Simulation Of Convection Heat Transfer Research Articles

Numerical simulation of convective heat transfer of microencapsulated phase change material slurrys in a circular tube

For the Microencapsulated Phase Change Materials slurry(MPCMs)having a large latent heat during the phase change period and having a higher heat convection coefficient than the single-phase fluid, it has become a new thermal fluid of widespread investigation. In this paper, the model of equivalent specific heat is presented to numerical simulate the laminar convective heat transfer performances of MPCMs in a tube under the condition of constant heat flux. The heat transfer of MPCMs in a tube is investigated under various concentrations of MPCMs and heat flux and the correlation of the convective heat transfer with MPCMs in a tube is obtained.

SADI approach programming on GPU: convective heat transfer of nanofluids flow inside a wavy channel

In this study, the numerical simulation of convective heat transfer of nanofluids (Al2O3/water and CuO/water) inside a sinusoidal wavy channel is performed using the Graphics Processing Units (GPU). The governing equations including stream-function, vorticity transport, and energy are discretized using the fourth-order Spline Alternating-Direction Implicit (SADI) approach in combination with the curvilinear coordinates mapping. The final tridiagonal-matrices are solved by Parallel-Thomas-Algorithm (PTA) on GPU. A homogenous one-phase model is also applied to consider the effective characteristics of the nanofluids flow. In the first part of the results section, the effects of nanoparticle volume fraction, Reynolds number, and amplitude of the wavy wall on average Nusselt number and the skin friction coefficient of the channel are investigated. In the second part of the results section, the ability of GPU to accelerate the computation (or runtimes) is compared to the classic Thomas algorithm that runs on a Central Processing Unit (CPU). The results demonstrate that the speedup of PTA against CPU runtime for the finest grid is around 18.32×.

The Effect of Swirl Intensity on Heat Transfer of Swirling Coaxial Impinging Jet

The results of numerical simulation of convective heat transfer under coaxial jet impinging on a surface are presented. The effect of jet’s peripheral component swirling on the heat transfer enhancement by changing the number of tangential nozzles for creating jet is analyzed.

CFD simulation of convective heat transfer in vessel with mechanical agitation for milk.

Computational fluid dynamics (CFD) analysis using ANSYS Fluent software has been carried out to investigate velocity profiles and thermal characteristics of milk during heating under mechanically agitated condition. In earlier article experimental data on forced convection heat transfer coefficient and correlations of the form for cow milk, standardised milk and full cream milk in Baffled vessel and Unbaffled vessel with scraping, using Propeller, Flat Six Blade Turbine (FBT), Inclined Six Blade Turbine (IBT) and Paddle impellers were reported. It was noted milk in Baffled vessel with Paddle impeller provided highest even at lower rotational speeds followed by Propeller, FBT and IBT impellers. In Unbaffled vessel with scraping, Propeller provided the highest followed by FBT and IBT impellers. Hence, the present investigation has been carried out to validate and understand how different velocity of flow currents and their magnitude influence the heat transfer coefficient values in CFD simulation. It also justifies the relative performance of the impellers delineated in the earlier paper. In addition, theoretical values of heat transfer coefficients computed using CFD shows close agreement with experimental values.

Numerical simulations of convection heat transfer in porous media using a cascaded lattice Boltzmann method

Convection heat transfer in porous media is a universal phenomenon in nature, and it is also frequently encountered in scientific and engineering fields. An in-depth understanding of the fundamental mechanism of convection heat transfer in porous media requires efficient and powerful numerical tools. In this paper, a cascaded lattice Boltzmann (CLB) method for convection heat transfer in porous media at the representative elementary volume (REV) scale is presented. In the CLB method, the flow field is solved by an isothermal CLB model with the D2Q9 lattice based on the generalized non-Darcy model, while the temperature field is solved by a temperature-based CLB model with the D2Q5 lattice. The key point is to incorporate the influence of the porous media into the CLB method by introducing the porosity and heat capacity ratio into the shift matrices. The effectiveness and practicability of the present method are validated by numerical simulations of several heat transfer problems in porous media at the REV scale. It is shown that the present method for convection heat transfer in porous media is second-order accurate in space. Moreover, in comparison with the Bhatnagar-Gross-Krook lattice Boltzmann method, the present method has sufficient tunable parameters and possesses better numerical stability.

Heat Transfer by Mixed Convection of Casson Nanofluid with Activation Energy

This paper aims to present a numerical simulation of convective heat transfer of magnetohydrodynamic Casson nanofluid flow on stretching surface. Energy equation includes nonlinear thermal radiation, heat source/sink, Joule and viscous dissipation whereas mass transfer equation incorporates Arrhenius activation energy. An accurate numerical solution of dimensionless system describing the flow is achieved by applying multi domain spectral relaxation method (MDSRM). Changes in flow, temperature and nanoparticle concentration profiles due to effects of various physical parameters, namely, activation energy parameter, radiation, heat source/sink controlled by space and temperature, Casson fluid parameter, Brownian motion, thermophoresis, Eckert number, Lewis number and magnetic parameter are explained by replicating the obtained numerical results in graphical form. A variation in the value of flow parameters induces a substantial impression on the boundary layers.

Study on the Influence of Tube Curvature on Heat Transfer Characteristics of High Efficiency Air Pre-cooler

High-efficiency pre-cooler is one of the key components of RBCC combined engine. To explore the influence of tube row curvature on heat transfer, a convection heat transfer simulation of pre-cooler composed of different curvature tube rows is established. The model and numerical calculations show that when the curvature is small, the heat transfer efficiency increase slowly with curvature increasing, but the flow resistance increase obviously by increasing curvature. However, when the curvature is large, the effect of curvature increasing on the heat transfer efficiency is obvious and the increase of flow resistance get slower. Based on this, a ring pre-cooler is designed and the heat transfer effect is simulated. It has reference application value for the design of high efficiency pre-cooler.

Direct numerical simulation of convective heat transfer in a pipe with transverse vibration

A series of direct numerical simulations is conducted to investigate the convection in a pipe with transverse vibration aiming at the heat transfer enhancement in a catalytic converter. Assuming that the turbulent inflow enters a thin tube of the honeycomb converter, friction Reynolds number which is defined by the friction velocity and the pipe radius is set to be 60 with the initial condition of the fully developed turbulent field of higher Reynolds number. The parameters of vibration control are amplitude η* and frequency f*. For a case of (2η*, f*) = (1.6, 0.4), the Nusselt number periodically increases and decreases in time to achieve 70% augmentation on average as compared to the uncontrolled case. It can be observed through visualization of the flow field that twin vortices play a dominant role in enhancing the heat transfer. High-temperature fluid is transported by the twin vortices toward the pipe wall in the vibration direction to increase the Nusselt number there. However, after the breakdown of the twin vortices, the high-temperature fluid remains at the center of the pipe and the effect of heat transfer enhancement is suppressed. It is also confirmed from a parametric study that the velocity amplitude of the induced vibration is an important parameter for heat transfer enhancement.

CFD Simulation of Convective Heat Transfer on Vernacular Sustainable Architecture: Validation and Application of Methodology

The global background of energy shortages and climate deterioration demands bioclimatic sustainable buildings. Vernacular architecture can provide a useful resource of passive strategies and techniques for creating inner comfort conditions with minimum heating, ventilation, and air conditioning (HVAC) assistance. The identification and verification of such knowledge are essential for climate responsive or energy passive building design. Among the methods, computational fluid dynamics (CFD) is a useful tool for simulating convective heat transfer of vernacular architecture and predicting the convective heat transfer coefficient (CHTC) and flow field. Geometric complexity and diversity of building samples are crucial in the development of an effective simulation methodology in terms of computational cost and accuracy. Therefore, this paper presents high-resolution 3D steady Reynolds-averaged Navier–Stokes (RANS) CFD simulations of convective heat transfer on Japanese vernacular architecture, namely, “machiya.” A CFD validation study on the CHTC is performed based on wind-tunnel experiments on a cube heated by constant heat flux and placed in a turbulent channel flow with a Reynolds number of 3.3 × 104. Three steady RANS models and two boundary layer modeling approaches are compared and discussed. Results show that the SST k-ω model applied with low Reynolds number modeling approach is suitable for CHTC simulations on a simplified building model. The RNG k-ε model applied with wall functions is an appropriate choice for simulating flow field of a complicated building model. Overall, this study develops a methodology involving RANS model selection, boundary layer modeling, and target model fitting to predict the convective heat transfer on vernacular architecture.

Experimental Investigation and Simulation of Convective Heat Transfer in a Solar Still

This paper mainly focuses on the design of a water distillation solar still that can purify and desalinate water from any source in an affordable, portable and sustainable manner. It attempts to efficiently produce clear water by solar energy conversion. Since, low productivity is of the limitation of the usage of such stills, this paper makes an attempt to evaluate the heat transfer coefficient of single slope basin type solar still by Simulation Analysis and checking the optimum conditions. A design prototype was constructed by studying the optimized configurations from various researchers. After carrying on the experiments, the effect of various parameters was evaluated. The parameters identified include temperatures, properties of inlet water, wind velocity and relative humidity. Simulation results were then compared to the experimental results at the obtained optimum conditions.

Application of four-equation closure for turbulent heat flux in prediction of convective heat transfer to hydrocarbon fuels at supercritical pressures

Accurate modelling of the turbulent thermal fields is of great importance for simulations of convective heat transfer to fluids at supercritical pressures. The widely adopted Reynolds analogy between turbulent momentum transfer and turbulent heat transfer may fail for variable property flows under certain conditions, especially as the fluid approaches the pseudo-critical temperature (Tpc). In order to accurately predict the flow and heat transfer behaviors, the two-equation turbulence model for the thermal field by Hattori, Nagano, and Tagawa (HNT kt−εt) in association with the low-Reynolds number model for the velocity field by Myong and Kasagi (MK k−ε) were incorporated in an in-house code developed within the framework of OpenFOAM. Numerical simulations of convective heat transfer to supercritical pressure hydrocarbon fuels (RP-3 aviation kerosene and n-decane) in vertical heated tubes were performed using the MK-HNT model, MK k−ε model with Prt set as 1.0, and SST k−ω model with Prt set as 1.0. The validity of the models was examined through comparisons with the available experimental data under a variety of operating conditions. All three models performed reasonably well for the cases of normal heat transfer regime. Meanwhile, improvements in the prediction of inner wall temperature could be obtained by the use of the MK-HNT model for cases of heat transfer in the thermal entrance region, heat transfer enhancement (HTE) under forced convection conditions, and heat transfer deterioration (HTD) under mixed convection conditions. Moreover, the different heat transfer mechanisms were investigated by analyzing the predicted turbulent flow and thermal fields. The results indicated that the development of the thermal boundary layer in the entrance region and the drastic variation of specific heat and density in the trans-pseudo-critical region would have considerable effects on the distributions of the Reynolds stress and turbulent heat flux. In addition, it was found that the computational cost was not severely increased by solving two additional turbulence equations.

Simulation of convection heat transfer of magnetic nanoparticles including entropy generation using CVFEM

An investigation has been conducted to study Lorentz effect on nanomaterial behavior within a permeable space including innovative numerical technique namely CVFEM. Iron oxide has been mixed with H2O and porous domain was filled with this nanomaterial. The impacts of the flow and geometric variables on entropy generation along with the heat transfer have been examined. The simulations have been carried out with wide ranges of the magnetic force, permeability and Rayleigh numbers. The outcomes indicate that the Darcy term has inverse relationship with temperature of hot surface. Stronger convection mode and lower exergy loss appear when buoyancy forces augment. Entropy generation goes up with growth of Hartmann number.

A general approach of unit conversion system in lattice Boltzmann method and applications for convective heat transfer in tube banks

A general unit conversion system based on the analogy with the Planck unit system is put forward in this article for most physical quantities in lattice Boltzmann simulations. Comparing with the traditional unit conversion methods, the approach has more systematic, programmatic and standardized operating process and can be applied in programming easily. In addition, a two-dimension exemplary simulation of convective heat transfer in tube banks is implemented to illustrate the feasibility and advantage of the approach, with verification of coupled flow and heat transfer by the empirical formula in literature. Furthermore, a uniform scheme for three kinds of boundary conditions for heat and mass transfer is developed and applied herein.

Direct numerical simulation of convective heat transfer in porous media

Convective heat transfer in turbulent flow in porous media is, in general, less understood compared to laminar and creeping flows. It is broadly integrated into industrial applications even though a lack of understanding in microscale. In the present study, we report a direct numerical simulation (DNS) based microscopic analysis of heat and fluid flow in synthetic porous media with an aim to link the macroscopic statistics and qualitative observations with pore-scale signatures of the same. DNS is conducted with two computational codes with a cautious validation on the microscale. The conventional finite-volume solver shows an excellent agreement with high-order spectral/hp element solvers. The synthetic porous media are comprised of square cylinders in a staggered array. Macroscopic observation indicates an increased pressure loss and increased Nusselt number (Nu) as a result of high Reynolds numbers. However, a further examination of the ratio of Stanton number to skin friction coefficient St/Cf reveals that increasing Reynolds numbers lead to more pressure loss than improved heat transfer. Microscopic analysis shows that Nu is highest on the impinging surface, whereas lowest on the wake surface. In addition, it tends to be homogeneously distributed on surface area in the high porosity case. In the low porosity case, Nu on the sharp corners, is significantly higher than on other locations. Probability density function (PDF) of streamwise velocity fluctuation u′ shows Gaussian like distribution within two standard deviation. The high porosity group owns a spike around zero abscissa on PDF of both u′ and temperature fluctuation T′, which is an indication of less chaotic flow motions.

CFD simulations of convective heat transfer in actively heated tube bundle

Active heating is used as a flow assurance technique to prevent the huge temperature drop of crude oil while transporting from wells to facilities, which creates a friendly environment for hydrate formation and solid depositions. In the present study, convective heat transfer in tube bundle with three internal tubes was investigated through computational fluid dynamics simulation. A three dimensional model for existing bundle was developed. The model described the heat transfer occurring inside the bundle, aiming to heat up or at least maintain the production fluid temperature. The heat transfer from heating pipe to the whole bundle can be visualized through the temperature contours and the temperature gradient at the outlets. The effect of heating medium temperature and flow velocity are studied in the developed model.

Numerical investigation on convective heat transfer to aviation kerosene flowing in vertical tubes at supercritical pressures

Numerical simulations of convective heat transfer to aviation kerosene (China RP-3) flowing in vertical circular tubes at supercritical pressures are reported in this study. Firstly, performance of a variety of Reynolds-Averaged Navier-Stokes turbulence models in predicting the fluid-thermal behaviours under both forced and mixed convection conditions are evaluated. Under forced convection conditions, all models predict a gentler growth of wall temperature along the flow direction than experimental measurements. Under mixed convection conditions, the effect of buoyancy become significant and there are large discrepancies in the predicted wall temperature by different models. Only the low-Reynolds number k-ε models are found to be able to qualitatively predict the flow laminarization and heat transfer deterioration. Profiles of thermal, flow and turbulence fields obtained using various models are studied to explain the differences in predictions. For mixed convection conditions, an examination on the turbulence production due to shear and density fluctuation indicates that the direct effect of buoyancy on the turbulence production is negligible compared with the indirect effect. Furthermore, the effect of turbulent Prandtl number on the predicted heat transfer is studied. It is found that turbulent Prandtl number has a significant influence on the simulation results. Under the conditions considered in the present study, the value of 1.0 for turbulent Prandtl number leads to a closest agreement with the experimental data.

Computational Simulation of Convective Heat Transfer of Turbulent Gas Flows

The refined regularities of the transfer of the momentum and heat in an eddy boundary layer have been given. It has been shown that it is necessary to take them into account in the mathematical modeling of convective heat transfer from the eddy gas flow. The correctness of the proposed method has been verified by comparing the results of computational simulation with experimental data on the convective heat transfer of the eddy air flow.

Numerical simulation of convective heat transfer of nonhomogeneous nanofluid using Buongiorno model

The aim is to study the assessment of the flow and convective heat transfer of laminar developing flow of Al2O3–water nanofluid inside a vertical tube. A finite volume method procedure on a structured grid was used to solve the governing partial differential equations. The adopted model (Buongiorno model) assumes that the nanofluid is a mixture of a base fluid and nanoparticles, with the relative motion caused by Brownian motion and thermophoretic diffusion. The results showed the distribution of nanoparticles remained almost uniform except in a region near the hot wall where nanoparticles volume fraction were reduced as a result of thermophoresis. The simulation results also indicated there is an optimal volume fraction about 1–2% of the nanoparticles at each Reynolds number for which the maximum performance evaluation criteria can be obtained. The difference between Nusselt number and nondimensional pressure drop calculated based on two phase model and the one calculated based on single phase model was less than 5% at all nanoparticles volume fractions and can be neglected. In natural convection, for 4% of nanoparticles volume fraction, in Gr = 10 more than 15% enhancement of Nusselt number was achieved but in Gr = 300 it was less than 1%.

Lattice Boltzmann simulation of convective heat transfer of non-Newtonian fluids in impeller stirred tank

Lattice Boltzmann simulation of convective heat transfer of non-Newtonian fluids in an impeller stirred tank is performed. The curved and moving boundary methods combined with the unknown-index algorithm are used to solve the flow and thermal fields induced in a cold tank by an oscillating hot impeller. For a given maximum radius of the blades, the simulation results show that a rectangular impeller of large aspect ratio induces stronger heat transfer effect on the tank walls than the small aspect ratio. This is because the latter would cause worse field synergy than the former, i.e. the induced local velocities of fluid are mostly perpendicular to the temperature gradients. The convection effects on the tank walls are also improved as the oscillation amplitude of impeller increases until the swept areas of impeller are close to whole azimuth of the tank, i.e., oscillation amplitude of 90°. The maximum Nusselt number on the tank walls for power-law fluid flows of n=0.7, 1 and 1.5 occurs at oscillation amplitude of 75°. Finally, it is found that the heat transfer effect on the tank walls is reduced as the power-law index of fluid increases.

Estimation of Heat Transfer Coefficients for Biomass Particles by Direct Numerical Simulation Using Microstructured Particle Models in the Laminar Regime

Direct numerical simulation of convective heat transfer from hot gas to isolated biomass particle models with realistic morphology and explicit microstructure was performed over a range of conditions in the laminar regime. Steady-state results demonstrated that convective interfacial heat transfer is dependent on the wood species. The computed heat transfer coefficients were shown to vary between the pine and aspen models by nearly 20%. These differences are attributed to the species-specific variations in the exterior surface morphology of the biomass particles. We also quantify variations in heat transfer experienced by the particle when positioned in different orientations with respect to the direction of fluid flow. These results are compared to previously reported heat transfer coefficient correlations in the range of 0.1 < Pr < 1.5 and 10 < Re < 500. Comparison of these simulation results to correlations commonly used in the literature (Gunn, Ranz–Marshall, and Bird–Stewart–Lightfoot) shows that the...