Search

Three-phase current unbalance is a common winding fault of the motor, which will bring local overheating, cause security risks and economic losses, accurate temperature rise calculation and thermal flux characteristics analysis of the motor working in three-phase current unbalance are necessary and challenging. However, little research has been conducted on the thermal characteristics and analysis methods for the permanent magnet synchronous linear motor (PMSLM) working in three-phase current unbalance. To address this problem, a multilayer composite flat wall model contained heat source of the primary is proposed firstly to analysis the heat transfer characteristics of the PMSLM caused by three-phase current unbalance qualitatively. Then, the heat transfer and temperature distribution characteristics of the PMSLM are obtained by calculating the fluid-thermal coupling model of the PMSLM directly. What's more, the effect of current grade on heat transfer is analyzed by comparing the heat transfer characteristics of the PMSLM working in four different three-phase current balance cases. Finally, the qualitative analysis and fluid-thermal analysis results are verified experimentally with a PMSLM adopting four different three-phase current unbalance conditions. Thermal analysis of the PMSLM working in three-phase current unbalance makes it is possible to prevent local heat accumulation and avoid unexpected interruptions for the redundant motor system and the fault tolerant motor system. • A multilayer composite flat wall model contained heat source of the primary is proposed in this paper. Based on this, the heat flux and average temperature of the primary that with three-phase unbalanced current can be analyzed. The temperature distribution characteristics and thermal flux transfer of a PMSLM working in three-phase current unbalanced fault is calculated by establishing the simplified fluid model and coupling fluid-thermal field model, which is useful for analyzing the thermal characteristics of the PMSLM detailedly. Besides, the thermal characteristics of the PMSLM working in 4 different three-phase current balance cases are compared. This work can be used to analysis the thermal characteristics of the PMSLM changing with the excited unbalanced current density. [ABSTRACT FROM AUTHOR]

Abstract Currently higher requirements on accurate thermal analysis of rolling bearing are put forward for high precision bearing-spindle system. To this end, this paper first presents a reverse solution method for thermal transfer analysis of high speed ball bearing, based on the internal multi-point temperature data by direct experimental method. Firstly, temperatures of bearing rotating components were obtained by a novel non-contact quantum dots fluorescence method and were treated as the target variables, and thermal convection coefficients and bearing temperature field obtained by traditional empirical formula were treated as the initial conditions. Parameters such as thermal convection coefficients between bearing inner ring/cage and lubricant, bearing housing and the air were optimized via the multi-objective optimization method. As evaluation, thermal elongation of a precision bearing-spindle was tested and the results prove the necessity of the coefficients optimization and the reliability of the presented method in this paper. Highlights • A reverse solution method for thermal coefficients of high speed ball bearing was proposed. • Temperatures of bearing rotating components (inner ring and the cage) were simultaneously monitored. • Parameters such as thermal convection coefficients between bearing inner ring/cage and lubricant were all optimized. [ABSTRACT FROM AUTHOR]

Abstract Thermal fluid processes are inherently multi-physics and multi-scale, involving mass-momentum-energy transport phenomena at multiple scales. Thermal fluid simulation (TFS) is based on solving conservative equations, for which – except for "first-principles" direct numerical simulation – closure relations (CRs) are required to provide microscopic interactions or so-called sub-grid-scale physics. In practice, TFS is realized through reduced-order modeling, and its CRs as low-fidelity models can be informed by observations and data from relevant and adequately evaluated experiments and high-fidelity simulations. This paper is focused on data-driven TFS models, specifically on their development using machine learning (ML). Five ML frameworks are introduced including physics-separated ML (PSML or Type I ML), physics-evaluated ML (PEML or Type II ML), physics-integrated ML (PIML or Type III ML), physics-recovered (PRML or Type IV ML), and physics-discovered ML (PDML or Type V ML). The frameworks vary in their performance for different applications depending on the level of knowledge of governing physics, source, type, amount and quality of available data for training. Notably, outlined for the first time in this paper, Type III models present stringent requirements on modeling, substantial computing resources for training, and high potential in extracting value from "big data" in thermal fluid research. The current paper demonstrates and investigates ML frameworks in three examples. First, we utilize the heat diffusion equation with a nonlinear conductivity model formulated by convolutional neural networks (CNNs) and feedforward neural networks (FNNs) to illustrate the applications of Type I, Type II, Type III, and Type V ML. The results indicate a preference for Type II ML under deficient data support. Type III ML can effectively utilize field data, potentially generating more robust predictions than Type I and Type II ML. CNN-based closures exhibit more predictability than FNN-based closures, but CNN-based closures require more training data to obtain accurate predictions. Second, we illustrate how to employ Type I ML and Type II ML frameworks for data-driven turbulence modeling using reference works. Third, we demonstrate Type I ML by building a deep FNN-based slip closure for two-phase flow modeling. The results show that deep FNN-based closures exhibit a bounded error in the prediction domain. Highlights • The work has the potential to motivate researchers to employ machine learning for thermal fluid simulation. • Five machine learning strategies have been classified in this research work for thermal fluid simulation. • The classification helps to identify the strength and weakness of each ML framework based on available data and knowledge. • Three tutorials of ML frameworks are formulated including heat conduction, turbulent flow, and two-phase flow. [ABSTRACT FROM AUTHOR]

In this paper, a new approach of the Hot Disc method is presented based on the explicit calculation of the average temperature of a constant heat source on a semi-infinite medium. The Transient Plane Source (TPS) technique developed in the 90 uses a linear regression between the evolution of temperature of the source and a function. This function needs to perform an integral whose calculation can be complex and slow. Therefore, we propose a new approach based on the explicit analytical expression of the average temperature of the heat source to obtain simultaneously by inverse method, the thermal characteristics of the medium, i.e. the conductivity and diffusivity. Besides, we propose to estimate simultaneously the experimental unknown parameters, namely the correction time due to the sensor and the establishment of micro constriction phenomena and the thermal contact resistance between the sensor and the material to be characterized. This approach also makes explicit, for the first time, the sensitivities of the problem and thus to make a complete and accurate sensitivity analysis based on their analytical expressions. Thus, an uncertainty estimation analysis of the parameter estimation using a stochastic approach is carried out to predict confidence intervals on each parameter as a function of the measurement noise. A Monte Carlo method confirms the obtained results. An optimization of the experimental parameters is then conducted based on the minimization of the confidence interval of the estimated parameters. • A new approach of the TPS method is presented. • An explicit analytical calculation is used to perform the identification of the thermal conductivity and diffusivity. • A fully analytical sensitivity analysis is conducted. • A stochastic approach is carried out to predict confidence intervals on each parameter as a function of the measurement noise. [ABSTRACT FROM AUTHOR]

Artificial neural networks (ANN) have been widely used for thermal analysis of heat exchangers during the last two decades. In this paper, the applications of ANN for thermal analysis of heat exchangers are reviewed. The reported investigations on thermal analysis of heat exchangers are categorized into four major groups, namely (i) modeling of heat exchangers, (ii) estimation of heat exchanger parameters, (iii) estimation of phase change characteristics in heat exchangers and (iv) control of heat exchangers. Most of the papers related to the applications of ANN for thermal analysis of heat exchangers are discussed. The limitations of ANN for thermal analysis of heat exchangers and its further research needs in this field are highlighted. ANN is gaining popularity as a tool, which can be successfully used for the thermal analysis of heat exchangers with acceptable accuracy. [ABSTRACT FROM AUTHOR]

In this article, first the design procedure of the thermal model of a EDLC type wound capacitor (Electrochemical double layer capacitor) is described, whereby the main objective of modeling is achievement of a very close accordance of simulation results compared to measurements in various operating conditions. Development process is supported by the mathematical analysis of the internal structure of EDLC. Based on the requirements on high degree of model's accuracy, three alternatives of model's complexity are shown. Instead of accuracy the proper model has to fulfill also requirement on the computation time. Next, to meet further demands of complex modeling of supercapacitor modules, mentioned abilities (accuracy of simulation results and fast computation time of solution) must be as lowest as possible. The second important aim of this paper is the description of the development procedure of thermal simulation model of EDLC module (multi-cell supercapacitor system). Consequently simplifications targeting lowest simulation time with achievement of high model's accuracy are provided. At the end of the paper, reader is able to find simulation experiments which are confirming the proposed design procedure. [ABSTRACT FROM AUTHOR]

The Korea fourth-generation storage ring (Korea-4GSR) has a low electron beam emittance of 60 p.m.-rad, and provides a photon beam that is 100 times brighter and 100 times more coherent than the third-generation Pohang Light Source (PLS-II). However, the new source imposes a higher heat load on beamline optics. In particular, the first mirror (M1), which receives the broad-bandwidth white beam will be distorted by the thermal load from X-ray beam and the heat bump will degrade the beam quality. For the thermal analysis of M1, a method is developed to solve the thermal deformation with temperature gradient and absorbed power density. To implement the method in the analysis of heat load effect on M1, a benchmark study was performed on beamline 8A at PLS-II. In this paper, we describe the thermal analysis of M1 in Korea-4GSR after verifying our simulation method in a benchmark study. [ABSTRACT FROM AUTHOR]

Abstract: This paper is intended to provide very accurate analytical solutions modeling transient heat conduction processes in 2D Cartesian finite bodies for small values of the time. Analysis of diffusion of thermal deviation effects indicates that, when the space and time coordinates satisfy a criterion developed in the paper, the simple transient 1D semi-infinite solutions may be “used” for generating extremely accurate values for temperature and heat flux at any point of a finite rectangle. Also, they may be “used” with excellent accuracy as short-time solutions when the time-partitioning method is applied (so avoiding the usually difficult integration of the short-cotime Green''s functions). A complex 2D semi-infinite problem is solved explicitly and evaluated numerically as part of the analysis. The proposed criterion is based on an accuracy of one part in 10 n (n = 1,2,...,10,...), where n = 2 is for engineering insight and visual comparison while n = 10 is for verification purposes of large numerical codes. [Copyright &y& Elsevier]

Abstract Predicting temperature evolution of sliding bodies plays a key role in many industrial designs. Temperature-dependent material properties, microstructure evolution of material while heating and quenching, and residual stress comprise these factors importance. Despite existing theoretical, numerical, and experimental methods for predicting surface temperature of sliding bodies, there are some restrictions relating to each one. This paper aims to present a strategy and numerical method for finding the temperature evolution of sliding bodies with arbitrary geometry of the contact patch. Preserving generality, temperature evolution of sliding railway flat wheels is the main problem of this study. A finite element model (FEM) is developed with ANSYS APDL software (Canonsburg, PA, USA). The model is validated with existing analytical formulas in steady state and transient cases and a good agreement is achieved. Six real cases from full-scale field tests are considered and a comparison is made between the results. As an application of the method, the obtained time-history of surface temperature is applied to a 3D FE model of a flat wheel as a boundary condition. Graphical abstract Image 1 Highlights • A new strategy for finite element modeling of thermal analysis of sliding bodies is developed. •Thermal analysis of railway wheel and rail during formation of wheel flat is among the applications. • Validation of new model is performed with existing theoretical and experimental data. • Applying thermal contact resistance to the model leads to accurate steady-state temperatures. • The time-dependent surface temperature result is applied to a 3D model to perform thermal analysis. [ABSTRACT FROM AUTHOR]

Abstract Many studies have been conducted on the mechanical aspects of friction interfaces. The importance of temperature is often highlighted, but very few studies have modeled and measured this fundamental aspect of a sliding contact. In many industrial fields, the thermal phenomenon is a dimensioning criterion (space industry. railway...). The friction of materials leads to increased temperatures which can generate degradations of the contact surfaces. It is for this reason that it is fundamental to have a thermal model representative of the sliding interface. One of the thermal models describes the heat transfer in the sliding interface introduces three macroscopic thermal contact parameters h sc , α and φ g. This paper presents experimental results about the simultaneous estimation for these three thermal parameters of a sliding contact from several experiments for the couple of materials steel/bronze. Highlights • The heat transfer in the sliding interface could be described by three macroscopic thermal contact parameters h sc , α and φ g. • An original set up is used in order to measure the temperatures. • The experimental identification of theses parameters using inverse method is performed from several experiments. • This work presents a new result of the effect of the velocity on the thermal contact parameters. [ABSTRACT FROM AUTHOR]

Abstract Laminar natural convection in a vertical annulus with inner wall covered by a porous layer is numerically studied in this paper by using a multiple-relaxation-time lattice Boltzmann (MRT LB) model for the axisymmetric thermal flow in porous media at the representative element volume (REV) scale. The effects of the Rayleigh number, Darcy number, thermal diffusivity ratio and thickness of the porous layer on the overall heat transfer rate are investigated. It is found that wrapping with a porous layer can serve as a useful tool for heat transfer augmentation or reduction, which is strongly depending on the physical parameters, especially the Darcy number and thermal diffusivity ratio. [ABSTRACT FROM AUTHOR]

Abstract Compared with other underground cables, low voltage cables are most intensely heated by the sun due to the low laying depth. Accordingly, the main purpose of this paper is to show how the heat of solar radiation affects the ampacity of a 0.4 kV multi-core cable through different cool pavements at laying depths between 0.4 and 1.0 m where this effect is significant. The objectives of this study are as follows: (i) to simulate experimentally the effect of thermal emissivity of the cool pavement surface on the cable in known laboratory conditions, (ii) to express the effect of solar absorptivity of the cool pavement surface on the cable based on an analogy between the thermal effect of the laboratory interior and the thermal effect of outdoor solar radiation, and (iii) to simulate numerically the thermal effect of solar radiation using a large-size FEM-based model for the most unfavourable summer conditions and the most common winter conditions. All the defined objectives have been successfully met and it has been shown that the ampacity of the cable installed at a depth of 0.7 m can be increased up to 45% in summer and up to 12.1% in winter compared to the corresponding base cases. Highlights • Controlling the thermal environment of cables using cool pavements – a new method. • Cool pavements significantly increase the ampacity of underground power cables. • Filling the trench completely with bedding additionally increases the ampacity. • For cool pavements, the ampacity rises as laying depth declines. • Solar irradiance affects the ampacity differently for white and gray pavements. [ABSTRACT FROM AUTHOR]

The present paper reports the results from modelling and experimentation with a lithium-ion battery pack operating at room temperature and under varying discharge rates. The variation in the internal resistance of the cell with change in the temperature is investigated experimentally. The prismatic Li-ion battery pack is discharged at 1C, 2C, 3C and 4C and significant parameters, such as pack voltage, temperature, and state of charge, are obtained. This is accomplished by connecting three LiFePO 4 20 A h capacity prismatic batteries in series and applying 18 thermocouples at various locations on the surface of all three cells. The results show that there is a significant increase in battery surface temperature with an increase in discharge rate. The highest average surface temperature of the battery pack (56.5 °C) is observed experimentally at a 4C discharge rate, and the lowest (30.7 °C) at 1C based on modelling. Similarly, the maximum total heat generation (59.2 kJ) is observed at 4C experimentally and the minimum (37.5 °C) at 1C from modelling. A comparison of the modelling results with the experimentally determined temperature, voltage and heat generation shows good agreement. Also, the internal resistance of the cell is observed to increase as the state of charge decreases, and to decrease with increasing cell temperature. [ABSTRACT FROM AUTHOR]

Abstract: This paper is the first part of a three paper series studying the overall performance of a micro pin-fin heat sink with single phase liquid flow and different pin-fin geometries operating under and similar conditions. Two different heat sinks, one with square shaped pin-fins and the other with circular pin-fins are selected for study in this paper. The paper focuses on studying the effect of thermal resistance and pressure drop of micro heat sinks when subjected to various factors such as pitch distance in axial and transverse directions, aspect ratio of the pin-fin, hydraulic diameters of the pin-fin, and the liquid flow rate through the device. A figure of merit (FOM) involving both the thermal resistance and pressure drop across the heat sink is introduced in the paper and the performance is evaluated on the basis of this FOM. The heat sinks are subjected to uniform heat flux at the bottom of the heat sink and the characteristic study is based on constant Reynolds number of liquid flow at the entrance of the channel. Water is used as the fluid in this study. The study is conducted over the Reynolds number range of 50–500. The characteristic study is carried out with the help of simulations developed using commercially available computational fluid dynamics software CoventorWare™. The characteristic study carried out in this paper is divided into four cases. In the first case the axial pitch distance is varied between 350 μm and 650 μm by keeping the aspect ratio of the pin-fin structure constant at 0.5. For the second case the transverse pitch distance is varied between 150 μm and 300 μm and the aspect ratio is kept the same as in the first case. Third case studies the effect of varying the aspect ratio (between 0.33 and 1) of the pin-fin structures by keeping both pitches constant. Case four studies the variation in the performance of the heat sink with the change in the hydraulic diameter of the pin-fins. The study conducted in this paper reveals the importance of considering the pressure drop along with the thermal resistance in evaluating the overall performance of the micro pin-fin heat sink. At low Reynolds number (below 300) the heat sinks with circular pin-fins shows better performance compared with heat sinks with square pin-fins and vice versa at high Reynolds number (above 300). FOM varies considerably with the change in the parameters like axial pitch distance, transverse pitch distance, aspect ratio and hydraulic diameter of the pin-fins. [Copyright &y& Elsevier]

Abstract: Thermal actuators are extensively used in microelectromechanical systems (MEMS). Heat transfer through and around these microstructures are very complex. Knowing and controlling them in order to improve the performance of the micro-actuator, is currently a great challenge. This paper deals with this topic and proposes a dynamic thermal modelling of thermal micro-actuators. Thermal problems may be modelled using electrical analogy. However, current equivalent electrical models (thermal networks) are generally obtained considering only heat transfers through the thickness of structures having considerable height and length in relation to width (walls). These models cannot be directly applied to micro-actuators. In fact, micro-actuator configurations are based on 3D beam structures, and heat transfers occur through and around length. New dynamic and static thermal networks are then proposed in this paper. The validities of both types of thermal networks have been studied. They are successfully validated by comparison with finite elements simulation and analytical calculations. [Copyright &y& Elsevier]

Abstract: This paper faces the problem of geometric optimisation for exchanger profiles with innovative shapes. In particular it was analysed the Y shape, keeping the dimensionless thermal conductance as reference parameter like in the thematic technical literature. The use of suitable geometrical constraints allows wide comparisons with papers in literature using different kinds of geometries. The methodological approach here chosen is numerical and utilises a CFD software. The geometries examined are obtained by varying the angle between the two arms of the Y, starting from the T-shaped profile that allows the best performances, as obtained in a previous work. Results show that the new shape proposed for the fins, together with the assessment of the horizontal width, leads to a novel performance evaluation criterion. [Copyright &y& Elsevier]

Thermal radiation is a significant mode of energy transmission besides conduction and convection in most combustion systems. Accurate treatment of thermal radiation is a crucial element for predicting the flame structure and pollutant formation. However, thermal radiation to fuel droplet evaporation is often neglected in the numerical simulations of two-phase spray combustion systems. In this paper, computational analysis on the thermal radiation to evaporation and combustion of fuel droplets in two-phase spray combustion is conducted. The influence of flame radiation on droplet evaporation and combustion is studied by adding radiation source term to the energy equation describing droplet evaporation process. Radiation transfer equation is solved, in which the radiation of CO 2 , H 2 O and soot is imposed to consider radiation effect of the flame. The partially premixed combustion model is employed, in which radiation heat transfer between droplet and ambient gases is taken into account. A reduced chemical reaction mechanism for n-heptane consisting of 76 species and 349 reactions is used. Four different numerical setups have been used and compared, and the simulation results coincide with the experiment data in terms of spray statistics and flame shapes. The peak flame temperature increases by 28 K when the radiative heat source term in the evaporation process is considered. The droplet evaporation is significantly enhanced by thermal radiation, leading to a promotion of 34.8% in C 7 H 16 concentration in the center region of combustor. The concentration of combustion products, such as H 2 O and CO 2 , increases by 13.2% in the reaction region. [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]

This paper presents the stability, convergence and optimization characteristics of interface treatments for steady conjugate heat transfer problems. The Dirichlet-Robin and Neumann-Robin procedures are presented in detail and compared on the basis of the Godunov-Ryabenkii normal mode analysis theory applied to a canonical aero-thermal coupling prototype. Two fundamental parameters are introduced, a “numerical” Biot number that controls the stability process and an optimal coupling coefficient that ensures unconditional stability. This coefficient is derived from a transition of the amplification factor. A comparative study of these two treatments is made in order to implement numerical schemes based on adaptive and local coupling coefficients, with no arbitrary relaxation parameters, and with no assumptions on the temporal advancement of the fluid domain. The coupled numerical test case illustrates that the optimal Dirichlet-Robin interface conditions provide effective and oscillation-free solutions for low and moderate fluid-structure interactions. Moreover, the computation time is slightly shorter than the time required for a CFD computation only. However, for higher fluid-structure interactions, a Neumann interface condition on the fluid side presents good numerical properties so that no relaxation coefficients are required. [ABSTRACT FROM AUTHOR]

In this paper, dispersion effects on forced convection heat transfer in a gaseous slip flow through a microtube filled with anisotropic porous medium are investigated semi-numerically. Microtube is subjected to constant heat flux and a local thermal non-equilibrium condition is assumed. Rarefaction effects are taken into account by applying first-order velocity slip and temperature jump boundary conditions. Dispersion is proven to have a significant impact on heat transfer in rarefied gases. Temperature distributions for both solid and fluid phases are obtained. Nusselt number variation with respect to porous shape factor and Biot number is illustrated, indicating enhancement up to 10% in predicted heat transfer due to dispersion. The influence of Reynolds number on thermal dispersion is proven to be insignificant. Dispersion plays a significant role as gas becomes more rarefied. It is seen that an increase in shape factor of a porous media can improve Nu for a non-rarefied gas, but as rarefaction effects grow, this can affect heat transfer negatively. Also, effects of dispersion on heat transfer diminishes for higher values of Biot Number due to the overcoming of interstitial heat transfer to thermal dispersion effect. [ABSTRACT FROM AUTHOR]

Partitioned approaches for the simulation of coupled conjugate heat transfer are gaining popularity in fields that require accurate thermal predictions. Considerable efforts have been put into determining stable coupling schemes, but performance enhancements have been neglected. This paper presents, for the first time, a detailed and comprehensive study of the numerical properties of Dirichlet-Robin coupling procedures, used in conjugate heat transfer simulation, with emphasis put on the optimal local coupling formulation that was recently derived from a stability analysis. This all-new optimal coupling approach provides local adaptability and has never been tested on a complex setup. This investigation looks to determine the relevance and the limitations of the theory when applied to complex conjugate heat transfer setups. The stability theory of the optimal Dirichlet-Robin coupling scheme is first recalled, then, a realistic 3D application, with complex geometry and flow structures, is used to evaluate the performance and sensitivity of Dirichlet-Robin couplings, with respect to various numerical parameters. This detailed study allows, for the first time, to evaluate the advantages and limitations of the recently proposed optimal procedure, when used on realistic 3D CHT problems. It turns out that the local optimal Dirichlet-Robin formulation outperforms all what is found in literature, and insures unconditional stability with monotone convergence for all considered setups of the 3D model. [ABSTRACT FROM AUTHOR]

In this paper, the heat transfer rate and the pressure drop of metal porous media inserts are analyzed in the single phase. The testing range of the Reynolds number is between 3654 and 14617. Tap water is used as the working fluid. The effect of particle size and particle shape on the heat transfer performance is studied. The results show that an optimal value existed among the testing samples for dendritic particle. The best heat transfer rate is resulted by the sample D-125 instead of by the sample D-25 with the small particle size, which is approximately 2.2–3.0 times as that of the smooth tube. This is mainly because the velocity at the inlet of inserts increases greatly and the fluid mixing intensity at the annular is also high. Two factors work together to bring about a best heat transfer coefficient. The friction factor increases with the decrease in the particle size. The best Performance Evaluation Criterion (PEC) value is resulted by sample D-125, which is about 1.26–1.71. The particle shape also has an impact on the heat transfer rate. The heat transfer coefficient of the spherical particle is higher than that of dendritic particle. However, the higher heat transfer rate is paid at the cost of high flow resistance. This high flow resistance finally deteriorates the heat transfer performance. As a result, the best heat transfer performance is achieved by the dendrictic particle, which brings a high heat transfer rate as well as a low flow resistance. Therefore, the PEC values have to be taken into consideration in the design of heat exchanger. [ABSTRACT FROM AUTHOR]

Particle migration in nanofluids has received less than due attention in the literature, and is generally an open research topic requiring more investigation. Particle migration can have great influences on the characteristics of nanofluids through disturbing the distributions of nanoparticle concentration and thermophysical properties. This paper attempts to review and summarize the studies conducted on nanofluids, considering particle migration, including those conducted via methods such as Eulerian-Lagrangian, Buongiorno model, molecular dynamics simulation, and different theoretical approaches. Several important issues are highlighted that deserve greater attention. It is shown that there are still several hot debates for flow and thermal mechanisms in nanofluids, particularly regarding the behavior of nanoparticles. Besides, this survey identifies the challenges and opportunities for future research. [ABSTRACT FROM AUTHOR]

The paper presents a study of possibilities to extend the present methodology for thermal characterization of thin solid samples by photoacoustic techniques. The present methodology consists of linear fitting of the experimental data to approximate the expressions derived from the composite piston model of photoacoustic response and it is mainly used for calculation of thermal diffusivity of thin samples. The study has shown that the methodology may be extended to calculation of thermal diffusivity, thermal conductivity and thermal expansion coefficients of thin samples by linear fitting in multiple frequency ranges and by analysis of the intersection frequency, which is the frequency where the magnitudes of two components of photoacoustic response in the composite piston model are equal. The analysis of numeric errors of the methodology has revealed the dominant sources and magnitude of the errors, leading to the conclusion that photoacoustic techniques should be carefully used as a tool for extensive thermal characterization of thin samples in the cases when other techniques are not applicable or have larger errors. [ABSTRACT FROM AUTHOR]

In this paper, the effects of magnetic field, nonlinear thermal radiation and homogeneous-heterogeneous quartic autocatalysis chemical reaction on an electrically conducting (36 nm) alumina-water nanofluid containing gyrotactic-microorganism over an upper horizontal surface of a paraboloid of revolution is presented. The case of unequal diffusion coefficients of reactant A (bulk-fluid) and reactant B (catalyst at the surface) in the presence of bioconvection is presented. In this article, a new buoyancy induced model for nanofluid flow along an upper horizontal surface of a paraboloid of revolution is introduced. The viscosity and thermal conductivity are assumed to vary with volume fraction and suitable models for the case 0% ≤ ϕ ≤ 0.8% are adopted. The transformed governing equations are solved numerically using Runge-Kutta fourth order along with shooting technique (RK4SM). Good agreement is obtained between the solutions of RK4SM and MATLAB bvp5c for a limiting case. The influence of pertinent parameters are illustrated graphically and discussed. It is found that at any values of magnetic field parameter, the local skin friction coefficient is larger at high values of thickness parameter while local heat transfer rate is smaller at high values of temperature parameter. [ABSTRACT FROM AUTHOR]

Active pipe-embedded building envelope can allow for substantial heat flow for relatively small temperature difference due to the embedded pipes in the external wall/roof. This structure can directly utilize the low-grade sources for reducing building cooling/heating load and improving indoor thermal comfort by intercepting the heat gain/loss through the building envelope due to the circular water inside the embedded pipe. This paper presents the experimental validation of a semi-dynamic simplified model of the active pipe embedded building envelope. The experiment test rig consists of two environment chambers with one for simulating the ambient environment and one for indoor environment with a pipe-embedded building envelope sample separating both chambers. A small chiller and a buffer tank are installed to provide stable water temperature for the test sample. The temperatures and heat fluxes on both sides of the test sample, the inlet and outlet water temperature as well as flow rate are measured. The measured boundary conditions are used as the inputs of the semi-dynamic simplified model for calculating the thermal performance of the active structure. The results show the semi-dynamic simplified model can predict the semi-steady or pure dynamic thermal performance of the pipe-embedded building envelope very well by comparing with the measurement. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of the thermal performance of axial flow air cooling for lithium-ion battery pack. A thermal model for a battery pack with 32 single cells is developed and is numerically solved with coupling the fluid governing equations. The heat generation rate of the battery is calculated by a UDF (user defined function) program, which is based on a pseudo 2D model of the lithium-ion batteries. The effects of the radial interval between cells and air flux on the thermal performance of the axial flow air cooling system are investigated by numerical simulations. The results show that increasing the radial interval leads to a slight average temperature rise but benefits to the temperature uniformity of the battery pack. A larger radial interval can significantly reduce the power cost of the cooling system; however it causes a decrease of space efficiency mildly. A larger air flux is found to be benefit to the temperature uniformity within battery pack. An optimal region based on the assessment of the power cost, space efficiency and temperature homogeneity for the parameter designs of the battery cooling system is presented. [ABSTRACT FROM AUTHOR]

For considering the non-equilibrium effect, the present paper uses the generalized dual-phase-lag model of bioheat transfer to describe the thermal behavior in a laser irradiated living tissue. The thermal damage is also estimated with the Arrhenius equation. The hybrid application of the Laplace transform and the modified discretization technique is employed to solve the present problem. The non-reduction of the generalized dual-phase-lag model to the Pennes equation is further explored. The effects of that the phase lag times depend on the porosity, heat capacities of blood and tissues, coupling factor, and the ratio of thermal conductivity of tissue and blood are taken into account. The results show that the generalized DPL bioheat transfer equation cannot reduce to the Pennes and classical DPL bioheat transfer equations, even with the effect of spatial heating source. Porosity and coupling factor are particularly important to the generalized DPL model. The relation between the phase lag times would demonstrate the characteristics of thermal response in tissue. [ABSTRACT FROM AUTHOR]

The paper focuses on modeling of heat, momentum and concentration transport in stable film boiling of a nanofluid over a vertical surface. An approximate analytical model of the transport processes in the vapor film was employed in simulations. The model takes into account effects of the Brownian and thermophoretic diffusion. The novelty of the model consists in pinpointing six major non-dimensional parameters, which describe effects of the nanoparticles on heat transfer and fluid flow in the vapor film. They include: (i) parameter A that accounts for the relation between the thermophoretic and Brownian diffusion; (ii) the nanoparticle concentration φ ∞ in the vapor; (iii and iv) the normalized densities of the nanoparticles R pυ and R pf ; (v) the relative thermal conductivity of the nanoparticles K ; and (vi) parameter m that characterizes the viscosity of nanofluids. Novel analytical solutions resulting from this model characterize velocity profiles, the mass flow rate, the thickness of the vapor film and the Nusselt number as the functions of the aforementioned parameters. It was demonstrated that an increase in the nanoparticles concentration fosters the processes of momentum, mass and heat transfer. [ABSTRACT FROM AUTHOR]

Active pipe-embedded building envelope is a new kind of pipe-embedded building external wall/roofs. Usually, pipes are embedded in the wall slab or roof slab to allow water circulating in these pipes for heat transfer. Low-grade energy sources can be used for this structure since the enlarged heat transfer surface between the slab mass and water in the pipe allowing for substantial heat flow for relatively small temperature difference. This structure may reduce building cooling/heating load and improve indoor thermal comfort by intercepting the heat/coolth from the ambient air to indoor space. This paper presents a semi-dynamic model of this structure for thermal performance evaluation for system design or indoor environment control etc. This semi-dynamic model is a coupled model. The first part is a simplified dynamic RC model (i.e., resistance and capacitance model). The heat transfer along the width of this structure can be predicted easily by the RC model. The second part is a classical NTU model for evaluating the heat transfer along the pipe and total heat transfer on both surfaces of this structure. A CFD model is developed to act as a virtual experimental test rig to simulate the thermal characteristics of this structure. The simulated results are used to validate this semi-dynamic model and its performance prediction. [ABSTRACT FROM AUTHOR]

In this paper, an uncertainty propagation methodology considering correlations among the input variables for heat transfer analysis through fibrous composite insulation material subjected to severe aerodynamic conditions is presented, based on Monte Carlo (MC) simulation with Cholesky decomposition. The effects of correlation coefficient on the thermal evolution uncertainty, failure probability, and Sobol sensitivity indexes are discussed. The results show that the thermal response outputs become more scattered after taking into account the dependence of variables. The failure probability increase with the rise of the correlation coefficient, and nearly 15% increase is observed when the temperature limit is 470 K under the current uncertainty level. Sobol sensitivity analysis demonstrates that the correlated group variables of aerodynamic thermal and pressure load have the most significant first order and total effect on the thermal response simulations. However, the mean fiber diameter and the correlated group variables of density, specific heat and thermal conductivity of virgin material have weak contributions to the first order effect, but have relatively strong contribution to the interaction effect with other variables. The correlation effect of input parameters causes different influences on the sensitivity indexes of different variables. In all cases, the weakest correlation gives the highest total sensitivity index. The provided analyses demonstrate that incorporation of correlation information of stochastic variables is essential in random variable characterization, thermal evolution uncertainty level quantification, parameter importance identification and risk assessment, and it is especially imperative for thermal protection components with high reliability requirement to prevent the occurrence of catastrophic event. [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]

If a gel is formed when the flow of waxy crude oil within a pipeline is stopped for a period of time, the required restart pressure may be high and the line is costly to operate. The conventional method of predicting the restart pressure for gelled crude oil assumes a constant yield stress across and along the pipe section; this often leads to excessive over sizing of pump and piping system. Many researches highlighted that the presence of gas voids upon cooling of waxy crude may have an impact on the yield stress of gelled crude. This paper describes the use of Magnetic Resonance Imaging (MRI) to investigate the formation behaviour of gas voids within a gelled crude oil sample from a field in the South China Sea. Scanning of gelled crude at selected temperatures was performed following cooling in the circular pipe section within an experimental flow loop rig. Gas voids within the range of 7–12% were observed in the gelled samples resulted from different cooling temperatures and cooling rates. The cooling temperature and cooling rates were observed to influence significantly the location and volume of gas voids formed within the gelled samples. Higher cooling rates resulted in higher volume of gas voids close to pipe wall while lower cooling rates resulted in more gas voids located around core of the pipe. [ABSTRACT FROM AUTHOR]

Based on the blood circulatory system, a model is established for living biological tissue represented by a vascular network and surrounding tissue. In this paper, we analyze the heat transfer in living biological tissue and present an analytical model for the effective thermal conductivity of living biological tissue by taking into account the effects of geometric structures of branching vascular network and convection caused by blood flow. The proposed model is expressed as a function of the thermal conductivities of solid tissue matrix and blood, structural parameters of branching vascular network, porosity and properties of blood. It is found that the effective thermal conductivity of living biological tissue decreases with the increase of branching levels, length ratio and diameter ratio. It is also found that there exists a thermal conductivity ratio, at which the effective thermal conductivity is same for different porosities, below which the effective thermal conductivity increases with the increase of porosity, and above which the effective thermal conductivity decreases with the increase of porosity. A good agreement is obtained between the proposed model predictions and available experimental data for living tissue. The present results show that blood flow plays an important role in increasing the effective thermal conductivity, and the proposed model with blood flow is more reasonable and can reveal more physical mechanisms of heat transfer in living biological tissue. [ABSTRACT FROM AUTHOR]

This paper presents the development of a nano-pore silicon-based (NPSB) substrate as a thermal substrate for multi-chip array light-emitting diodes (LEDs) using a YAG phosphor supported chip-on-board (COB) package structure. The proposed structure of the substrate has a nanoporous anodised aluminium oxide (AAO) layer and silicon dioxide (SiO 2 ), that are deposited by electroplating plasma-enhanced chemical vapour deposition (PECVD) on a thermally oxidised silicon wafer, respectively. To analyse the thermal characteristics of the proposed substrate, we use an InGaN blue LED with a 5 W multi-chip array and an individual LED chip size of 900 μm × 900 μm × 150 μm. The thermal performance was investigated, the junction temperature was estimated using the computational fluid dynamic (CFD) solver package, and the measurement results were validated using an infrared (IR) camera and the thermal transient tester (T3ster). Due to the effect of the cerium-activated yttrium aluminum garnet (YAG:Ce 3+ ) yellow phosphor package on an NPSB thermal substrate, the parallel heat flow generates and induces reduction of the overall thermal resistance by as much as 0.3 K/W. [ABSTRACT FROM AUTHOR]

Characterizing and tracking the properties variation in conductive material such as electrical conductivity, magnetic permeability and thermal conductivity have promising potential for the detection and evaluation of material state undertaken by fatigue or residual stress. This is a challenge task for the research field of non-destructive testing and evaluation. This paper proposes a spatial-transient-stage tensor mathematical model of inductive thermography system and Tucker decomposition algorithm for characterizing and tracking the variation of properties. The inductive thermography has advantages in such as rapid inspection and high sensitivity of defect detection. The links between mathematical and physics models have been discussed. The simulation experiments of tracking physic properties of steel material are investigated and verified. In addition, the real experiment of the measurement for gears with different cycles of fatigue tests is evaluated. The estimation of normalized stage basis by using Tucker decomposition has shown high correlation relationships with different variation of physics properties in material. [ABSTRACT FROM AUTHOR]

Due to the cyclical nature of the high pressure casting process, there will be a thermal periodic steady state of the high pressure die casting dies (hpdc-dies) during operation. A continuous temperature pattern (as a function of time), that is recurring during each process step can be observed. The quality of the castings as well as the life span of the tools is highly dependent on these periodic temperature patterns. It would be state of the art to simulate the hpdc-process with highly-specialized process simulation software. However, because of the high initial costs and the necessary human and computational resources, their use during operation to adjust the parameters of the cooling management is generally not utilized. Instead, the input parameters of the cooling management are chosen by trial and error. This paper focuses on the development a simple linear thermal model to describe the temperature patterns within the die. This is helpful to control the cooling management more effectively during operation. Approaches of dynamic systems simulation are used to create a model of the energy transport phenomena within the hpdc-die. Here it is shown in general terms how to model fluid-cooled solids by the combination of n sub process steps in n state space models to depict the whole thermal cyclical process. The set up of sets of balance equations are shown with a simplified example, using formal matrix operations. The obtained results of the simulation are discussed and evaluated. The conclusions of measured data from the experimental hpdc-die are compared to the solution of the simulation using the thermal model approach described above. [ABSTRACT FROM AUTHOR]

This paper describes a thermal model of sliding electric contacts with mechanical friction in electric rails system. The model has been validated for two electric contacts which are connected in parallel on the same contact line. The obtained mathematical model can be used to analyse the thermal behaviour of electric contacts system in steady-state conditions at different values of the electric current, friction coefficient, contact force, line cross-section, distance between contacts, speed of the contacts and ambient temperature. Also, the thermal model allows the computation of the temperature at different ratio between the currents which flow through electric contacts. There is a good correlation between calculated values and experimental results. [ABSTRACT FROM AUTHOR]

Abstract: A composite-medium line-source model has been recently developed for modeling short-time thermal processes of borehole ground heat exchangers. The composite-medium line-source model is attractive for applications where the short-term or high-frequency responses of borehole ground heat exchangers are important. In this paper, the short-time performance of this analytical model is examined in depth by comparing it with a two-dimensional finite volume model. The numerical model can address the heat capacity of circulating water by using a novel time-varying boundary condition on the inner walls of the U-shaped tube, in addition to the heat capacities of U-shaped tube and grouting material. Both the numerical and the analytical composite-medium models are validated using an independent sandbox experiment. Comparisons between the two models are also made for different parameters, including heating rate, the spacing of the U-tube legs, thermal properties, and borehole radius. Overall, the composite-medium line-source model gives the virtually same results as the numerical model except for the first several minutes: the analytical solution overestimates temperature responses during the first 3 min, which is caused by the line-source assumption ignoring the heat capacities of the fluid and the U-shaped pipe. [Copyright &y& Elsevier]

Abstract: This paper presents a numerical study of heat transfer from spheres settling under gravity in a box filled with liquid. Three-dimensional Lattice Boltzmann Method is applied to simulate fluid-particle interaction. Firstly the developed numerical model is validated in comparison with experimental and numerical data for a falling sphere in a box filled with liquid. Then the effects of Reynolds, Prandtl and Grashof numbers (Re, Pr, Gr) are investigated for a settling particle at fixed/varied temperature. The time variations of velocity, height and Nusselt number of the settling particle are also investigated. The results depict that the maximum settling velocity of the particle at varied surface temperature is higher at lower Reynolds numbers. As the Reynolds number increases, the settling velocity of the particle for both cases of constant and varied temperature is the same. However, the Nusselt number of the particle at varied temperature is lower compared with that for the particle at constant surface temperature. Increasing the Grashof number leads to slower settling and larger average Nusselt number. Finally sedimentation of 30 hot spherical particles in an enclosure and their hydraulic and heat transfer interactions with the surrounding fluid are studied. The results depict how the presence of heat transfer phenomena can significantly alter the behavior of settling particles. [Copyright &y& Elsevier]

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]

This paper investigated the effect of separation distance on the flame appearance and radiation heat flux of medium-scale pool fires dominated by radiation. A series of experiments were conducted on two adjacent heptane pool fires with diameters of 20 cm, 40 cm and 60 cm at separation distances ranging from 0 to 60 cm. According to experimental results, flame height and flame inclination angle increase monotonously with the increase of pool diameter. As separation distance increases, flame height increases first and decreases gradually for 3 different sized pool fires. However, the variation law of flame inclination angle with separation distance varies with pool diameter. The normalized flame height (H f / D) is found to increase exponentially with the dimensionless heat release rate (Q *) with an exponent of 0.71. The radiative heat flux at the center of the pool surface peaks at the critical separation distance of flame merging, which results from increased flame emissivity and view factor. Based on thermal analysis, a model to predict the radiative heat flux on the fuel surface is developed. The predicted radiative heat fluxes quantitatively match the experimental results but with 20% overvalued, due to the neglection of radiation blockage effect of cool fuel vapors zone and soot. The blockage effect is more pronounced for the merging pool fires with a diameter of 60 cm. • Experiments of medium-scale double heptane pool fires were conducted. • Flame morphological characteristics of pool fire were quantified. • A unified model was established to predict the radiative heat flux delivered to the pool surface at different conditions. • Radiation blockage due to fuel vapors and soot was quantitively analyzed. [ABSTRACT FROM AUTHOR]

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: In the aerospace industry, the manufacturer Airbus must ensure that for all flight conditions, the temperature of each aircraft powerplant system must be less than its corresponding maximum declared temperature. In our days, based on flight test data, Airbus needs to develop temperature extrapolation methods in order to predict equipments'' thermal behavior at the worst conditions. The proposed techniques are based on the system identification theory which consists on heuristically determining an analytical model using physical insights and measurements. More precisely, this paper validates ARX models as a tool for the identification of the system''s temperature. This is done through the understanding of the physical insights of this type of structures and based on numerical simulations and laboratory representative tests. [Copyright &y& Elsevier]

Abstract: Our previous study has demonstrated that the conical strip inserts have a good thermo-hydraulic performance in the tubular turbulent flow regime. This paper investigates its thermo-hydraulic performance of laminar flow numerically. Effects of some geometrical parameters are studied. Computation results show that the average Nusselt number of enhanced tube is augmented by 3.70–5.51 times (average Nu = 16.15–24.05), while the average friction factor increases by 5.31–14.77 times (average f = 0.59–1.51) those of plain tube. The values of performance evaluation criterion (PEC) range between 1.17 and 2.97. Numerical results indicate that larger strip size (characterized by a geometry angle), smaller strip-wall gap and smaller strip pitch can effectively enhance the heat transfer rate, but also increase the flow resistance. The impact of slant angle depends on the magnitude of Reynolds number. Moreover, it is shown that the Nusselt number and friction factor are sensitive to the geometry angle, while the most sensitive factor of PEC value is the strip pitch. Relatively high PEC value is obtained at a parameter combination with small slant angle, strip-wall gap, strip pitch, and moderate geometry angle (α = 30°, δ/D = 0.10, s/D = 1.5, β = 60°) among all the investigated conditions. [Copyright &y& Elsevier]

Abstract: The present paper deals with CFD study of flow and thermal characteristics in air-conditioned rooms under turbulent mixed convection conditions. Air enters room from a sidewall slot flush with isothermal ceiling and leaves through a slot in opposite wall flush with floor. Velocity and temperature distributions are determined by a CFD model that has been previously validated by comparison with experimental data. Rigorous dimensional analysis shows that performance of the air-distribution system depends on: supply Reynolds number Re d , Grashof number Gr d (or Archimedes number Ar d ), room aspect ratio L/H, dimensionless heights of supply and return ports (d/H and t/H), where H is room height. For a room with fixed geometry, the effects of Re d and Gr d (or Ar d ) are investigated systematically by varying one parameter at a time. Results show that ceiling average Nusselt number (Nu d,av) increases with Re d and decreases with Gr d (or Ar d ). For a given Gr d , the heat removal index (HRI) increases with Re d up to Re d  ≈ 9000, then stays practically constant thereafter. For a given Re d , HRI decreases with increasing Gr d (or Ar d ). A criterion for distinction between forced and mixed convection situations is developed, resulting in a critical Archimedes number of 0.11. Results further indicate that Ar d alone, irrespective of the particular values of Re d and Gr d , determines to a reasonable extent Nu d,av and HRI when Ar d is above its critical value. Streamlines and temperature contours are found to be consistent with other results and helped explain them. [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 study of the thermal performance of two fins mounted on the bottom wall of a horizontal channel and cooled with either pure water or a Cu–water nanofluid. The bottom wall of the channel is heated at a constant temperature and cooled by mixed convection of laminar flow at a relatively low temperature. The top wall is adiabatic. The effects of pertinent parameters such as the Reynolds and Richardson numbers, the solid volume fraction, and the distance and the thermal conductivity of the fins on their thermal performance are studied. The results of the numerical simulation indicate that the heat transfer rate of fins is significantly affected by the distance and the thermal conductivity of the fins. The influence of the solid volume fraction on the increase of heat transfer is more noticeable at higher values of the Reynolds number. The fins behave differently in terms of their thermal performances at higher values of the Reynolds number. [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]