CFD Simulation Of Heat Transfer Research Articles

CFD Simulation of Heat Transfer Through a Window Frame

The use of various coatings with a low level of radiation on the glass elements of window structures, filling the interglacial space in double-glazed windows with inert gases instead of air, increasing the number of cameras in double-glazed windows, other constructive measures aimed at improving the thermal insulation properties of double-glazed windows, led to a significant increase in the thermal resistance of the fenestration system. However, little has changed in the design and construction of window frames and edge areas adjacent to building facades, leaving these elements responsible for heat transfer through modern windows. In this article, with the help of three-dimensional CFD modeling, the thermal insulation properties of window frames are investigated in the most complete setting, taking into account the effect on heat transfer through the profile of the window frame of the adjacent walls of the building facade on one side and the double-glazed unit on the other. Finding out the thermal insulation parameters of the window frame will help to make appropriate changes in its design.

Heat transfer analysis of a liquid cooling device using thermoelectric elements

This article deals with the CFD simulation of heat transfer inside a heat exchanger of a unique liquid cooling device which innovatively combines a two-circuit liquid cooling system with an accumulator and a new cooling core consisting of Peltier modules. Peltier modules have been used as power elements to cool the medium, which allows heat to be transferred from one side of the cell to the other without moving or noisy elements, thus achieving quiet cooling without vibrations, which can be very beneficial for specific purposes. The used custom-made heat exchanger is specific for its open primary circuit, which also serves as a heat accumulator. In order to obtain data that serve as input conditions for CFD simulation and for subsequent comparison and evaluation, experimental measurements were performed on a physical device. The aim of the simulation is to predict the total time required to cool the medium under given conditions, model the flow of media inside this type of exchanger, and determine the efficiency of the whole device in cooling a specific amount of media using a set of Peltier modules and exchanger, which can be useful in situations where it is undesirable for the refrigerated medium to come into contact with the cooling elements, either due to a hazardous environment or in order to maintain cleanliness standards. This device was able to cool down 2 L of secondary circuit media in slightly over 40 min while showing overall efficiency 14.376%. The efficiency of the exchanger during the experiment was 94.1%. This points to the fact that the Peltier modules are responsible for the significant decrease in efficiency, and the use of this cooling configuration is appropriate in situations where efficiency is not a major requirement.

CFD simulation of heat transfer and phase change characteristics of the cryogenic liquid hydrogen tank under microgravity conditions

The heat transfer and phase change processes of cryogenic liquid hydrogen (LH2) in the tank have an important influence on the working performance of the liquid hydrogen-liquid oxygen storage and supply system of rockets and spacecrafts. In this study, we use the RANS method coupled with Lee model and VOF (volume of fraction) method to solve Navier-stokes equations. The Lee model is adopted to describe the phase change process of liquid hydrogen, and the VOF method is utilized to calculate free surface by solving the advection equation of volume fraction. The model is used to simulate the heat transfer and phase change processes of the cryogenic liquid hydrogen in the storage tank with the different gravitational accelerations, initial temperature, and liquid fill ratios of liquid hydrogen. Numerical results indicate greater gravitational acceleration enhances buoyancy and convection, enhancing convective heat transfer and evaporation processes in the tank. When the acceleration of gravity increases from 10−2 g0 to 10−5 g0, gaseous hydrogen mass increases from 0.0157 kg to 0.0244 kg at 200s. With the increase of initial liquid hydrogen temperature, the heat required to raise the liquid hydrogen to saturation temperature decreases and causes more liquid hydrogen to evaporate and cools the gas hydrogen temperature. More cryogenic liquid hydrogen (i.e., larger the fill ratio) makes the average fluid temperature in the tank lower. A 12.5% reduction in the fill ratio resulted in a decrease in fluid temperature from 20.35 K to 20.15 K (a reduction of about 0.1%, at 200s).

EXPERIMENTAL STUDY AND CFD SIMULATION OF HEAT TRANSFER AND FRICTION FACTOR CHARACTERISTICS IN THE CROSSFLOW TUBE BANK

EXPERIMENTAL STUDY AND CFD SIMULATION OF HEAT TRANSFER AND FRICTION FACTOR CHARACTERISTICS IN THE CROSSFLOW TUBE BANK

Heat transfer from wall to dense packing structures of spheres, cylinders and Raschig rings

This paper investigates the validity of azimuthal averaging of 3D temperature fields in the analysis of lateral heat transfer in dense particle packings. This is conducted by synthetic generation of 3D packing surrogates of spheres, cylinders and Raschig rings with tube-to-pellet diameter ratio, 3 < N < 6, using an in-house Rigid Body Dynamics packing algorithm, followed by detailed discrete pellet CFD simulations of heat transfer from wall to bed for laminar, transient and turbulent flow regimes. The CFD results of hydrodynamics and temperature fields are benchmarked against empirical correlations for pressure drop and interphase heat transfer Nusselt number, Nu, offering the best fits with correlations proposed by Eisfeld and Schnitzlein (for cylinders and spheres) and Nemec and Levec (for rings) for pressure drop, and by Gunn and Sun and coworkers for the prediction of Nu. The CFD results demonstrate that fluctuations in local temperature are completely neglected by azimuthal-averaging of 3D temperature fields over the bed volume, leading to more than 150 °C deviations from the local temperature data. Furthermore, it is found that deviations between azimuthally-averaged axial velocity profile and true local velocities are in an analogous fashion transmitted to the temperature field. This is evidenced by the coincidence of the peaks in the deviation profiles of azimuthally-averaged temperature and velocity from the local data over the bed radius. This is due to thermal disequilibrium between fluid and pellet phases which is partially omitted by the azimuthal-averaging of the 3D temperature field and basically neglected in pseudo-homogenous ker-hw models.

Multiphase-thermal simulation on BOG/BOR estimation due to phase change in cryogenic liquid storage tanks

The purpose of the study is the high-precision, numerical calculation of the Boil-off-Gas (BOG) and Boil-off-Rate (BOR) of cryogenic liquid for the design of containment cargo system (CCS) by using high-fidelity multi-physics CFD simulation of heat transfer of insulation system and phase change of multiphase-thermal flow in the cryogenic liquid tank. The results are compared with those predicted by the conventional low-fidelity methods which are based only on the total heat transfer and does not consider detailed physics related to the phase change of the cryogenic liquid in the storage tank. The unsteady Reynolds-averaged Navier-Stokes (URaNS) equations with the realizable k-ε turbulence model and the Rohsenow boiling model for phase change calculation are solved by commercial software of STAR-CCM+. First, for the validation of the phase change model, the cryogenic liquid stored in an independent tank of type C is calculated to study thermal fluid behaviors inside the tank and the corresponding values of BOG and BOR are compared with the experiments as well as the results from numerical simulations by other researchers. The estimated BOR value showed an excellent agreement with discrepancy less than 1%, resolving precisely the thermal convection caused by the vaporization of the cryogenic liquid. Subsequently, the multiphase-thermal flow in a membrane-type LNG (liquefied natural gas) storage tank was calculated for the BOR estimation, coupled with thermal conduction through the insulation system. It is concluded from those simulations that the high-fidelity CFD calculation with the phase change model was able to precisely predict the vaporization of the cryogenic liquid and to calculate the correct BOR values based on the actual BOG amount.

CFD Simulation of Heat Transfer from Elliptic Tube Bundle Buried in a Bubbling Fluidized Bed

In the present work, numerical simulations are performed to study heat transfer characteristics and fluid flow around elliptic tube heat exchanger. The results for heat transfer coefficient between immersed inline and staggered bundles of horizontal smooth tubes and air-fluidized bed of pulverized coal, dp = 2 mm, are reported within the range of fluidization number, Usup/ Umf, ranges from 1 to 1.4. Heat transfer as well as multiphase flow dynamics in fluidized bed is modelled using the Eulerian-Eulerian and the Two-Fluid Model (TFM) with Kinetic Theory of Granular Flow (KTGF) to describe the granular flow characteristics of the solid phase. The average heat transfer coefficient for the present work is compared with that obtained from the well-known correlation of circular cylinder and a noticed improvement is observed. It is noticed that, the average Nusselt number increases with fluidization number. Also, it is noticed that, the average Nusselt number in case of staggered tubes bundle is higher than the case of inline tubes bundle. The inline tube bundle has lesser pressure drop than the staggered tube bundle.

CFD Simulation of Heat Transfer of Liquid Nitrogen in Heat Exchanger

CFD Simulation of Heat Transfer of Liquid Nitrogen in Heat Exchanger

3D CFD Simulation of Heat Transfer and Friction Characteristics of Laminar Flow of Water through a Circular Duct with Centre-Cleared Twin Twisted Tape

Heat transfer behavior of laminar flow inside circular duct with centre-cleared twin twisted tape (CTTT) swirl generator was investigated numerically. The governing equations were solved with a finite-volume-based numerical method. A three-dimensional non uniform grid was generated, in order to critically examine the flow and heat transfer. The centre-cleared twin twisted tapes were tested in the current work; investigations were performed in the Reynolds number range of 100- 1,000 with four different CTTTs at twist ratio (TR) of H/W = 1.0, 2.0, 3.0 and 4.0. Water is used as working fluid (Pr = 7). The effects of Reynolds number, Nusselt number, friction factor, convective heat transfer coefficient were examined and discussed. The use of CTTT was found to increase the heat transfer considerably when compared with plain tube. The Nusselt number increased with the increase of Reynolds number. The overall enhancement ratio has been calculated in order to discuss the overall effect of CTTT and the working parameters. The present findings would be useful inputs for the design of solar thermal heaters and heat exchangers.

Comparative evaluation of heat conduction and radiation models for CFD simulation of heat transfer in packed beds

The existing major heat conduction and radiation models for packed bed of particles are reviewed and evaluated by comparing the predicted results with experimental data. For low-temperature condition, it is found that the Zehner-Bauer-Schlünder (ZBS) model is less sensitive to the effect of contact area and is thus recommended for the calculation of effective thermal conductivity of packed bed. For high-temperature condition, although numbers of models can be used to calculate the radiative heat transfer behavior in packed bed, the Breitbach and Barthels (B-B) correlation is the optimal method applicable for different particle diameters, emissivities and voidages. The results of CFD simulations using the identified optimal heat transfer models agree well with the thermal measurements by thermocouple in four coal pyrolysis fixed-bed reactors mounted with or without particularly designed internals.

CFD simulations of heat transfer in internally helically ribbed tubes

Abstract Heating surfaces in power boilers are exposed to very high heat flux. For evaporator protection against overheating, internally helically ribbed tubes are used. The intensification of the heat transfer and the maintenance of the thin water layer in the intercostal space, using ribbed tubes, enables better protection of the power boiler evaporator than smooth pipes. Extended inner surface changes flow and thermal conditions by influencing the linear pressure drop and heat transfer coefficient. This paper presents equations that are used to determine the heat transfer coefficient. The results of total heat transfer, obtained from CFD simulations, for two types of internally ribbed and plain tubes are also presented.

CFD Simulation of Heat Transfer in Fluidized Bed Reactor

This study aims to predict heat transfer from a heated bed in a gas fluidized bed using Syamlal-OBrien drag coefficient. Discrete particles model with the Navier-Stokes equation and Eulerian multiphase are used to approach heat transfer simulation. Coefficient of heat transfer which is related to Nusselt Number and volume fraction are calculated using Gunn model which was compiled from C++ program language. The effect of fluidization velocity variation on the heat transfer coefficient comes to the fore, indicating the heat transfer and solid volume fraction at the bed height are very dependent. Contour of solid volume fraction and temperature distribution are also presented.

CFD Simulation of Heat Transfer Augmentation in a Circular Tube Fitted with Alternative Axis Twisted Tape in Laminar Flow under a Constant Heat Flux

CFD simulation of heat transfer and friction factor characteristics in a circular tube fitted with twisted tape inserts in laminar flow and constant heat flux is conducted using FLUENT version 6.3.26. Plain and alternate axis twisted tape inserts with twist ratios (y = 2.93, 3.91, 4.89) and alternative angles (β = 30°, 60°, 90°) have been used for the simulation. The simulated results are matched with the literature correlations for a plain tube with a discrepancy of less than ±8% for Nusselt number and ±6.25% for friction factor. The results also revealed that the heat transfer in terms of the Nusselt number increased with increases of Reynolds number, alternative angles, and decreases of twist ratio. Among the various twist ratios and alternative angles, the twist ratio of y = 2.93 and alternative angle β = 90° offered a maximum heat transfer enhancement. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(4): 384–396, 2014; Published online 3 October 2013 in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21089

CFD Simulation of Heat Transfer and Friction Factor Augmentation in a Circular Tube Fitted with Elliptic-Cut Twisted Tape Inserts

This paper presents the application of a mathematical model for simulation of the swirling flow in a tube induced by elliptic-cut and classical twist tape inserts. Effects of the twist ratio (y=2.93, 3.91, and 4.89) and cut depth (w=0.4, 0.8, and 1.4 cm) on heat transfer enhancement (Nu) and friction factor (f) in laminar flow are numerically investigated. The simulation is carried out using commercial CFD package (FLUENT-6.3.26) to grasp the physical behaviour of the thermal and fluid flows of a constant heat-fluxed tube fitted with elliptic-cut twist tape in the laminar flow regime for the Reynolds number ranging from 200 to 2100. The simulated results matched the literature correlations of plain tube for validation with 8% variation for Nusselt number and 10% for friction factor. The results show that the heat transfer rate and friction factor in the tube equipped with elliptic-cut twist tape (ECT) are significantly higher than those fitted with classical twist tape (CTT). Moreover the results also reveal that the Nusselt number and the friction factor in the tube with elliptic-cut twisted tape (ECT) increase with decreasing twist ratios (y) and cut depths (w).

CFD Simulation of Heat Transfer and Turbulent Fluid Flow over a Double Forward-Facing Step

Heat transfer and turbulent water flow over a double forward-facing step were investigated numerically. The finite volume method was used to solve the corresponding continuity, momentum, and energy equations using theK-εmodel. Three cases, corresponding to three different step heights, were investigated for Reynolds numbers ranging from 30,000 to 100,000 and temperatures ranging from 313 to 343 K. The bottom of the wall was heated, whereas the top was insulated. The results show that the Nusselt number increased with the Reynolds number and step height. The maximum Nusselt number was observed for case 3, with a Reynolds number of 100,000 and temperature of 343 K, occurring at the second step. The behavior of the Nusselt number was similar for all cases at a given Reynolds number and temperature. A recirculation zone was observed before and after the first and second steps in the contour maps of the velocity field. In addition, the results indicate that the coefficient pressure increased with increasing Reynolds number and step height. ANSYS FLUENT 14 (CFD) software was employed to run the simulations.

Transfer of Low-Potential Heat from a Deep Borehole by Means of a Heat Pipe and Heat Pump

The paper presents a design of equipment for the usage of low-potential heat collected from rock in a deep borehole by means of heat pipes (HP) and a description of its realization. The borehole model together with a CFD simulation of heat transfer from rock to a soil probe enabled dimensioning of a heat exchanger on the condenser part of the heat pipe and choice of a suitable heat pipe charge. Part of the paper deals with the processing of measurement results gathered from the comparative experimental equipment requiring forced and unforced circulation(heat pipe) of the working substance on the primary side of the heat pump.

Experimental validation of high Reynolds number CFD simulations of heat transfer in a pilot-scale fixed bed tube

CFD simulations of heat transfer in fixed beds of spheres were validated by comparison to experimental measurements in a pilot-scale rig. The comparisons were made for particle Reynolds numbers in the range 2200<Re<27000 for tube-to-particle diameter ratio N = 5.45, and in the range 1600<Re<5600 for N=7.44. Radial temperature profiles were obtained at four axial positions in the heated bed spaced 0.16m apart.CFD models of a 0.72m long tube containing 1000 spheres (N=5.45) and a 0.35m long tube of 1250 spheres (N=7.44) were solved to obtain well-developed flow fields. These provided inlet velocity profiles to reduced models of 0.20m heated packed length, consisting of 304 spheres for N=5.45 and 722 spheres for N=7.44. The measured temperature profiles were used as inlet boundary conditions and profiles 0.16m downstream were computed. A mesh verification study showed negligible difference between the profiles from a medium and a fine mesh.Contact points were treated by one of three methods: global reduction of sphere size resulting in gaps, or local insertion of bridges at particle–wall contact points with either surface flattening or bridges at the particle–particle contact points. The gaps method gave slightly poorer results; the two bridges methods were better and indistinguishable from each other. CFD simulations compared well to the experimental data: trends with Re, N and bed depth were captured, and quantitative agreement of temperature profiles was reasonable.

EFFECTS OF BUOYANCY ON THE PERFORMANCE OF A VERTICAL DOUBLE-PIPE HEAT EXCHANGER

CFD simulations of heat transfer between two fluids in a parallel-flow vertical double-pipe heat exchanger, taking into consideration conduction in the walls, viscous dissipation, variable fluid properties, and axial diffusion in the fluids, illustrate the effects of buoyancy on the velocity and temperature profiles as well as on the Nusselt numbers and friction coefficients. In particular, the results show that flow reversal occurs at different positions depending on the flow direction. In the developing region, the fluid bulk temperatures, the wall temperature, and the local Nusselt numbers for both fluids depend on the flow direction. For the conditions under consideration, the Nusselt number for the fully developed flow in the inner pipe lies between the corresponding forced convection values for the constant heat flux and constant temperature conditions, while the one in the annulus is smaller than both these forced convection values. It is established that the flow and thermal fields in the inner cylinder and the annulus cannot be predicted correctly by studying each one separately since the thermal condition at the solid wall separating the two fluids depends on flow characteristics such as the Richardson number in the inner tube.

CFD simulation of heat transfer in a two-dimensional vertical enclosure

In order to predict the variation in heat transfer coefficient setup by natural convection, independent CFD simulations have been performed for various tall slender vertical geometries (100 mm < H < 1000 mm) with varying gap widths (5 mm < L < 84.7 mm) and temperature differences (5 K < Δ T < 90 K) covering the ranges reported in the literature (Batchelor, G.K., 1954. Heat transfer by free convection across a closed cavity between vertical boundaries at different temperatures. Quart. Appl. Math., 12, 209–233; Newell, M.E., Schmidt, F.W., 1970. Heat transfer by laminar natural convection within rectangular enclosures. Trans. ASME C: J. Heat Transf., 92, 159–167; Yin, S.H., Wung, T.Y., Chen, K., 1978. Natural Convection in an air layer enclosed within rectangular cavities. Int. J. Heat Mass Transf., 21, 307–315; Elsherbiny, S.M., Raithby, G.D., Hollands K.G.T., 1982. Heat transfer by natural convection across vertical and inclined air layers. Trans. ASME J. Heat Transf., 104: 96–102; Lee, Y., Korpela, S., 1983. Multicellular natural convection in a vertical slot. J. Fluid Mech., 126, 91–124) and compared with their own experimental and numerical studies. A good agreement of Nusselt number (±10%) has been found between the CFD predictions and the literature data. Further, simulations were carried out for gap widths (5 mm ≤ L ≤ 25 mm), heights (100 mm ≤ H ≤ 1000 mm) (4 ≤ AR ≤ 200) and temperature differences (20 K ≤ Δ T ≤ 90 K, 5.99E + 02 ≤ Ra ≤ 3.15E + 05) and a correlation for the estimation of Nu has been proposed. The sensitivity analysis shows %deviation of heat transfer coefficient only in the range of ±10%. A generalized correlation based on all the above results encompassing the effect of height, gap width and temperature difference has also been proposed, which can be used to accurately estimate heat losses from a vertical air gap acting as an insulation.

A general implementation of the H1 boundary condition in CFD simulations of heat transfer in swept passages

A methodology has been developed to study laminar flow and heat transfer behaviour in periodic non-straight passages with a heat transfer boundary condition of constant axial heat flux and constant peripheral temperature ( H1). The technique uses Newton iteration to determine the wall temperature distribution required to satisfy the H1 boundary condition. The methodology is validated for hydrodynamically developed and thermally developing flow, as well as for hydrodynamically and thermally developed flow in straight ducts with various cross-sections. The methodology is extended to study fully developed flow in a periodic serpentine channel, consisting of a number of bends and straight sections, with a semi-circular cross-section. The results show the existence of a non-monotonic temperature distribution along the serpentine channels which exists because increased rates of heat transfer at bends lead to reductions in the local wall temperature in order to maintain a constant axial heat flux. Hot spots within the passage cross-section, typical of the H2 boundary condition, are removed in the H1 case.