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The submerged combustion vaporizer (SCV) is indispensable general equipment for liquefied natural gas (LNG) receiving terminals. In this paper, numerical simulation was conducted to get insight into the flow and heat transfer characteristics of supercritical LNG on the tube-side of SCV. The SST model with enhanced wall treatment method was utilized to handle the coupled wall-to-LNG heat transfer. The thermal–physical properties of LNG under supercritical pressure were used for this study. After the validation of model and method, the effects of mass flux, outer wall temperature and inlet pressure on the heat transfer behaviors were discussed in detail. Then the non-uniformity heat transfer mechanism of supercritical LNG and effect of natural convection due to buoyancy change in the tube was discussed based on the numerical results. Moreover, different flow and heat transfer characteristics inside the bend tube sections were also analyzed. The obtained numerical results showed that the local surface heat transfer coefficient attained its peak value when the bulk LNG temperature approached the so-called pseudo-critical temperature. Higher mass flux could eliminate the heat transfer deteriorations due to the increase of turbulent diffusion. An increase of outer wall temperature had a significant influence on diminishing heat transfer ability of LNG. The maximum surface heat transfer coefficient strongly depended on inlet pressure. Bend tube sections could enhance the heat transfer due to secondary flow phenomenon. Furthermore, based on the current simulation results, a new dimensionless, semi-theoretical empirical correlation was developed for supercritical LNG convective heat transfer in a horizontal serpentine tube. The paper provided the mechanism of heat transfer for the design of high-efficiency SCV. [ABSTRACT FROM AUTHOR]

Abstract: This paper considers the numerical optimization of a T-shaped assembly of fins cooling a cylindrical solid body. The objective is to minimize the maximum excess of temperature between the solid cylindrical body and the ambient. Internal heat generation is distributed uniformly throughout the solid body. The assemblies of fins are bathed by a steady stream with constant ambient temperature and convective heat transfer. The outer surfaces of the cylindrical body are adiabatic. The total volume of the body and the total volume of the fins are fixed, but the lengths of the fins can vary. The initial simulations demonstrated that the optimal performance is achieved when the tributaries shape becomes slender and the stem thicker so that the system has more freedom to morph. However, when the number of assembly exceeds 2, the best configuration is the one that presents slender stems and shorter tributaries. The reason of this sudden change in behavior is that the tributaries length is limited by the presence of the neighbor assembly of fins: the system becomes “locked” and has no more freedom to morph. Finally, a digression on how the number of T-shaped fin assembly affects the configuration patterns concludes the paper. [Copyright &y& Elsevier]

Keeping the excess temperature of heat generating mediums and circuitry devices below an allowable level is a great challenge. To facilitate the heat transfer process, it is significant to improve and optimize the geometric structure of the cooling tools. The present paper deals with the shape optimization of a tree-shaped inverted fin (‘cavity’) that is penetrated into a heat generating body and extracts the generated heat from the hot piece to a cold environment. The objective is to obtain the optimal geometry of the tree-shaped cavity that minimizes the peak (maximum) temperature of the medium subject to the volume (space) constraint. A numerical solution is performed to deliver the temperature field within the medium and the direct search method is used to reach the optimal situation. The optimization results indicate that the final (optimized) tree-shaped configuration performs the best over the existing single-root cavities introduced in the open literature. For example, the maximum excess temperature calculated in the final tree-shaped cavity with four branches was found about 50% lower compared to the best configuration investigated in the open literature. [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]

Abstract: This paper aims at developing an analytical model for the coupled heat and mass transfer processes in a counterflow Reversibly Used Cooling Tower (RUCT) based on operating conditions, which is more realistic than most conventionally adopted Merkel approximations. Temperature and moisture content differences are chosen as the driving forces of heat and mass transfer correspondingly and a system of specific difference equations is developed to solve the model more efficiently. The model is investigated by using an iterative algorithm, which is validated with the experimental data reported. The analytical model also accommodates the direct and quick calculation of air and water temperature profiles, moisture content of air and the water mass flow rate change along the vertical length of the RUCT. With the aid of the developed model, the thermal behavior of the counterflow RUCT under various operating and environmental conditions is also studied in this paper. The results reveal that the proposed model can provide a theoretical foundation for practical design and performance evaluation of counterflow RUCT. [Copyright &y& Elsevier]

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

Large Eddy Simulation of knocking in piston engines requires high-fidelity physical models and numerical techniques. The need to capture temperature fields with high precision to predict autoignition is an additional critical constraint compared to existing LES in engines. The present work presents advances for LES of knocking in two fields: (1) a Conjugate Heat Transfer (CHT) technique is implemented to compute the flow within the engine over successive cycles with LES together with the temperature field within the cylinder head walls and the valves and (2) a reduced two-step scheme is used to predict both propagating premixed flames as well as autoignition times over a wide range of equivalence ratios, pressures and temperatures. The paper focuses on CHT which is critical for knocking because the gas temperature field is controlled by the wall temperature field and knocking is sensitive to small temperature changes. The CHT LES is compared to classical LES where the temperatures of the head and the valves are supposed to be homogeneous and imposed empirically. Results show that the skin temperature field (which is a result of the CHT LES while it is a user input for classical LES) is complex and controls knocking events. While the results of the CHT LES are obviously better because they suppress a large part of the empirical specification of the wall temperatures, this study also reveals a difficult and crucial element of the CHT approach: the description of exhaust valves cooling which are in contact with the engine head for part of the cycle and not in the rest of the cycle, leading to difficulties for heat transfer descriptions between valves and head. The CHT method is successfully applied to an engine studied at IFP Energies Nouvelles where knocking characteristics have been studied over a wide range of conditions. [ABSTRACT FROM AUTHOR]

Heat transfer, pressure drop and effectiveness in a double pipe heat exchanger made of corrugated outer and inner tubes have been experimentally investigated in this paper. Both of the inner and outer tubes were corrugated by means of a special machine. New various arrangements of convex and concave corrugated tube were investigated. Heat transfer coefficient was determined using Wilson plots. Hot water (inner tube) and cold water (outer tube) inlet temperatures were maintained at around 40 °C and 8 °C respectively. Experiments were performed over the Reynolds number range of 3500–18,000, based on the hydraulic diameter of the annular space between the two tubes. Hot water Reynolds number was kept constant at around 5500. Findings indicated that the outer tube corrugations and arrangement type of corrugated tubes have significant effect on thermal and frictional characteristics. Maximum effectiveness was obtained for heat exchanger made of concave corrugated outer tube and convex corrugated inner tube. [ABSTRACT FROM AUTHOR]

Anterior eye diseases are commonly treated by topically applied drugs in the form of eye drops or ointment. In order to assess the effectiveness of topical drug administration, it is crucial to understand temporal evolution and spatial distribution of the drug in the anterior eye. In this paper, a numerical model of topical drug transport in the anterior human eye is developed, which is coupled with heat transfer and fluid flow in the anterior eye. Spatio-temporal evolution of drug concentration is then investigated numerically, with an emphasis on the drug concentration at three targets: the trabecular meshwork (TM), iris and lens. The results show that after the drug diffuses across the cornea, convection by the aqueous humor (AH) flow is the dominant mechanism of transport of topically applied drugs in the anterior human eye, which is due to temperature difference across the eye. Effects of eye orientation and ambient temperature are also analyzed. Ambient temperature is found to play an important role in the transport of topically applied drugs to various target tissues in the anterior eye. With the increase of ambient temperature, the peak concentration at the target first decreases, and then increases, and the minimum value is reached when ambient temperature is close to the body core temperature. Eye orientation is found to influence the maximum drug concentration at different targets, as well as the time it takes to reach the maximum. The results may help to understand the drug transport process in the anterior human eye, and provide guidelines of drug administration in order to improve the delivery efficacy. [ABSTRACT FROM AUTHOR]

The Selective Laser Melting (SLM) fabrication process is complex and it is crucial to understand the phenomena that will occur to better control it. In this paper, an FE model on SLM that considers powder-to-solid transition together with an effective method to achieve volume shrinkage and material removal has been created. Experiments were conducted to validate the model. A detailed discussion on the progression of the melt pool and the rate of temperature change has been made. Parametric study with the laser power and scan speed as variables has been conducted to identify their relationships with the melt dimensions, melting and evaporation of powder and rates of temperature change. [ABSTRACT FROM AUTHOR]

In this paper, a numerical investigation of thermal and thermodynamic performance of a receiver for a parabolic trough solar collector with perforated plate inserts is presented. The analysis was carried out for different perforated plate geometrical parameters including dimensionless plate orientation angle, the dimensionless plate spacing, and the dimensionless plate diameter. The Reynolds number varies in the range 1.02 × 10 4 ⩽ Re ⩽ 7.38 × 10 5 depending on the heat transfer fluid temperature. The fluid temperatures used are 400 K, 500 K, 600 K and 650 K. The porosity of the plate was fixed at 0.65. The study shows that, for a given value of insert orientation, insert spacing and insert size, there is a range of Reynolds numbers for which the thermal performance of the receiver improves with the use of perforated plate inserts. In this range, the modified thermal efficiency increases between 1.2% and 8%. The thermodynamic performance of the receiver due to inclusion of perforated plate inserts is shown to improve for flow rates lower than 0.01205 m 3 /s. Receiver temperature gradients are shown to reduce with the use of inserts. Correlations for Nusselt number and friction factor were also derived and presented. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a detailed investigation on temperature overshoot characteristic of a realistic thermoelectric module (TEM) that operated with a square current pulse. A numerical model for TEM is developed and validated. Based on the model, obtained simulation results reveal that the transient temperature variation of realistic TEM cold side is more moderate due to the effect of the metal strips and the ceramic plates. Furthermore, the temperature overshoot characteristic of TEM cold side is analyzed for different current pulse parameters and operation conditions. For the square current pulse operation, the temperature overshoot occurs only when the current pulse amplitude is greater than a critical value, which is jointly determined by original steady current, cooling load and thermal conductance of heat sink. From the results obtained here, we propose a general principle to make a judgment whether a temperature overshoot will occur under a square current pulse operation. The present study will provide beneficial guidance for design of a TEM under current pulse operations. [Copyright &y& Elsevier]

Abstract: This paper introduces a new methodology for the generation of thermal response factors of geothermal bore fields using the concept of g-functions introduced by Eskilson. Boreholes are divided into segments to consider the variation of the heat extraction rates along the length of the boreholes and the analytical finite line source (FLS) solution is used to calculate the temperature variations at the wall of each borehole segment along the axial direction. The proposed methodology accounts for the time variation of the heat extraction rates among boreholes and along the length of individual boreholes to obtain a uniform borehole wall temperature equal for all boreholes in accordance with the original boundary conditions proposed by Eskilson. In addition, the methodology is generalized to account for boreholes of different lengths and buried depths. g-Functions calculated with the proposed methodology are compared to the numerical technique used by Eskilson to derive the g-functions for fields of 1 to 12×12 boreholes. The difference between the two models is within 5% for all studied bore fields, except for fields of boreholes located on a single row. The variation of the heat extraction rates of individual boreholes along their length as well as in time also showed good agreement with the numerical model. It is shown that using 12 borehole segments is adequate to calculate the g-functions in most practical cases. For instance, the error on the g-function of a 10×10 bore field calculated using 12 borehole segments is 2.2% after 20years and 4.7% at steady-state. [Copyright &y& Elsevier]

Abstract: The present paper deals with the longitudinal heat transportation by an oscillatory flow in a curved tube heat transportation pipe. The velocity and temperature fields during oscillatory water flow in a curved tube with inner diameter of 10mm were numerically simulated using the commercial software FLUENT. To clarify the effect of the curvature on heat transportation, the ratio of the tube radius to the curvature radius was varied from 0.0125 to 0.075, and oscillatory flow frequency was varied from 0.1 to 2.0Hz. The effective thermal diffusivity exhibited a peak at a curvature ratio around 0.05–0.07 and reached a value 12 times higher than that of a straight tube. It was also found that the dispersion of fluid particles due to secondary flow caused the enhancement of heat transportation. [Copyright &y& Elsevier]

Abstract: In this paper, numerical study of the gas flow velocity space is presented in a convection type reflow oven. Convection reflow ovens usually apply the nozzle-matrix heater system which generates numerous gas streams perpendicularly to surface of the soldered assembly. The ovens are divided into zones; every zone contains an upper and a lower nozzle-matrix. The temperature can be independently controlled in each zone; however the velocity of the influent streams is usually fixed. The gas flow velocity space is one of the most important parameter of the local heat transfer coefficient in the oven. The gas flow space cannot be examined by classical experimental methods due to the extreme circumstances in the reflow oven. Therefore the effect of the soldered assembly, the different component sizes, the position of the conveyor belt and the vent hood between the zones on the gas flow velocity space was studied by CFD simulations. These results can be useful during the overview of the actual assembly design and manufacturing rules. [Copyright &y& Elsevier]

Abstract: The problem of unsteady natural convection induced by a temperature difference between a cold outer square enclosure and a hot inner circular cylinder is studied in this paper. The cylinder temperature is assumed to vary sinusoidally with time about a fixed mean temperature. The coupled momentum and energy equations have been solved numerically over a wide range of values of the amplitude and the frequency of the source temperature signal, as well as the source radius. It is found that the heat transfer rate tends to increase by oscillating the source temperature signal. The maximum heat transfer augmentation was obtained for frequency between 25π and 30π for a high amplitude and a moderate source radius. [Copyright &y& Elsevier]

Abstract: Heat may transport as waves under ultrafast heat pulse conditions. In this paper, our numerical analyses considering typical thermal wave modes, i.e. Cattaneo–Vernotte (CV), dual-phase-lagging (DPL), and thermomass (TM), disclose that dispersion may occur during the heat propagation processes like water, sound, and light waves. The unified implicit finite difference method for the Fourier, CV, DPL, and TM models was adopted to analyze the heat propagation process in solids. The validity of this numerical method for the Fourier, CV, DPL and TM models was confirmed. The dispersion of thermal waves was observed in their propagation processes for the first time. As the thermal waves moving forward, many peaks appear in the rear of the thermal waves relative to the propagation direction. The underlying mechanism for the dispersion of the thermal waves is that they can travel faster in the points with higher temperature considering the temperature dependence of the relaxation time. For the CV-waves and DPL-waves, the origins of the dispersion are both due to the inertia term of heat flux to time . For the TM-waves, the origins are due to the inertia term of heat flux to time, inertia term of temperature to time, and inertia term of heat flux to space in the TM model, and effects of the inertia term of temperature to space on the dispersion can be neglected, where the inertia term to space comes from the nonlocal effects. The dispersion of the TM-waves is mainly dominated by the inertia term of heat flux to time. In the TM model, the characteristic time τTM decreases with the increase of temperature, and therefore the dispersion will appear in the propagation process of the TM-wave. For actual materials, if considering that τq decreases with the temperature increasing, the dispersion of the CV-wave and DPL-wave will also appear under the appropriate amplitude of heat flux pulse, relaxation times τq and τT . The increase of the amplitude of heat flux pulse and the decrease of the initial temperature both can enhance the dispersion of the TM-wave. The increase of the amplitude of heat flux pulse and the relaxation time τq can both enhance the dispersion of the CV-wave and DPL-wave, while the increase of the relaxation time τT will weaken the dispersion of the DPL-wave. [Copyright &y& Elsevier]

Abstract: The technology of embedding heat exchange tubes in diaphragm walls is a new direction for Ground-coupled Heat Pumps (GCHP). This paper examines the heat transfer model and design method for geothermal heat exchangers in diaphragm walls, which are seldom investigated in the world. Two-dimensional (2D) heat transfer models for diaphragm wall heat exchangers (DWHE) are established. A design method for DWHE is further developed to calculate the hourly heat exchange capacity of DWHE and to get the reasonable design parameter of DWHE. The DWHE model over the excavation line has the same changing trend with numerical solutions, and the relative errors between them are less than 2%. The relative errors of calculated heat exchange rate per meter using DWHE model and measured data are less than 6% after running 10h. The relative errors of temperature between DWHE model under the excavation line and the measured data at different positions are no more than 9%, whereas the relative error between the tradition models in GCHP (line source model and finite-line source model) and the measured data may reach as much as 40%. [Copyright &y& Elsevier]

Abstract: In this paper, a three-dimensional (3D) hydrogen desorption model is applied to the thin double layered annulus ZrCo based hydrogen storage bed to precisely study the hydrogen desorption reaction and resultant heat and mass transport phenomena inside the bed. The 3D hydrogen desorption simulations are carried out and calculated results are compared with the experimental data measured by Kang et al. [1]. The present model reasonably captures the bed temperature evolution behavior and the hydrogen discharging time for 90% desorption. In addition, the thin double layered annulus metal hydride bed (MHB) design is numerically evaluated by comparing with a simple cylindrical MHB. More uniform distributions in the bed temperature and H/M atomic ratio and resultant superior hydrogen desorption performance are achieved with the thin double layered annulus bed owing to its high external surface to volume ratio and thus more efficient heating. This numerical study indicates that efficient design of the metal hydride bed is key to achieve rapid hydrogen discharging performance and the present 3D hydrogen desorption model is a useful tool for the optimization of bed design and operating conditions. [Copyright &y& Elsevier]

Abstract: Optimized convective heat transfer is applied to accelerate the thermal recovery of a large aperture multi-segment amplifier. The paper proposes a novel project of changing the structural parameters of the inlet jet to the Nd:glass slab in the multi-segment amplifier at the same flow rate. The convective heat transfer coefficient depends on the diameter of the inlet jet, as well as on the number of inlet jets. The simulation calculations indicate that at the same flow rate, different numbers of inlet jet lead to different temperature gradient contours and flow field distributions on the Nd:glass slab surface in the multi-segment amplifier. In addition, the convective heat transfer coefficient increases with the decrease of inlet diameter. This work analyzes the path of the coolant air over the slab surface to lessen the eddy and to achieve better convective heat transfer, as well as to determine the optimized number of inlet jets (5) and the optimized diameter (5mm). [Copyright &y& Elsevier]

Abstract: In this paper, a magnesium (Mg) reduction model considering both heat transfer and chemical reaction kinetics was firstly developed. The reduction model was carried out on a single retort to investigate the impact of different constant heating temperature on the magnesium reduction process in the retort. And then, the reduction model was incorporated into the conventional coal combustion model to describe the process of magnesium production in a coal-fired furnace. The comprehensive model was solved according to the actual industrial operation. The characteristics of magnesium production in the coal-fired furnace, such as thermal-flow field around the retorts in the furnace, the distribution of magnesium reduction extent in the retorts and the total extent of magnesium reduction with time were in detail studied. Especially, the impact of external thermal-flow around the retorts on the extent of magnesium reduction was investigated and discussed. [Copyright &y& Elsevier]

Abstract: In this paper, we investigate theoretically the problem of steady laminar two-dimensional boundary layer flow and heat transfer of an incompressible viscous fluid in the presence of buoyancy force over an exponentially shrinking vertical sheet with suction. The shrinking velocity and wall temperature are assumed to have specific exponential function forms. The governing equations are first transformed to similarity equations using an appropriate similarity transformation. The resulting equations were then solved numerically using shooting technique involving fourth-order Runge–Kutta method and Newton–Raphson method. The influence of mixed convection/buoyancy parameter λ, suction parameter s and Prandtl number Pr on the flow and heat transfer characteristics is examined and discussed. Numerical results indicate that the presence of buoyancy force would contribute to the existence of triple solutions to the flow and heat transfer for particular value of pertinent parameters. It is different for the non-buoyant flow case i.e. when the buoyancy force is absent, the problem admits only dual solutions. Further, this study also reveals that the features of flow and heat transfer characteristics are significantly affected by buoyancy parameter λ, suction parameter s and Prandtl number Pr. [Copyright &y& Elsevier]

Abstract: This paper investigated the thermal behaviour of an assembly of multi scale cylinders in a staggered counter-rotating configuration cooled by natural convection with the objective of maximizing the heat transfer density rate (heat transfer rate per unit volume). A numerical model was used to solve the governing equations that describe the temperature and flow fields and a mathematical optimisation algorithm was used to find the optimal structure for flow configurations with two degrees of freedom. The multi scale structure of the cylinder assembly was optimized for each flow regime (Rayleigh number) and cylinder rotation speed for two degrees of freedom. Smaller cylinders were placed at the entrance to the assembly, in the wedge-shaped flow regions occupied by fluid that had not yet been used for heat transfer, to create additional length scales to the flow configuration. It was found that there was almost no effect of cylinder rotation on the maximum heat transfer density rate, when compared to stationary cylinders, at each Rayleigh number; with the exception of high cylinder rotation speeds, which served to suppress the heat transfer density rate. It was, however, found that the optimized spacing decreased as the cylinder rotation speed was increased at each Rayleigh number. Results further show that the maximum heat transfer density rate for a multi scale configuration (without cylinder rotation) was higher than a single scale configuration (with rotating cylinders) with an exception at very low Rayleigh numbers. [Copyright &y& Elsevier]

Abstract: In this paper we investigate the flow and heat transfer of a Jeffrey fluid near the stagnation point on a stretching/shrinking sheet with a parallel external flow. The main concern is to analytically investigate the structure of the solutions which might be unique or multiple. It is shown that structure of the solutions strongly depends on a parameter measuring the ratio of strength of the external flow to surface stretching/shrinking, we name it as stretching strength parameter. When this parameter is set to zero, the solutions evolve into the multiple/triple solutions already given in Turkyilmazoglu (2011) [1,2]. For other values, closed-form formulae for the boundary layer equations of the flow are presented for the Jeffrey fluid. Heat transfer analysis is also carried out for a boundary heating process taking into consideration both a uniform wall temperature and a linearly increasing wall temperature. The flow field is found to be influenced by the presence of physical parameters, stretching/shrinking strength, Deborah number and suction/injection parameters, whereas the temperature field is additionally affected by Prandtl number. The velocity/temperature profiles and skin friction coefficient/Nusselt number are easy to conceive from the exact formulas presented, which also provide benchmark for testing other numerical schemes. [Copyright &y& Elsevier]

Abstract: This paper provides temperature and velocity distribution computations in heated annuli using RANS approach and employing three different turbulent viscosity models. In addition to comparison calculations an extensive sensitivity study was performed. The results show that the RANS approach and the turbulent viscosity models can be used for prediction of forced convection heat transfer to lead–bismuth-eutectic. However, the turbulent Prandtl number has to be carefully selected depending on the respective turbulence model. [Copyright &y& Elsevier]

Abstract: In this paper, the authors introduce a robust numerical strategy to estimate the temperature dependent heat capacity, thermal conductivity and porosity of a saturated porous medium, basing on the knowledge of heating curves at selected points in the medium. In order to solve the inverse problem, we use the least squares criterion (in which the sensitivity coefficients appear), leading to a system of ordinary differential equations (ODE). At the stage of numerical computations, we propose a new global approach, based on the method of lines and ordinary differential equations solvers, combined with a modified Newton method to deal with the nonlinearities presented in the system of coupled equations. [Copyright &y& Elsevier]

Particulate fouling of convective heat-transfer surfaces is usually assessed by empirical correlations. Nevertheless, constant progress in numerical calculation methods allows for prediction of deposition. This paper presents results of 2D modeling of powdery, medium-temperature deposit formation on superheater tubes. In contrast to other studies, presented approach results in shape prediction of deposits versus time of boiler operation. The mechanism includes the force of gravity, elastic rebound and adhesion forces acting at the moment of ash particle impaction. The forces determine if the particle bounces off the surface or stays onto it building up the deposit. Two practical cases are considered - an upward flue gas flow and a downward flow in the boiler. The results of simulations are compared with measurements in real boilers published earlier. The full-scale results are reproduced well. The simulations are carried out with use of Fluent code by means of User Defined Files. The described mechanism is implemented in Define_DPM_Erosion, and shape prediction is mirrored using Define_Grid_Motion functions of the Fluent code. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the influence of liquid fuel presence on the autoignition of n-heptane/air mixtures over a wide range of conditions encountered in internal combustion engines. To this end, evaporating droplet physics and skeletal chemistry mechanisms are simultaneously solved considering a homogeneous constant-pressure reactor. A skeletal mechanism is introduced to account for specific kinetics behavior in the Negative Temperature Coefficient (NTC) region. The impact of mass and heat source terms during evaporation is emphasized by comparing a two-phase flow scenario with a purely gaseous case. The competition between fuel vapor availability and the evaporation-induced gas temperature decrease is specific to two-phase flow autoignition. On the one hand, droplet evaporation delay restricts the gaseous local fuel/air equivalence ratio and consequently the kinetics runaway. On the other hand, temperature reduction due to evaporation may either reduce or enhance chemical reactivity, depending on the local thermodynamic conditions lying either inside or outside the NTC region. By simultaneously accounting for evaporation source terms and skeletal chemistry, we can reproduce the already experimentally observed transformation of the NTC region into a Zero Temperature Coefficient (ZTC) region depending on thermodynamic conditions and droplet size. The ZTC phenomenon appears when combustion heat-release starts before complete droplet evaporation. Since the ZTC behavior can be captured using the point source approach, in which droplets are considered only as zero-dimensional source terms of mass and energy, the present results pave the way for future exploration of NTC chemistry in sprays with a direct numerical simulation of discrete particles considering detailed chemistry and turbulent flows. [Copyright &y& Elsevier]

Abstract: The overall heat transfer performance of a tube bank fin heat exchanger is very important for engineering applications. Developing a fin pattern with good heat transfer performance for tube bank fin heat exchanger needs more our intensive effort. There are two methods to obtain the heat transfer performances of a fin pattern, i.e., one is experimental method, and the other is numerical method. If numerical method is used, the thermal boundary condition on the fin surfaces is necessary. Generally, there are two ways to treat the thermal boundary, i.e., one is to treat fin surface with uniform temperature, and the other is to use a conjugate numerical method. The former is very easy to be applied in numerical method, but the latter needs more numerical effort. This paper reports the condition under which whether a conjugate numerical method or a numerical method just specifying uniform temperature thermal boundary condition should be used. It is found that such condition is the fin efficiency. When the fin efficiency is less than 0.8, a conjugate numerical method must be used. Otherwise, the numerical results obtained by applying an uniform temperature thermal boundary condition on the fin surfaces has only slightly differences with the results obtained by a conjugate numerical method. The reported results will provide a criterion for the researchers to choose a suitable numerical method in finding a fin pattern more efficiently and reliably. [Copyright &y& Elsevier]

Abstract: Heat transfer from the flame to a surface located downstream of the fuel, in the flame spread direction, is likely to influence the spread rate and flame extents, as the coupled thermal and flow fields get altered. Additionally, if the fuel surface is inclined to the normal gravity direction, it can induce complex natural convection induced flow-fields that can further affect the flame characteristics. The primary focus of the present paper is on investigating the combined effects of downstream surface (over fire region) temperature conditions and angular orientation of condensed fuel surface, on the flame characteristics. Inclination angles in the range of −60°<θ<+60° with respect to the vertical axis, under normal gravity conditions are considered. A validated numerical model, which solves transient, two-dimensional, gas-phase governing conservation equations with appropriate interfacial coupling conditions, is employed. Methanol is employed as the condensed fuel. Global single-step reaction chemistry for methanol-air oxidation is used to model the finite rate chemical kinetics. An optically thin approximation based formulation for radiation heat transfer is used to account for losses by absorbing species in a non-luminous flame produced by methanol. The model is first validated against the experimental result for flame on a vertically oriented surface, in terms of a factor called local heat flux parameter (HFP). Heat transfer characteristics of the flame to the condensed fuel surface and to the isothermal wall is then presented and compared in terms of local HFP for all the orientation cases. The differences in the structure of the laminar diffusion flames are discussed in detail. Further, a comparison of the flame structure obtained in the present case against a case having an adiabatic surface in the over fire region is also presented. [Copyright &y& Elsevier]

Abstract: The study of the mechanics of evaporating thin-films is important for improving the performance of phase-change heat transfer equipment. Various factors, including the changing profile of the thin-film with superheating and the use of small-scale and one-dimensional higher-order nonlinear governing differential equations, create difficulties for the study of the conjugated heat transfer of the thin-film and its surrounding regions. In previous studies, models of the conjugated heat transfer are simplified. The shape of the evaporating thin-film is treated as fixed, or the constant substrate temperature (CST) thin-film model is used. In this paper, a full conjugated heat transfer model, including the evaporating thin-film, the near-solid substrate and the intrinsic liquid, is proposed to study the heat transfer characteristics in the contact line region in a micro channel or a micro groove. The results show that a temperature valley value exists on the surface of the solid substrate corresponding to the peak value of the heat flow rate in the thin-film. The apparent contact angle is smaller than that of the CST model. The CST model overestimates the peak and the total heat flow rate, especially when the thermal conductivity ks of the substrate is low. For convenience in engineering applications, two simplified conjugated models are developed and evaluated by the full model. For low ks substrates, the simplified models can be used directly. Changing the thickness of the substrates affects the relative errors only slightly. [Copyright &y& Elsevier]

Abstract: This paper numerically investigates the performance of composite spreaders comprised of Cu substrates and Cu micro-porous surfaces of different thicknesses for immersion cooling of 10×10mm underlying computer chip with a 2×2mm central hot spot. The local heat flux at the hot spot is three times the chip’s surface average outside the hot spot. The thickness of the Cu substrate changes from 1.6 to 3.2mm and that of the Cu micro-porous surface changes from 80 to 197μm. The spreaders are cooled by saturation nucleate boiling of PF-5060 dielectric liquid. The local values of the nucleate boiling heat transfer coefficients on the various Cu micro-porous surfaces are based on pool boiling experimental measurements. Results demonstrated the effectiveness of immersion cooling nucleate boiling for mitigating the effect of the hot spot. The spreaders decrease the maximum surface temperature and the temperature gradient on the chip surface and increase the dissipated thermal power by the chip and removed from the spreader surface. Increasing the thickness of the Cu substrate and/or decreasing the thickness of the Cu micro-porous surface increases the total thermal power removed, the chip surface temperature and the spreader’s footprint area. [Copyright &y& Elsevier]

Abstract: The paper presents an analysis of thermodynamic losses in thermal reservoirs due to irreversible heat transfer and frictional effects. The focus is upon applications to large-scale electricity storage for which it is the loss in availability (or exergy) that is most relevant. Accordingly, results are presented as loss coefficients which are defined as the fractional loss of the entering availability. Only losses stemming from irreversibility are considered – heat losses to the surroundings are not included in the analysis. A number of simplifying assumptions have been adopted, but the results nonetheless clearly demonstrate the dependence of the losses on operating temperatures, reservoir geometry and mode of operation, and point the way towards methods of optimisation. Estimates for a typical installation suggest that the losses are not insignificant, particularly for one-off charge and discharge (i.e., for long-term storage), but remain acceptable for cyclic operation, so as to make the use of thermal reservoirs attractive for electricity storage schemes. [Copyright &y& Elsevier]

Abstract: In this paper we study the flow and heat transfer characteristics of a viscous fluid over a nonlinearly stretching sheet in the presence of non-uniform heat source and variable wall temperature. A similarity transformation is used to transform the governing partial differential equations to a system of nonlinear ordinary differential equations. An efficient numerical shooting technique with a fourth-order Runge–Kutta scheme is used to obtain the solution of the boundary value problem. The effects of various parameters (such as the power law index n, the Prandtl number Pr, the wall temperature parameter λ, the space dependent heat source parameter A ∗ and the temperature dependent heat source parameter B ∗) on the heat transfer characteristics are analyzed. The numerical results for the heat transfer coefficient (the Nusselt number) are presented for several sets of values of the parameters and are discussed. The results reveal many interesting behaviors that warrant further study on the effects of non-uniform heat source and the variable wall temperature on the heat transfer phenomena at the nonlinear stretching sheet. [Copyright &y& Elsevier]

Abstract: In the present paper, free convection fluid flow and heat transfer of various water based nanofluids in a square cavity with an inside thin heater has been investigated numerically. The left and right walls of the cavity are maintained at constant temperature T c, while its top and bottom walls are insulated. A thin heater with the temperature of T h (T h > T c) is located inside the cavity which its location and length is varying. The governing equations were discretized using the finite volume method and SIMPLER algorithm. Using the developed code, a parametric study was undertaken, and the effects of pertinent parameters, such as, Rayleigh number, the position and location of the heater, the volume fraction of the nanoparticles, and various types of the nanofluids on the fluid flow and heat transfer inside the cavity were investigated. It was observed from the results that at low Rayleigh numbers the horizontal positioned heater have higher Nusselt number compared to the vertical positioned heater while at high Rayleigh numbers the position of the heater does not affect the heat transfer rate. For a horizontal heater when it is located in lower half of the cavity, more heat transfer occurs compared to the case of heater located in upper half of the cavity. Moreover, it was found that at high Rayleigh numbers, the Ag–water nanofluid is more effective to enhance the heat transfer rate while at low Rayleigh numbers the type of nanofluids does not affect the heat transfer rate. [Copyright &y& Elsevier]

Abstract: The reliable estimation of buildings energy needs for cooling is a crucial issue in the implementation of the EPB Directive 2010/31/EU (formerly 2002/91/EC), especially in central and southern Europe climates. On this purpose one of the main topics is to predict the behavior of the opaque envelope subjected to variable boundary conditions. The EN ISO 13786:2007 technical standard assumes sinusoidal boundary conditions and introduces dynamic thermal characteristics. The aim of this paper is to assess the deviation arising by the use of different approaches for the calculation of the dynamic thermal characteristics of an opaque envelope element under periodic non sinusoidal boundary conditions. The EN ISO 13786 procedure has been firstly applied by decomposing the external forcing temperature by means of the Fast Fourier Transform (FFT) analysis. A comparison with different approaches, such as Finite Difference Methods (FDM) and Transfer Function Methods (TFM), has been carried out. The predictions of the EN ISO 13786 with a sinusoidal forcing temperature (i.e., standard approach) have also been assessed, comparing the results to the ones obtained through the FFT analysis. Furthermore, corrections to the periodic thermal transmittance and to the time shift have been proposed, in order to improve the explicative worth of those parameters. [Copyright &y& Elsevier]

Abstract: This paper investigates the unsteady mixed convective boundary layer flow and heat transfer over a porous stretching vertical surface in presence of slip. Similarity solutions for the transformed governing equations are obtained and the reduced equations are then solved numerically. With increasing values of the unsteadiness parameter, fluid velocity and the temperature are found to decrease in both the presence and absence of slip at the boundary. Fluid velocity decreases due to increasing values of the velocity slip parameter resulting an increase in the temperature field. Skin-friction decreases with the velocity slip parameter whereas it increases with unsteadiness parameter. The rate of heat transfer decreases with the velocity slip parameter while increases with unsteadiness parameter. Same feature is also noticed for thermal slip parameter. Effects of increasing mixed convection parameter on the velocity boundary layer is to increase the velocity field and the temperature decreases in this case. [Copyright &y& Elsevier]

Abstract: The heat transferred to the turbine blade is substantially increased as the turbine inlet temperature is increased. Improved cooling methods are therefore needed for the turbine blades to ensure a long durability and safe operation. The blade tip region is exposed to very hot gas flow, and suffers high local thermal loads due to the external tip leakage flow. A common way to cool the tip is to design serpentine passages with 180° turn under the blade tip-cap taking advantage of the three-dimensional turning effect and impingement. Increased internal convective cooling is therefore required to increase the blade tip lifetime. In this paper, augmented heat transfer of a blade tip with internal hemispherical dimples has been investigated numerically. The computational models consist of two-pass channels with 180° turn and arrays of dimples depressed on the internal tip-cap. Turbulent convective heat transfer between the fluid and dimples, and heat conduction within dimples and tip are simultaneously computed. The inlet Reynolds number is ranging from 100,000 to 600,000. Details of the 3D fluid flow and heat transfer over the tip-walls are presented. Comparisons of the overall performance of the models are presented. It is found that due to the combination of turning impingement and dimple-induced advection flow, the heat transfer coefficient of the dimpled tip is up to two times higher than that of a smooth tip with less than 5% pressure drop penalty. It is suggested that the use of dimples is suitable for augmenting blade tip cooling to achieve an optimal balance between thermal and mechanical design requirements. [ABSTRACT FROM AUTHOR]

Abstract: The numerical modeling of the conjugate heat transfer and fluid flow through the micro-tube was presented in the paper, considering the viscous dissipation effect. Three different fluids with temperature dependent fluid properties are considered: water and two dielectric fluids, HFE-7600 and FC-70. The diameter ratio of the micro-tube was D i/D o =0.1/0.3mm with a tube length L =100mm. The laminar fluid flow regime is analyzed. Two different heat transfer conditions are considered: heating and cooling and three different Br=0.01, 0.1 and 0.5. The influence of the viscous heating on Nu and Po is analyzed and compared with Br=0. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents experimental data measured in a bed of gypsum boards in the transient moisture transfer (TMT) facility at the University of Saskatchewan. The relative humidity and temperature were measured at two depths in a gypsum bed and the moisture accumulation was measured for the entire bed. Experiments were conducted for both coated (acrylic and latex paint) and uncoated gypsum. These experimental data are compared to simulated data from eight different numerical models. The agreement between the experimental and numerical data is good and often within the experimental uncertainty bounds. A sensitivity analysis was performed to show the influence of material properties such as sorption, vapour permeability and the transfer coefficients on the simulated results. One model examines hysteresis of the sorption isotherm. [Copyright &y& Elsevier]

Abstract: In this paper, design and fabrication of a micro direct methanol fuel cell based on stainless steel in two kind of active and passive with cross strip and parallel flow field are presented. Dropping pressure, velocity and heat transfer of the cell is simulated by a 3D modeling in fluent software. An optimum operating condition of the cell is obtained by the mass flow and temperature limitation. The cell was tested in different temperatures and mass flow rate and the cell performance is investigated in different condition. Maximum power density of the cell in active condition and at 60°C was 170mW/cm2 and in passive condition was 85mW/cm2. A μDMFC with different flow field is investigated. Cross strip flow field has shown better performance and the effect of cell orientation on performance is also investigated. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we investigate the effects of thermophoresis on the forced convective laminar flow of a viscous incompressible fluid due to a rapidly rotating disk whose surface temperature is lower than the temperature of its surrounding fluid. The governing equations of continuity, momentum, energy and concentration are transformed using similarity analysis, and the solutions are obtained through numerical techniques. The results show that if the thermophoretic coefficient increases, thermophoretic velocity increases and it intensifies significantly when the relative temperature difference parameter increases. The results also show that axial particle deposition velocity increases as the thermophoretic coefficient as well as Schmidt number increases. [Copyright &y& Elsevier]

Abstract: In this paper, a two-phase two-dimensional PEM fuel cell model, which is capable of handling liquid water transport across different porous materials, is employed for parametric studies of liquid water transport and distribution in the cathode of a PEM fuel cell. Attention is paid particularly to the coupled effects of two-phase flow and heat transfer phenomena. The effects of key operation parameters, including the outside cell boundary temperature, the cathode gas humidification condition, and the cell operation current, on the liquid water behaviors and cell performance have been examined in detail. Numerical results elucidate that increasing the fuel cell temperature would not only enhance liquid water evaporation and thus decrease the liquid saturation inside the PEM fuel cell cathode, but also change the location where liquid water is condensed or evaporated. At a cell boundary temperature of 80°C, liquid water inside the catalyst layer and gas diffusion media under the current-collecting land would flow laterally towards the gas channel and become evaporated along an interface separating the land and channel. As the cell boundary temperature increases, the maximum current density inside the membrane would shift laterally towards the current-collecting land, a phenomenon dictated by membrane hydration. Increasing the gas humidification condition in the cathode gas channel and/or increasing the operating current of the fuel cell could offset the temperature effect on liquid water transport and distribution. [Copyright &y& Elsevier]

Abstract: This paper presents a heat and mass transfer simulation of an adsorber, taking into consideration the geometry of the heat exchanger and the diffusion in the adsorbent medium. In this model, an increment in the direction of heating/cooling fluid containing one (or more) fin pitch was considered. In the domain of this increment, the distribution of the adsorbent temperature was evaluated in the radial and axial directions. The model is validated by experimental data of different adsorbents, volume flows and temperatures. All data were collected in an adsorber test-bench at Fraunhofer ISE. As a result it was found a coefficient of multiple determination of around 0.94 and an error of 20% during the transient. Finally, the model was run on typical operation for cooling application and compared with data from literature. A numerical energy balance was also evaluated. In summary, the results obtained by a independent group shows the same range of confidence of the model developed here, in terms of the tendency of the curves and even the absolute values. [Copyright &y& Elsevier]

Abstract: Three-dimensional unsteady natural convections in an inclined porous cavity with time oscillating boundary conditions are numerically studied in this paper. The Darcy–Forchheimer–Brinkman model is adopted to model the fluid flow in the porous medium and the combination effects of inclination angles (α 1, α 2) and temperature oscillation frequency (f) on the convection characteristics with different Rayleigh numbers (Ra =106 and 107) are carefully investigated, especially when the porous cavity is seriously inclined (). It is revealed that, when the porous cavity is moderately inclined (), the natural convections inside are stable and quasi two-dimensional. However, if the cavity is seriously inclined (), the flow patterns inside are much more complicated and the three-dimensional multiple roll-cells with different intercrossing angles are established. It is also found that, when the porous cavity is inclined with three-dimensional method (α 1 >0°, α 2 >0°), the natural convections become quite different and a series of three-dimensional screw type flexural roll-cells appears. Furthermore, it is suggested that, with proper selection of inclination angles and oscillation frequency, the natural convection heat transfer will be significantly improved and the maximal heat fluxes are finally obtained at the optimal combinations of f =35π, α 1 =50°, α 2 =45° when Ra =106 and f =40π, α 1 =45°, α 2 =45° when Ra =107. [Copyright &y& Elsevier]

Abstract: This paper presents the large eddy simulation (LES) results of turbulent heat and fluid flows in a straight square duct (SSD) at higher Reynolds numbers ranged from to , which are based on the bulk mean velocity and the duct cross-sectional side length. A sub-grid model is proposed, which assumes that the sub-grid stress and heat flux are, respectively, proportional to the temporal increments of the filtered strain rate and temperature gradient, with the proportional coefficient determined by calibrating the friction factor. The temperature was taken as passive due to the neglect of buoyancy effect. The Taylor and Kolmogorov scales in the SSD are predicted and the results show that the LES results are better than c-DNS results. The LES results can explain why the c-DNS is applicable to the problem at a moderate Re, and reveal that the largest relative deviation of the overall mean Nusselt number is less than 10% as compared with existing experimental correlations. With the rise of Reynolds number, the mean secondary vortex pairs move towards the corners and have smaller size, while smaller vortices also occur in the instantaneous secondary flow. Empirical mode decomposition (EMD) was carried out to analyze the fluctuation of the -averaged cross-sectional origin temperature at . [Copyright &y& Elsevier]

Abstract: This paper presents a systematic numerical study of the effects of heat transfer and pressure drop produced by vortex promoters of various shapes in a 2D, laminar flow in a micro-channel. The liquid is assumed to be water, with temperature dependent viscosity and thermal conductivity. It is intended to obtain useful design criteria of micro-cooling systems, taking into account that practical solutions should be both thermally efficient and not expensive in terms of the pumping power. Three reference cross sections, namely circular/elliptical, rectangular, and triangular, at various aspect ratios are considered. The effect of the blockage ratio, the Reynolds number, and the relative position and orientation of the obstacle are also studied. Some design guidelines based on two figures of merit (related to thermal efficiency and pressure drop, respectively), which could be used in an engineering environment are provided. [Copyright &y& Elsevier]

Abstract: Although Large Eddy Simulation (LES) is identified today as the most promising method for turbulent flow problems, few applications of LES coupled to heat transfer solvers in solids have been published. This paper describes a coupling strategy of a LES solver and a heat transfer code within solids on parallel architectures. The numerical methods used in both solvers are briefly recalled before discussing the coupling strategy in terms of physical quantities to exchange (fluxes and temperatures), stability and parallel efficiency. The stability study is performed using an amplification matrix analysis on a one-dimensional case and allows the determination and optimization of coupling parameters. The coupled tool is then applied to a cooled turbine blade model where results demonstrate both the efficiency of the parallel implementation and the quality of the results. Coupled and non-coupled simulations are compared to experimental results and discussed in terms of cooling efficiency and flow structures. [Copyright &y& Elsevier]

Abstract: The paper deals with the study of the flow of an incompressible electrically conducting visco-elastic fluid referred to as Walter’s liquid B over a porous non-isothermal stretching sheet using quasilinearization technique adopting a numerical approach. The sheet is assumed to stretch uni-directionally and the fluid above the sheet is at rest if there were no stretching. The temperature profiles are obtained numerically and these are displayed through graphs for diverse values of Prandtl number, visco-elastic parameter, magnetic parameter, source/sink parameter, wall temperature parameter and wall heat flux parameter. The results are compared with those available in literature obtained through analytical procedures and are seen to be in good agreement. [Copyright &y& Elsevier]

Abstract: This paper is to investigate the growth of Nd:YVO4 (yttrium vanadate) crystal by the modified Czochralski technique with a submerged plate. Numerical studies are performed to examine melt convection and heat transfer during Nd:YVO4 growth. The attention is paid to study the effects of initial elevation of the submerged plate, crystal diameter, and melt level on melt inclusions. It is found that the increase in crystal rotation rate and crystal diameter, and the decrease in melt level will increase the axial temperature gradient at the edge and in the center of the crystal, and change the interface shape from convex to flat. The experiments are also carried out to confirm the feasibility of the proposed new technique for controlling melt inclusions in Nd:YVO4 crystal growth. [Copyright &y& Elsevier]