Search

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]

In this paper, a numerical model describing the heat transfer and air flow inside and outside the casing of the permanent magnet brushless direct current (PM BLDC) motor is presented. In the model, a conjugate heat transfer including the heat conduction with heat sources in windings, magnets, bearings, natural and forced convection and radiation phenomena within internal and external air domain were analysed. The complex geometrical model included windings, a magnet circuit, a rotor with neodymium magnets, a PCB electronic plate, plastic covers, internal air between solid parts as well as a portion of the external air. The validation process of the developed model was realised on the basis of the velocity and temperature fields. The experimental data were recorded by 7 constant temperature anemometers at 4 levels above the motor housing, Laser Doppler Anemometry sensors in two axes inside the rear portion of the motor and 25 thermocouples fixed inside and outside the motor. The experimental and numerical tests were performed for 4 motor loadings and 3 rotational speeds. The average temperature error for the internal point was of 9 K, while that of the external points was of 2 K. The velocity field was very well predicted close to the housing wall in terms of horizontal and vertical components. A slightly worse agreement was found for the vertical component, especially in the vicinity of the shaft. The results were consistent for all the considered motor loadings and rotational speeds. [ABSTRACT FROM AUTHOR]

The convection onset in a evaporation thermal model of a solute/solvent solution is numerically studied. The transient nature of the diffusion temperature profile requires to control the perturbations which will lead to the transition to a convective flow. Contrary to previous papers, we adopted here a perturbation mode, which is physical and experimentally reproducible, by accounting for a heat transfer at the lateral walls. Based on the Péclet number evaluated in the core flow field only, the critical viscosities and the corresponding times for the transition between a diffusion and convection regimes were calculated as a function of the fluid layer thickness, the aspect ratio and the convective heat transfer coefficient. The study of the spatio-temporal diagrams allowed us to characterize the way the convection propagates in the fluid domain as well as the evolution of the mean cell size and wavenumber. [ABSTRACT FROM AUTHOR]

The present paper presents fluid flow and mixed convective heat transfer characteristics past a semi-circular cylinder at incidence with a tandem square cylinder in cross flow. Using air ( Pr = 0.71 ) as an operating medium, numerical simulations are performed for the range of Reynolds numbers, 10 ≤ Re ≤ 45 and incidence angles, 0 0 ≤ α ≤ 180 0 . The effect of thermal buoyancy is brought about by varying the Richardson number in the range 0 ≤ R i ≤ 2 . The mathematical model is firstly validated with the experimental and numerical results from the literature and found to be in good agreement. The steady separated flow is observed to become unsteady periodic under the superimposed thermal buoyancy. Furthermore, apart from thermal buoyancy effect, angle of incidence is found to play a pivotal role in bringing hydrodynamic instabilities and thereby vortex shedding for such steady mixed convective flows. Functional dependence of drag ( C D ) , lift ( C L ) , and moment ( C M ) coefficients on the combined influence of α and R i , is explored and analysed in detail. Additionally, other global quantities, such as local and average Nusselt number distribution, Strouhal number ( S t ) are determined with respect to the various ranges of parameters considered in the present investigation. [ABSTRACT FROM AUTHOR]

The coordination between modeling, simulations, and experiments is critical for the design of the thermal protections of space vehicles. This paper illustrates a proof-of-concept of the coupling between a thermo-chemical ablation model and modern uncertainty quantification techniques with the aim of rebuilding the ablative material tests performed in the inductively coupled Plasmatron facility at the von Karman Institute. In Part I of this two-part work we presented the thermo-chemical ablation model and studied the effect of its uncertain parameters on the simulation outcomes. The present analysis is devoted to understand the effects of the uncertain estimates of the plasma wind-tunnel test conditions on the final results of the ablation model. A two-step uncertainty analysis is performed: the impact of the experimental uncertainties on the plasma flow rebuilding is first analyzed; then, the obtained mean, variance and distribution of the free-stream conditions are used as input, together with the model uncertain parameters, for the uncertainty analysis of the ablation model. Our results show that the experimental uncertainties have a substantial impact on the ablation model output when surface nitridation is not considered among the surface reactions. [ABSTRACT FROM AUTHOR]

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: 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 addresses two issues usually encountered when simulating thermal processes in forming processes involving tape-type geometries, as is the case of tape or tow placement, surface treatments, ⋯ The first issue concerns the necessity of solving the transient model a huge number of times because the thermal loads are moving very fast on the surface of the part and the thermal model is usually non-linear. The second issue concerns the degenerate geometry that we consider in which the thickness is usually much lower than the in-plane characteristic length. The solution of such 3D models involving fine meshes in all the directions becomes rapidly intractable despite the huge recent progresses in computer sciences. In this paper we propose to consider a fully space-time separated representation of the unknown field. This choice allows circumventing both issues allowing the solution of extremely fine models very fast, sometimes in real time. [Copyright &y& Elsevier]

The ammonothermal crystal growth technique is one of the most effective methods used for growing Gallium Nitride (GaN) crystals in terms of the final product quality and manufacturing efficiency. Popular applications of GaN crystals include light emitting diodes (LEDs) and high-frequency electronic devices. A laterally-heated cylindrical enclosure with a top to bottom temperature gradient is considered in this study to investigate the fluid mechanics and heat transfer in an ammonothermal crystal growth reactor. Three-dimensional (3D) large eddy simulations (LES) results of natural convection in a laterally heated cylindrical reactor, using the commercial computational fluid dynamics (CFD) software, ANSYS FLUENT, are presented in this paper for a Rayleigh number ( R a ) of 8.8 × 10 6 . The R a is defined based on a length scale that is equal to the ratio of volume to the lateral area of the cylinder ( R / 2 ). In addition, an experiment of a geometrically- and dynamically-similar geometry is developed, and particle image velocimetry (PIV)-based flow visualizations are carried out for the purpose of validating the numerical model. Comparisons between experiments and numerical simulations showed that flow patterns were qualitatively similar, and Fourier transforms of velocity magnitudes at selected points in the domain matched reasonably well. An added interesting observation in the simulation was the existence of temperature inversion, which has potential implications on the choice of mineralizer (acidic/basic). [ABSTRACT FROM AUTHOR]

In a jet cooling ball bearing, the oil is mixed with the air and air-oil two-phase flow field is formed. The flow behaviours and heat transfer characteristics of the two-phase flow are significant for cooling evaluation and temperature control of the bearing. This paper investigates the fluid flow and heat transfer characteristics of a jet cooling ball bearing. The air-oil distribution and temperature distribution inside the ball bearing are calculated. The results indicate that micro bubbles are mixed into the oil at high-speed operation conditions. The highest oil volume fraction position is close to the nozzle and moves along the rotation direction at different speeds. Considering the air-oil two-phase distribution, the heat transfer simulation model using the VOF method is well enough for the present analysis. There is a correlation between the temperature distribution and the air-oil distribution inside the bearing. The lower temperature always appears at the higher oil volume fraction position. Optimizing the cooling mechanism according to the oil volume fraction distribution is helpful to achieve greater cooling effect. [ABSTRACT FROM AUTHOR]

This paper deals with the numerical investigation of heat transfer by mixed convection inside ventilated cavities with supply and exhaust slots, and filled with air under a steady and turbulent flow regime. Four configurations, rated A, B, C and D are considered here, according to the position of the inlet and outlet air ports: A, the inlet is on the top of the left vertical wall, while the outlet is on the bottom of the right vertical wall; B, the inlet is on the bottom of the left vertical wall and the outlet at the top of the opposite wall; C, the two slots are on the same side, i.e. the inlet is at the bottom and the outlet at the top of the left vertical wall, and D, the inlet is at the top and the outlet at the bottom of the left vertical wall. The bottom of the cavity is kept at a temperature T H and other walls are fixed at a temperature T C , with T H > T C . The cavity is provided with two slots: an inlet slot for introducing fresh air, and an outlet slot to extract hot air. The main aim sought here is to analyze the ventilation efficiency for temperature distribution, and fix the best configuration providing the thermal comfort targeted. We also address the influence of heating on the behavior of flow and thermal comfort, while considering different Rayleigh numbers ranging from 6.4 × 10 8 to 3.2 × 10 9 . Numerical studies have been yet devoted to these configurations, using RANS simulations. The RNG k-ε turbulence model has been adopted for the turbulence closure, and the set of governing equations was then numerically solved via the finite volume method. The SIMPLEC algorithm was associated to ensure the pressure-velocity coupling. In terms of results achieved, the configuration D provides a better ventilation effectiveness for temperature distribution ε T and ensures an even temperature in the occupied zone. As for configurations A and C, they maintain an acceptable level of heat and can be used in winter period to ensure good indoor air quality, while configuration B provides an efficiency close to unity and can be used to insure indoor air quality in temperate climate zones. [ABSTRACT FROM AUTHOR]

Abstract: The proper interpretation of bubble rising in a liquid column is critical in the investigation of the water–vapour two phase flow and heat transfer. In this paper, the bubble behaviours are studied using the combination of Level Set Method (LSM) and moving mesh method in a collocated grid. Level set method is used to track the interface of the bubble, which has many advantages over other interface tracking methods such as it can accurately calculate the curvature of the interface and easily expand to three dimensions. But if the uniform grid was adopted, the bubble interface cannot adapt well with the grid which may cause great numerical errors. Hence, moving mesh method is implemented in this paper to increase the numerical accuracy. The numerical model developed in this paper is benchmarked with the experimental data. The results show that the grid distributions used in this paper can catch the interface continuously in space and time. The process of bubble starting from deformation until break into three small bubbles is clearly shown from the numerical results. In addition, the changing of bubble behaviour with the temperature and pressure is also investigated. It is found that as the pressure and temperature increase, the deformation process will slow down and this tendency accelerates. [Copyright &y& Elsevier]

This study numerically examines three-dimensional natural convection of air induced by temperature difference between a cold outer cubic enclosure and a hot inner cylinder. Simulations have been carried out for Rayleigh numbers ranging from 10 3 to 10 7 and a titled angle of the enclosure varying from 0° to 90°. The developed mathematical model is governed by the coupled equations of continuity, momentum and energy and is solved by finite volume method. The effects of cylinder inclination and Rayleigh number on fluid flow and heat transfer are presented. The distribution of isocontours of temperature, components of velocity and streamtraces eventually reaches a steady state for Rayleigh numbers ranging from 10 3 to 10 7 for titled inclination of 90°. However, for the remaining inclinations, Rayleigh numbers must be in the range 10 3 –10 6 to avoid unsteady state which is manifested by the subdivision of the area, containing the maximum local heat transfer rate, into three parts for a Rayleigh number equal to 10 7 and an inclination of 90°. We mention that instability study is not included in the present paper which is solely devoted to three dimensional calculations. Results indicate also that optimal average heat transfer rate is obtained for Rayleigh number set to 10 6 and an inclination of 90° for both cases of the inner cylinder and lateral walls of cubical enclosure. [ABSTRACT FROM AUTHOR]

In this paper, a numerical investigation is presented to study Buongiorno's mathematical model for hydromagnetic free convection flow in an isosceles triangular cavity filled with nanofluid. The inclined walls of the cavity are maintained at constant cold temperature whereas various combinations of the thermal boundary conditions at the bottom heated wall are considered. The cavity is permeated by an inclined uniform magnetic field and the effects of Brownian motion and thermophoresis are incorporated into the nanofluid model. The Galerkin weighted residual finite element method has been employed to solve the governing partial differential equations after converting them into a non-dimensional form using a suitable transformation of variables. In the numerical simulations, alumina-water based nanofluid has been taken into account. Comparisons with previously published work are performed and excellent agreement is obtained. The effects of various parameters such as Hartmann number, Rayleigh number and inclined magnetic field angle on streamlines, isotherms and isoconcentrations have been displayed graphically. The heat transfer augmentation for various combination of model parameters as well as various thermal boundary conditions have been done in light of the average Nusselt number from the bottom heated wall. The results show that the heat transfer rate can be decreased with the increasing values of the Hartmann number and inclination angle of the magnetic field but it can be increased by increasing the Rayleigh number and by reducing the diameter of the nanoparticles. The obtained numerical results also indicate that the variable thermal boundary conditions have significant effects on the flow and thermal fields. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the approximate analytical models of temperature and thermal stress in a two-dimensional axis-symmetry object. The models can be used to deal with some non-linear factors caused by temperature-dependent properties using multiple parameter perturbation method. Two cases have been used to test the models proposed in this paper. The first case study is the comparison of analysis of the rotor with our models and FEM (finite element method) and it is shown that our models have a satisfactory accuracy. The second case is the application of our models to sensitivity studies. The models proposed reduce computational time significantly compared with FEM method and hence can be used for online analyzing of thermal state of a two-dimensional axis-symmetry object and inverse heat conduction problems. [Copyright &y& Elsevier]

This paper presents a theoretical study on the optimization of key material parameters of multilayer clothing assemblies for thermal comfort in cold climate. A mathematical model of heat and moisture transfer through a multilayer clothing assembly is established. The existence and uniqueness of the solution of the model are verified by using the fixed point theorem. The model predicts the optimum thicknesses and porosities of the two internal layers of the clothing assembly, with which the thermal comfort index will fall within the required intervals with the greatest probability. This study is significant for the optimum design of multilayer clothing assembly for thermal comfort. [ABSTRACT FROM AUTHOR]

The present paper deals with the heat flux estimation and the thermal characterization of the poorly attached Surface Carbon Layer (SCL) to the Plasma Facing Component (PFC) observed on the inner vertical tiles of the JET Tokamak. A nonlinear unsteady calculation combined with the Conjugate Gradient Method (CGM) and the adjoint state is achieved in order to estimate the time variation of the heat flux necessary to characterize in situ the space and time variations of the thermal resistance R th of the SCL. The method is applied on L mode power step plasma discharge (#58850). One embedded thermocouple (TC) is used to the heat flux estimation (another embedded TC is used for validate the estimation) and infrared (IR) measurements coming from the IR camera KL3 are used to estimate the SCL thermal resistance. The estimated SCL thermal resistance is compared to the history of the strike point location to highlight the correlation between the spatial distribution of the SCL thermal resistance and the location of the maximum heat flux. [ABSTRACT FROM AUTHOR]

Based on the perturbation technology and fuzzy theory, this paper proposes a first-order subinterval perturbation method (FSPM) and a modified subinterval perturbation method (MSPM) to solve the uncertain heat conduction problem with large fuzzy parameters. Using the level-cut strategy and subinterval methodology, the original fuzzy parameters with subjective probability are firstly decomposed into several subinterval variables, while the eventual fuzzy temperature responses are reconstructed by the interval union operation and decomposition theorem. In both perturbation methods, the subinterval matrix and vector are expanded by the Taylor series. The inversion of subinterval matrix in FSPM is approximated by the first-order Neumann series, whereas the modified Neumann series with higher order terms is adopted to calculate the subinterval matrix inverse in MSPM. Comparing the results with traditional Monte Carlo simulations, two numerical examples evidence the remarkable accuracy and effectiveness of the proposed methods to predict uncertain temperature field in engineering. [ABSTRACT FROM AUTHOR]

This paper presents a mathematical model and corresponding numerical results for a power-law fluid flowing in a channel partially filled with a homogeneous and isotropic porous medium. At the interface between the clear fluid and the porous material, a model for the stress jump condition takes into consideration the behavior of a power-law fluid. This study shows that the use of a modified permeability, K * , satisfactorily describes the friction factor of the flow for Re η ∗ ≤ 1 (Darcy regime). The mathematical modeling presented, supported by comparisons with analytical and numerical results, also shows that the form drag must be taken into account in the momentum equation, even for a power-law fluid. The mathematical modeling presented has been used to simulate Newtonian as well as power-law fluids flowing in both porous and unobstructed media. For a channel partially filled with porous material and under a fixed mass flow rate, results indicated that the pressure drop is a function of porosity, Darcy number, shear jump coefficient, β , and flow behavior index, n . [ABSTRACT FROM AUTHOR]

In this paper, a distributed parameter model for tubular reactor in the ethylene cracking furnace based on 3-D temperature reconstruction is developed. The mathematical model was formulated to predict the distributions of the heat flux and the tube temperature while considering a non-uniform distribution of the surface heat transfer and the ethylene pyrolysis process. The results show that the heat flux distribution on the tubular reactor has four high heat flux zones, and the tube temperature reaches a maximum of 1088 °C. The value of the maximum tube temperature decreases compared with the value of the maximum heat flux due to the heat exchange coefficient of pyrolysis gas increasing slowly in the bend region. The tube temperature distribution was validated by using a spectrometer system and the errors between three major product yields at the tube outlet obtained by the proposed model and in-situ measured values were within 5%. This distributed parameter model can be used as a guide for ethylene cracking furnace operators and as a tool for design. [ABSTRACT FROM AUTHOR]

This paper describes a methodology for the modeling and simulation of a pulsed thermography inspection of carbon fiber-reinforced composites. A thermal–numerical model based on the 3D transient heat conduction equation for heterogeneous media is proposed to model the thermal response of the composite medium when a thermal pulse is applied to its surface. The solution of the model is developed using the finite volume method, in which the approximated equations are obtained by performing energy balances for each elementary volume. The experimental validation of the thermal–numerical model consisted of a comparison of the thermal decay curves for defective areas obtained through numerical simulation and with a pulsed thermography inspection of a laminated composite specimen with simulated defects (Teflon inserts). A parametric study was carried out in order to analyze the influence of the irradiation power density, non-uniform heating and characteristics associated with the defects on quantitative variables such as the onset time and thermal contrast. Numerical results showed that the variable thermal contrast is highly sensitivity to changes in the defect thickness, aspect ratio and parameters related to the external stimulation. Furthermore, an increase in the detectability of defects – especially those with lower aspect ratios – can be achieved by increasing the irradiation power. [ABSTRACT FROM AUTHOR]

This paper presents development of numerical heat conduction model for prediction of transient three dimensional temperature field in the billet. The model is applied to billet heating process in the reheat furnace. The discretization of governing equation is done by control volume approach and implicit scheme of finite difference method. The model captures various time dependent boundary conditions corresponding to the billet reheat in the reheat furnace, in addition to this it also accounts for the growth of oxide scale layer on the billet surfaces during reheat simulations. The set of discretized equations is solved using own developed MATLAB ® code. The proposed model is capable of predicting the temperature field in the billet and scale growth on the billet surfaces. The model is validated with analytical results and published experimental results. The results obtained through the model simulations are in concurrence with the anticipated trend. The proposed methodology of numerical modeling will be helpful for the temperature and scale growth predictions, which are vital for a variety of reasons like energy efficiency, process optimization, roll force calculations, carbon segregation control and product microstructure control, etc. [ABSTRACT FROM AUTHOR]

Abstract: Active pipe-embedded building envelope is a new building envelope, which is an external wall or roof with pipes embedded in it. This structure has the advantages to utilize directly low-grade energy sources for reducing building cooling/heating load and improving indoor thermal comfort. This structure may also use some phase change materials (PCM) to be pasted as a thin layer for further enhancing these benefits. This paper presents a dynamic simplified thermal model of this structure with the thermal network structure of lumped thermal mass, and the parameter identification of the simplified model based on frequency characteristic analysis. These resistances and capacitances are identified in frequency domain by using generic algorithm (GA) by comparing the frequency characteristics of the simplified model with the theoretical frequency characteristics of this structure obtained with Frequency-Domain Finite Difference (FDFD) method. Firstly, the FDFD model of this structure is established, and the theoretical frequency characteristics under various disturbances are calculated for the reference of parameter identification. Then, an equivalent dynamic simplified thermal model with lump thermal network structure is developed, and its frequency characteristics are also deduced and calculated. Finally, GA estimator is used to identify these parameters of the simplified model for allowing the frequency responses of the simplified model to match the theoretical frequency responses by using FDFD method. Various case studies are presented to validate the accuracy of the simplified models and the effectiveness of the parameter identification for the model. [Copyright &y& Elsevier]

Abstract: The paper presents a new proposal of a discrete event simulation (DEVS) model for heat transfer in an enclosure. To our knowledge this is the first proposal in this direction, therefore the model is not comprehensive (has no windows, no ground coupling, etcetera). It is a first step of DEVS into the heat transfer in buildings. The model presented is just one possible implementation for a single thermal zone, although it has been designed to be used in multi-zone models. Common methods like CTF (conduction transfer functions) or RTF (response transfer functions) cannot be used. Instead it employs the successive transition state formulation for the 1D conduction heat transfer through multi-layered walls. An example test room has been calculated and the results compared with software that uses well known methods (CTF, RTF). Finally the DEVS model has been tested with a random convective internal-load signal. [Copyright &y& Elsevier]

Abstract: A new methodology to solve a heat transfer problem in a complex porous structure has been proposed in this work. The 3D numerical model considers combined conductive–radiative heat transfer with the finite volume method integrated with a blocked-off region approach. The model is capable of considering grey, diffuse behaviour of the surfaces of the solid. The work demonstrates the simplicity of this approach for solving problems with porous structure by eliminating the complexity of grid generation generally needed for any conventional methods. The representative porous structures considered for this analysis are cubic cell and honeycomb structures. The effective thermal conductivity is determined for different temperature, emissivity and thermal conductivity of the solid and absorption coefficient of the fluid. Various problems are also solved in order to validate the formulation and the subsequent implementation with the results from FLUENT 6.3 as well as literature. A good agreement of the results has been observed and reported in the paper. [Copyright &y& Elsevier]

Abstract: This paper describes a high breaking capacity fuse with improved cooling. The fuse is equipped with only heat sinks or heat sink and fan, an idea derived from the power semiconductor devices field. Some 3D thermal models are proposed for every analysed case of natural and forced cooling. The best solution was the fuse with three aluminium identical heat sinks mounted on the ceramic body. The influence of the fin length, base plate thickness of the heat sink, number of fins and the shape of the fin cross-section, has been investigated. There is a good correlation between experimental and simulation results. [Copyright &y& Elsevier]

Abstract: The present paper describes a mathematical study on peristaltic flow of viscoelastic fluids (with the robust Jeffrey model) through a finite length channel under the influence of heat transfer. The study is motivated by the need to further elucidate the mechanisms inherent in swallowing of diverse food bolus types (bread, fruit jam and almost all edible semi-solids) through the oesophagus, by taking account of the viscous and elastic effects. The expressions for temperature field, axial velocity, transverse velocity, volume flow rate, pressure gradient, local wall shear stress, mechanical efficiency, stream function, and reflux limit are obtained, when the Reynolds number is small and the wavelength is large, by using appropriate analytical and numerical methods. The computational results are presented in graphical form. The influence of thermophysical (heat transfer), relaxation time and retardation time parameters on pressure distribution, local wall shear stress profiles, temperature profiles and velocity profiles are studied in detail. Furthermore we investigate the effects of these parameters on two inherent phenomena (reflux and trapping) characterizing peristaltic flow using streamline plots. The present study emphasizes an important observation, namely that pressure along the entire length of the channel reduces when the magnitude of relaxation time (retardation time is fixed) or Grashof number or indeed thermal conductivity increase, whereas pressure is enhanced by increasing the magnitude of retardation time (relaxation time is fixed). [Copyright &y& Elsevier]

Abstract: Air is a cheap and safe fluid, widely used in electronic, aerospace and air conditioning applications. Because of its poor heat transfer properties, it usually flows through extended surfaces, such as finned surfaces, to enhance the convective heat transfer. In this paper, experimental results are reviewed and numerical studies during turbulent air forced convection through extended surfaces are presented. The thermal and hydraulic behavior of a reference trapezoidal finned surface, experimentally evaluated by present authors in an open-circuit wind tunnel, has been compared with numerical simulations carried out by using the commercial CFD software COMSOL Multiphysics. Once the model has been validated, numerical simulations have been extended to other rectangular finned configurations, in order to study the effects of the fin thickness, fin pitch and fin height on the thermo-hydraulic behavior of the extended surfaces. Moreover, several pin fin surfaces have been simulated in the same range of operating conditions previously analyzed. Numerical results about heat transfer and pressure drop, both for plain finned surfaces and for pin fin surfaces, have been compared with empirical correlations from the open literature, and more accurate equations have been developed and proposed. As shown with an optimization example, these new equations can be used as an easy-to-implement calculation approach for heat sink design in electronic thermal management. [Copyright &y& Elsevier]

Abstract: Compared with other making methods, vacuum binary ice making is high in efficiency, simple in structure and easy to operate. In this paper, a mathematical model for the entire process including flash evaporation and ice making in vacuum environment is established. The binary ice-vacuum experimental system is introduced. Experimental and simulation studies of IPF (ice packing factor) influencing factors for vacuum binary ice making method were carried out. Those factors include environmental temperature, environmental pressure, water temperature, droplet size and droplet initial velocity. The results show that the binary ice''s IPF are related to environmental pressure, droplet size, initial velocity and flash chamber size, less affected by environmental temperature and water temperature. [Copyright &y& Elsevier]

Abstract: Accurate heat transfer prediction is important to structural fire engineering in order to analyze thermal–mechanical behavior of structures in fire. However, the presence of cavities and participating media complicates radiative calculations. A numerical approach with finite element and discrete ordinates method is presented in this paper to predict fire imposed radiative heat fluxes to these type of structural members. This approach is used to simulate heat transfer to unprotected steel I-sections with symmetrical cavities exposed to post-flashover fires. Results show that the cavity geometry could strongly attenuate the radiative energy, while the presence of hot smoke enhances radiative transfer by emission. Average radiative fluxes for inner surfaces of the I-sections are seen to increase with smoke opacity. In addition, the radiative fluxes are observed to decrease faster for I-sections with higher section factors. This work also shows that the self-radiating mechanism of I-sections is important in the optically thin region, and existing methodologies neglecting these physics could significantly underpredict steel temperatures. [Copyright &y& Elsevier]

Abstract: The purpose of this study is to present a coupled electro-magnetic and thermal model for numerical analysis of an induction heating system including the workpieces moving relative to the inductors. In this paper, a finite element method-based numerical analysis of a low-frequency (60 Hz) induction heating system for the one-dimensional solution of a stationary circular billet and the two-dimensional solution considering the dynamic effect of circular billets moving along the skid rails with constant speed are presented and compared against each other. The non-linearities of both the electro-magnetic and thermal material properties are also taken into account in the model. The computational results have been compared with experimental data. As a result, it is suggested that the presented numerical model may be a very cost-effective tool in predicting the temperature of a workpiece in a variable flux field where the interested workpieces undergo an arbitrary change in the electro-magnetic fields. It is possible to obtain some preliminary results more accurate than those calculated from previous works using a stationary model on electro-magnetic field and temperature distribution of workpieces by applying the presented numerical model. [Copyright &y& Elsevier]

Abstract: There are several methods adopted by the scientists in modeling the heat transfer phenomenon during solid–liquid phase change. However, the validity of the various models developed and the complexity required for a given problem is not well reported in the literature. This paper presents a comparative study of three different mathematical models for the packed bed latent heat storage system, comprised of a cylindrical storage tank filled with paraffin encapsulated spherical containers. The enthalpy formulation technique is used in the models to accommodate the phase change behavior of the paraffin over a range of temperatures. The results obtained by solving the models using the fully explicit finite difference method are initially validated with experimental results. Further numerical analysis is performed using the models for two different heat transfer fluids of air and water at different mass flow rates and ball sizes and the validity of the models are compared and reported. It is found that one model is sufficient when air is the heat transfer fluid and another model is recommended when water is the heat transfer fluid. [Copyright &y& Elsevier]

Abstract: Propagation of uncertainty through the physical model has been investigated in the present paper by solving two specific simple stochastic problems using the Non-Intrusive Spectral Projection method. The uncertain parameters are described by either a Gaussian or a LogNormal probability distribution function. For each of the problems, the stochastic and the deterministic mean solutions have been compared and the respective confidence intervals have been obtained. For the deterministic problems, the confidence intervals have been estimated using both one-dimensional and multi-dimensional bound methods. From the results it has been observed that the differences between the stochastic and the deterministic mean solutions are apparent only when large uncertainties are introduced in the random variables. For both the specific problems, considered in the present study, the confidence intervals for the stochastic problems have been exactly predicted by the deterministic limits when uncertainty is introduced only in one of the parameters. For more than one uncertain parameters, the multi-dimensional bound method produces better agreement with the stochastic confidence intervals than the one-dimensional bound method. The findings are expected to be applicable to problems in heat and mass transfer with similar characteristics or input–output relations. [Copyright &y& Elsevier]

Abstract: As we know, the mean temperature difference approach perfectly solves the problem of thermal design of a two-fluid heat exchanger. However, so far, the equivalent method has not been found for that of three-fluid heat exchanger. In this paper, a mean temperature difference method called IMTD (integral-mean temperature difference) is developed in detail for a parallel stream three-fluid heat exchanger with two communications. It includes the derivation of IMTD formulae, the illustration of design and simulation procedures of IMTD thermal model, the corresponding exemplary calculations and discussion, and the validation of IMTD thermal model. The research shows that the derived IMTD formulae and accelerated method proposed in the present IMTD model significantly improve the design process in the past analytical models. It realizes a fast convergence which is usually within 10 steps for all parallel stream flow arrangements. Moreover, the present model has the same accuracy as past exact analytical models and simultaneously can be comparable to past approximate analytical models in simplicity. [Copyright &y& Elsevier]

Abstract: This paper presents a numerical investigation for examining the secondary vortex motion and associated heat transfer process in fluid flow through curved passages. Overcoming current modelling limitations, the study formulates an improved simulation model based on 3-dimensional vortex structures for describing secondary flow and its thermal characteristics. For developing laminar fluid flow through curved rectangular ducts, the analysis performs a detailed parametric study involving the contours of helicity and outer duct wall pressure gradient for a range of flow rates, duct aspect ratios, duct flow curvatures and external wall heat fluxes. The flow conditions leading to hydrodynamic instability and Dean vortex generation in curved passages are carefully analysed, identifying the flow and geometrical parametric influences. Active interaction of buoyancy force on fluid motion arising from wall heating is considered where aspects of boundary layer separation is used in recognising thermal enhancement due to secondary flow. The simulated results are validated with the available experimental data. Surpassing precision and reliability of current practise, the study develops two numerical approaches offering improved capabilities for capturing the onset of hydrodynamic instability and resulting Dean vortices. These techniques are compared and assessed for their merits of application in determining the onset of secondary flow hydrodynamic instability with and without external wall heating. [Copyright &y& Elsevier]

Abstract: In this paper, an attempt has been made to study the thermal and fluid flow behavior of Al2O3–water nanofluid, independent of any external surface influences due to conventional surface heating methods. This has been achieved through natural convection flow induced by volumetric heat generation through microwave heating. Both experimental and numerical investigations were carried out and the numerical results were validated with the experimental data. Numerical simulations were carried out by single-phase and two-phase (Eulerian–Lagrangian) modeling approaches. The effects of nanoparticles in the base fluid, various particle forces and concentration dependence on the hydrodynamics and thermal behavior are presented through isotherms, stream function and time evolution of the fluid flow. The present studies demonstrate that additional fluid flow behavior in nanofluids is induced by the heated nanoparticles due to particle migration effects. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to furnish the research and design communities with a simple and convenient means of predicting quantities of engineering interest for slip flow in doubly connected microchannels. Slip flow in doubly connected microchannels has been examined and a simple model is proposed to predict the friction factor and Reynolds number product. As doubly connected regions are inherently more difficult to solve than simply connected regions, and for slip flow no solutions or graphical and tabulated data exist for nearly all doubly connected geometries, the developed simple model fills this void and can be used to predict friction factor and Reynolds number product, mass flow rate, pressure distribution, and pressure drop of slip flow in doubly connected microchannels for the practical engineering design of doubly connected microchannels. The proposed models are preferable since the effects of various independent parameters are demonstrated and the difficulty and investment is completely negligible compared with the cost of alternative numerical methods. [Copyright &y& Elsevier]

Abstract: In the present paper the thermal performance of nanofluid flow in microchannel heat sinks (MCHSs) was analyzed using three different nanofluids. The fluid flow and heat transfer in the MCHS are modeled using the Darcy–Brinkman–Forchheimer and two-equation model, respectively. In order to check the validity of the results, they were compared with available experimental and numerical data in the literature and excellent agreement was found between them. The key novelties of present work are (i) using a novel and complex temperature dependent thermal conductivity model for nanofluids, based on Brownian motion induced micro mixing, (ii) using new nanofluids with three types of nanoparticle materials i.e. aluminum oxide (Al2O3), zinc oxide (ZnO) and copper oxide (CuO) and 60:40 (by mass) EG–water for the base fluid, (iii) investigating the effect of nanoparticles size and Brownian motion of particles on thermal performance of MCHS. [Copyright &y& Elsevier]

Abstract: Thermal accumulation phenomena are one of the hardest problems to solve in thermal load and energy calculations in buildings. The evolution in the mathematical modeling of building envelopes wants to provide a response to the growing need for accuracy in equipment dimensioning and energy certification calculation methods. Among all existing methods, the response factors method and the transfer function method, developed by Mitalas (1967) and Stephenson (1971), stand out due to their simplicity, accuracy and widespread use. After that, with the release of the RTS (Radiant Time Series) method, developed by J.D. Spitler, D.E. Fisher and C.O. Pedersen in 1997, the concept of periodic response factors is introduced, adding the hypothesis of 24-h periodicity of the input conditions. The main difficulty of the method lies in obtaining these so called response factors or weighting factors, which requires an approximate, complex, and high computing cost procedure. In this paper, a new method to obtain 24 h periodic wall response factors called the Harmonic Method is presented, which constitutes an improvement over usual methods used to obtain wall response factors. It will be shown that this method is able to reduce computational effort and increase accuracy compared to previous calculation algorithms. [Copyright &y& Elsevier]

Abstract: The flash evaporation of superheated water in direct contact with its own vapor involves very high heat transfer rates and the existing solutions for the problems of heat diffusion in the superheated water drops underestimate the actual heat transfer rates, even when the gas-side heat transfer coefficient is assumed to be extremely high. This happens due to the poor thermal conductivity of the water which causes the heat transfer to be dominated by the heat flow within the liquid. Accommodation between the analytical results of the heat diffusion in superheated water and those obtained from the experimental measurements requires considering the effective thermal conductivity of the liquid owing to the violent nature of the flow, which is thought to be much larger than the mere molecular thermal conductivity. This paper presents initial attempts on modeling the liquid-side heat transfer process accompanying the surface evaporation of superheated water drops resulting from the flashing of superheated water jets. [Copyright &y& Elsevier]

Abstract: This paper is concerned with the exact solutions for thermal diffusion in a straight fin with varying exponential shape when the thermal conductivity and heat transfer coefficients are temperature dependent. The conduction and heat transfer terms constitute the strong nonlinearity given by power laws. Explicit analytical solutions are derived for the relevant parameters in terms of special functions of advanced mathematics. The effects of parameters of physical interest such as the fin tip temperature, the fin efficiency and the fin base heat transfer rate can be better captured from the presented formulas. Moreover, with the help of the analysis here, the best shape of the straight fin is identified under a variety of operating conditions. Analysis further shows that the efficiency and base heat transfer rate of the exponential profiles are higher than those of the rectangular fin. [Copyright &y& Elsevier]

Abstract: The wave-finned flat tube heat exchangers are widely used in air-cooled condensers of a power plant. Due to the oblique arrangement of the wavy fins on the A-frame tube bundles of the air-cooled condenser, the finned tube is prone to fouling thus the thermo-flow performances of air-cooled condensers are likely to become deteriorated. A new configuration of wave-finned flat tube, in which the fin surface rotates to be perpendicular, is proposed in this paper to prevent the fouling from gathering on the finned tube. The physical and mathematical models for the fluid and heat flows of the cooling air through the present and proposed wave-finned flat tube bundles are setup, and the thermo-flow characteristics are compared. For the proposed finned tube, the influences of the fin pitch, height and the Reynolds number on the flow and heat transfer performances are investigated, and the correlations of the friction factor and Nusselt number are recommended. The results show that the buoyancy effect should be taken into account for the correlation of the friction factor at low Reynolds numbers, but this buoyancy force can be ignored for the Nusselt number. [Copyright &y& Elsevier]

Abstract: Thermal performance in oil-immersed power transformers is governed by the flow of oil, acting both as an electrical insulator and a medium for the transfer of heat generated in the core and windings toward the tank and the surrounding air. This paper presents the development of an advanced three-dimensional (3D) finite element model for the coupled solution of heat transfer and fluid flow equations governing transformer thermal performance. The main advantages of the proposed method are: (i) no need to predefine the convection coefficients at the interfaces between the active part/tank walls and the circulating oil, (ii) detailed representation of specific transformer parts that play an important role in the accurate representation of oil flow and heat dissipation (such as winding cooling ducts and corrugated tank panels) through an automated design process, enhancing the model accuracy with the least possible computational effort and (iii) accurate definition of the transformer heat sources (core and windings loss). The proposed methodology provides an integrated tool for thermal simulation, able to predict detailed thermal distribution in a specific transformer, without requiring prior knowledge of nodal temperature or temperature gradient values. [Copyright &y& Elsevier]

Abstract: The design of technological devices and systems, with reduced size but unchanged or increased performances, has been one of the most important scientific challenges faced in the last decade by many fields of the world industry. The capability to remove and exchange heat in more compact components has allowed great advantages in the optimization of all final products as well as in industrial processes. However the never-ending race to miniaturization of appliances has been taking into account problems concerning computational models and design criteria developed in the past for macro-systems. Nowadays most of these methods are no longer reliable for emerging micro-systems because of the substantial differences in transport phenomena and heat exchange, mainly in two-phase flow (scaling effects). This paper aims to provide its contribution to the burgeoning research activity on boiling heat transfer under forced convection in microchannels. The BO.E.MI.A. experimental facility was designed and specifically developed to perform different regimes heat transfer tests on mini and microchannels: a total of 150 tests were performed using a fluorinert fluid FC-72 as coolant. The test section consists of a horizontal 1mm inner diameter stainless steel tube having a heated length (Joule effect) of approximately 60mm. The mass flux range is between 1000 and 2000kgm−2 s−1 while the applied heat flux is between 10 and 150kWm−2. By means of a preheater we are able to change coolant inlet temperature and by setting the operating pressure in a range between 3 and 7bar, a broad spectrum of subcooling degree at inlet test section is achieved. The local heat transfer coefficients were evaluated for both subcooled and saturated flow boiling regimes. The experimental data show an increase of local heat transfer coefficient for increasing values of heat flux, with a weak dependence on the vapour quality. The experimental values obtained were compared with those from the adoption of one of the main heat transfer correlations in the literature. [Copyright &y& Elsevier]

Abstract: Gas–liquid two-phase flow in microchannels with hydraulic diameters of 100–500μm exhibits drastically different flow behaviors from its counterpart in conventional macroscopic channels. Of particular interests are the two-phase flow patterns and the two-phase frictional pressure drop for given flow conditions in these microchannels. This paper presents an experimental study of the effects of channel size and superficial phasic velocity on the two-phase flow pattern and pressure drop of air–water mixture in circular microchannels with inner diameters of 100, 180 and 324μm. Two-phase flow patterns were visualized using high-speed photographic technique. Four basic flow patterns, namely, bubbly flow, slug flow, ring flow and annular flow, were observed. The two-phase flow regime maps were constructed and the transition boundaries between different flow regimes identified. In an effort to unify the flow transition boundary in microchannels of different sizes, a new flow map was developed using the modified Weber numbers as the coordinates. The two-phase frictional pressure gradient in the microchannels was measured and the data were compared with predictions from the separated flow model, the homogeneous flow model and the flow pattern-based phenomenological models. Results show that the flow pattern-based models provide the best prediction of the two-phase pressure drop in the microchannels. [Copyright &y& Elsevier]

Abstract: A fouling process is often preceded by an induction period in which no significant fouling is observed. In this paper, a simple lumped parameter model based on fractional surface coverage θ has been developed to correlate experimental data in the induction period. The model assumes that active foulant species stick to the surface and gradually cover it, the rate of change of surface coverage dθ/dt being proportional to the fractional free surface (1− θ). It is further assumed that the foulant already on the surface acts as a seed, attracting more foulant in a micro-growth manner such that the growth rate is first order in θ with a rate constant k 1. Adopting the concept of removal mechanism similar to that used in adsorption science, the removal rate of the coverage is set to be proportional to the coverage with a rate constant of k 2. The three assumptions are combined to obtain the relationship dθ/dt = k 1 θ(1− θ)− k 2 θ. The fouling layer grows on the covered surface and the fouling rate can be expressed as θR f′ where R f′ can be any established fouling rate expression. Experimental data, including data obtained during induction periods have been successfully correlated for systems including crude oil fouling, water scaling and whey protein fouling. The physical meanings of the model parameters are discussed. The model supports experimental observations in which shorter induction periods are found with higher surface temperatures. The effects of the surface material and the flow velocity are also analysed. [Copyright &y& Elsevier]

Abstract: In this paper, a distributed parameter model for the evaporation system of a subcritical once-through, coal-fired, twin-furnace boiler based on 3-D temperature field reconstruction is developed. The imaginary wall surface was put forward to simplify the twin-furnace problem. The mathematical model was formulated for predicting the transient distributions of parameters, such as the heat flux, the metal-surface temperature and the steam quality; while considering the non-uniform distributions of the surface heat transfer coefficient and frictional resistance coefficient. The model was based on the 3-D temperature distribution got by a flame image processing technique. The model was validated by some measurable parameters of the evaporation system at three typical loads. The results show that the heat flux and the temperature which are located at the overlapping region of the two tangential flames are higher than those in other corners. This distributed parameter model on evaporation system reflects the in-situ operating status of the power plant boiler, which may lead to the subsequent research on a supercritical boiler. [Copyright &y& Elsevier]

Abstract: The aim of the present paper is to investigate numerically the energy separation mechanism and flow phenomena within a vortex tube. A 3D computational domain has been generated considering the quarter of the geometry and assuming periodicity in the Azimuthal direction which was found to exhibit correctly the general behaviour expected from a vortex tube. Air is selected as the working fluid. The flow predictions reported here are based upon four turbulence models, namely, the k–ɛ, k–ω and SST k–ω two-equations models and the second moment closure model (RSM). The models results are compared to experimental data obtained from the literature. Four cases have been considered by changing the inlet pressure from 200 up to 380kPa. It has been observed that all the above mentioned models are capable of predicting fairly well the general flow features but only the advanced RSM model is capable of matching correctly the measured cold and hot outlet temperatures. All the other models over predict the mean temperature difference by values up to twice the measured data. [Copyright &y& Elsevier]

Abstract: A one-dimensional mathematical model of the R744 two-phase ejector for expansion work recovery is presented in this paper. Governing equations were formulated for all passages of the ejector based on the differential equations for mass, momentum, and energy balance as well as a differential representation for the equation of state. For two-flow sections (mixer and diffuser) closing equations for mass, momentum and energy transfer between the primary and secondary flow were introduced. This model utilises the Delayed Equilibrium Model along with the Homogeneous Nucleation Theory for the purpose of the metastable state analysis for a transcritical flow with delayed flashing over the motive nozzle. The thermal properties model was based on a real fluid approach, where the REFPROP 8.0 database was used. Based on the results of experimental tests performed at SINTEF Energi Laboratory, the model was validated for a typical range of operating conditions. The range of available simulation output allowed for the creation of 1D profiles of local values for the flow variables and the computation of the overall indicators, such as pressure lift and expansion work recovery efficiency. [Copyright &y& Elsevier]

Abstract: The work presented in this paper investigates the degradation effect of flow maldistribution on the thermal and hydraulic performance of a heat exchanger. A new mathematical model is derived based on Taylor series expansion to describe the contribution of each of the four statistical moments of distribution on the degradation problem. It is found that the first two moments, i.e. mean and standard deviation, have the highest effect on the performance degradation. Subsequent higher moments will give declining degradation effects until the fourth moment, kurtosis, which has no significant effect. Maldistribution with low standard deviation and high positive skew will give low thermal deteriorations, though a distribution with negative skew is preferred for low hydraulic performance losses. The design of the heat exchanger could be modified to give these favourable moments which would minimize the degradation effects of the maldistribution. Consequently, any effort to modify the flow distribution profile should be focused on optimizing the first three moments. [ABSTRACT FROM AUTHOR]