Search

Abstract The solid-liquid phase change technology has been widely used in the efficient use and controllable management of heat in engineering. It is important to reveal the transfer mechanism of phase change interface for the optimization of solid-liquid phase change technology. A composite model of heat transfer and fluid flow in mushy zone is established by using the modified enthalpy method based on the combination of porous medium flow and multiphase flow theory. Lattice Boltzmann Method is used to solve the transient model of multi-field coupling in mushy zone in pore scale. The transfer mechanism in solid-liquid phase change, especially at the solid-liquid interface in mushy zone is focused on in this paper. The numerical results show that the thickness of mushy region is directly related to the phase change temperature radius of the mushy region. A smaller phase change temperature radius of the mushy region leads to a thinner mushy region thickness. The results also indicate that the mushy region constant (C) and demarcation point (r tr) of high-low liquid fraction area, phase change materials and the structure of mushy region have a close relationship with each other. The dimensionless parameters (Pr , Ra , Ste) of phase change process have an obvious influence on the mushy region and the phase change process. [ABSTRACT FROM AUTHOR]

Abstract Owing to enormously high surface area and high thermal conductivity, copper foam based heat sinks for electronic cooling are investigated in this paper. Copper foam1 with porosity 0.95 and pore density 15 pores per inch and copper foam2 with 0.97 porosity and pore density 35 pores per inch are used to investigate the performance of heat sinks filled with phase change material (PCM). Various configurations of heat sink with PCM volume fractions 0.0, 0.6, 0.7 and 0.8 are investigated under heat load of 8–24 W to figure out the optimum performance of the heat sink. Experimental results revealed that base temperature of the heat sink is reduced as the volume fraction of PCM is increased. Anyhow, discharging process is not affected significantly. Furthermore, copper foam1 (0.95 porosity) exhibited better heat transfer both in charging and discharging as compared to that of copper foam2 (0.97 porosity). Maximum temperature reduction of 9.81% was found for copper foam1/PCM at 8 W and PCM volume fraction of 0.8 when it is compared with copper foam2/PCM composite. For the same porosity, maximum reduction in base temperature was observed for 0.8 volume fraction of PCM at 16 W heat input. Finally, it is concluded that copper foam1/PCM composite impregnated with 0.8 volume fraction is an optimized configuration of heat sink. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the experimental study is carried out on the convective heat transfer performance of the graded and uniform rectangular honeycomb structure fabricated by additive manufacturing under the constant temperature boundary. The samples are made of the 316 L stainless steel powder. The graded and uniform honeycomb samples have the same mass, overall size, cell width and wall thickness. The cell height is variable for the graded honeycomb and is constant for the uniform honeycomb. First, the overall pressure drop and the surface temperature of the upper and lower surfaces of the samples are directly measured under the different air velocities. The overall convective heat transfer coefficient of the sample is calculated based on the measured data. Then, the whole process of the experiment is simulated in detail based on the numerical method of computational fluid dynamics (CFD). Results show that the experimental results of graded honeycomb and uniform honeycomb are in good agreement with the numerical simulation results, which indicate that the experimental and numerical results are reliable. In addition, the experimental results also confirm that the assumption of Constant Cross-sectional Fluid Temperature (CCFT) will lead to relatively large error, and the cross-sectional temperature distribution of cooling fluid must be considered in analyzing the heat transfer performance of graded honeycombs. The new assumption that every individual channel has the same fluid temperature is reasonable. These results provide basis for further optimization design of the graded metal honeycomb to improve the heat transfer performance. [ABSTRACT FROM AUTHOR]

Abstract: Three-dimensional numerical analysis for fully developed incompressible fluid flow and heat transfer through triangular microchannels over the slip flow regime is simulated in this paper. In order to study the flow through the channel, the Navier–Stokes equations are solved in conjunction with slip/jump boundary conditions. The influences of Knudsen number (0.001< Kn <0.1), aspect ratio (0.2< A <4.5), and Reynolds number (1< Re <15) on the fluid flow and heat transfer characteristics are extensively investigated in the paper. The numerical results reveal that the rarefaction decreases the Poiseuille number, while its effect on the Nusselt number completely depends on the interaction between velocity slip and temperature jump. It is also found that the aspect ratio has an important role in the analysis, but the variation of Reynolds number is less remarkable. [Copyright &y& Elsevier]

Abstract: This paper presents a new analytical solution of heat and mass transfer processes in a packed bed liquid desiccant dehumidifier based on the equilibrium humidity on the interface is assumed to be constant. In order to maintain the partial pressure difference on the interface, a high liquid desiccant flow rate is often applied in the practical absorber. Therefore, for a narrow range of operating conditions for practical dehumidification process, we can assume that the equilibrium humidity ratio on the interface is constant. The assumption of constant humidity ratio is applied in this paper for derivation of the analytical solution. The model and the analytical solution predictions were compared against a reliable set of experimental data available in the literature, with very good agreement. According to the Lewis definition in this present study, the Lewis number obtains 0.9. The effects of variables such as air and liquid desiccant flow rate, air temperature and humidity, desiccant temperature and concentration have been investigated on the condensation rate. The results present that design variables such as desiccant concentration, desiccant temperature, air flow rate, and air humidity ratio have the greatest impact on the performance of the dehumidifier. The liquid flow rate and the air temperature have not a significant effect. Furthermore, the effects of air and liquid desiccant flow rate have been reported on the humidity effectiveness of the column. [Copyright &y& Elsevier]

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

Abstract: Thermal management of packages consists of external cooling mechanisms, heat dissipaters, and thermal interfaces. While keeping cooling condition constant, junction temperature of LEDs with higher thermal resistance increases more rapidly; hence the luminous efficiency decreases more obviously. This paper includes the discussion about the calculation methods of the lighting''s heat transfer. The calculation process has been demonstrated by an example of cooling of LEDs lighting in this paper. In particular, the operation package heat transfer enhancement is required by most package manufacturers with a decrease of 20% ~ 30% of the thermal resistance over conventional package geometries. [Copyright &y& Elsevier]

The present comment concerns some doubtful mathematical formulations and numerical results included in the above paper. Hence, this analysis is a comparison and correction of the paper "Effects of inclination angle on conduction-natural convection in divided enclosures filled with different fluids" by Y. Varol, H. F. Oztop, A. Koca, Int. Comm. Heat Mass Transfer 37 (2010) 182–191. [ABSTRACT FROM AUTHOR]

Abstract: The present paper analyses the entropy generation of the fully developed laminar convection in a helical coil with constant wall heat flux and presents the optimal design based on the minimum entropy generation principal. The important design parameters, including Reynolds number (Re), coil-to-tube radius ratio (δ) and nondimensional coil pitch (λ) are varied to investigate their influences on the entropy generation. The results presented in this paper cover Re range of 100–10,000, δ and λ range from 0.01 to 0.3. Compared with Re and δ, the coil pitch λ is found to have minor influence on the entropy generation. For a demonstrated case, the minimum entropy generation occurs in the range bounded by Re from 2271 to 4277 and δ from 0.17 to 0.3, within which the irreversibility of the system is lowest and the system performance would be optimum. The details show that there is an optimal Re for a helical coil with a fixed δ; meanwhile for a helical coil flow with a specified Re, the smaller δ should be selected when the Re is larger than 5000, and the larger δ should be selected when the Re is less than 5000. These results provide worthwhile information for heat exchanger designers to find the optimal helical coil design from the viewpoint of the thermodynamic second law. [Copyright &y& Elsevier]

A heat pipe (HP) is a two-phase heat transmission device with very high effective thermal conductivity, extensively employed in multiple industrial fields. In the nuclear engineering area, numerous experimental and numerical studies are widely produced for its thermal behavior performance in high temperatures. In this paper, a HP that potassium as the working fluid with a capillary wick structure was taken into consideration under marine conditions through numerical simulations. The physical properties of potassium and the additional force method of rolling motion are utilized with user-defined functions (UDFs). This CFD model verified with available experimental results, is employed to investigate the influence of HP surface wall temperature distribution and thermal resistance by several parameters including inclination angle, filling ratio (FR), and rolling period. Besides, the charts of phase change and wall temperature distributions are visible with the help of CFD simulation under static and rolling condition. Therefore, the high temperature HP application of design and evaluation is provided as a reference in present work under marine condition. [ABSTRACT FROM AUTHOR]

Abstract This paper has presented a novel method for cooling a motorized spindle shaft based on two-phase loop thermosiphons (TPLTs) which have a high heat transfer performance and work without external power. The evaporator section and the condenser section of the TPLT were on the same pipeline due to the thermal conduction of the shaft in the process of exporting the heat inside the shaft. An experimental investigation of a copper TPLT was carried out using R600a as the working fluid, under the special heating and cooling conditions in a stationary. Then the heat transfer performance of an R600a TPLT was compared with that of an N-pentane TPLT. According to the experimental results, the cooling effect on the shaft was numerically calculated. The results showed that the TPLT worked well and the average equivalent thermal conductivity was 3712–8048 W·m−1·K−1 under the special cooling and heating conditions, which was higher than that of an N-pentane TPLT when the temperature of the evaporation section was below 387 K. The optimum liquid filling ratio of the R600a TPLT was 40%–60%, in this filling ratio range the R600a TPLT had a growing thermal conductivity and a falling heat transfer limit. The maximum temperature rise of the motorized spindle shaft was reduced by 44%, from 55 K to 31 K after using the R600a TPLTs cooling structure. [ABSTRACT FROM AUTHOR]

Abstract A deep learning approach combining with the traditional solid isotropic material with penalization (SIMP) method is presented in this paper to accelerate the topology optimization of the conductive heat transfer. This deep learning predictor is structured based on the deep fully convolutional neural network. The validity and accuracy of this deep learning approach is investigated based on the typical ‘Volume-Point’ heat conduction problems. The time consumption of the optimization process will be reduced significantly by introducing the deep learning approach. [ABSTRACT FROM AUTHOR]

In order to study the heat transfer characteristics (HTCs) of molten salt outside the tube bundle in a shell-and-tube heat exchanger (STHE) without baffle plates, the HTCs of molten salt (204.06 °C~236.91 °C) are experimentally and numerically investigated in this paper. Firstly, the HTCs of molten salt (3514 <  Re  < 5482) is experimentally studied based on the test platform with HITEC salt and oil. Then the empirical heat transfer equations of molten salt applied in the shell side of STHE are fitted. Finally, the comparison between the experimental and numerical results is conducted. The results show that the fitted equations agree well with the experimental data and the fitted deviations are only 8%. The error is about 11% between the simulation and experiment results which indicates that the HTCs of molten salt STHE would be predicted well using the simulation method. The numerical results also show that there exist flow dead zones in the STHE which could weaken the molten salt HTCs. [ABSTRACT FROM AUTHOR]

In this paper, an experimental and numerical study was conducted to evaluate the impacts of momentum and thermal diffusivity comparing to the thermal conductivity of various types of nanofluids on turbulent forced convection heat transfer. 1%, 2%, and 3% volumetric concentrations of different nanofluids such as Al 2 O 3 -DW, SiO 2 -DW, and Cu-DW were considered in this study and their properties were evaluated numerically at the flow inlet temperature of 30 °C. The experimental works were conducted with distilled water as a working fluid to validate the 2-D numerical model. A two-dimensional domain was constructed using ANSYS-Fluent package, and the standard k–ε turbulence model was employed to solve the continuity, momentum, and energy equations. The flow was maintained in the Reynolds range between 6000 and 12,000, and the data obtained experimentally were validated by results from empirical correlations. The numerical solutions for the average Nusselt number and pressure drop presents a good agreement with the experimental results as the average error was less than 5% for both the cases of heat transfer and pressure loss data. The results showed that Al 2 O 3 -DW nanofluid has the best enhancement in convection heat transfer coefficient compared with the DW and other nanofluids of the same concentration while Cu-DW nanofluids shown the lowest enhancement though it shown the highest value of thermal conductivity. Also, the results showed that the product of kinematic and dynamic viscosities had the greatest effect on pressure drop in the fluid domain. [ABSTRACT FROM AUTHOR]

In this paper, the convective heat transfer and flow characteristics of nanofluids consisting of distilled water and 0.25, 0.5 wt% and 1 wt% Al 2 O 3 nanoparticles were studied experimentally and compared to predicted results using computational fluid dynamics (CFD) that using laminar model was performed to examine the heat transfer characteristics. The Al 2 O 3 nanoparicles with a nominal diameter of 40 nm are dispersed in distilled water to form stable suspensions containing various kind of volume concentrations of nanoparticles. For the even dispersion of the nanoparticles in the base liquid, ultrasound was applied for 3 h. The nanoparticle dispersion on alumina concentration was measured using UV spectroscopy. Thermal conductivities of nanofluid solutions are measured by the transient hot wire method. Heat transfer characteristics were investigated by changing pressure pulsation at each concentration. Finally, calculated heat transfer characteristics results using CFD are compared to experimental results and discussed successfully. Results indicate that the heat transfer coefficient and Nusselt number increase with increasing the Reynolds number and it is also seen that the Prandtl number is getting down when the concentration of nanofluids enlarge and showed the equation by the linear method of the result value. [ABSTRACT FROM AUTHOR]

Transport Membrane Condenser (TMC) is a promising technology that works based on the capillary condensation property of the nano-scale ceramic porous membrane materials and can recover both waste heat and water in various industrial applications. For applications with high volume flow rate such as in power plants, a large number of TMC heat exchangers are required, which highlights the importance of the optimum design for the TMC exchangers in order to obtain the maximum heat transfer and minimum cost of the TMC heat exchanger unit. In this paper, the effects of different tube spacing and the inlet water vapor mass fraction on the overall performance of a membrane-based heat exchanger have been studied numerically using a combined condensation model based on the capillary condensation and condensation on a solid wall. The results were obtained in terms of the Euler number, dimensionless volumetric heat transfer density, and contours of the water mass fraction and temperature distribution inside the TMC heat exchanger. [ABSTRACT FROM AUTHOR]

It is commonly believed that the significant energy saving advantages are belonged to the logic circuits which operate at low temperature as less energy is needed for cooling them to the threshold temperature after operation. Also, nanoscale thermal management, efficient energy usage in nanoscale and especially thermal optimization are the most challenging issues, while dealing with the new generation of transistors as the miniaturizing unlimitedly the silicon channels of the transistors has resulted in an increase in the energy consumption of computers and the leakage currents. In this paper, the non-Fourier thermal attitudes of well-known two-dimensional crystalline materials of graphene, blue phosphorene, germanene, silicene and MoS 2 as the silicon channels replacements are studied by using the phonon Monte-Carlo method. We show that graphene and blue phosphorene have the least maximum temperature, representor of the reliability of the transistors, among the all five investigated nano-channels during the Monte-Carlo simulation. The established hotspots of these two materials are always cooler, not reaching the temperature threshold level, and they lose the heat much faster as the heat generation zone is switched off. The obtained results considered along with the electrical disadvantages of the graphene layer, suggests the blue phosphorene as the more thermally appropriate and optimal choice for the silicon channel replacement in new designed field effect transistors. That is to say that the limit of the energy and economic cost of the producing the advanced blue phosphorene chips meets the value of the product for the computing enterprise. [ABSTRACT FROM AUTHOR]

This paper attempted to investigate the effects of ionic liquids (ILs) addition on the startup, operation and thermal performance of a closed loop copper oscillating heat pipe (OHP, four turns). The liquid slug oscillation characteristics and flow pattern of the OHP with various heat input were also experimentally examined utilizing high-speed camera. The experimental results showed that for higher ILs mass fractions, the OHP behaved a lower startup power (decrease of 29 W) and startup temperature (decrease of 11 °C), which are favorable of not only facilitating a faster startup of the OHP but also effectively avoiding the “dry-out” problem. When the mass fraction of ILs was 0.67%, the ILs-water based OHP substantially had the same amplitude and the velocity as water-based OHP. When the ILs addition was respectively 19.1% and 44.4% (mass fraction), the oscillation liquid slug displayed a high frequency and small amplitude characteristics. In case of a low mass fraction of ILs, ILs-water based OHP nearly perform the same heat transfer performance as the water based OHP presented. However, the heat transfer performance of the ILs-water based OHP showed a slight decrease of 10% at higher heat input (>220 W), which in general did not affect the overall thermal performance and operational stability of the OHP. A modified correlation of Kutateladze number ( Ku ) was established and could basically predict the thermal performance within approximately ±10% deviation in the vertical closed loop OHP at a filling ratio around 65% considering the effects of ILs addition. [ABSTRACT FROM AUTHOR]

This paper presents experimental results obtained during tests on the evaporation heat transfer inside tube of a coaxial heat exchanger for residential and industrial geothermal heat pumps. The experimental device and instrumentation of the test section using evaporation inside a water heated double tube, have been described. The results obtained for evaporation local heat transfer of refrigerants R134a and R407C have been compared to the existing correlations. The aim of this comparison is to evaluate the validation of the well-known correlations to predict evaporation heat transfer in the geothermal operating conditions. A complete experimental analysis of the local evaporation of the R134a and R407C is carried out as a function of vapor quality inside a smooth horizontal tube. Various refrigerant mass fluxes are tested. Moreover, new correlations for local heat transfer and pressure drop predictions have been developed and validated basing on the measurements. [ABSTRACT FROM AUTHOR]

This paper constructs a three-dimensional model to numerically investigate the heat transfer and fluid flow characteristics of combined microchannel with cone-shaped micro pin fins (MCPF) for inlet Re number ranging from 147 to 637. Firstly, the cases of micro pin fins located in the upstream (case1), middle (case2), downstream (case3) of microchannel and distributed throughout the microchannel (case4) are studied with fixed number of fins. Thereafter, the dimensionless parameters of relative fin diameter, relative space between the fins and relative height of the fin are studied to optimize the design. The variations of apparent friction factor f app,ave and average Nusselt number Nu ave with inlet Re number have been conducted, and the thermal enhancement factor ( η ) has been adopted as evaluation criteria to determine the best comprehensive thermal-hydraulic performance of MCPF. The results show that the microchannel inserted cone-shaped micro pin fins improves the heat transfer accompanied with a higher pressure drop as compared with the smooth rectangular (Rec) microchannel. Microchannel with uniform fins distribution (case4) has the largest η and the bottom wall temperature is the lowest and well-distributed among all cases. When Re < 500, the overall thermal performance of case3 is better than case1 but when Re > 500, it displays a contrary tendency. The geometric configuration optimization of MCPF suggests that there is an optimum pin diameter, fin space and fin height that satisfy the demands of heat transfer and pressure drop. [ABSTRACT FROM AUTHOR]

In order to improve the refrigeration system performance, researchers are introduced nanorefrigerants and nanolubricants in the recent development of HVAC system. However, the explanations of the nanoparticles contribution on the basis physical phenomena which affecting the vapor compression refrigeration system (VCRS) are limited in the literature. Hence, this paper presents a review on mechanism for improvement in VCRS performance by using nanorefrigerants and nanolubricants. The heat transfer augmentation, the refinement of refrigerant-oil mixture characteristic, and the tribology properties enhancement are among the major mechanisms that affect the VCRS performance. The performance parameters of VCRS such as compressor work and COP of refrigeration system using nanorefrigerants and nanolubricants have been discussed to relate between the mechanisms with overall system performance. The results showed that the utilization of nanorefrigerants and nanolubricants in the system was increased the heat transfer coefficients from 12 to 101% and the thermal conductivity enhancement for up to 4%. The solubility and miscibility of refrigerant-oil mixture with nanoparticles additives was enhanced for up to 12% although some reported that it was remained unchanged. The nanolubricants were behaved better tribology characteristics with 32% and 13% reduction of friction coefficient and wear rate, respectively. The effect of nanorefrigerants and nanolubricants on heat transfer, refrigerant-oil mixture and tribology had increased the overall performance of VCRS with 11% compressor work reduction and 24% of COP enhancement. Therefore, the nanorefrigerants and nanolubricants are expected to become the best candidate towards improving the efficiency of the VCRS. [ABSTRACT FROM AUTHOR]

In this paper, a quick and easy method to fabricate oil infused nanograss (OIN) thin hydrophobic films for dropwise condensation enhancement is presented. Droplet sliding experiments on an inclined surface coated with this thin film infused with oil show that the droplet dripping rate can be increased considerably. Experiments of condensation heat transfer on the outer surface of a cold tube with this OIN coating show that heat transfer can be enhanced up to approximately 50% compared to raw copper surface. The enhanced condensation heat transfer by OIN coatings is due to the combination of dropwise condensation and faster removal of water droplets. [ABSTRACT FROM AUTHOR]

This paper develops an efficient finite volume approach using OcTree mesh for simulation of hyperthermia treatment by injection of nanoparticles. A three-dimensional nonlinear Pennes' model is employed to simulate the heat transfer in a heterogeneous blood perfused living tissue. The OcTree mesh is a good compromise between regular grid from finite difference method and unstructured meshes from finite element method due to the possibility of applying local refinement using a nonconforming mesh in a straightforward manner. Implicit time-marching scheme coupled with the Picard method and explicit method are used. A numerical example is analyzed, illustrating the advantages of the approach. [ABSTRACT FROM AUTHOR]

The phase change material (PCM) receives more and more attention on account of the large amount of heat absorption and release during the process of phase change. In order to further investigate the heat transfer behavior of phase change, a discrete unified gas kinetic scheme (DUGKS) derived from Boltzmann equation for solid-liquid phase change has been developed in this paper. The phase change problems, including the phase change by conduction and by convection, are solved to verify the present DUGKS. The results of DUGKS agree well with that of analytical solution or benchmark solution. In the simulations of natural convection with phase change, the non-uniform mesh has been considered to evaluate the performance of DUGKS. Besides, no phase interface effect, with which the temperature is lower than the initial one in lattice Boltzmann (LB) method, is obtained in present DUGKS. [ABSTRACT FROM AUTHOR]

Falling film on horizontal tube banks is widely used in heat and mass transfer processes, because it leads to a higher heat and mass transfer performance. In this paper, a series of experiments were conducted to investigate the temperature distribution and local temperature evolution feature of liquid film at low spray density on superhydrophilic surfaces by thermal tracing method. The experimental results revealed that the temperature distribution of liquid film on the superhydrophilic surfaces presented a sub-region effect for different flow mode, a uniform and repeated distribution for jet mode and two totally different zones for droplet mode. Besides, for there existed a new high temperature band, which was first observed in the center of saddle-shaped lamella for droplet mode and a lower temperature region coinciding with the interaction ring between each pair of jets for local temperature feature due to the effect of the collision and overlap of spread film on superhydrophilic surfaces. [ABSTRACT FROM AUTHOR]

The paper deals with the problem of heat conduction in a nonhomogeneous rigid body which is a homogeneous conductive layer with a periodic composite coating. The coating layer is a composite in which every unit cell in general case is composed of four rigid beams with rectangular cross-sections. The assumed structure permits to analyse some special cases of coatings: laminated composites with layer parallel or perpendicular to the boundary, composites with periodically distributed inclusions with rectangular cross-section and a homogeneous layer. The distributions of temperature and heat flux distributions on the interface between the coating and the homogenous layer are investigated. [ABSTRACT FROM AUTHOR]

The heat transfer and flow of nanofluids in microchannel heat sink is usually numerically investigated by the single-phase model. The thermal conductivity and viscosity of nanofluids are calculated in the whole computational region because the single-phase model, assumes the nanofluids is static and nanoparticles concentration is uniform. However for the actual forced flow process, the concentration distribution of the nanofluids is not uniform. So the thermal properties of the nanofluids vary within different computational regions. With the increase of the velocity of the nanofluids, the deviation between the prediction of single-phase model and experimental results increases. In this paper, a new simulation method is proposed to consider the inhomogeneous and dynamic thermophysical properties of the nanofluids by obtaining the nonuniformly distributed nanoparticle concentration in each numerical cell. At the same time, it takes into account the following factors: the interactions between the nanoparticles, the solid wall and the base fluid, the axial conduction, the slip boundary conditions and fluid-solid coupling. The results show that the proposed numerical simulation method further improve the simulation accuracy for the forced flow and heat transfer process of nanofluids in the microchannel in a wider range. The effects of the nanoparticles concentration, Reynolds number and axial heat transfer on the thermophysical properties of the nanofluilds, the flow and heat transfer characteristics of a rectangular microchannels with hydraulic dimensions of 341 μm were analyzed using the proposed simulation model. The main results are as follows: the nanoparticles are enriched at the near wall for the fully developed region; the nonuniformity of the nanofluilds thermal conductivity coefficient distribution at the channel cross section increases with the increase of the mass flow rate and the inlet centration; under the same Reynolds number, the higher the nanofluids concentration the better the heat transfer characteristics, but there is no linear relationship between the enhancement amplitude and concentration; the heat transfer coefficient of nanofluid with 1% and 2% alumina nanoparticles concentration is about 5.86% and 8.49% higher than that of deionized water, respectively; the axial conduction effect cannot be ignored for the microchannel, which significantly affects the inlet and outlet region of the microchannel especially when the Reynolds number is low. The nanofluilds temperature in the microchannel increases with the curve and does not match the conventional linear growth hypothesis. [ABSTRACT FROM AUTHOR]

Making clear how thermal loads are equilibrated and transferred through a structure is of importance for identifying optimal heat conduction topologies in problems of cooling scheme design. This paper proposes a new method for computing the orientations and locations of heat transfer paths from a standard finite element analysis. First, a non-dimensional parameter ( C ⁎ ) is introduced, based on the variation in thermal compliance of the structure, to quantify the contribution of an arbitrary point in the structure to heat conduction performance. Then, a plotting algorithm is presented to search for the ridge lines of the calculated C ⁎ curved surface, which provide the steepest ascent in C ⁎ values from the points of heat sink to the points of heat source. Based on this, mathematical conditions (termed uniformity and continuity requirements) are discussed in detail and utilized as new criteria for tailoring the layouts of heat transfer paths in order for conductive cooling to be more effective. Finally, the derived criteria are incorporated into a commonly used topology optimization algorithm (SIMP algorithm), and validated though several benchmark cases. Unlike the conventional methods, the suggested approach optimizes only the orientations and locations of heat transfer paths and does not intentionally concern the overall temperature distribution, the application of which can potentially lead to worthwhile improvements at the conceptual stage of cooling design processes. [ABSTRACT FROM AUTHOR]

Presented research paper is an investigation of water, paraffin and ethylene glycol based Al 2 O 3 nanofluid. Heat transfer coefficient is measured using shell and tube heat exchanger under the conditions of fully developed laminar and turbulent flow. Concentration of nanoparticles in the respective base fluids was varied from 0.01 vol% to 0.08 vol% in the step of 0.1%. Nanofluids were used as the working fluid and sent to tubular side. The effects of Reynold's number and concentration of nanoparticles in nanofluid on heat transfer characteristics were studied. A significant enhancement in heat transfer coefficient and thermal conductivity of nanofluid over base fluid is found in the study. As the concentration of nanoparticles was increased, heat transfer coefficient was also improved marginally. At greater turbulence, the improvement in the heat transfer coefficient of nanofluid over base fluid was found to be more than that at lower turbulence. This is due to homogeneous distribution of nanoparticles in a base fluid at higher temperatures was achieved. The various factors that were considered in the characterization of nanofluid heat transfer coefficients are: sonication time, temperature, pressure difference, base fluid (water, paraffin and EG). Pressure drop in case of nanofluid was higher than base fluid in the turbulent regime; however, no significant change was observed in the laminar region. [ABSTRACT FROM AUTHOR]

In order to avoid the costs of experimental evaluations, soft computing methods like artificial neural network (ANN) and genetic algorithm have remarkably grabbed the attentions of investigators for predicting the hydrothermal characteristics of different types of nanofluids. In this paper, the implementation of ANN and genetic algorithm for modeling and multi-criteria optimizing the hydrothermal behavior of SiO 2 /water nanofluid has been investigated. Using the data obtained from the experimental analysis, an ANN model is developed to estimate the pressure drop and Nusselt number as a function of volume concentration, Reynolds number, and inlet temperature. Different network structures were assessed and it has been achieved that a network with 2 hidden layers and 6 neurons in every layer provides the most accurate prediction. It is revealed that the developed network is satisfactorily accurate to determine the Nusselt number and pressure drop of SiO 2 /water nanofluid compared to the empirical correlations. To optimize the hydrothermal behavior of the nanofluid (i.e. to find the optimal cases with highest Nusselt number and the relatively least pressure drop), the genetic algorithm coupled with compromise programming approach has been implemented considering decision maker's attitude. [ABSTRACT FROM AUTHOR]

This paper reports the effect of changing the aspect ratio on the heat transfer and flow quantities over in-line tube banks. Two types of in-line arrangements were employed; square and non-square configurations. The models that were examined are a standard k-ε model, SST k-ω model, v2-f model, EB k-ε model and EB-RSM model. The closer results to the experimental data and LES were obtained by the EB k-ε and v2-f models. For the square pitch ratios, the solution has faced a gradual change from a strong asymmetric to asymmetric and then to a perfect symmetry. The strong asymmetric solution was found by the very narrow aspect ratio of 1.2. However, the behaviour of cases of 1.5 and 1.6 became less strong than that predicted in the case of 1.2. In the larger aspect ratio of 1.75, the flow behaviour is seen to be absolutely symmetric for all variables under consideration except Nusselt number. For the very large pitch ratio of 5, the flow has recorded maximum distributions for all parameters on the windward side of the central tube with a perfect symmetric solution around the angle of 180° while the vortex shedding frequency has recorded minimum value and the Strouhal number; therefore, has given the smallest value. However, for the non-square pitch ratio of constant transverse distance, the solution is still asymmetric for all parameters with merely one stagnation at the angle of 52° at the case of the 1.5 × 1.75 while by increasing the longitudinal distance to 2 and 5, the solution provided a comprehensive symmetry for all variables with two vortices are fully developed mirrored in shape on the leeward side of the central tube. On the contrary, for the non-square pitch ratio of constant longitudinal distance, the flow of the case of 1.75 × 1.5 provided two stagnation locations at around 52° and 308° with a very similar solution to the case square ratio of 1.75 for all variables whereas by increasing the transverse distance to 2 and 5, the solution recorded was not perfectly symmetric resulting in two different vortices and one stagnation position located at the leading edge of the cylinder provided by the case of 5 × 1.5. In terms of vortex shedding effect, the reduction in the Strouhal number at a constant transverse pitch is less steep than those at a constant longitudinal pitch. [ABSTRACT FROM AUTHOR]

The aim of this paper is to propose the PV roof solar collector (PV-RSC) to investigate the natural convection heat transfer and estimated the convective heat transfer coefficient in the channel. The experimental set-up was composed of a PV panel on the upper layer and the lower layer is aluminum plate of the channel. The inclination angle and air gap of channel were fixed at 30° and 15 cm, respectively. The channel width is 0.7 m, and length is 1.2 m. The data analysis were confirmed the effect of radiative exchange influent to natural convection within the channel. On the basis of the experimental results, an empirical formula is found; the Nu as a function of Ra s sin30, that is Nu s = 0.3282 ( Ra s sin30) 0.2249 . The correlation obtained to range 3 × 10 8 < Ra s sin30 < 7 × 10 8 . A comparison between PV-RSC and normal PV panel, it was confirmed that the PV-RSC could be generated electric power than that normal PV panel by about 30 W; and also the percentage of power generation increase was rising about 25% throughout the day. [ABSTRACT FROM AUTHOR]

Droplet evaporation widely exists in the daily life and industrial production. In most of previous experimental studies, the evaporation of sessile droplets was conducted under a constant substrate temperature condition. However, drops often evaporating on a heating surface under a constant heat flux condition in many practical applications. In this paper, we have carried out an experiment on sessile 3 μl DI water droplets evaporated on hydrophilic and hydrophobic heating surfaces under constant heat flux in the range from 1153 W/m 2 to 6919 W/m 2 . A high-speed camera was used to record the changing shapes of two sessile droplets on a hydrophilic and a hydrophobic heating surface placed side by side. The droplet height, dynamic contact angle, droplet contact diameter, evaporation mode and evaporation rate are presented. [ABSTRACT FROM AUTHOR]

Natural heat convection, mixed heat convection and heat transfer by conduction and convection with solidification of a ternary alloy are described by the finite volume method using a geometric multigrid approach. The objective of this paper is to analyze the effects of the multigrid technique on the accuracy and efficiency in describing convective heat transfer in closed and open cavities with and without liquid-solid phase changes of Newtonian and shear-thinning non-Newtonian fluids. It is found that the multigrid scheme reduces the computation time in natural convection in a square cavity from two times for Rayleigh number Ra = 10 5 up to seven times for Ra = 10 3 , between 50% and 2.7 times for mixed convection with an inner solid when the Richardson number decreases from Ri = 10 to 0.1 and the Reynolds number Re = 100, and 20% for natural convection/heat conduction in solidification of a ternary aluminum alloy (Ra = 10 4 ) with a shear-thinning rheology and a power index equal to 0.5. [ABSTRACT FROM AUTHOR]

Slug flow is one of types of flow in two-phase flow in porous media, and this type of flow widely exists in oil and gas pipelines, underground water reservoirs, and nuclear reactor cooling systems, etc. Study of the mechanisms and characteristics of slug flow in porous media has the great significance in the reservoir engineering, power engineering, aerospace engineering, and chemical engineering etc. In this paper, we propose analytical models for seepage characteristics, both permeabilities and relative permeabilities, for slug flow in a capillary by unit cell approach. Then, we extend the methodology to analyze the seepage characteristics of slug flow in fractal porous media. The proposed relative permeabilities for slug flow in porous media are expressed as a function of micro-structural parameters of porous media and fluid properties, such as maximum and minimum capillary sizes, fractal dimensions, the surface tension, as well as capillary numbers. The parametrical effects on the relative permeabilities are also investigated. The validity of the proposed model for slug flow is verified by comparing the model predictions with the available experimental data. [ABSTRACT FROM AUTHOR]

In present paper, solar air heater duct having aspect ratio 12 roughened with broken arc rib has been investigated. The broken arc is formed by creating symmetrical gap in continuous arc with gap width equal to roughness height. It has been planned to investigate the influence of position of gap in arc rib on Nusselt number as well as on friction factor. For this purpose, five broken arc rib roughened plates having relative gap position ranging 0.2–0.8 have been investigated for values of Reynolds number 2000–16000. The remaining roughness parameters like relative roughness height, arc angle, and relative roughness pitch were taken as 0.043, 30 o and 8 respectively. The presence of broken arc ribs enhanced the Nusselt number, friction factor and thermo-hydraulic performance up to 2.37, 2.55 and 1.94 respectively, compared to smooth duct. The results of ducts roughened with broken arc rib and continuous arc rib have been compared under similar flow conditions. The effect of gap in continuous arc rib on the flow pattern has also been observed using ANSYS Academic Research CFD 15.0. [ABSTRACT FROM AUTHOR]

This paper investigates the phenomena of liquid fuel jets in gaseous crossflow for two types of fuels, namely n-Hexane and n-Octane. In this regard, a numerical model is developed to predict a droplet behavior including trajectory, velocity, evaporation and combustion, size degradation, breakup time and radius of produced child droplets. Therefore, the mass, concentration, energy and momentum conversation equations are derived to evaluate the droplet acceleration from initial conditions. The velocity distribution is then obtained through a numerical integration of the acceleration over time. A further integration is made to determine the droplet position. In addition, evaporation and combustion and Taylor Analogy Breakup (TAB) models are integrated to assess droplet evaporation, combustion rate, and breakup behavior during the injection process. The professional version of the Engineering Equation Solver (EES) software is used to solve the model which has the advantage of providing the thermodynamic properties of the different fluids involved through predefined functions. The behaviors of droplets are investigated for two injection cases: evaporation only and evaporation and combustion. The results obtained are presented in the variations in trajectories, velocities, droplet size and surface temperature corresponding to each case and type of fuel. [ABSTRACT FROM AUTHOR]

In this paper, a numerical study of double hole water jet condensation is presented, and the heat transfer mechanism of double hole jet is obtained. Firstly, the flow characteristics along the axis of plume were investigated, and the mechanism of interaction between adjacent plumes was analyzed. With the increasing of the inlet pressure of steam, the plume length increases gradually. Then it is found that the temperature of the subcooled liquid had a restraining effect on the length of plume, and the higher temperature difference in heat transfer increases the mass exchange of interface between liquid and gas. The effect of the structural parameters of the nozzle on the plume was also analyzed. As the hole spacing decreases, the degree of plume convergence increased. The plume was more susceptible to mutual influences with the increase of nozzle diameter. Finally, a new correlation for double-hole plume length was proposed by comparing with the existing prediction correlation. • The steam jet plume characteristics in double-hole with water flow were studied • The interfacial turbulent kinetic energy and mass transfer rate were analyzed • The influence of different nozzle structure parameters on the characteristics of jet condensation was compared • A dimensionless plume length relationship was proposed based on different steam mass flux. [ABSTRACT FROM AUTHOR]

LBE HCOTSG, which combines the benefits of lead‑bismuth eutectic (LBE) and helical coil once-through tube steam generator (HCOTSG), has the potential to be an excellent heat exchanger choice. Given the similarity of the structure, the analysis of cross/oblique bundle flow heat transfer can help reveal the heat transfer characteristics of the HCOTSG shell side. In this paper, a numerical method for LBE in cross/oblique bundle flow is proposed. Based on the validated method, the application range of the correlation on the flow of the LBE cross/oblique bundle obtained from experiments is broadened based on the numerical simulation work. The influence of tube geometric arrangement in the bundle is also taken into account, including the inclination angle (θ), S min / d, and various staggered arrangements. The difference between numerical simulation results and experimental data is less than 15%. For LBE cross/oblique bundle flow, the extended correlation taking geometric parameters into account also has good applicability. The alternating inclination angle arrangement at an angle of 8° can greatly enhance heat transmission efficacy by up to 33%. The impact of geometric arrangement is estimated in relation to local temperature. This work provides a correlation for the flow of the LBE cross/oblique bundle that is more broadly applicable. Furthermore, this work will significantly benefit the design optimization and program development of LBE HCOTSG or other innovative heat exchangers with cross flow of LBE. • A numerical method for LBE cross/oblique bundle flow is proposed and validated. • The application range of the correlation is broadened based on the method. • Heat transfer performance of LBE flow cross tube bundle is numerically studied. [ABSTRACT FROM AUTHOR]

In the present paper the behaviour of human cardiac tissue during cryo-ablation is simulated with a finite difference algorithm which solves the Pennes' equation including the phase change during freezing of the cardiac tissues. The evolution of temperatures at different points is calculated and the movement of the ice front is obtained from simulation results. All phenomena related to heat transfer in living tissue are considered: heat conduction, heat release and absorption due to heat capacity, metabolism and blood perfusion. Although the geometry and the assumed boundary conditions are quite simple, the structure of the developed model can be easily adapted to more complex geometries. Model results show for instance that with a power of 10 W tissues distant 0.5 mm from the probe are ablated, while the other tissues more than 0.5 mm remain at −20 °C, so undamaged The results also show that the outcome of cryo-ablation treatment depends on many parameters: operational parameters such as the power heat absorbed by the probe (i.e. the mass flow rate of the cryo-fluid) and the duration of therapy application; biothermal parameters such as metabolic heat flux and blood perfusion; thermophysical properties of the tissue. Among these the effects of both blood perfusion and metabolic rate result less influencing. The numerical model presented could be useful to estimate the best conditions for the application of the probe during treatment and the possible change of the cure parameters to adapt the therapy to different patients. [ABSTRACT FROM AUTHOR]

For a linear heat transfer system, the unit step response of the temperature field to any system inputs, such as internal and external heat sources, is specific. This means that there is a definite temperature response correlation between any spatial points in the system spatiotemporally, which is independent of the system inputs. It is significant to achieve a quantitative description of the temperature response spatiotemporal correlation between the spatial points for solving the temperature field reconstruction problem of the heat transfer system with unknown inputs. In this paper, a temperature response spatiotemporal correlation model (RSTCM) of the heat transfer system is established originally to reveal the inherent quantitative relationship between the responses of any system spatial points theoretically. Firstly, an external description of the spatiotemporal mapping relationship of the heat transfer process is established according to the heat transfer equations. Furthermore, a basic RSTCM form is proposed and a response spatiotemporal correlation matrix is determined with the help of the external description. Finally, considering the ill-posed characteristic of the response spatiotemporal correlation problem, the regularization technology is employed to transform the original problem into a well-pose problem and to provide a response spatiotemporal correlation matrix with regularization. Effectiveness of the RSTCM is verified by the existing heat transfer experimental data. Besides, adaptability of the proposed model is demonstrated by the achieved numerical experiment results on a two-dimensional heat transfer system. [Display omitted] • The temperature response spatiotemporal correlation is revealed for a heat transfer system. • A temperature response spatiotemporal correlation model (RSTCM) of the heat transfer system is established. • The response spatiotemporal correlation matrix is constructed by regularization. • Effectiveness of the RSTCM is verified by experimental data. • The RSTCM lays a foundation for temperature field reconstruction independent of heat sources. [ABSTRACT FROM AUTHOR]

This paper presents a numerical analysis of a horizontally oriented constant surface area isothermal helical coil under natural convection heat transfer and surface radiation. Numerical computations are carried out in the laminar regime of Rayleigh number (104 ≤ Ra ≤ 108), surface emissivity (0 ≤ ε ≤ 1), and geometrical parameters of the helical-coil, like diameter of the coil (8 ≤ D / d ≤ 24), pitch (3 ≤ p / d ≤ 7.5), and coil height (40 ≤ H / d ≤ 60) to study the heat transfer characteristics. This study is used for effectively designing the helical coils, which are typically manufactured at an extremely high temperature. The numerical computation has been validated by comparing the average Nusselt number (Nu) with the previous experimental results. Temperature-dependent fluid properties are incorporated to achieve precise results over a wide range of temperatures. The effect of the geometrical parameters on the heat transfer characteristics has been depicted graphically in terms of average Nu , relative convection and radiation heat transfer rate, and the temperature profile. It is found that the relative contribution of radiative heat transfer is 87.8% at an emissivity of 0.9 and Ra of 10(Ali, 1994 4), whereas, for an emissivity of 0.1 and Ra of 10(Moawed, 2005 8), the relative contribution of radiation heat transfer is only 6.4%. Lastly, a correlation has been developed for the average Nu based on all the pertinent parameters which can be beneficial to the engineers in the industry and also academic researchers. The developed correlation has been used to predict the cooling curve of the helical coil in certain situations. [ABSTRACT FROM AUTHOR]

In this paper, a novel butterfly wing type hydrocarbon fuel cooling channel structure is proposed and applied for the first time in the cooling of rotating power generation turbine blades of hypersonic vehicles. The effects of rotating butterfly wing-type channel root height and cross-critical temperature on the friction factor and heat transfer performance of hydrocarbon fuel are investigated in depth. Numerical results show that the thermal performance of the butterfly wing type channel corresponding to the root height of 0.8 D is the highest. Compared to the 1 D channel, the thermal performance of the butterfly wing type channel corresponding to the root height of 0.8 D is increased by a maximum of 1.8 times. Compared to the 1 D channel, the Nusselt number of the wing type channel corresponding to the root height 0.2 D is increased by a maximum of 1.03 times. Compared to the inlet temperature greater than critical temperature, the thermal performance of the wing type channel at inlet temperature less than critical temperature is increased by a maximum of 2.1 times. Compared to the 1 D channel, the wing type channel reduces the first channel backflow and vortex area by almost 50%. • A novel butterfly wing type hydrocarbon fuel cooling channel is proposed and firstly used in hypersonic vehicles. • Thermal performance of the channel with a root height of 0.8 D is increased by maximum 1.8 times. • The butterfly wing type channel can improve the thermal performance of the fuel at high rotation speed. • The wing type channel can reduce the backflow and vortex area by almost 50%. • Fuel "upward convexity" and "downward concavity" cause the wing channel heat transfer level to increase. [ABSTRACT FROM AUTHOR]

An action of CNTs flow access an unstable motion of a Newtonian fluid past a stagnation point on a stretched sheet using a penetrable medium is investigated in this paper. Once the fluid commences circulating with the flow of time, it flows. Flow is influenced by heat exchange with the surroundings. The implicitly limited component method is employed to track an unstable system of non-dimensional PDE with an associated boundary layer. Approaches, along with the relevant barrier circumstances, are acquired analytically. An influence of mass transpiration, volume fraction, and thermal radiation is investigated on Newtonian fluid flow using the penetrable medium. Heat transmission in a liquid with electrical conductivity, including heat source /sink across a continually stretched /shrinking surface with a Biot number. The importance of the present exertion is the stream of carbon nanotubes owing to Darcy porous media using linear heat radiation and an analytical approach. The nanoparticles provide important properties in enhancing the heat exchange procedure as well as thoroughly achieved applications in industry. It is discovered that the basic resemblance models accept two-phase for both extending /contracting sheets. In presence of calculation upon momentum with temperature jump conditions is accessible plots aimed at varying predictions of certain physical properties. Analyzing the properties of Darcy porous media of heat transport in the presence of radiation from a flat surface, the problem is solved analytically using incomplete gamma functions. Depending on the kind of boundary heating, the analytical equation for temperature is obtained in terms of power series. • Unsteady flow over permeable plates in porous media with thermal radiation is studied. • The analytical solution is obtained by using incomplete gamma functions. • Velocity and temperature are presented in terms of power series depending on BCs. • Effects of physical parameters on the flow and heat transfer are characterized. • Velocity boundary layer decreases and thermal boundary layer increases in porous media. [ABSTRACT FROM AUTHOR]

In this paper, the middle double swirl cooling (M-DSC) models for diverse nozzle aspect ratios (C ar) are established for flow and heat transfer behavior research. The k-ω turbulence model and the 3D viscous steady RANS equations are utilized for numerical calculation. The finite volume method and coupled implicit solver are chosen for simulation calculation. Influences of C ar values, namely 0.375, 0.67, 1.5, 2.67, 4.17 and 6 on the flow characteristics and thermal performance for the M-DSC are investigated when keeping vortex nozzle inlet area constant. Moreover, the cooling performance for diverse inlet Reynolds numbers 12,500, 22,500, 32,500 and 42,500 is studied with the model owning the optimal C ar. Results show that the velocity of the crossflow will increase along in the outlet direction. As C ar decreases, the velocity where the jet coolant scours the target will decay more significantly toward the outlet. There are four typical shapes of high heat transfer regions on the target. The uniformity of heat transfer will increase with the growth of C ar. When the C ar is 4.17, the thermal performance factor is the highest. The flow and heat transfer regulations are almost constant when the inlet Reynolds number is altered. • Middle double swirl cooling models with different nozzle aspect ratios are established. • Effects of different nozzle aspect ratios and inlet Reynolds numbers on flow and heat transfer characteristics are explored. • Optimal nozzle aspect ratio with the best cooling performance is obtained. [ABSTRACT FROM AUTHOR]

The following comments address an inappropriate implementation of a theoretical relationship and some incorrect qualitative and quantitative findings in the paper, as mentioned above. Therefore, this analysis clarifies the article "Numerical study on the conjugate effect of joule heating and magneto-hydrodynamics mixed convection in an obstructed lid-driven square cavity." [International Communications in Heat and Mass Transfer 37 (2010), 524–534]. [ABSTRACT FROM AUTHOR]

We present Large Eddy Simulation (LES) results of heat transfer and flow evolution of a turbulent two-dimensional rectangular jet of air, of height H, impinging upon a flat wall. Rectangular jet is quasi-two dimensional, i.e. planar jet with infinite slot-width. Exit of jet is set at four distances, D , from wall, D = 4H, 3H, 2H, H. Distance of slot exit to wall modifies flow evolution, reported as mean and instantaneous, compared to experimental data. In mean flow Undisturbed Region of Flow, URF, and, in instantaneous flow, Negligible Disturbances Flow, NDF, and Small Disturbances Flow, SDF, are reported for the various distances D/H. In order to evaluate influence of flow parameters on heat transfer and flow evolution, two levels of turbulence are imposed on slot jet exit, i.e. 1% and 6%. The level of turbulence modifies heat transfer results, as far as convective heat transfer and Nusselt number are concerned. The shape of Nusselt number distribution along impinged wall is different according to level of turbulence. The paper presents a very good comparison with experimental Nusselt numbers, for the first time in literature. • A quasi-two dimensional jet, i.e. with infinite slot-width, of air impinges a flat wall. • Large Eddy Simulation approach is compared successfully to experiments. • Distance from the wall influences flow evolution and heat transfer. • Lengths of URF, NDF and SDF are influenced by the distance from wall. • Heat transfer is compared successfully to experimental results, for the first time in literature. [ABSTRACT FROM AUTHOR]

Light propagation in three-dimensional (3D) graded index (GRIN) media has a complex spatial path, making it difficult to solve thermal radiative transfer problems. In this paper, a mesoscopic lattice Boltzmann method (LBM) that implements simple steady-state and transient radiative transfer solutions in 3D GRIN media is proposed. During the construction of the lattice Boltzmann (LB) model, the concept of the "local radiative transfer direction", which addresses complex curved trajectories in 3D GRIN media simply, is introduced. The radiative transfer equation of 3D GRIN media can be strictly recovered from the LB model by adopting the Chapman-Enskog analysis. Numerical results indicate that radiative transfer problems in 3D GRIN media can be solved effectively by the LBM. Additionally, the influences of different optical parameters on steady-state and transient radiative transfer in 3D GRIN media are discussed. The LBM is a promising mathematical tool for radiative transfer in 3D GRIN media. • The LBM is developed to simply solve radiative transfer problems in 3D GRIN media. • The "local radiative transfer direction" is proposed to handle curved trajectories. • Complete LB model and rigorous Chapman-Enskog analysis are given. • The effects of different parameters on steady and transient problems are discussed. [ABSTRACT FROM AUTHOR]

Nowadays, utilization of micro/mini channel heat sinks (MCHS) has become a popular solution for cooling of electronic systems and maintaining their operating temperature in a desired range. Increasing the contact surface area between fluid and solid zones by geometrical modifications is a promising solution that significantly affects thermal performance and heat transfer in these systems. In this paper, considering thermohydraulic performance, the effect of creating grooves on the middle-placed barriers of a minichannel heat sink is investigated to access a criterion for favorable temperature performance. Evaluating different geometrical parameters of barriers and grooves including cross section, depth and position of horizontal groove as well as vertical groove distance, simultaneous employment of optimal horizontal and vertical groove in the channel at different Reynolds numbers is studied. Outputs including channel base temperature, friction factor ratio and total thermal resistance are studied to evaluate the performance of the proposed minichannel. Results indicate that vortex formation adjacent to solid walls considerably enhances the heat transfer and variation of each geometrical parameters offers a performance enhancement. Moreover, the best thermal performance is obtained by simultaneous employment of the horizontal rectangular groove (x = 0.45 mm, y = 0.2 mm and h g = 0.6 mm) and the vertical groove (d g = 0.4 mm). In the optimal case, the channel base temperature and the total thermal resistance reduces by 11.88 K and 27%, respectively. [ABSTRACT FROM AUTHOR]

A Moving droplet impacting a moving particle has been investigated numerically and experimentally. However, the collision with heat transfer is still absent. Therefore, this paper presents a moving droplet impacting a moving particle with heat transfer using the lattice Boltzmann method coupled with a modified immersed boundary method. The influence of Prandtl number (0.1 ≤ Pr ≤ 10) and Grashof number (−100 ≤ Gr ≤ 100) are taken into account. The results show that the vertical velocity of the particle (Uz) grows up against the increment of Pr and Gr. Uz has three stages based on Pr and Gr ≥ 0. And for Gr = −100, Uz is classified into four stages. Especially, for the last stage (at that time, the droplet separates from the particle), Uz varies slightly. [ABSTRACT FROM AUTHOR]