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In this paper the aerothermal heating of a reusable launch vehicle is reconstructed on the basis of temperature measurements taken in the thermal protection system of this vehicle. The discussed integrated thermal protection system is composed of three layers. Mathematical model, describing the problem, takes into account the dependence on temperature of the material parameters as well as the thermal resistances occurring in the contact zones of the layers, which is a novelty in the proposed approach. For solving the direct problem, the implicit scheme of the finite difference method is applied. Next, by using the solution of the direct problem, the Tikhonov functional is created, which describes the error of the current approximate solution. Whereas for determining the solution of the inverse problem the Levenberg-Marquardt method, modified and adapted to the Tikhonov functional, is used. The paper presents the mathematical model of the problem and the method of solution together with the selected examples illustrating its exactness and stability. In order to better examination of the solution method some various values of parameters are taken in the demonstrated examples. • Reconstructing an aerothermal heating in space vehicle protection system with temperature dependent material properties. • Reconstructing an aerothermal heating taking into account the thermal resistance between layers. • Solving the problem for three layers model of the thermal protection system. • Inverse problem solved for input data taken from NASA measurements. • Heat flux measured by NASA reconstructed with good precision and stability. [ABSTRACT FROM AUTHOR]

In the state of the art of steel production, the temperature evolution of steel strips is typically controlled to regulate the phase contents indirectly and, with this, their material properties. This paper proposes a novel computationally efficient, real-time capable dynamic model that captures both the temperature evolution and the phase transformations in the steel strip. The steel strip is processed in a cooling section after a continuous annealing furnace. The phase transformations cover the austenite decomposition which is mainly controlled by specifically decreasing the temperature during the cooling process. For this, a phenomenological state-space model is derived, which is inspired by the Johnson-Mehl-Avrami-Kolmogorov and the Koistinen-Marburger model. Phase transformations generally change the specific latent heat of the material, which is captured in the proposed distributed-parameter model of the strip temperature by an energy balance. Lumped-parameter models are used for the temperature evolution of the wall, the rolls, and the radiant tubes. Heat transfer due to convection, radiation, and conduction couple the individual thermal submodels. A comparison of simulation results and measurements from both experimental material tests and the real plant operation demonstrate the accuracy and feasibility of the proposed model. The model is computationally inexpensive and serves as a solid basis for advanced real-time control and optimization. • A mathematical model is proposed to describe the evolution of temperature and phases in a steel strip during cooling. • The austenite decomposition is captured by a phenomenological phase transformation model. • The model is computationally efficient and real-time capable. • The accuracy and the suitability of the proposed model is demonstrated by comparing simulation results with measurements. [ABSTRACT FROM AUTHOR]

• Evolution and disappearance of condensation of R507A refrigerant in pipe mini-channels. • Condensation process occurring in mini-channels. • Comparison of the results of experimental studies with R404A obtained for R507A. • Proposition of a regression function for the description of dynamic instability. This paper presents the results of experimental research and mathematical modelling on the influence of dynamic instabilities on the condensation phase change of R507 refrigerant in tubular mini-channels. This agent is currently being utilised as a temporary substitute for R404A, with R448A intended as the target substitute. In addition to the results, this paper contains a dimensional analysis procedure based on the Π-Buckingham theorem that has allowed for the development of a regressive model for the velocities of the dynamic instabilities. The experimental part of this paper was conducted using tubular mini-channels with internal diameters of 1.44, 2.3, and 3.3 mm. [ABSTRACT FROM AUTHOR]

Experimental data demonstrates that the breakthrough curves of column adsorption exhibit qualitative differences related to the size of the adsorbent particles. Standard models do not account for particle size, consequently, in this paper we develop a new formulation that incorporates the diffusion of the adsorbate into the adsorbent particles. Two kinetic models are considered, Langmuir adsorption and a linear driving force. Approximate analytical solutions are developed for these two models coupled to mass flow and intra-particle diffusion equations. The accuracy of the analytical solutions is verified through comparison with numerical solutions of the full mathematical model. Comparison with experimental data confirms that the new analytical solutions show better agreement than previous models. However, in certain cases, neither form of model predicts the behaviour suggesting a combination of different effects contribute to the breakthrough form. • Mathematical model for column adsorption including particle size effect. • Simple analytical expressions for breakthrough concentration. • Good agreement with a variety of experimental data. [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]

In the context of geothermal applications, the thermal response of the ground is a primary concern. Many models use the concept of g-function introduced by Eskilson in the eighties. These functions were associated with a special field arrangement and libraries of tabulated values were pre-calculated and made available for simulation. In order to increase the flexibility, several analytical models were recently proposed and the model of Cimmino and Bernier is the most precise of such models. In their approach, they split each borehole into segments where they assume an unknown constant heat flux. In this paper, we modify their approach where we replace the piecewise-constant heat flux profile assumption by a piecewise-linear distribution. Doing so, it is possible to achieve the same precision with fewer segments in the model. The model needs however a new mathematical treatment of the thermal response which is developed in the present paper. Comparison between both approaches and original Eskison g-function is done. [ABSTRACT FROM AUTHOR]

• Analytical solution describing fluid extraction from an adsorption column. • Excellent agreement with a range of experimental data. • Proof that previous accepted models do not work. • Demonstration that to accurately characterise experiments both breakthrough and isotherm data are required. • Development of a novel analytical solution including a SIPS mass sink. In this paper we investigate the standard one-dimensional model for adsorption of a contaminant in a packed column. Initially we focus on two mass sink models: a full nonlinear Langmuir equation, including adsorption and desorption and the linearised version which neglects the local concentration. Travelling wave solutions are developed for both cases, providing exact analytical formulae for the concentration and adsorbed fraction throughout the column. Comparison is made with experimental data for the adsorption of toluene on activated carbon (dominated by physical adsorption) and Cr(III) on zeolite NaX (dominated by ion exchange). For toluene the nonlinear model provides good agreement but it is less accurate for Cr(III). The linear model apparently works well for Cr(III) but only at the expense of violating the model assumptions. This motivates extending the travelling wave solution to a Sips sink model, which has a power law dependence on local concentration. Comparison with data provides excellent agreement in all cases and also indicates why the previous models fail. Following from the investigation of the linear sink model, we prove that previously accepted results frequently fail due to a violation of assumptions made in their derivation. Specifically we challenge the belief that widely used models such as Bohart–Adams, Yoon–Nelson, Bed Depth Service Time, etc can accurately predict breakthrough data. Their success instead may be attributed to: at times, having a similar shape to the breakthrough curve rather than being the correct solution; treating measurable quantities as fitting parameters and a willingness to accept that constant parameters vary. In contrast to these previous models, the travelling wave solution of the present paper, based on a Sips sink, provides analytical solutions consistent with the model assumptions for a wide range of experimental data. [ABSTRACT FROM AUTHOR]

• A model was developed for forced convection condensation in the presence of air. • Condensation influences the mixture flow only through the boundary condition. • The proposed model was verified using published experimental data. • The tube bundle case was viewed as more closely reflecting industrial devices. This paper presents a description and the results of verification of an unsteady model for forced convection condensation on a smooth single horizontal tube in the presence of noncondensables. The external flow is described by the two-dimensional (2D) unsteady Navier–Stokes equations for a laminar regime or by the unsteady Reynolds-averaged Navier–Stokes (URANS) equations for a turbulent regime, and the condensate film is considered using a one-dimensional model. Details of the numerical implementation of the developed algorithm are described. The available literature data were employed to verify the proposed model for forced convection condensation for an arbitrary flow direction of vapour with and without noncondensables. The numerical results are in good agreement with the published experimental data. In the proposed model, condensation influences the air-vapour mixture flow only through the boundary condition; therefore, this model can be easily implemented using different computational fluid dynamics (CFD) codes (in this work, an "in-house" CFD code ANES) for modelling more complex configurations, like tube bundles. Results for condensation on five tubes in a tube bundle are also presented in this work. The influence of mutual irrigation of pipes by drops coming off was also approximated. [ABSTRACT FROM AUTHOR]

• The thermodynamic compatibility of initial conditions is investigated. • Analytical solutions of the Guyer-Krumhansl equation is provided. • The maximum principle for the Guyer-Krumhansl equation is proved. • The results are supported by computational calculations. In the literature, one can find numerous heat conduction models with different backgrounds. In general, a heat equation beyond Fourier consists of additional time and spatial derivatives, which makes it more challenging to solve the mathematical model correctly. In the present paper, we revisit the famous Guyer-Krumhansl heat equation for which it has been reported earlier that can lead to negative temperatures by violating the maximum principle. We show that for proper initial and boundary conditions with thermodynamic compatibility, the maximum principle is fulfilled. Our work further emphasizes the importance of the thermodynamic origin of heat equations and their compatibility with the second law. Furthermore, we use two different approaches how to determine the initial state in a thermodynamically compatible way. Computational simulations support our results. [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]

• The application of the cold plate device to thermal management has evolved in the past fifty years from the cooling of computer chips to aviation thermal management, which is the application of interest in this paper. Numerical solution procedures for performance analysis of the device are currently being used in a commercial software package for automotive and aviation thermal management. A major objective of the present paper is to report on an elaborate and successful experimental work carried out at The Boeing Aerospace company for the purpose of validating the software package. For this purpose, powder fusion additive manufacturing (AM) procedures were used to build metallic cold plate test articles. The excellent agreement between the software predictions and measured performance provides confidence in the implementation of the software package. Additional relevant results are provided in the paper on the thermalhydraulic performance analysis of cold plates for aviation thermal management. This study, which has been motivated by the recent applications of the cold plate device in aviation thermal management, reports on physics-based mathematical models derived from the conservation laws of mass, momentum, and energy, and empiricism-based models. One of the objectives of the present work is to report on an elaborate and successful experimental work carried out on an additively manufactured device for the purpose of rigorously validating the numerical predictions. The excellent agreement between the numerical predictions and measured performance provides much needed confidence in the implementation, in the software package, of the offset-strip fin passage correlations, as well as in the software implementation of user-defined wavy fin correlations for aerospace heat exchangers and cold plates operating with ram air at Reynolds numbers below 8000. The contributions of this work can also be found in the development of a new and accurate thermal-hydraulic analysis procedure, referred to in this paper as plate-fin analogy. Results from this procedure are compared with those from thermal resistance network. The comparative study in this paper of the bulk and discrete enthalpy flux method is also new, as is the relative assessment of four off-set strip fin thermal-hydraulic models. [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]

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]

Highlights • The Constructal law is applied to thermochemical energy storage design. • Equipartition of imperfections leads to several layers of reacting salt. • The best design meets overall performance and compactness objectives. Abstract This paper documents an analytical and numerical study of thermochemical energy storage in an open reactor. The analysis of the pressure losses and temperature distributions allows to predict what the geometrical features of the reactor should be. A numerical model simulating the thermochemical process is then presented and validated. In accord with the Constructal design methodology, the module configuration is morphed following the trends obtained in the analytical part, to head for better overall performances. The results show that the ratio between the heat produced by the chemical reaction within the entire module and the overall pumping power necessary to blow the fluid through the module increases as the imperfections reach equipartition. In terms of module configuration, this means (i) an increase in the number of salt layers and (ii) aspect ratios moving the module volume towards more compactness. [ABSTRACT FROM AUTHOR]

Highlights • A novel spacetime meshless method for solving the backward heat conduction problem. • Numerical approximation using the Trefftz basis function of the heat equation. • Collocating the boundary points in the spacetime coordinate system in the Trefftz method. • Highly accurate numerical solutions can be obtained comparing to that from conventional time-marching scheme. • Boundary data on the inaccessible boundary can be recovered even the partial data on the final time boundary are absent. Abstract This paper presents a novel space–time meshless method for solving the backward heat conduction problem (BHCP). A numerical approximation is obtained using the Trefftz basis function of the heat equation. The Trefftz method, which differs from conventional collocation methods based on a set of unstructured points in space, is used in this study to collocate boundary points in the space–time coordinate system such that the initial and boundary conditions can both be treated as boundary conditions on the space–time domain boundary. Because the solution in time on the boundary of the domain is unknown, the BHCP can be transformed into an inverse boundary value problem. The numerical solution is obtained by superpositioning the Trefftz base functions that automatically satisfy the governing equation. The validity of the proposed method is established for several test problems, including the one-dimensional BHCP and two-dimensional BHCP. The accuracy of the proposed method is compared with that of a conventional time-marching scheme based on the finite difference method. The results demonstrate that highly accurate numerical solutions can be obtained and errors may not accumulate over the entire time domain. Moreover, the boundary data on the inaccessible boundary can be recovered even when the partial data on the final time boundary are absent. [ABSTRACT FROM AUTHOR]

Highlights • 1-D freezing behavior assessment of ice-rich sandy soil considering the phase change of water. • Numerical simulation model shows reliable prediction results for 1-D freezing test. • Freezing behavior of ice-rich sandy soil are dependent on various geotechnical properties. • The larger the porosity of the specimen, the greater the increase in the time for fully frozen. • Height of specimen has the greatest impact on the time for fully frozen. Abstract This paper evaluates a methodology that enables one-dimensional freezing to make a homogeneous frozen soil specimen. Numerical analyses that simulate one-dimensional freezing are conducted, considering the phase change of pore water. After evaluating the applicability of the numerical analysis model, the effects of geotechnical characteristics on the freezing behavior of ice-rich sandy soil are evaluated through parametric studies. In addition, a nonlinear regression model is proposed that can predict the time required for complete freezing of saturated soil. According to the results from nonlinear regression analysis, the model demonstrates reliable accuracy (R2 = 0.998) in predicting the amount of time required for complete freezing, even with data from testing datasets not used in the developing stage. [ABSTRACT FROM AUTHOR]

Highlights • PCM flat-plate solar collector system with antifreeze characteristics is proposed. • A mathematical model for the system is present. • The antifreeze performance of the system is analyzed. • Factors influencing the performance of the system are investigated. Abstract This paper proposes a flat-plate solar collector system (FPSCs) with antifreeze characteristics which uses the phase change material (PCM) to store up a moderate amount of thermal energy during the daytime and release the energy during the night to prevent the FPSCs from freezing damage. Previous studies about the FPSCs exploiting the PCM are mainly focus on the purpose of balancing the tank water temperature between the daytime and night. In the present work, the study on the characteristics of the PCM-FPSCs for the purpose of antifreeze has been conducted. A mathematical model with high precision for the daytime working and night freezing of the system is present. The daytime working and night antifreeze performance of the system are evaluated. The results show that the conventional FPSC system will get frozen when the daily average temperature is less than 5 °C. The PA-FPSC system can work when the daily average temperature is in the range of 0–5 °C. [ABSTRACT FROM AUTHOR]

Highlights • An electrical heating method to enhance shale gas production is proposed. • A mathematical model of shale gas production by electrical heating is developed. • The effects of parameters on gas production are investigated by numerical simulation. • Numerical simulation suggests that electrical heating method has a good performance to enhance shale gas recovery. Abstract Gas production from shale gas reservoirs can be enhanced by increasing the temperature of the reservoirs due to the increased desorption of the adsorbed gas. However, limited techniques are currently available for practically introducing heat into such low permeability reservoirs. This paper investigates the feasibility of an electrical resistance heating method to promote shale gas production by increasing the temperature of the reservoirs. To achieve our research goal, a mechanistic numerical model is developed to describe electrical field, temperature field, and pressure field. To capture gas flow in a shale gas reservoir, non-linear flow, diffusion and adsorption/desorption which are all dependent on temperature are incorporated into a dual continuum media model. In our study, the gas production enhancement by electrical heating with two parallel horizontal electrode wells is evaluated using this model. We then assess impacts of the thermal properties of the formation, electrode length, electrical power, Langmuir volume and starting time of heating on gas production. The results indicate that the electrical heating method using two parallel horizontal electrodes can be an efficient method to enhance shale gas production. The heat capacity and conductivity of the formation have significant impacts on gas production. Reservoirs with low conductivity and low heat capacity tend to produce more gas due to heating. Meanwhile, shale gas reservoirs with high Langmuir volume also tend to yield more gas due to heating for. To maximize gas production, electrical power should be optimized based on the properties of shale gas reservoir and heating equipment. Longer electrodes heat more formations of the reservoir and thus lead to higher gas production by using the electrical heating method. In order to efficiently enhance shale gas production, electrical heating should start later in gas production, instead of earlier. [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]

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]

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]

The transient response of heat exchangers plays a significant role in the time-dependent performance of thermal management systems, particularly in resource-limited situations with high power density and fast-acting heat sources. A scaled thermal management testbed with a plate-frame heat exchanger was built to emulate a thermal subsystem. This paper describes a methodology for dynamically characterizing the behavior of a commercial, off-the-shelf plate-frame heat exchanger both experimentally and computationally. Statistical design of experiments principles was used to develop a test plan composed of 20 test cases for dynamic model validation. The dynamic performance of the heat exchanger was evaluated with a physics-based model, and statistical surrogate models were derived from the experimental results. Additionally, a lumped mass model was employed to determine the dynamic parameters of the heat exchanger using the experimental data. The model efficiently and accurately predicts the experimental results across the entire experimental exploration space. The lumped mass model predicts the transient response without using computationally expensive resources such as a full numerical, thermo-fluid dynamic solvers. This approach has significant implications for developing practical models of thermal components particularly for the field of thermal controls. [ABSTRACT FROM AUTHOR]

The complexity of thermal management increases as integrated circuits evolved into 3D architectures. Because of the large variation that exists in the thermal conductivity of materials and the geometrical size of structures in the 3D-stacked IC (3D-SIC) network, the extensive computational costs typically render a full-chip-scale numerical simulation impossible. Thus, this paper proposes a fast and implementable full-chip-scale numerical simulation method for thermal management of 3D-SIC. A compact thermal resistance network, with both lateral and vertical heat dissipations considered, is analyzed to establish an accurate anisotropic equivalent thermal conductivity model. The key heat dissipation component, the high thermal conduction path (HTCP) constructed using through-silicon vias (TSVs), micro-bumps, and Cu wires in the redistribution layer (RDL), is fully analyzed by modeling a compact thermal resistance network. The equivalent thermal conductivity of each stacked layer is extracted in blocks from the network and then applied in a finite element calculation for full-chip-scale numerical simulation. Three partitioning strategies to block each stacked layer are tested. As compared to the results of direct finite element simulation of a small-scale 3D-SIC, the proposed method yields improved simulation accuracy (temperature difference <7.5%) and a considerable computational cost reduction (grid number reduced by >77%). As a demonstration, the temperature distribution of a large-scale 3D-SIC with 306 TSVs and 1647 hotspots is successfully simulated within 82 min by implementing this method using a personal computer (Intel Core i5 6300HQ, 60 GB memory). [ABSTRACT FROM AUTHOR]

Despite the fact that the conventional one-dimensional model for counter-flow spray separation tower is advanced in reasonable accuracy as well as time and computational resources saving, it fails to describe the physical processes in details. In this paper, the concept of supersaturated state of the moist air was introduced, then a new sectional one-dimensional model was developed with a detailed derivation. A prototypic apparatus was set up and the reliability of the model was validated by the experimental study. When predicting the outlet solution temperature and outlet moist air wet bulb temperature, the relative errors would be more pronounced with a bigger heat and mass transfer driving potential, but they would not exceed 3.59% and 9.54% respectively under the experimental conditions. The simplifying assumptions, the ignored heat and mass transfer at cyclone region and the measuring errors are mainly blamed for the predicted errors. An in-depth heat and mass transfer investigation was conducted with the help of the validated model by studying the profiles of humidity ratio and moist air dry bulb temperature. The proposed model succeeded in capturing the state transformation of the air flow along the axis of the tower and the effects of the operating parameters on the process profiles are discussed. [ABSTRACT FROM AUTHOR]

This paper presents the mathematical model of the gas extraction from a reservoir initially saturated with methane and its hydrate, under conditions of negative (below 0 °C) initial temperature of the reservoir. The algorithm is proposed and the numerical scheme is constructed which makes it possible to find the main parameters of the nonisothermal filtration flow in a hydrate-saturated reservoir, taking into account the hydrate decomposition to gas and ice. The analysis of the influences of the mass flow rate of gas extraction, the porous medium permeability, the initial reservoir temperature, and the initial hydrate saturation on the regime and rate of the gas hydrate decomposition was carried out. [ABSTRACT FROM AUTHOR]

The present paper deals with the micromechanical modeling of the effective thermal conductivity of composite materials containing ellipsoidal inclusions with highly conducting interfaces. At these interfaces between inclusions and the surrounding medium, the temperature field is assumed continuous while the heat flux undergoes to a discontinuity. The proposed model is based on the solution of the Eshelby's inclusion problem with highly conducting interfaces. Moreover, the present study is conducted in the general case of an anisotropic thermal conductivity per phase and ellipsoidal inclusions. Results in terms of the thermal intensity field inside each phase are proposed and then analyzed in light of the effects of some model parameters. The effective thermal conductivity of the composite has been predicted through classical homogenization schemes such as the Dilute medium, the Mori-Tanaka and the Differential schemes. The model predictions have been also compared with some results provided by previous investigations. [ABSTRACT FROM AUTHOR]

A nonuniform heat generating model in a triangular area is built in this paper. Constructal optimizations of the models with constant and discrete variable cross-sectional high conductivity channels (HCCs) are performed by choosing minimum maximum temperature difference (MTD) as optimization objective. Optimal constructs of the triangular element and triangular first order assembly (TFOA) are obtained, respectively. The results indicate that for the TFOA with constant cross-sectional HCCs, the minimum MTD is reduced by increasing the nonuniform heat generating (NUHG) coefficient p , namely the heat conduction performance (HCP) is better when more heat generation is generated near the heat sink. The HCP of TFOA is also improved by increasing its complexity of internal structure. Furthermore, the minimum MTD of TFOA with discrete variable cross-sectional HCCs is reduced by 12.57% than that with constant cross-section. Therefore, the HCP of TFOA can be further improved by adopting discrete variable cross-sectional structures for the HCCs. The optimization results obtained from numerical calculations can provide some theoretical guidelines for the optimal heat dissipation designs of electronic devices. [ABSTRACT FROM AUTHOR]

This paper is the second part of a two-part study on pool boiling critical heat flux (CHF) from flat surfaces. While the first part reviewed different CHF models and associated mechanisms and parametric trends, the present part is dedicated to the assessment of both models and correlations. The assessment is based on a new consolidated CHF database consisting of 800 data points amassed from 37 sources, and includes 14 working fluids, pressures from 0.0016 to 5.2 MPa, orientation angles from 0 to 180°, and contact angles from 0 to 113°. It is shown that a modified hydrodynamic instability model and the interfacial lift-off model provide the best predictions for CHF from horizontal, upward-facing surfaces. Modified with a correlation for surface orientation effects, the same models also provide the best predictions for inclined surfaces. However, all models and correlations lose accuracy at or near the downward-facing orientation, which points to the need for more data and improved understanding of near-wall interfacial behavior for these orientations. Finally, recommendations are provided for prediction of contact angle effects. [ABSTRACT FROM AUTHOR]

The paper presents Large Eddy Simulations (LES) of mass transfer and fluid flow evolutions of a submerged rectangular free jet of air in the range of Reynolds numbers from Re  = 3400 to Re  = 22,000, with the Reynolds number, Re , defined with the hydraulic diameter of the rectangular slot, of height H. The numerical simulations are 3D for Re  = 3400 and 6800, while 2D for Re  = 10,400 and 22,000 to reduce computational time costs. The average and instant LES numerical simulations are compared with the concentration visualizations, obtained with the Particle Image Velocimetry (PIV) technique, and the fluid dynamics variables, velocity and turbulence, measured with the PIV technique and the Hot Film Anemometry (HFA). In the numerical simulations, the Schmidt number is equal to 100 to compare the air concentration in the PIV experiments, while the turbulence on the exit of the slot is equal to the value measured experimentally, and ranging between 1% and 2%. The average 2-3D LES simulations are in agreement with the concentration and the fluid dynamics experimental results in the Undisturbed Region of Flow (URF) and in the Potential Core Region (PCR), while the vortex breakdown is captured only by the 3D LES approach. As far as the instant flow evolution is concerned, the 2-3D LES simulations reproduce the Negligible Disturbances Flow (NDF), where the jet height maintains constant, and the Small Disturbances Flow (SDF), where the jet height oscillates, with contractions and enlargements, but without the vortex formation. Average and instant velocity and turbulence numerical simulations on the centreline are in good agreement to the experimental PIV measurements. [ABSTRACT FROM AUTHOR]

This paper investigates effects of geometrical and coolant flow parameters for a three-row compound angle hole design over a flat plate. These included β = +45° and −45°, in-line and staggered arrangement, hole spacing (4d, 6d and 8d), five blowing ratios (0.5–1.5) and three density ratios (1.0, 1.5, 2.0). Spanwise averaged effectiveness plots and contours were developed using Pressure-Sensitive Paint (PSP) technique and cross comparisons were carried out. The parametric results obtained from experiment generally agreed with widely accepted trends: the cascade effect of coolant jets for multi-hole design increases film effectiveness especially at large x/d, increasing density ratio increases effectiveness particularly at higher blowing ratio and increasing hole spacing has a detrimental effect on film cooling. However, some interesting observations are discovered including: staggered arrangement is not always the most optimum design (β = +45°, −45°, −45° with staggered 2 nd and 3 rd row reported the lowest effectiveness for all blowing ratios and density ratios); in-line arrangement of holes with opposing orientation angles (β = +45°, −45°, −45°) yields better effectiveness; blowing ratio effect is strongly dependent on geometric design. Moreover, hole spacing effect is closely related to neighboring coolant jet coalescence and interaction with mainstream flow. Currently, little data is available on three-row design in open literature; this study provides systematic, baseline information for future studies. [ABSTRACT FROM AUTHOR]

Flow resistance and enhanced heat transfer characteristics of TiO 2 -water nanofluids in a stainless-steel corrugated tube and a circular tube are investigated by experimental and numerical methods respectively. The flow and heat transfer characteristics of TiO 2 -water nanofluids and deionized water in test tubes are compared in this paper. In addition, effects of Reynolds number ( Re ) and nanoparticle mass fraction ( ω ) on flow and heat transfer performances are discussed respectively, and Nusselt number ( Nu ) and resistance coefficient ( f ) are studied respectively. Finally, comprehensive performance of flow resistance and heat transfer enhancement is evaluated. It can be obtained that adding nanoparticle into deionized water doesn’t cause a large additional resistance loss in some degree, while the combination of corrugated tube and TiO 2 -water nanofluids shows an excellent heat transfer enhancement, which can enhance the heat transfer by 53.95% at maximum extent. In addition, the corrugated tube has a strong sustainability in enhancing heat transfer. The enhanced heat transfer rising part (6000 ≤ Re ≤ 10,000) has a large rising slope (about 7.90E−5), and the descending slope (about 7.16E−6) of enhanced heat transfer part (10,000 ≤ Re ≤ 12,000) is small. [ABSTRACT FROM AUTHOR]

Existence of magnetic field causes heat transfer to reduce in free convection but in several engineering uses for example: electronic application; enhancing heat transfer is a purpose. Thus, nanofluid should be selected as working fluid. Nanofluid is dispersion of very small metal particles in the base fluid. Two phase and single phase are two ways for estimating the behavior of nanofluid. At first model, nanofluid suppose as homogenous fluid without any slip mechanism. But in second method, slip velocities are included. Brownian motion and Thermophoresis impacts are taken into consideration in second approach. In this paper, previous publications about nanofluid hydrothermal treatment in existence of magnetic field are reviewed. Rely of variable and constant magnetic fields, Ferrohydrodynamic (FHD) and Magnetohydrodynamic (MHD) can take role in simulations. Numerical and analytical methods are considered by authors. Results proved that temperature gradient augments with augment of solid particle concentration and buoyancy forces, while it decreases with augment of magnetic field. [ABSTRACT FROM AUTHOR]

The lattice Boltzmann method (LBM) has been used in various fluid flow analyses as an alternative to the traditional method of computational fluid dynamics. In the study reported here, the LBM was used to simulate a simple Hele–Shaw melt flow of polymers considering their actual physical properties, whereas the Carreau fluid model was used to evaluate the polymer melt viscosity. Since the Reynolds number of a polymer melt flow is typically quite low due to its high viscosity, which in turn lowers its convergence rate in the LBM, introducing a new density offset method improved that rate. In this paper, cases of simulations with pressure or velocity inlet boundary conditions are discussed in which the density offset method is applied. [ABSTRACT FROM AUTHOR]

The heterogeneous nucleation process is important for the study of the nucleate boiling of the mixed refrigerants. In this paper, the onset of heterogeneous bubble nucleation of non-azeotropic mixtures was analysed based on the change in the Gibbs free energy. From the calculated results, the critical radius, change in availability, onset of boiling (ONB) superheat and heat flux were determined. The results showed that the critical radius and the maximum change in the availability of the mixtures was higher than that of the corresponding pure fluids. The ONB superheat first increased and then decreased when the mole fraction of the high boiling point component was increased. In addition, experimental tests were conducted to measure the ONB temperature and heat flux of R124, R22 and R124/R22 mixtures on a copper surface at the pressure of 0.7–0.85 MPa. The ONB superheat and heat flux first increased and then decreased when the concentration of R124 was increased. Additionally, the experimental ONB superheat and heat flux were used to validate the correlations of other models as well as the model presented here. Our model shows much better agreement with the experimental data. Most of the experimental results had an error of +20% to −40%. [ABSTRACT FROM AUTHOR]

Accurate prediction of boundary layer transition is extremely important for the aerodynamic and aerothermodynamic design of a hypersonic vehicle. Crossflow instability plays a crucial role in inducing transition in three-dimensional (3D) boundary layer. In this paper, a crossflow timescale τ cross based on crossflow velocity and crossflow Reynolds number is proposed and incorporated into the k-ω-γ transition model. Additionally, a grid pretreating method that can calculate boundary layer parameters with massive parallel execution is also proposed. HIFiRE-5, circular cone at angle of attack and X-33 vehicle are considered as test cases to assess the performance of the improved k-ω-γ transition model. Simulation results demonstrate that the boundary layer edge of complex hypersonic 3D flow can be obtained accurately with the help of grid pretreating method. It has been shown that if crossflow is taken into consideration, the shapes and locations of the transition onsets predicted by the improved k - ω - γ transition model are more consistent with experimental and direct numerical simulation results compared to the original transition model. This indicates that the improved k - ω - γ transition model provides significant improvement when crossflow-induced transition in hypersonic 3D boundary layer flow is predicted. Furthermore, application of the improved k - ω - γ transition model to X-33 vehicle flow shows that this model can be successfully used to predict crossflow-induced transition on complex full aircraft hypersonic configuration. [ABSTRACT FROM AUTHOR]

Soil thermal conductivity is an important parameter in the thermal simulations of geo-environmental structures. It is, however, difficult to measure the thermal conductivity as it is affected by several parameters, especially the soil water content. The objective of this paper was to present a measurement methodology based on least squares finite element method (LSFEM). The LSFEM algorithm was developed to directly solve the heat conduction equation, in which the measured temperatures served as input data and the thermal parameters were the unknown variables. The appeal of the LSFEM algorithm lied in its high efficiency and accuracy because no iterations were needed. To obtain the temperature data used for LSFEM solution, we designed a laboratory experiment to produce measurable temperature gradients. The spatial and temporal differences in the temperature measurements were identified to ensure the uniqueness and nonsingularity of the LSFEM solution. The corresponding water content can be simultaneously obtained from the methodology. The measured results suggest that the proposed methodology is promising for measuring the soil thermal conductivity. [ABSTRACT FROM AUTHOR]

Numerical simulations of laser welding could provide unprecedented insight into the physical details of the welding process; however, it remains a central challenge to understand laser welding with a high-efficiency and high-resolution method. This paper reports an octree-based adaptive mesh refinement method for efficient process modeling of laser welding in three dimensions. Based on multiresolution analysis algorithm, we also propose a hybrid adaptive mesh refinement strategy depending on local temperature, fluid velocity, and volume of fluid (VOF) value of weld pool of laser welding. Using the proposed method, the predicted heat transfer, and fluid flow behaviors of weld pool are consistent with experimental and previous theoretical results. Spatter formation at the beginning stage of laser welding is observed with a grid resolution in tens of microns. Under certain circumstances, the liquid jet can be produced when the fluid speed near the top surface of the weld pool is 1 m/s. The time for breakup of a liquid jet into spatters is about 0.065 ms. Furthermore, using the method, we just need 7 hours to complete a simulation of a 40-ms real laser welding process on a small workstation (2.60 GHz CPU, 16 cores), comparing with 120 hours needed using uniform grids. In a word, this method shows great potential for efficient computer simulation-based process optimization of laser material processing. [ABSTRACT FROM AUTHOR]

This paper is the second part of a comprehensive two-part review of spray cooling. The first part addressed the mechanisms and predictive tools associated with the relatively low-temperature single-phase liquid cooling and nucleate boiling regimes, as well as critical heat flux (CHF). The present part is focused on the relatively high-temperature transition boiling and film boiling regimes, and the Leidenfrost point. Discussed are dominant mechanisms, data trends, and predictive correlations and models. This information is especially important to the quenching of metal alloy parts from high initial temperature during heat treating. It is shown how correlations for the different spray cooling regimes and transition points can be implemented into boundary conditions for heat diffusion models to predict the temperature-time (quench) curve everywhere within the quenched part. It is also shown how the quench curve can be combined with the alloy’s transformation kinetics to predict mechanical properties. By properly configuring the sprays used to quench complex-shaped parts, it is also possible to greatly enhance the mechanical properties while minimizing residual stresses. [ABSTRACT FROM AUTHOR]

In this paper, a numerical study of heat and mass transfer in counter-flow indirect evaporative air coolers is presented using an approach proposed by previous work. The mathematical model equations of continuity, momentum, energy and concentration are solved by the finite volume method to obtain the value of primary outlet dimensionless temperature. This mathematical model developed is validated against published data acquired from literature. The key target of presented analysis is to develop a performance correlation based on five dimensionless factors: ratio of channel length to half width of secondary air channel, ratio of water to secondary air mass flow rate, primary air inlet Reynolds number, secondary air inlet dimensionless temperature and water film inlet dimensionless temperature. Numerical simulations are performed by changing the value of each dimensionless factor under a constant value for other parameters. The simulation results are regressed to obtain the empirical constants of the correlation. The value of outlet dimensionless temperature is varied from 0.47 to 0.92. The developed correlation can predict the performance of the counter-flow indirect evaporative air coolers within a discrepancy of 12.6%. The correlation would be helpful to provide a simpler equation to improve the calculation speed within the engineering allowable accuracy range. [ABSTRACT FROM AUTHOR]

Phase Change Materials (PCMs) are gaining importance in energy storage applications. Many PCM are poor thermal conductors and thus can gain from the optimal use of appropriate fins. Phase change process is inherently nonlinear in behavior due to the latent heat, thus simulations are usually based on finite difference or finite element approaches, which can be computationally inefficient for optimal design of latent energy storage systems. A novel modeling approach called Layered Thermal Resistance (LTR) model is proposed for the first time in this paper for efficient PCM simulations in multi-dimensions. The LTR model can be coupled with multidimensional fins for PCM-fin structure optimal design. Compared with CFD results, the results by the LTR model are high accurate in estimating the solidification time and the highlight is it has negligible simulation cost. Moreover, accurate heat flux of a finned PCM system is also obtained. The LTR model represents the nonlinear solidification process in a finned latent energy storage structure with analytic equations, thus it has bright applications in PCM heat sink optimization with internal fins. [ABSTRACT FROM AUTHOR]

The paper deals with the development of convective flows in a complex system of thin liquid layers occurring under the effect of thermal load. To study this process a mathematical model which is based on the decomposition of complex problem into unitary elements (modules) with some set of rules allowing their linkage with each other was constructed. Each module represents a monotypic local model. The fluid flow and heat transfer in each of these modules are described by the Navier-Stokes and thermal conductivity equations. The boundary conditions required to solve these systems of equations are represented explicitly and written in the form of conservation laws. The numerical analysis of effect of thermal load on the characteristics of the liquid layers movement depending on the Marangoni number is carried out. It is shown that physical and thermophysical properties of liquid layers play the decisive role. It is exactly they control the convective flows in layers and determine the position and shape of interfaces. The results of model problem solutions are presented. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of channel shape on the micro-channel and slot-jet module with the realizable k -ε turbulent model. Cooling performance of three channels with a same cross-section area but different shapes (rectangular, trapezoid and circular) are comparatively discussed. The hybrid module with circular channel has the maximum pressure drop at the same flow rate. While the hybrid module with trapezoid channel achieves the best cooling performance. Its superiority in the cooling performance enlarges with the heat flux rising and the pump power increasing, as compared with the other two hybrid modules. The local thermal resistance in the trapezoid channel exhibits peak-shape distribution, which is very different from the other two shapes channel. In addition, the cooling performance of the trapezoid channel module can be further improved by the optimization of the three geometric parameters (channel height, channel bottom width, and channel corner angle). When the optimal value for the three parameters is respectively adopted, the temperature on the bottom surface of the module can be reduced by 12.22%, 14.85% and 7.15% as compared with the worst design, and the temperature difference can also be reduced by 63.60%, 74.86% and 57.16%. What's more, the influence level of these parameters is also compared. Before the reference value, the channel height has the greatest influence on the module bottom surface temperature, whereas after the reference value, the corner angle becomes the largest influence factor. As for the temperature difference on the module bottom surface, it is just opposite. [ABSTRACT FROM AUTHOR]

This paper studies supercritical fluid extraction in which we take the effects of solute concentration variation on mass transport into account. A kinetics model with variable mass transfer coefficients proposed to describe supercritical fluid extraction of grape and almond seed oil. Three distinct stages are found for extraction process, i.e., fast-extraction, slow-extraction, transition period, with a very short overflow oil in first stage. The overflow oil period is so short and the concentration variation is so slight that we think this period belongs to the fast-extraction stage. Theoretical predictions for yield distributions of supercritical fluid extraction are highly in agreement with the experimental data in literatures, which implies that the proposed model can be used to predict more mechanism for the extraction process. Moreover, the effects of involved parameters on mass transport and supercritical extraction process are shown graphically and analyzed. [ABSTRACT FROM AUTHOR]

The performance of the commonly-used transient hot wire technique for measuring the thermal conductivity of materials near their liquid-solid transition point is reported in this paper. Adopting a 1-D transient formulation, the computational methodology is discussed in detail and predictions of the wire temperature are compared to the limiting analytical solutions without and with phase change. By varying the initial solid-state temperature of an eicosane sample, six cases which undergo phase change to different extent were studied. The results exhibit a monotonic dependence of the predicted thermal conductivity value on the initial temperature of the solid medium. As the initial temperature of the solid-state sample approaches the melting point, the predicted thermal conductivity value moves toward the value of the liquid eicosane. Recommendations were provided for performing measurements of thermal conductivity using the transient how wire technique involving phase change. [ABSTRACT FROM AUTHOR]

This paper presents numerical studies of large-size and high-quality fused silica glass synthesis by SiCl 4 flame hydrolysis deposition method, specifically the correlation of uniformities of SiO 2 deposition and OH concentration with the optimal location of the substrate placement. A comprehensive computational model is developed to describe the complex turbulent reacting flow with the detailed SiCl 4 -H 2 -O 2 reaction mechanism. Numerical simulation is first conducted to obtain the characteristics of SiCl 4 hydrolysis flame without considering the substrate and the SiO 2 particle formation. The distribution of SiO 2 accumulation is then calculated. The potential region and location for placing substrate are initially determined based on the criterion of a uniform SiO 2 accumulation. Further, the effects of H 2 -O 2 equivalence ratio and the SiCl 4 flow rate on the distributions of the temperature, SiO 2 concentration and OH concentration are investigated. It is found that the H 2 -O 2 equivalence ratio is sensitive to the temperature and the OH concentration, and the flow rate of SiCl 4 mainly affects the temperature and SiO 2 concentration. This finding indicates that the H 2 -O 2 equivalence ratio and the flow rate of SiCl 4 have equally important roles in determining the optimal location for the deposition substrate placement. The presence of the substrate also changes the distributions of the temperature and compositions concentrations in the furnace. Adjusting the substrate location is an effective strategy to achieve optimal location with more uniform distributions of the SiO 2 accumulation and the OH concentration on the deposition surface. [ABSTRACT FROM AUTHOR]

In this paper, an analysis is presented of the influence of electric field on the Rayleigh-Taylor instability (RTI) of two leaky dielectric fluids. A numerical model is developed based on the coupled solution of the governing equations of the electric field ( i.e ., Poisson equation) and the fluid flow ( i.e ., Navier-Stokes equation), where the leaky dielectric model is employed to take into account the free charges in the fluids. These equations are formulated within the framework of phase field and solved simultaneously. The numerical model, after validated with existing data, is applied to study the effect of the electric field on interfacial morphology associated with the RTI. Different from the perfect dielectric model, the free charges originating from the conductivity in a leaky dielectric fluid plays an important role in the evolution of the RTI under the influence of an applied field. Various interfacial morphologies have been observed in the electrohydrodynamic RTI, suggesting that the electric field has a significant influence on the RTI. An electric field (horizontal or vertical) may suppress or aggravate the instability depending on the system parameters the permittivity ratio and the conductivity ratio of the two leaky dielectric fluids. [ABSTRACT FROM AUTHOR]

This paper reports different characteristics of bubble growth within a superheated water droplet and in superheated water due to rapid depressurization through numerical calculations. Two mathematical models including the classical bubble growth model and the nonequilibrium bubble nucleation model are developed. The classical bubble growth model is based on the momentum equation of bubble growth coupling with the energy conservation equation. The heat transfer due to flash evaporation is considered at the droplet surface. The nonequilibrium bubble nucleation model considers the mechanical nonequilibrium on the formation of bubble nucleus. The numerical results show that a smaller pressure difference ( P v − P ∞ ) leads to a longer initial stage, and the variation of bubble radius simulated by the nonequilibrium model achieves a shorter initial stage and a faster bubble growth rate. The bubble growth is mainly affected by the competition of pressure difference and surface tension, and the prominent character of bubble growth process within a droplet is the occurrence of accelerating stage. With the bubble interface approaching the droplet surface, the boundary layer becomes thinner, leading to a rapid bubble growth rate. The influencing factors of superheat degree, pressure difference and ambient pressure on bubble growth within a water droplet due to depressurization are analyzed. The results reveal that the pressure difference plays an important role on bubble growth. However, bubble grows slower with a higher ambient pressure, even under the same initial pressure difference. The reason is due to a faster bubble interfacial temperature drop under higher pressure environment. The results can provide insight into bubble growth process during spray and atomization. [ABSTRACT FROM AUTHOR]

In this paper, mixed convection of non-Newtonian nanofluid, using the Buongiorno’s mathematical model in a cavity has been analyzed by Finite Difference Lattice Boltzmann method (FDLBM). The cavity is filled with nanofluid which the mixture shows shear-thinning behavior. The Prandtl number is fixed at Pr = 1. This study has been performed for the certain pertinent parameters of Richardson number ( Ri = 0.001, 0.01, and 1), buoyancy ratio number ( Nr = 0.1, 1, and 20), power-law index ( n = 0.2–1), Lewis number ( Le = 1, 5, and 10), Thermophoresis parameter ( Nt = 0.1, 0.5, 1), and Brownian motion parameter ( Nb = 0.1, 1, 5). Results indicate that the augmentation of the power-law index causes heat and mass transfer to drop at Ri = 0.001 and 0.01. The drop of Richardson number from Ri = 1 to 0.001 enhances heat and mass transfer for various power-law indexes. The increase in the Lewis number augments mass transfer while it causes heat transfer to drop. The rise of the Thermophoresis and Brownian motion parameters ameliorates mass transfer and declines heat transfer significantly. The augmentation of buoyancy ratio number enhances heat and mass transfer. [ABSTRACT FROM AUTHOR]

A newly developed mechanistic model of bubble dynamics in single microchannel is presented in this paper. The comparison between high-speed visualization and simulation results shows that this model is capable of capturing the transient flow regime and slug velocity inside of single microchannel and predicting flow reversal. The model quantitatively demonstrates the mechanism of flow reversal. Within one periodic cycle, the evolvement of flow regime, pressure distribution along channel length and mass flux at tube inlet are well correlated with each other. The local pressure peak caused by the build-up of downstream flow resistance can cause negative pressure gradient, which induces flow reversal. [ABSTRACT FROM AUTHOR]

Gas coolers are heat rejection heat exchangers in vapour compression refrigeration systems that use carbon dioxide (CO 2 ) as refrigerant. The design of gas coolers has a significant influence on the performance of CO 2 refrigeration systems as it determines to a large extent the gas cooler/condenser pressure and the power consumption of the system. This paper investigates local refrigerant and air heat transfer coefficients in plain fin-and-tube gas cooler coils using Computational Fluid Dynamics (CFD) modelling. The aims were to provide insights into the variation of the local heat transfer rates in the coil and determine the influence of a) design enhancements such as the use of slit fins and b) to develop correlations for overall refrigerant and air heat transfer coefficients to be used in CO 2 refrigeration component and system modelling. The results from the model which was validated against experimental measurements showed that a horizontal slit on the fin between the first and second row of tubes can lead to an increase in the heat rejection rate of the gas cooler by between 6% and 8%. This in turn can lead to smaller heat exchanger heat transfer area for a given heat rejection capacity or lower high side pressure and higher efficiency for the refrigeration system. The results and heat transfer correlations developed are a valuable resource for researchers and manufacturers of CO 2 and other heat exchanger coils that experience a wide variation in refrigerant temperature during the gas cooling process. [ABSTRACT FROM AUTHOR]