with the composite structural aspects of the tyre, the material properties used for the proposed numerical model were established experimentally. In the analyses completed, the tyre behaviour was studied by simulations at various inflation pressures, loads and rolling velocities. The numerical tyre defection was within an 8% deviation from the actual tyre behaviour. Thermal simulation results were used to derive an equation that can be used to predict the maximum temperature that would occur in the tyre’s cross-section as a function of its vertical deflection, its forward rolling velocity and the ambient temperature of the surroundings. The numerical models and simulations presented in this paper were completed using MSC.Marc/Mentat. [ABSTRACT FROM AUTHOR]

In industrial applications, most of fluids have non-Newtonian fluid characteristics. It is of great significance to the economic development and energy consumption reduction to study the heat transfer of non-Newtonian power law fluid. In this paper, the heat transfer of non-Newtonian power law fluid in pipes with different cross sections are studied. The mathematical model and physical model of the non-Newtonian fluid are briefly introduced first, and the physical model is divided by the structured mesh. Then the numerical simulation of the laminar heat transfer of non-Newtonian fluid in different cross sections is carried out. On the basis of discussing the distribution of temperature field, many parameters which have influenced on the temperature field and the heat transfer is analyzed in this paper, such as tube shape, the power-law index ( n ) the Peclet number ( Pe ) and so on. The results show that the heat transfer characteristics of non-Newtonian fluid are related to the parameters we mentioned. [ABSTRACT FROM AUTHOR]

This paper designs and discusses a Micro-Plate Loop Heat Pipe which is suitable for the heat dissipation of various electronic chips, discusses and explains details of the loop heat pipe components. This paper also discovers the reliable sintering temperature and thermal insulation time for a sintering porous capillary wick which is made up of nickel powder using the method of cold pressure forming and sintering with vacuum protection. It can lay a solid foundation for the development of efficient Micro-Plate Loop Heat Pipe equipment. It is also important for circular heat pipe further research and development. [ABSTRACT FROM AUTHOR]

It is a hot topic whether the choice of heating supply is necessary and what is the most suitable form of heating system for hot summer and cold winter regions. Apparently, the difference of climate and building envelope makes it a complex problem, which cannot rely on the northern heating measures directly. At the same time, the form of building envelope is closely related to energy consumption and indoor thermal environment. Thus, this paper looked at the importance of different thickness of building external insulation for residential building in Chongqing. This paper discussed the thickness of building external insulation in Chongqing based on the intermittent heating system, which used Dest to draw the conclusion. Economic and technical analyses were also carried out in order to find the balance point between the growth of cost and the amount of energy saving, due to the different form of building envelopes. [ABSTRACT FROM AUTHOR]

In the present investigation, a non-linear mathematical model is developed for the analysis of Septuple effect flat falling film evaporator (SEFFFE) system used for concentrating black liquor in a nearby paper mill. This model is capable of simulating process of evaporation considering variations in boiling point rise (τ), overall heat transfer coefficient (U), heat loss (Q loss), flow sequences, liquor/steam splitting, feed, product and condensate flashing, vapor bleeding and physico-thermal properties of the liquor. Based on mass and energy balance around an effect a cubic polynomial is developed and solved repeatedly in a predetermined sequence using generalized cascade algorithm. For development of empirical correlations for τ, U and Q loss, plant data have been collected from SEFFFE system. These correlations compute τ, U and Q loss within average absolute errors of 2.4%, 10% and 33%, respectively, when their results are compared with the plant data. [Copyright &y& Elsevier]

Thermal output of the piping system is investigated. The system was formed from a tube of circular section, made of multilayer polyethylene - aluminum. It was subsequently wound into a planar spiral. The paper contains the calculation of the thermal output by a mathematical model, which replace the real model. The experimental measurements were measured with a variable distance winding. The paper compare heat output results with experimental measurements. [ABSTRACT FROM AUTHOR]

This paper presents a computational heat transfer model of a rotary kiln used for the production of rutile titanium dioxide by the calcination of paste-like hydrous titanium dioxide. The work details the modelling of several chemical reactions occurring in the solid bed region along with turbulent convection of gas, radiation heat exchange among hot gas, refractory wall and the solid surface, and conduction in the refractory wall. Finite-difference techniques are used and the steady state thermal conditions are assumed. The kiln is divided into axial segments of equal length. The solution is of marching type and proceeds from the solid inlet to the solid outlet. The direction of gas flow is opposite to that of the solids. Mass balance of each species in the solid charge, and mass and energy balances of the solid and gas in an axial segment are used to obtain solids and gas temperatures, and species concentration at the exit of that segment. The kiln length predicted by the present model is 45.75 m as compared to 45 m of an actual kiln reported by Ginsberg and Modigell (2011). The steady-state axial gas and solid temperature profiles have been also satisfactorily validated with the numerical results of the aforementioned paper. The output data consist of refractory wall temperature distribution, the axial solids and gas temperature profiles, axial solids composition profile, the length required for drying of the solid charge and the total kiln length required to achieve 98% conversion of anatase TiO 2 to rutile TiO 2 . A detailed parametric study with respect to the controlling parameters such as percent water content (with respect to dry solids), solids flow rate, gas flow rate, kiln inclination angle and kiln rotational speed lent a good physical insight into the rutile-TiO 2 production process in a rotary kiln. [ABSTRACT FROM AUTHOR]

In this paper a new viscosity model is proposed in order to predict the viscosity of the nanofluids in order to bridge the gap on this issue. The effective viscosity expression proposed in this paper is based on the regression analysis of a number of carefully selected published papers which covers theoretical, experimental and numerical results. Compared with the other theoretical models that are available in literature, the presented model has a good accuracy and reliability. The proposed model has been tested in 3D horizontal pipe and the results with Nusselt number show good agreement with available data. The model was tested for a wide range of volume concentration and temperature and shows wider applicability. [ABSTRACT FROM AUTHOR]

Ice slurry heat transfer characteristics in a straight horizontal tube were numerically studied in this paper. By using of CFD software, the VOF model in FLUENT 6.3, the simulation of ice slurry was performed to cover laminar and turbulent flow regimes with C is varying from 0% to 20%. The obtained results were firstly validated by the published experimental values. It is found that the discrepancy between the measured and calculated Nu is number is mainly in the range of ±15%. Then the model was applied to analyze the impact of initial conditions on ice slurry heat transfer. The present work shows that, ice slurry heat transfer performance are strongly dependent on the flow velocity and ice mass fraction, and heat flux density only has a small influence on the value of Nu is when ice slurry flows in turbulence. This paper aimed to use this model as a design tool to analyze ice slurry flow in different operating conditions. [ABSTRACT FROM AUTHOR]

The multi-term time-fractional diffusion equation is a useful tool in the modeling of complex systems. This paper aims to develop a high order numerical method for solving multi-term time-fractional diffusion equations. Based on the space-time spectral method, a high-order scheme is proposed in the present paper. In this method, the Legendre polynomials are adopted in temporal discretization and the Fourier-like basis functions are constructed for the spatial discretization. Such a space-time spectral method possesses high efficiency and exponential decay in both time and space directions. Rigorous proofs are given here for the stability and convergence of the scheme. Numerical results show good agreement with the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper numerically investigates the performance and heat and mass transfer processes that occur in counter-flow indirect evaporative air coolers. Different types of counter-flow air coolers were compared: a typical counter-flow unit, the same unit operating as a heat recovery exchanger, a regenerative unit and a novel modified exchanger, proposed by authors. Additionally the paper investigated impact of location of the perforated holes in the channel plate of regenerative air cooler. The numerical model is based on a one-dimensional heat and mass transfer analysis that was validated against existing experimental data. The results obtained from the simulation reveal the high effectiveness of the presented units. It was established that selected arrangements of the presented exchangers are characterized by the different efficiency in different air-conditioning applications. [ABSTRACT FROM AUTHOR]

• Normal mode stability analysis performed on counjugate heat transfer (CHT) 1D problem. • Stability analysis reveals existence of lower stability bound for coupling coefficient in Robin-Dirichlet interface boundary conditions. • Validity of stability analysis results is verified empirically. • Stability analysis is extended to more general CHT problems. This paper aims to evaluate and validate a mathematical coupling model, based on a normal mode stability analysis, for steady conjugate heat transfer problems. In order to achieve this goal, an aerothermal computational code was designed specifically ex novo to meet the needs of the current study. A large number of numerical simulations were carried out within the framework of the Dirichlet-Robin fluid-solid interface procedure and with conditions strictly identical to those adopted in the mathematical model. These coupled computations have been synthesized in five representative cases. The computed results show that the stability limit and the numerical Biot number derived from the coupling model are very reliable parameters. Many other physical and numerical aspects, such as the splitting of the coupling period are also considered in this work from which some interesting and promising results are obtained. At the end of this paper, we assess the general potential, limits and constraints of the mathematical model and its extension to multidimensional cases is discussed. [ABSTRACT FROM AUTHOR]

In consideration of droplet flash evaporation and film flash evaporation, a comprehensive mathematical model of vacuum flash evaporation cooling (VFEC) was presented in this paper. Pure water was considered to be the working fluid. The droplet flash evaporation was modeled based on the diffusion-controlled evaporation model, while the film flash evaporation was modeled based on the film penetration theory. The droplet flash model coincided well with the experimental results reported in the literature and the comprehensive mathematical model was validated by experiment results in this paper. The droplet temperature and diameter after droplet flash evaporation were obtained numerically, and then analyzed. The effect of droplet flash evaporation on the surface temperature distribution, heat flux density, and heat transfer ratio of different mechanisms was studied based on the model. It can be concluded that the droplet flash evaporation, which can be expressed by the ratio of droplet-wall impaction heat transfer, had a great effect on vacuum flash evaporation cooling heat transfer. The droplet-wall impaction and film flash heat transfer were dominant in the vacuum flash evaporation cooling. The spray characteristics such as droplet diameter and temperature decreased a lot after droplet flash evaporation, compared to the initial parameters (measured by the PDA). After taking droplet flash into account, the surface temperature decreased and the heat flux increased. [ABSTRACT FROM AUTHOR]

This paper discusses the effect of temperature polarization in Vacuum Membrane Distillation (VMD). The main motivation for using VMD in this work is that this module configuration is much simpler and more suitable for this kind of investigation than the other MD configurations such as Direct Contact Membrane Distillation (DCMD). The coupling between heat and mass transfer mechanisms at the feed-membrane interface is presented from a theoretical point of view. In addition, a new simple graphical method and a mathematical model for determining VMD flux are presented. The two methods used in evaluating the extent of temperature polarization effect on water vapor flux (flux sensitivity factors and temperature polarization coefficient (TPC)) are also analyzed and compared. The effect of integrating a heat recovery system in a large scale module on the TPC coefficient has also been studied and presented in this paper. [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]

Abstract: Modeling subcooled flow boiling in vertical channels at low pressures requires not only the consideration of the dynamic behaviors of two-phase flow and bubbles undergoing coalescence, breakup and condensation in the bulk subcooled liquid but also the characterization of the single-phase and local boiling heat transfer phenomena in the near-wall region. The focus of this paper is the assessment of the heat flux partitioning model in handling the latter physics of subcooled flow boiling. In order to achieve closure to the model, the current prevailing approach has always been the utilization of empirical correlations particularly for the active nucleation site density, bubble departure diameter and bubble departure frequency. A comprehensive survey of existing empirical correlations is presented in the first part of this paper to assess the performance of these empirical models. Selected combinations of empirical correlations are compared and validated against axial and local radial experiments encompassing a wide range of different mass and wall heat fluxes and inlet subcooling temperatures for subcooled flow boiling at low pressures. Based on the comparisons made against the axial and local distributions of void fraction and bubble Sauter diameter, not one single combination of empirical correlations has shown the propensity of providing satisfactory predictions covering the entire axial and local conditions. For the modeling of subcooled flow boiling at low pressures to become an effective predictive tool, it must therefore be complemented with further consideration of first principal models of the underlying physical phenomena. [Copyright &y& Elsevier]

Abstract: This paper proposes a new frequency domain method to model the heat transfer between the injected/extracted heat and the temperature of the fluid exiting a borehole heat exchanger. The method is based on in situ measurements and focuses particularly on the short-term borehole heat transfer. It uses a rational function of the Warburg variable in the Laplace domain to model the borehole heat transfer. The rational model is transformed to a time domain model using inverse Laplace transformation. This time domain model makes it possible to calculate the temperature response on a random heat variation signal. The paper also demonstrates a new way to perform the classical thermal response test. Instead of injecting a constant amount of heat, the experiments have been performed using multiple short-duration heat injections. In this way, the obtained rational heat transfer model contains information about both the short- and the long-term heat transfer. The results obtained using the proposed modeling method are compared with those obtained from a state-of-the-art analytical method. The time domain model can be used to design a controller to optimize the performance of a Ground Source Heat Pump system, the efficiency of which depends strongly on the temperature of the fluid exiting the borehole. [Copyright &y& Elsevier]

Abstract: Along with the developments of lattice-Boltzmann method in simulation of fluid flow, its thermal features should be also improved. An important problem which is encountered in many cases is the conjugate heat transfer or heat transfer at the fluid–solid interface. In this case, a strict technique is required to calculate the heat exchange between fluid and solid. Only a few works have been published regarding this phenomenon. In this paper, we have presented a model for analysis of the conjugate heat transfer. The model has been validated by two benchmarks: (I) Fluid flow and heat transfer in a backward-facing step channel with heated thick wall, and (II) Fluid flow and heat transfer in a channel with infinite number of heated obstacles mounted on the wall. The numerical tips concerned in the simulation of these problems by lattice-Boltzmann method have been also represented in the paper. [Copyright &y& Elsevier]

Abstract: In this paper, a transient numerical model for a liquid-to-air membrane energy exchanger (LAMEE) is developed and the results are compared to the experimental data. The data for the sensible, latent and total effectiveness are compared with transient and steady-state simulations for various values of NTU and operating parameters (Cr∗, inlet temperature and humidity) while the exchanger undergoes a step change in inlet conditions and reaches a new steady-state. The transient and steady-state performances are shown to be a function of the design and operating parameters. The paper also shows that buoyancy forces become important and affect the LAMEE performance under certain operating conditions. The verified numerical model is used to investigate the impact of outdoor air conditions on the LAMEE performance. [Copyright &y& Elsevier]

Abstract: The inlet fog cooling scheme has been considered as an economic and effective means to augment gas turbine output power on hot or dry days. A previous paper developed a stage-by-stage wet-compression theory for overspray and interstage fogging using the equilibrium droplet evaporation model with given compressor and blade configurations. This paper extends the previous work by including the non-equilibrium droplet heat transfer model. The equilibrium model assumes that water evaporates to saturation according to psychrometry at each stage without considering water evaporation rates, whereas the non-equilibrium model considers water evaporation rates according to heat and mass transfer of droplets. The non-equilibrium model can predict the different evaporation from different droplet sizes, but equilibrium model can''t. An 8-stage, 2-D compressor airfoil geometry and stage settings at the mean radii are employed. Eight different cases including saturated fogging, overspray with different droplet sizes with both equilibrium and non-equilibrium heat transfer models have been investigated and compared. The results show saturated fogging increases the pressure ratio and reduces the compressor power consumption; however, overspray actually increases both the specific and total compressor power consumption. For small droplet size of 10 μm, the droplet evaporation rate is fast, so the non-equilibrium method predicts results close to the equilibrium method. Larger droplets lead to slower evaporation, reduction of pressure ratio, and less effective compressor performance than the smaller droplets. The equilibrium method predicts that wet compression increases axial velocity, blade inlet velocity, incidence angle, and tangential component of velocity. The non-equilibrium methods predict a similar trend except with lesser increments as the droplet size increases. In the present study, the equilibrium method predicts that all the water droplets evaporate completely at the end of stage 3, while the non-equilibrium approach predicts that the completion of evaporation delays, but all droplets completely evaporate in the compressor except the biggest droplets (30 μm). Saturated fogging increases air density; however, both equilibrium and non-equilibrium methods predict that overspray wet compression actually reduces air density in the earlier 70% of the compressor. The non-equilibrium model predicts that small droplets relax the load in the earlier stages but increase the load in the later stages. Larger droplets show less load changes. Detailed stage-to-stage performance and property value changes are analyzed and discussed in this study. [Copyright &y& Elsevier]

Abstract: This paper introduced the concept, potential application and benefits relating to a novel solar photovoltaic/loop-heat-pipe (PV/LHP) heat pump system for hot water generation. On this basis, the paper reported the process and results of characterizing the performance of such a system, which was undertaken through dedicated thermo-fluid and energy balance analyses, computer model development and operation, and experimental verification and modification. The fundamental heat transfer, fluid flow and photovoltaic governing equations were applied to characterize the energy conversion and transfer processes occurring in each part and whole system layout; while the energy balance approach was utilized to enable inter-connection and resolution of the grouped equations. As a result, a dedicated computer model was developed and used to calculate the operational parameters, optimise the geometrical configurations and sizes, and recommend the appropriate operational condition relating to the system. Further, an experimental rig was constructed and utilized to acquire the relevant measurement data that thus enabled the parallel comparison between the simulation and experiment. It is concluded that the testing and modelling results are in good agreement, indicating that the model has the reasonable accuracy in predicting the system’s performance. Under the given experimental conditions, the electrical, thermal and overall efficiency of the PV/LHP module were around 10%, 40% and 50% respectively; whilst the system’s overall performance coefficient (COPPV/T ) was 8.7. Impact of the operational parameters (i.e. solar radiation, air temperature, air velocity, heat-pump’s evaporation temperature, glazing covers, and number of the absorbing heat pipes) to the performance of the system (in terms of efficiencies of the PV/LHP module and the system’s overall performance coefficient COPPV/T ) was investigated individually. The results indicated that lower solar radiation, lower air temperature, higher air velocity and smaller cover number led to enhanced electrical efficiency but reduced thermal efficiency of the module; whereas lower heat-pump’s evaporation temperature and larger number of heat absorbing pipes gave rise to both thermal and electrical efficiencies of the module. The research results would assist in developing a high efficient solar (space or hot water) heating system and thus contribute to realisation of the energy saving and associated carbon emission targets set for buildings globally. [Copyright &y& Elsevier]

Abstract: This paper discusses results of simulations conducted for non-contacting face seals showing the influence of the operational parameters on the distributions of temperature in the structural elements and the fluid film separating the sealing rings. The mathematical model developed for noncontacting face seals consists of cross-coupled differential equations with partial derivatives. We solved it analytically, taking into account various boundary conditions. The heat equations were solved using the method of separation of variables. The derived relationships were based on Bessel functions of the first and second kinds. By defining the relationships describing the distributions of temperature in the sealing rings and the fluid film separating them, we could determine the effect of the operational parameters on the variability of temperature fields. Confirmation of the simulation results with experimental data is essential to better recognize the phenomena taking place in the sealing assembly and improve the design of non-contacting seals so that they can be used in various industrial applications. In this paper, we also describe a specially designed test stand for compensation of the misalignment of the flexibly mounted ring and automatic control of the radial clearance height. The test stand can also be used to verify the results of analytical studies. [Copyright &y& Elsevier]

Abstract: This paper presents experimental and numerical studies on periodic convection flow and heat transfer in a lid-driven arc-shape cavity with temperature differential. Three cases were considered: Gr=2×105, 5×105 and 1.2×106 at Re=100 (Gr = Grashof number; Re = Reynolds number). The mathematical model was proposed in our previous study. The current study performs an experiment to validate this model, to corroborate the existence of the periodic flow, and to more deeply probe the internal flow and temperature characteristics. The experimental setup primarily comprised an arc-shape cavity, a moving lid, a thermo-system, a smoke generator and an image acquisition system. The periodic convection flow in the cavity was visualized using kerosene smoke. The numerical and experimental results consistently reveal that the periodic flow pattern was observed in the case with Gr=5×105, whereas the steady-state flow pattern took place in the other two cases (Gr=2×105 and Gr=1.2×106). The numerical simulation produced reasonable and satisfactory agreement with the experiment for the periodic flow pattern and period. The difference between the predicted and measured periods is less than 5%. The transport properties, such as average kinetic energy, overall Nusselt number, stream function, phase space trajectory, local kinetic energy, velocity history and temperature distribution, were further analyzed and discussed in this paper. The proposed numerical simulation not only confirms the experimental observation, but also enhances the understanding of periodic convection in an arc-shape cavity subjected to a moving lid and temperature differential. [Copyright &y& Elsevier]

Abstract: Combustion in fired heaters, boilers and furnaces often accounts for the major energy consumption on industrial processes. Small improvements in efficiency can result in large reductions in energy consumption, CO2 emissions, and operating costs. This paper will describe some useful low cost modelling techniques based on the zone method to help identify energy saving opportunities on high temperature fuel-fired process plant. The zone method has for many decades, been successfully applied to small batch furnaces through to large steel-reheating furnaces, glass tanks, boilers and fired heaters on petrochemical plant. Zone models can simulate both steady-state furnace operation and more complex transient operation typical of a production environment. These models can be used to predict thermal efficiency and performance, and more importantly, to assist in identifying and predicting energy saving opportunities from such measures as: [•] Improving air/fuel ratio and temperature controls. [•] Improved insulation. [•] Use of oxygen or oxygen enrichment. [•] Air preheating via flue gas heat recovery. [•] Modification to furnace geometry and hearth loading. There is also increasing interest in the application of refractory coatings for increasing surface radiation in fired plant. All of the techniques can yield savings ranging from a few percent upwards and can deliver rapid financial payback, but their evaluation often requires robust and reliable models in order to increase confidence in making financial investment decisions. This paper gives examples of how low cost modelling techniques can be applied to improve confidence in implementing energy efficiency improvements whilst safeguarding manufacturing output and quality. [Copyright &y& Elsevier]

Abstract: A model for predicting the flux and evaporation ratio in direct contact membrane distillation (DCMD) using a compressible membrane is presented. Polytetrafluoroethylene (PTFE) membranes, one of the most common types of membranes employed in MD, are characterised with high porosity (∼90%) and high hydrophobicity, and therefore have high water vapour permeability and high wetting resistance. However, the PTFE membrane is compressible due to its structure. Compression of the membrane will cause a change of its physical structure, such as porosity, thickness, and pore size. As a result, the thermal conductivity and vapour permeability of the membrane will be altered, causing a change in flux and energy efficiency. Such effects need to be accounted for when scaling up from laboratory data to full scale design, because there may be significant differences in the applied pressure. Therefore, in this paper, the influence of pressure on the flux of the compressible PTFE membrane was modelled. This paper also provides a mathematical method to correlate the applied pressures with physical structure changes based on the assumption of constant tortuosity. The modelling results were compared with experimental results over a range of variable process parameters, i.e., temperatures, velocities, membrane lengths, and pressure applied to the membrane. The errors between the model predictions and experimental results were less than 10% within the operating range used in this investigation. [Copyright &y& Elsevier]

Highlights • The optimal pitch ratio of the ribs mounted in a channel is provided based on inverse analysis. • The entransy dissipation was taken as the objective function in the inverse method. • Taking entransy dissipation as objective function leads to a fast and stable convergence process. Abstract The ribbed surface is a widely used convection heat transfer enhancement technology. The geometric parameters of the ribbed surface have great influences on its heat transfer performance. It is crucial to determine the optimum geometric parameters. In the present work, the optimal arrangement of ribs mounted in a rectangular channel is provided by solving the inverse optimization problem with the entransy dissipation as the objective function. The parameter analysis based on the direct solution is firstly carried out to get an approximate range near the optimal pitch ratio which can provide the initial value for the inverse optimization problem; afterwards, the inverse optimization problem is solved by a modified simplified conjugate gradient method, and the accurate optimal pitch ratio is obtained; finally the optimization results are discussed in detail. The results indicate that, (1) the inverse optimization analysis presented in this paper can provide an accurate optimal value of the pitch ratio; (2) taking the entransy dissipation as the objective function could lead to a faster converge process and give a more stable result than taking the temperature data as the objective function; (3) the optimal value under the fixed heat flux boundary condition is slightly larger than that under the fixed temperature boundary condition. [ABSTRACT FROM AUTHOR]

Abstract: Based on the problem of underground vertical U-tube heat exchangers in ground source heat pump systems in Shenchi station of Shuohuang railway, the transient heat transfer physical and mathematical model of the soil and borehole temperature field is established. Finite element numerical simulation is made by virtue of MATLAB software. Through the method of numerical simulation, the paper analyzes the soil temperature, obtains the distribution of isotherms around the pipes and the scope of the heat transfer, and understands the heat transfer performance around the pipe intuitively. Based on the model and numerical solution, the paper analyzes the changes of temperature field about the soil around ground heat exchangers in different ways which involve geological conditions operating mode, layout, pipe depth, and pipe coupling interval situation, and then the dates are obtained to help the engineering design of ground heat exchangers. [Copyright &y& Elsevier]

Abstract: Snow cover is a common and relatively stable land cover condition in winter for cold north regions in China. Snow cover has significant effects on water and heat transfers in frozen soil; it needs to be considered in the study of frozen soil water–heat coupled movements. On the basis of previous research results and physical process analysis of water and heat movements in snow cover and soil, a snow cover–soil union water–heat coupled movements model is established in this paper. The numerical simulation was conducted by using a finite difference method. The results indicate that the simulated values have a similar trend to the measured values and the numerical simulation had big relative errors. However, the average absolute errors of the total and liquid moisture content in frozen soil were all less than 4%, and that of the frozen soil temperature was 1.37 °C. The errors of the numerical simulation were still within the acceptable range. Thus, the snow cover–soil union water–heat coupled movement model constructed in this paper is rational. [Copyright &y& Elsevier]

Abstract: This paper explores the through-/in-plane characteristics of water transport in the cathode gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC). Theoretical analysis is performed on the non-isothermal two-phase flow under flow channels. A dimensionless group Da (Damkohler number for PEFC operation), defined as the ratio of water generation rate to water vapor-phase removal rate, is formulated to characterize the flow regimes in a PEFC. This group, lumping geometrical parameters and physical properties, compares the water vapor-phase removal capability (via water diffusion and holding capacity) with the rate of water production by the oxygen reduction reaction. We find that this dimensionless group can be used to characterize the non-isothermal, two-phase phenomena: when Da→0, the fuel cell is subjected to single-phase operation; while as Da→∞ we have full two-phase operation. A more precise expression is explored for the dimensionless group at the channel central line, i.e. Da 0: when Da 0>1 the entire cathode GDL–CL (catalyst layer) interface is in two-phase region, whereas part of the interface is free of liquid water for Da 0<1. The latter scenario is the concept that this paper proposes for improving fuel cell water management: the consequent co-occurrence of single- and two-phase flows in the in-plane direction at Da 0<1 is beneficial to avoid severe dryout and flooding. A two-phase transport model, describing the water and heat transport on the PEFC cathode side, is employed to perform a two-dimensional numerical study. Detailed liquid and temperature distributions are displayed. Simulation predictions are in reasonably good agreement with the dimensionless-group analysis. [Copyright &y& Elsevier]

Abstract: An experimental investigation has begun concerning the hygrothermal behaviour of wooden frame houses. The experimental set-up, consisting in a full-scale wooden frame house exposed to natural exterior climate is presented in the paper. It is located in Grenoble (South-East of France), and is equipped with over 150 sensors in order to collect a large amount of data (temperatures, relative humidity). The experimental data presented in the paper enable to get better understanding of coupled hygrothermal phenomena, and can be used to allow the validation of numerical models for heat, air and moisture transfers in wooden frame buildings. The analysed results demonstrate the importance of temperature-driven moisture diffusion from hygroscopic panelling. [Copyright &y& Elsevier]

In numerical heat transfer, the model validation problem with respect to epistemic uncertainty, where only a small amount of experimental information is available, has been recognized as a challenging issue. To overcome the drawback of traditional probabilistic methods in dealing with limited data, this paper proposes a novel model validation approach by using evidence theory. First, the evidence variables are adopted to characterize the uncertain input parameters, where the focal elements are expressed as mutually connected intervals with basic probability assignment (BPA). In the subsequent process of predicting response focal elements, an interval collocation analysis method with small computational cost is presented. By combining the response BPAs in both experimental measurements and numerical predictions, a new parameter calibration method is then developed to further improve the accuracy of computational model. Meanwhile, an evidence-theory-based model validation metric is defined to test the model credibility. Eventually, the famous Sandia thermal challenge problem is utilized to verify the feasibility of presented model validation method in engineering application. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the application of exergy analysis to human heat and mass exchange with the indoor environment. The basis for this paper is the existence of a formal similarity between the parameters defining human heat and mass transfer governed by physiological processes and the parameters defining exergy destruction. Basic heat and mass transfer is calculated using a standard two-node human physiological model. To enable an exergy analysis the model was divided according to heat and mass transfer over appropriate boundaries. The exergy analysis was performed for each process with regard to the type of exergy that participates in heat and mass exchange with respect to the indoor environment. The results provide insight into the complex interactions between the human body and environment as characterized by exergy destruction. Furthermore, the analysis indicates that at given physiological parameters only a certain combination of environmental conditions ensures minimal exergy destruction. These environmental and human conditions coincide with expected level of thermal comfort. [ABSTRACT FROM AUTHOR]

Abstract: In the last years, there has been a rapid growth of research and development activities on high temperature molten salts for nuclear and non-nuclear applications. The study of their heat transfer characteristics is a key issue in the current development of the molten salt reactor (MSR) that is one of the innovative nuclear reactors proposed by the Generation IV International Forum. The MSR is a sort of circulating fuel reactor (CFR), which adopts a molten halide salt mixture containing the fissile material and playing the distinctive role of both fuel and coolant. In a thermal-neutron-spectrum MSR, the reactor core is composed by a graphite matrix (neutron moderator), through which the liquid nuclear fuel flows and leads to a strong and intrinsic coupling between thermo-hydrodynamics and neutronics. This peculiar feature requires a suitable and qualified multi-physics simulation environment for a proper description of the system (fuel/coolant+graphite) behaviour. With reference to such complex and non-linear system, the present work is intended to give two different but linked contributions, in the perspective of a multi-physics modelling able to accurately describe the synergy of the involved different physical phenomena (e.g., by means of software). [(I)] On one hand, this work is aimed at establishing a useful validation framework for the assessment of computational fluid-dynamics (CFD) analyses of liquids with internal heat generation. For this purpose, an analytic approach for both fluid velocity and temperature fields in a circular pipe surrounded by a solid region has been developed. It is an extension of the approach elaborated for pipe flow in (Di Marcello, V., Cammi, A., Luzzi, L., 2010. A generalized approach to heat transfer in pipe flow with internal heat generation. Chemical Engineering Science 65, 1301−1310), in order to take into account the heat conduction in the solid domain (represented by the graphite matrix in the specific case of interest). [(II)] On the other hand, the paper presents a preliminary investigation of the thermal-hydraulic behaviour occurring in a typical graphite-moderated MSR core channel. The developed analytic approach has been conveniently applied to this case study: (i) by testing the capabilities of to evaluate the heat transfer characteristics and the hydrodynamic behaviour of such system; and (ii) by investigating the applicability of correlations for the Nusselt number to fluids with internal heat generation. For a deeper insight into the numerical solutions provided by COMSOL, a code-to-code comparison has been also carried out, adopting a dedicated CFD finite volume software (i.e., FLUENT®). As a result, a satisfactory agreement has been found between the analytic solution and the numerical computations provided by COMSOL and FLUENT for a wide range of Reynolds numbers. As concerns the Nusselt number evaluation, the correlations usually adopted for molten salts have been proved as unsuitable for the analysed system, whereas the correlation advanced in the above mentioned paper (that explicitly takes account of the internal heat source) appears more appropriate. The results of the present work are thought to be useful because they provide: (i) a “generalized” analytic approach to the heat transfer that is applicable in a more general context; (ii) an insight into the heat transfer characteristics of the considered graphite-moderated MSR core channel; and (iii) a preliminary assessment of computations that is essential in view of the adoption of multi-physics tools (like COMSOL) for more complex and representative simulations of the dynamic behaviour of the molten salt reactor, and more in general of other kinds of CFRs. [Copyright &y& Elsevier]

Abstract: Mathematical modeling of the convective processes caused by impact of various forces on the fluid and gas media is rather important nowadays. The increased interest to these problems is caused also by the preparation of experiments on the International Space Station in the frame of the scientific project “Convection and Interfacial Mass Exchange” (CIMEX) of the European Space Agency. They are the experiments to investigate the convective flows of the fluids with a thermocapillary interface between liquid and gas phases. In the case, when a gas flow generates the tangential stresses on a free boundary of liquid, the additional characteristics of the convective flows should be identified. In this paper a stationary coupled problem of gravitational, thermocapillary convection in a horizontal layer with free boundary under conditions of a co-current gas flow is studied. The kinematic and dynamic conditions are fulfilled exactly on the gas–liquid interface. The exact solutions for different types of thermal boundary conditions have been obtained. An evaporation effect through the gas–liquid interface is modeled qualitatively with the help of a heat transfer condition. It has been found that the direction of the velocity at the gas–liquid interface is determined by the governing parameters. The equal-zero condition for the interface velocity has been found, as well. The paper presents the velocity and temperature profiles in the conditions, which correspond qualitatively to the CIMEX experiments. [Copyright &y& Elsevier]

Abstract: Thermodynamic optimization models of gas-hydrate cool storage and cool release processes are established in this paper. The optimal temperature configuration at the sensible heat transfer stage and the optimal gas hydrate phase change rate configuration at the phase change stage in the processes of gas hydrate charging and discharging are obtained by taking entropy generation minimization as optimization objective. The optimal control strategies of the cool storage system are determined. The research results indicate that the optimal operating characteristic of the gas-hydrate cool storage system can be achieved by keeping the phase change rates uniform, which are regulated and controlled according to constant heat transfer rates in the charging and discharging processes of gas hydrate. The analysis method and the results presented in this paper can provide important guidelines for optimal design and operation of gas-hydrate cool storage system. [Copyright &y& Elsevier]

Abstract: We present a two-phase multiscale solidification model, which accounts for coupled heat, mass, solute and momentum transfer and notably describes the motion of globular equiaxed grains. On the microscopic scale the model takes into account nucleation, finite diffusion in both solid and liquid phases, and resolves the diffusion-controlled phase change by a solute balance at the solid–liquid interface coupled with a thermodynamic equilibrium condition for the interface. The main idea of the paper is the solution algorithm of the multiscale model. We propose and present in detail an operator splitting method that resolves the global conservation equations in two stages. In the first solution stage we resolve and integrate globally only the convection terms. In the second solution stage we resolve and integrate locally the contributions of the grain growth kinetics, i.e. the phase change and the microscopic diffusion. We analyze this splitting method based on a scaling analysis that shows that the justification of the method stems from the separation of time scales of convection, diffusion and phase change. We discuss this scale separation in detail and define a test case that is presented and analyzed in a companion paper. [Copyright &y& Elsevier]

Abstract: This paper presents a numerical study on laminar forced convection of water in offset strip-fin microchannels network heat sinks for microelectronic cooling. A 3-dimensional mathematical model, consisting of N–S equations and energy conservation equation, with the conjugate heat transfer between the heat sink base and liquid coolant taken into consideration is solved numerically. The heat transfer and fluid flow characteristics in offset strip-fin microchannels heat sinks are analyzed and the heat transfer enhancement mechanism is discussed. Effects of geometric size of strip-fin on the heat sink performance are investigated. It is found that there is an optimal strip-fin size to minimize the pressure drop or pumping power on the constraint condition of maximum wall temperature, and this optimal size depends on the input heat flux and the maximum wall temperature. The results of this paper are helpful to the design and optimization of offset strip-fin microchannel heat sinks for microelectronic cooling. [Copyright &y& Elsevier]

Abstract: Enthalpy exchangers have been used as an efficient means to recover both sensible heat and moisture from exhaust ventilation air. A cross-flow plate-fin structure is the most popular arrangement for the exchanger core due to its compactness and high mechanical strength even with very small channel wall thickness. Traditionally, hygroscopic paper is selected as the plate and fin materials. Though the sensible effectiveness with this material is satisfactorily high, the latent effectiveness is disappointingly low due to the low moisture diffusivity in paper. To solve this problem, in this study, a novel concept is proposed to augment moisture transfer in the exchanger. Plates and fins are made with different materials. A novel membrane – the composite supported liquid membrane (CSLM) is used as the plate material. Paper is still used as the fin material for its cheapness and high support strength. To make comparisons, two cores, one is paper-fin and paper-plate, and another one is paper-fin and membrane-plate, are constructed and tested for heat and moisture recovery. Simultaneous heat and moisture transfer in the plate-fin core is studied. Mathematical model governing the heat and moisture transfer in the cores is set up and numerically solved. Both the experimental data and numerical results indicate that the latent effectiveness of the paper-fin and membrane-plate core is 60% higher than the traditional paper-fin and paper-plate core, due to the high moisture diffusivity in the CSLM. [Copyright &y& Elsevier]

Abstract: Agricultural residues (agro-biomass) can produce energy by thermochemical conversion. Gasification is becoming one of the best clean technologies for power production. Thermochemical process of gasification sets free the solid fuel inherent energy and converts the solid phase into a mixture of gases (producer gas or syngas) that carries a percentage of this energy. Fluidized bed reactors may be used for biomass gasification offering many advantages such as: (1) the superior mixing properties and (2) the enhanced heat transfer rates between the gas and the particles as well as between the particles and the heat exchanger surfaces. In this paper gasification process applied to agricultural residues is reviewed by means of modelling. Description of various stages of the biomass gasification in a fluidized bed is made and the whole spectrum of problems from the processes in an individual biomass particle (drying, pyrolysis, fragmentation and charl burning) to the global mass transfer and chemical processes in a fluidized bed reactor and freeboard is presented. The paper discusses also the specific problems arising from using agricultural residues as raw material and recommends further experimental studies necessary for process optimisation and for scale up. Extensive investigation of gasification plant behaviour depending on various operating parameters is always required in order to support the optimisation procedure and mathematical models are helpful to reduce the temporal and financial efforts. [Copyright &y& Elsevier]

Abstract: The thermal problem defined for the validation challenge workshop involves a simple one-dimensional slab geometry with a defined heat flux at the front face, adiabatic conditions at the rear face, and a provided baseline predictive simulation model to be used to simulate the time-dependent heatup of the slab. This paper will discuss a clustering methodology using a surrogate heat transfer algorithm that allows propagation of the uncertainties in the model parameters using a very limited series of full simulations. This clustering methodology can be used when the predictive model to be run is very expensive, and only a few simulation runs are possible. A series of time-dependent statistical comparisons designed to validate the model against experimental data provided in the problem formulation will also be presented, and limitations of the approach discussed. The purpose of this paper is to represent methods of propagation of uncertainty with limited computer runs, validation with uncertain data, and decision-making under uncertainty. The final results of the analysis indicate that the there is approximately 95% confidence that the regulatory criteria under consideration would be failed given the high level of physical data provided. [Copyright &y& Elsevier]

Abstract: In this paper, the porous NiTi shape memory alloy (SMA) fabricated by self-propagating high-temperature synthesis (SHS) has been investigated experimentally and numerically. The mathematical models about the ignition and the sintering were constructed to investigate the effect of the preheating temperature and the coil temperature on the combustion. The results showed that the temperature difference between the ignition face and the bottom face was large due to low heat transfer conductivity. The ignition time would increase with the decrease of the coil temperature and the preheating temperature. The temperatures for different locations showed a strong dependence on the combustion time for lower preheating temperature, for the preheating temperature 1173K, this mode of the combustion has transferred from SHS to thermal explosion. The transient partial molten phenomenon occurred during the process of combustion, which was more homogenous for preheating temperature 873K. The mean velocity of the combustion wave was investigated systematically. An experiment was also carried out to investigate the ignition and SHS reaction for porous NiTi alloy in this paper. It was found that the results of experiment and numerical simulation were shown in good consistence. [Copyright &y& Elsevier]

Abstract: A sequence of mathematical models describing the electrothermal ribbon printing process is developed. The models describe the electrical processes, heat generation and heat transfer within the ribbon and the transfer of ink from the ribbon to paper. Account has been taken of the nonlinear electrical properties of the ribbon. A model of the paper surface has been developed in order to model the transfer of the ink from the ribbon to the paper. The partial differential equations describing the electric field, the heat flow and the stresses in the ink have been solved using standard techniques. [Copyright &y& Elsevier]

Abstract: This paper deals with the modeling of the thermal field during machining processes by laser beam local heating. The analysis refers to the identification of mathematical models suitable to describe the large variety of complex phenomena which occur during the machining process. Specifically, this paper provides the modelling assessment to deal with the solution of mathematical problems toward simulation and with specific engineering applications related to the above technological system. [Copyright &y& Elsevier]

In this paper, integral mathematic model of fluid flow and heat transfer of GTAW arc and weld pool was established. This model built in this paper may avoid the assumption which surface temperature of weld pool is constant and at the same time provide reliable boundary conditions for analyzing of weld pool. Using finite element analysis software ANSYS, behavior of welding arc and weld pool was systematically analyzed including welding arc temperature field, current density distribution, fluid flow in weld pool and effects of a few forces on weld pool shape. The calculated results were proved by experiments. [Copyright &y& Elsevier]

• The desirable operating conditions to achieve high operational efficiency are obtained. • The performance of the IEC under different operating conditions is investigated. • The mathematical model is validated against published data. • The optimal dimensions that give good efficiency in climates with moderate humidity are highlighted. [Display omitted] This paper presents a study investigating and analyzing the effect of heat and mass exchanger (HMX) dimensions and the flow parameters on the indirect evaporative cooler (IEC) system's performance. For this purpose, a mathematical model based on heat and mass transfer concepts was developed, and the model was verified using experimental and simulation results from published papers. Simulations were performed based on different operating and structural conditions affecting the outlet air temperature, cooling capacity, coefficient of performance, and wet-bulb efficiency. Results showed that the optimal dimensions that give good efficiency in climates with moderate humidity, the length of the duct should be between 0.6 to 1.0 m , the width of the channel between 0.3 to 0.5 m , and the channel gap between 0.004 to 0.008 m. It has also been observed that the increasing working air velocity has a positive effect on cooling performance, and its velocity should not be less than 1 m / s. As for increasing the product air velocity, it reduces the heat exchange period, which is undesirable, so it should not exceed 1 m / s. The prescribed flow rate ratio between product and working air should be 0.3 to 0.5. This analysis provides desirable operating conditions to achieve high operational efficiency as well as optimal dimensions for designing such a cooler. [ABSTRACT FROM AUTHOR]