Numerical Heat Transfer Model Research Articles

Numerical Network Modeling of Heat and Moisture Transfer through Capillary-Porous Building Materials.

The article presents the modeling of the dynamics of the vapor-gas mixture and heat and mass transfer (sorption-desorption) in the capillary structure of the porous medium. This approach is underpinned by the fact that the porous structure is represented by a system of linear microchannels oriented along the axes of a three-dimensional coordinate system. The equivalent diameter of these channels corresponds to the average pore diameter, and the ratio of the total pore volume to the volume of the entire porous material corresponds to its porosity. The entire channel area is modeled by a set of cubic elements with a certain humidity, moisture content, pressure and temperature. A simulation is carried out taking into account the difference in temperatures of each of the phases: solid, liquid and gas.

Numerical Modeling of Flow Pattern and Heat Transfer at Injection of Counter-Flowing Wall Jet

Numerical Modeling of Flow Pattern and Heat Transfer at Injection of Counter-Flowing Wall Jet

Influence of gas flow turbulence scale on heat exchange intensity in a long smooth pipe

It is known that the initial level of gas flow turbulence has a noticeable effect on the development and structure of the boundary layer and on the intensity of heat transfer, respectively. Many scientists have evaluated the influence of the flow turbulence number on the level of heat transfer for various applications, among them Dyban E.P., Kestin J., Simonich JC, Isomoto K., Dreitser G.A., Terekhov V.I., MacMullin R. and etc. In all cases, the turbulence of the flow led to the intensification of heat transfer. However, insufficient attention is paid to studies of the effect of turbulence on the heat transfer of flows in pipes. The studies were carried out on the basis of numerical modeling of gas dynamics and heat transfer of stationary flows based on the CFD method. The results of numerical modeling to assess the influence of the turbulence scale of gas flows on heat transfer in a long smooth pipe are presented in the article. It has been established that a growth in the heat transfer coefficient by about 3% occurs with an increase in the turbulence scale from 10 to 30% with a Reynolds number equal to 250,000.

The Influence of Droplet Dispersity on Droplet Vaporization in the High-Temperature Wet Gas Flow in the Case of Combined Heating

The change in the thermal and energy state of the water droplet is defined numerically. The influence of droplet dispersity on the interaction of the transfer processes was evaluated. In influence of the Stefan flow was considered as well. The internal heat transfer of the droplet was defined by the combined heat transfer through effective conductivity and radiation model. The results of the numerical modeling of heat and mass transfer in water droplets in a wet flue gas flow of 1000 °C highlight the influence of the variation in heat transfer regimes in the droplet on the interaction of the transfer processes in consistently varying phase change regimes. The results of the investigation shows that the inner heat convection diminishes intensively in the transitional phase change regime because of a rapid slowdown of the slipping droplet in the gas. The radiation absorption in the droplet clearly decreases only at the final stage of equilibrium evaporation. The highlighted regularities of the interaction between combined transfer processes in water droplets are also valid for liquid fuel and other semi-transparent liquids sprayed into high-temperature flue gas flow. However, a qualitative evaluation should consider individual influence of dispersity that different liquids have.

Numerical investigation of the temperature field and thermal insulation design of cold-region tunnels considering airflow effect

Abstract Recently, an increasing number of tunnels have been constructed in cold regions, leading to an urgent necessity to analyse the temperature fields in these tunnels and design reasonable thermal insulation layers under ventilation. This investigation aimed to numerically obtain the actual temperature field of a cold-region tunnel and optimise the design of the thermal insulation layer considering the airflow effect. A three-dimensional numerical model of convection heat transfer was established. Model test results and field data were used to validate the numerical model. Four formulas were developed to consider the effects of airflow velocity, initial temperature, volumetric specific heat capacity, and thermal conductivity on the temperature of the surrounding rock. The results indicated that the temperature variation at the preliminary surface becomes stable in the 5th year after tunnel excavation. Meanwhile, the thermal conductivity of the surrounding rock is the most influential factor affecting the temperature of the primary lining surface, followed by the volumetric specific heat capacity, initial temperature, and airflow velocity. The initial temperature has the most pronounced effect on the temperature of the surrounding rock with a buried depth of 4 m. The effects of thermal conductivity and airflow velocity are minimal. Furthermore, the thermal resistance, rather than the thickness of the insulation layer, is recommended for assessing the freeze-proof performance. The thermal resistance of the insulation layer of a highway tunnel should be larger than 0.048 °C/W. The optimal ratio of the thermal conductivity to the thickness of the insulation layer was observed to be 1.49.

Numerical modeling of fluid flow, heat, and mass transfer for similar and dissimilar laser welding of Ti-6Al-4V and Inconel 718

Most of the researches published on the numerical modeling of laser welding are looking at similar welding, mainly due to the difficulty of simulating the mixing phenomenon that occurs in dissimilar welding. Furthermore, numerical modeling of dissimilar laser welding of titanium and nickel alloys has been rarely reported in the literature. In this study, a 3D finite volume numerical model is proposed to simulate fluid flow, heat, and mass transfer for similar and dissimilar laser welding of Ti-6Al-4V and Inconel 718. The laser source was simulated by volumetric heat distribution, which considers the effects of keyhole and heat transfer on the workpiece. The heat source parameters were calibrated through preliminary experiments, by comparing the simulated and experimental weld pool shapes and dimensions. The model was used to simulate both homogenous and dissimilar laser weldings of Ti-6Al-4V and Inconel 718, and a systematic comparison was carried out through a number of selected experiments. The effects of three distinct levels of laser power (1.25 kW, 1.5 kW, 2.5 kW) on temperature distribution and velocity field in the welds pool were analyzed. Results highlighted the effects of Marangoni forces in the weld pool formation. Furthermore, in order to analyze the mass transfer phenomenon in dissimilar welding, species transfer equations were considered, demonstrating the important role played by the mass mixture in the weld pool formation. Finally, a high level of agreement between simulations and experiments—in terms of weld pool shape and dimensions—was observed in all cases analyzed. This proves the ability of the proposed numerical model to properly simulate both the similar and dissimilar welding of Ti-6Al-4V and Inconel 718 alloys.

A novel pulse width modulation for metal radiant panels to control the condensation risk in a hot and humid environment

A novel pulse width modulation (PWM) control method with surface condensation-evaporation cycle was proposed for metal radiant panels to control the condensation risk in hot and humid environments. Through an on-off solenoid valve, a whole cycle of the PWM consists of a fixed on-period duration, i.e., 20 min and an adjustable off-period duration in order to guarantee the formed condensate water on the panel during the on period evaporated completely at the end of the off period. A numerical heat transfer model of the radiant panel validated by experiment was utilized to evaluate the dynamic thermal performance of the PWM. According to the simulation results, the maximum accumulated condensation mass in the whole cycle was far smaller than the falling criteria of condensate droplets, revealing the ability of the PWM in eliminating the negative effects of surface condensation on the indoor environment. Furthermore, compared with the variable temperature control method with a supply water temperature equal to the dew point temperature, the radiant panel utilizing the PWM provided a 10% higher cooling capacity. The radiant metal panels using the PWM has an application prospect for retrofit buildings with low airtightness of the envelope in hot and humid regions by a significant reduction of condensation risks.

Comprehensive simulation based thermal performance comparison between single and double U-tube borehole heat exchanger and sensitivity analysis

In the ground coupled heat pump system that delivers space heating and cooling to the buildings, often questions are raised as to which borehole heat exchanger configuration (single or double U-tube) provides higher thermal performance. To answer this question, in this paper, detailed comparative transient heat transfer analysis between single and double U-tube borehole heat exchanger (BHE) with two independent circuits (that can operate with the same or different mass flowrate and inlet fluid temperature) is conducted. Validated numerical heat transfer model was applied to perform the dynamic simulation and analysis. The two borehole heat exchangers are compared from the perspectives of their thermal performance in the heating and cooling mode of operation. Detailed sensitivity analysis of the BHE has also been performed by investigating the impact of the important borehole parameters, thermal properties and working fluids on the thermal performance of the double U-tube BHE. The simulation result revealed that the heat injected and extracted by the double U-tube BHE at steady state is 21.8 (77%) and 10.2 W/m (71.8%) more than that of the single U-tube BHE respectively. The simulation results also indicate that the thermal effectiveness of the single and double U-tube BHE at steady state are 0.24 and 0.31 respectively. The single U-tube BHE showed higher borehole thermal resistance than that of the double U-tube BHE with values of 0.47 and 0.31 m.K/W, respectively. The results of the study also revealed that among the studied working fluids, CaCl2 (25%) solution showed better thermal performance than other anti-freeze solutions with thermal effectiveness of 35.6%. The simulation result of this work is crucial as an input for the optimization studies made to obtain a single set of optimal borehole paramaters and thermal properties that results in the best performance of BHE coupled to ground source heat pump system designed to provide space heating and cooling of buildings.

Numerical modelling for the diameter increase of silicon crystals grown with the pedestal method

The pedestal method is one of crucible-free crystal growth methods, that has been less researched than the well-known floating zone (FZ) method. However, the pedestal method may be a cost-effective alternative to FZ, if large diameter feed rods are available. The investigated system contains two electromagnetic inductors: high-frequency inductor for pedestal top surface melting and middle-frequency inductor for pedestal side heating. The present work describes recent advances in numerical modelling of heat transfer and phase boundaries in axially symmetrical approximation, neglecting the melt flow. The shape of high-frequency inductor was optimized with the algorithm of gradient descent. As the risk of melt freezing is substantial during both the seeding and the cylindrical phase, the distance between the centres of melting and crystallization interfaces was used as a target function. Optimal inductor geometry and system geometrical parameters were obtained for systems with crystal diameters from 20 mm to 100 mm, thus sketching a pathway for crystal diameter increase in industrial growth system prototypes.

Nonsteady Heat Loses to the Ground from a Building with Heated Underground Floor or Slab on Ground

Numerical model and research results of nonsteady heat transfer between building and ground basement are in the article. Two most common cases of heat contact between building and ground basement are compared: building with heated underground floor and building on the slab on ground. Nonsteady heat loses over period about several years of building exploitation are analyzed that made possible to establish a patterns of heat transfer between building and ground with taking into account of ground around of building inertness. Heat loses from building represented using mean values at the one unit of length of building perimeter. In case of building with underground floor calculated nonsteady heat loses of floor and underground wall are shown. Also shown results of nonsteady heat transfer to ground from outdoor air and groundwater. Numerical methodic used in research based on explicit finite-difference method applicated to boundary value problem of nonsteady heat transfer in ground. The problem taking into account existence of moveable groundwater without heat transfer calculation in the volume of groundwater.

Experimental and numerical thermo-mechanical analysis of wire-based laser metal deposition of Al-Mg alloys

• Set-up, calibration and experimental validation of numerical LMD heat transfer model. • Sequential mechanical coupling to calculate residual stresses and displacements. • Simulation-based sensitivity study of process conditions on stresses and displacements. A finite element model is employed to perform a sequentially coupled thermo-mechanical analysis for enabling rapid process simulations of temperature fields, residual stresses and distortions for the production of additively manufactured parts via laser metal deposition. Experimental identification of characteristic process features such as temperature distribution, melt pool dimensions and bead geometries were used for the initial built-up and calibration of the model. The addition of material during process simulation is realised through reactivating inactive elements during the transient heat transfer analysis and through reactivating a combination of inactive and quiet elements during the mechanical analysis. The travelling heat source is geometrically bounded to precisely control the volume of its energy distribution. The results of the transient heat transfer analysis are sequentially coupled to a mechanical analysis for obtaining information on the resulting residual stresses and deformation. Based on the good agreement between numerical and experimental results of the thermal analysis, conclusions on the corresponding residual stress distributions and deformation are made. It is shown that the model represents an efficient tool for process prediction regarding thermal history, residual stresses and final-part deformations. Finally, the model is utilised to identify parameters and conditions of the process that lead to reduced residual stresses and deformations of the investigated additive part.

Evaluation of the Rotor Temperature Distribution of an Automotive Turbocharger Under Hot Gas Conditions Including Indirect Experimental Validation

Abstract While turbocharging is a key technology for improving the performance and efficiency of internal combustion engines, the operating behavior of the turbocharger is highly dependent on the rotor temperature distribution as it directly modifies viscosity and clearances of the fluid film bearings. Since a direct experimental identification of the rotor temperature of an automotive turbocharger is not feasible at an acceptable expense, a combination of numerical analysis and experimental identification is applied to investigate its temperature characteristic and level. On the one hand, a numerical conjugate heat transfer (CHT) model of the automotive turbocharger investigated is developed using a commercial CFD-tool and a bidirectional, thermal coupling of the CFD-model with thermohydrodynamic lubrication simulation codes is implemented. On the other hand, experimental investigations of the numerically modeled turbocharger are conducted on a hot gas turbocharger test rig for selected operating points. Here, rotor speeds range from 64.000 to 168.000 rpm. The turbine inlet temperature is set to 600 °C and the lubricant is supplied at a pressure of 300 kPa with 90 °C to ensure practically relevant boundary conditions. Comparisons of measured and numerically predicted local temperatures of the turbocharger components indicate a good agreement between the analyses. The calorimetrically determined frictional power loss of the bearings as well as the floating ring speed are used as additional validation parameters. Evaluation of heat flow of diabatic simulations indicates a high sensitivity of local temperatures to rotor speed and load. A cooling effect of the fluid film bearings is present. Consequently, results confirm the necessity of the diabatic approach to the heat flow analysis of turbocharger rotors.

New Insights into Hydrothermal Fluid Circulation Affected by Regional Groundwater Flow in the Asal Rift, Republic of Djibouti

The Asal Rift hosts a lake located in a depression at 150 m below sea level, where recharge is influenced by regional groundwater flow interacting with the Ghoubbet Sea along the coast of Djibouti. This regional groundwater flow is believed to influence hydrothermal fluid circulation, which we aim to better understand in this study, having the objective of developing concepts for geothermal exploration in the area. To this end, magnetotelluric data acquired in the Asal Rift were processed and analyzed. 1D inversion models of electrical conductivity were interpolated for interpretation. These data were then used to build a 2D hydrogeological model, allowing multiphase flow and heat transfer simulations to be performed, considering the regional groundwater flow near the surface and the site topography, in order to confirm the preferred path of fluid flow. Geophysical data analysis indicates the presence of normal faults, notably the H fault, which may act as a conduit for the circulation of hydrothermal fluids and where the hanging wall can be a hydrogeological barrier within the hydrothermal system of the Asal Rift. The results from the 2D numerical flow and heat transfer modelling show the importance of groundwater flow responsible for thermal springs located at the periphery of Asal Lake. Reservoir temperature inferred by means of geothermometry ranging from 200 to 270 °C was shown to correspond to simulated temperature at potential reservoir depth. Moreover, simulated temperature between 600 and 1700 m depth is close to the temperature profile measured in the geothermal well Asal 6 of the area, with less than 20 °C difference. Simulations indicate that hydrothermal fluid circulation is likely influenced by the regional groundwater flow controlled by the topography and the major water bodies, the Ghoubbet Sea and Asal Lake, feeding buoyant fluids interacting with a deep magmatic source and where tectonic activity created normal faults offering a preferred path for fluid circulation.

Numerical Investigation on Heat Transfer and Oxidation Deposition of Aviation Fuel in a Rotatory U-Channel

Abstract Liquid-fuel regenerative cooling is a promising turbine cooling technology. We developed a numerical model of heat transfer coupled with oxidation deposition in a rotatory channel for regenerative cooling applications. Source terms for the centrifugal and Coriolis forces caused by rotation were added to the momentum equations and turbulent transport equations. A kinetic model for the thermal oxidation and deposition of supercritical hydrocarbon fuel was used to predict the oxidation deposition process. Coupled fluid–solid simulations of the heat transfer and oxidation deposition of hydrocarbon fuel in a U-shaped channel at five rotation numbers showed that the rotation improves convective heat transfer in the cooling channel and prevents the occurrence of a heat transfer deterioration zone. The average deposition rate in the channel decreased with increasing rotation number. In the centrifugal section of the rotatory channel, the Coriolis force caused the temperatures of the leading wall to be higher than those of the trailing wall, but the differences became smaller and nearly disappeared in the elbow and centripetal sections. The deposition rate on the leading wall was higher than that on the trailing wall in the straight centrifugal channel. In the bending section, the oxidation deposits were more prone to form on the inner edge than on the outer edge.

Numerical simulation of heat transfer in semiconductor heterostructures

The paper deals with the construction of numerical models of heat transfer in a multilayer AlAs/GaAs nanostructure. The problem is solved using a hybrid finite-difference-mesh-free method based on radial-basis functions. The obtained solutions are compared for various bases, as well as with and without normalization of the approximating model. The possibility of increasing the speed of computations due to the parallelizability of computations is investigated, it is shown that, using multiprocessor systems, one can achieve a significant increase in performance.

Numerical study of an Evacuated Tube Solar Collector incorporating a Nano-PCM as a latent heat storage system

A new Evacuated Tube Solar Collector (ETSC) incorporating a Nano-PCM with fins is presented and studied. The numerical mathematical 2D model of phase change heat transfer is highlighted. The effect of adding nanoparticles of copper (Cu) to paraffin wax on system performance was investigated. The heat transfer during the energy storage process is simulated using the Ansys-Fluent. Moreover, the solid-liquid phase change characteristics of the paraffin within the system are analyzed. Additionally, an optimization analysis of fin parameters (i.e. fin thickness and fin spacing) is performed. Finally, a series of comparative simulations are carried out to investigate the performance of the ETSC system with and without the Solar Parabolic Trough Reflector (SPTR). The results showed that adding fins has a great effect on the phase change heat transfer of the paraffin in the ETSC. It was noted that the PCM melts faster as the thickness of the fins gets thinner. Also, the addition of 1% of Cu to the PCM was found to be the optimum mass concentration at which the HTF outlet temperature increased by 2 K. Moreover, it was found that the ultimate flow rate that caused the entire mass of the PCM to melt is 0.003 kg/s.

Multiphysics Coupling Simulation and Parameter Study of Planar Solid Oxide Fuel Cell.

In this paper, a numerical model of gas flow, heat transfer, mass transfer and electrochemical reaction multi-physics field coupling of a planar SOFC is established and solved. According to the calculation results, the distribution of velocity, temperature and concentration inside the SOFC cell is analyzed. The influence of cathode inlet flow rate, porosity, rib width and other parameters on the performance of SOFC is also discussed. The results show that within a certain range, increasing the cathode inlet flow rate can significantly increase the average current density of the cell. Increasing the porosity of the electrode can improve the gas diffusion of the porous electrode, thereby increasing the rate of the electrochemical reaction. Increasing the width of the ribs will result in a significant decrease in cell performance. Therefore, the rib width should be reduced as much as possible within the allowable range to optimize the working performance of the cell.

Numerical Modeling of Heat Transfer and Hydrodynamics in Compact Shifted Arrangement Small Diameter Tube Bundles

Numerical modeling of heat and hydrodynamics processes in the channels of compact small diameter tube bundles with different transverse shifted arrangement is carried out. The fields of velocities, temperatures, and pressures in the tube bundle channels were obtained, and their influence on heat transfer conditions and hydraulic losses were analyzed. The calculation of the thermohydraulic efficiency for different constructions of the tube bundles had been carried out, and their results with data of well-known tube bundles of different geometry are compared.

Hydrodynamics and Convective Heat Transfer in Open Cell Foam with Micropores

Open cell metal foams are promising materials for increasing heat transfer due to their tortuosity and developed surface area in car engine cooling. A new method of heat transfer intensification in open cell foam materials is proposed. The effect of micropores on the hydrodynamics and heat transfer of open cell foam material is studied. Three models of porous media were created. In the first case, the initial model with a porosity of 0.7. In the second, with the addition of micropores, the porosity became equal to 0.85. Thirdly, the porosity is 0.85, but without micropores. A micropore model was created by subtracting spheres from the framework of open cell foam. In all cases, the porous medium consists of many intersecting spheres. Numerical modelling of gas flow and heat transfer in a porous medium is performed by the control volume method in the ANSYS Fluent software package (v. 19.0) Research results can help create new types of heat exchangers.

Тепловая нагрузка биметаллической оребренной трубки

This study is devoted to the problem of numerical modeling of the conjugate heat transfer in a closed-type power installation. The working elements of that are ribbed bimetallic tubes using the openFoam toolbox. The heat transfer process modeling in bimetallic tubes is associated with solving the problem of determining the value of the contact thermal resistance at the metal / metal interface. Considered design of a bimetallic tube involves crimping copper washers on the surface of an aluminum cylindrical tube. Hence, the contact surface of the tube is not isotropic in its properties. A mathematical model of conjugate heat transfer for air / bimetal / coolant medium is proposed. The features of the organization of thermophysical processes at the metal contact interface and at the metal / air and metal / coolant medium are shown. A qualitative comparison of the obtained results with the famous experimental data is carried out. Generalized temperature profiles in the rib longitudinal section are obtained by mathematical modeling. The given distributions of temperature and heat flux make it possible to estimate the contribution of each individual rib to the investigated heat removal process from the air environment. The efficiency of the considered technology of manufacturing a bimetallic finned tube is shown.