Two-Phase Heat Transfer in a Wall-Driven Cubical Heat Sink

2016 ◽  
Author(s):  
Majid Molki
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Sink ◽  
Volume Fraction ◽  
Turbulent Heat Transfer ◽  
Liquid Volume ◽  
Turbulent Heat ◽  
Fluid Temperature ◽  
Complex Flow ◽  
Liquid Volume Fraction

Turbulent heat transfer for flow of water-air mixture driven by moving walls in a cubical heat sink is investigated. One wall is maintained at an elevated temperature, while the vertical walls are at a low temperature. The cubical enclosure functions as a heat sink using water-air mixture with no phase change. Different arrangements for wall motion are considered, which include 1 to 4 moving walls. As the number of moving walls increases, the flow and heat transfer become more complex. In general, the flow reveals complex and multi-scale structures with an unsteady and evolving nature. The larger structure of the flow is resolved using Large Eddy Simulation, while the sub-grid scales are captured by the dynamic k-equation eddy-viscosity model. The focus of this work is on thermal field and heat transfer as affected by the complex flow field generated by multiple moving walls. The results indicate that the Nusselt number for the heat sink varies from 5202.8 to 7356.1, depending on the number of moving walls. Contours of fluid temperature, liquid volume fraction, local and average values of Nusselt number are among the results presented in this paper.

The effect of viscous dissipation on laminar nanofluid flow in a microchannel heat sink

2009 ◽  
Vol 223 (11) ◽  
pp. 2697-2706 ◽  
Author(s):  
M Ghazvini ◽  
M A Akhavan-Behabadi ◽  
M Esmaeili
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Viscous Dissipation ◽  
Heat Sink ◽  
Volume Fraction ◽  
Numerical Study ◽  
Microchannel Heat Sink ◽  
Fluid Temperature ◽  
Nanofluid Flow ◽  
Aspect Ratios

The present article focuses on analytical and numerical study on the effect of viscous dissipation when nanofluid is used as the coolant in a microchannel heat sink (MCHS). The nanofluid is made from CuO nanoparticles and water. To analyse the MCHS, a modified Darcy equation for the fluid and two-equation model for heat transfer between fluid and solid sections are employed in porous media approach. In addition, to deal with nanofluid heat transfer, a model based on the Brownian motion of nanoparticles is used. The model evaluates the thermal conductivity of nanofluid considering the thermal boundary resistance, nanoparticle diameter, volume fraction, and the fluid temperature. At first, the effects of particle volume fraction on temperature distribution and overall heat transfer coefficient are investigated with and without considering viscous dissipation. After that, the influence of different channel aspect ratios and porosities is studied. The results show that for nanofluid flow in microchannels, the viscous dissipation can be neglected for low volume fractions and aspect ratios only. Finally, the effect of porosity and Brinkman number on the overall Nusselt number is studied, where asymptotic behaviour of the Nusselt number is observed and discussed from the energy balance point of view.

Pseudo-turbulent heat flux and average gas–phase conduction during gas–solid heat transfer: flow past random fixed particle assemblies

2016 ◽  
Vol 798 ◽  
pp. 299-349 ◽  
Author(s):  
Bo Sun ◽  
Sudheer Tenneti ◽  
Shankar Subramaniam ◽  
Donald L. Koch
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Gas Phase ◽  
Volume Fraction ◽  
Turbulent Heat Flux ◽  
Turbulent Heat ◽  
Fluid Temperature ◽  
Bulk Fluid ◽  
The Mean ◽  
Temperature Equation

Fluctuations in the gas-phase velocity can contribute significantly to the total gas-phase kinetic energy even in laminar gas–solid flows as shown by Mehrabadi et al. (J. Fluid Mech., vol. 770, 2015, pp. 210–246), and these pseudo-turbulent fluctuations can also enhance heat transfer in gas–solid flow. In this work, the pseudo-turbulent heat flux arising from temperature–velocity covariance, and average fluid-phase conduction during convective heat transfer in a gas–solid flow are quantified and modelled over a wide range of mean slip Reynolds number and solid volume fraction using particle-resolved direct numerical simulations (PR-DNS) of steady flow through a random assembly of fixed isothermal monodisperse spherical particles. A thermal self-similarity condition on the local excess temperature developed by Tenneti et al. (Intl J. Heat Mass Transfer, vol. 58, 2013, pp. 471–479) is used to guarantee thermally fully developed flow. The average gas–solid heat transfer rate for this flow has been reported elsewhere by Sun et al. (Intl J. Heat Mass Transfer, vol. 86, 2015, pp. 898–913). Although the mean velocity field is homogeneous, the mean temperature field in this thermally fully developed flow is inhomogeneous in the streamwise coordinate. An exponential decay model for the average bulk fluid temperature is proposed. The pseudo-turbulent heat flux that is usually neglected in two-fluid models of the average fluid temperature equation is computed using PR-DNS data. It is found that the transport term in the average fluid temperature equation corresponding to the pseudo-turbulent heat flux is significant when compared to the average gas–solid heat transfer over a significant range of solid volume fraction and mean slip Reynolds number that was simulated. For this flow set-up a gradient-diffusion model for the pseudo-turbulent heat flux is found to perform well. The Péclet number dependence of the effective thermal diffusivity implied by this model is explained using a scaling analysis. Axial conduction in the fluid phase, which is often neglected in existing one-dimensional models, is also quantified. As expected, it is found to be important only for low Péclet number flows. Using the exponential decay model for the average bulk fluid temperature, a model for average axial conduction is developed that verifies standard assumptions in the literature. These models can be used in two-fluid simulations of heat transfer in fixed beds. A budget analysis of the mean fluid temperature equation provides insight into the variation of the relative magnitude of the various terms over the parameter space.

Numerical Simulations of the Fluid Flow and Heat Transfer during a Solidification Phase Change of a Polymer in a Die

2010 ◽  
Vol 97-101 ◽  
pp. 2736-2743
Author(s):  
Shi Xiong Ren ◽  
Sha Sha Dang ◽  
Tao Lu ◽  
Kui Sheng Wang
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Liquid Volume ◽  
Liquid Volume Fraction ◽  
Three Dimensional Models ◽  
Lower Temperature ◽  
Thermal Oil

Three-dimensional models of heat transfer have been established and numerically solved using a commercial software package, Fluent, in order to obtain distributions of temperature, velocity, pressure, and liquid volume fraction of the polymer. The influences of the boundary conditions on the phase change of the polymer and the temperature distribution in the die have been evaluated. The results show that the temperature of the region close to the pelletizing surface is relatively low due to the cooling effect of the cool water, while the temperature deeper inside the die is higher, with a lower temperature gradient, as a result of the heating effect of the hot thermal oil and the polymer. A solidification phase change of the polymer occurs near the polymer outlet due to heat loss from the polymer to the water, while deeper inside the hole the polymer remains fluid without solidification, due to heating by the thermal oil. Numerical simulation provides a reliable method to optimize the design of the die, the choice of metallic material for the die, and the operating conditions of the polymer pelletizing under water.

scholarly journals A study of turbulent heat transfer in convergent-divergent shaped microchannel with ribs and cavities using CFD

2020 ◽  
Vol 14 (1) ◽  
pp. 6344-6361
Author(s):  
Pankaj Srivastava ◽  
Anupam Dewan
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Thermal Resistance ◽  
Average Nusselt Number ◽  
Three Dimensional ◽  
Fluid Mixing ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Rectangular Microchannel ◽  
Better Than

This paper presents the effects of microchannel shape with ribs and cavities on turbulent heat transfer. Three-dimensional conjugate heat transfer using the SST k-ω turbulence model has been investigated for four different microchannels, namely, rectangular, rectangular with ribs and cavities, convergent-divergent (CD) and convergent-divergent with Ribs and Cavities (CD-RC). The flow field, pressure and temperature distributions and friction factor are analyzed, and thermal resistance and average Nusselt number are compared. The thermal performance of the CD-RC microchannel is found to be better than that of other microchannels considered in terms of an average Nusselt number increased from 16% to 40%. Heat transfer increases due to a strong fluid mixing and periodic interruption of boundary-layer. It is observed that with an increase in Reynolds number (Re), the thermal resitance drops rapidly. The thermal resistance of the CD-RC microchannel is decreased by 30% than that of the rectangular microchannel for Re ranging from 2500 to 7000. However, such design of microchannel loses its heat transfer effectiveness due to a high pumping power at high values of Re.

Turbulent Heat Transfer Over a Free Rotating Disk: Analytical and Numerical Predictions Using Solutions of Direct and Inverse Problems

2001 ◽  
Author(s):  
I. V. Shevchuk
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Wall Temperature ◽  
Direct Problem ◽  
Rotating Disk ◽  
Analytical Form ◽  
Turbulent Heat Transfer ◽  
Radial Coordinate ◽  
Turbulent Heat ◽  
Numerical Predictions

Abstract All known analytical solutions of the integral equation of the turbulent thermal boundary layer for a rotating disk have been obtained for the case of direct problem. This means finding the Nusselt number at a given distribution of the wall temperature. This distribution is described by power law and is monotone (derivative of wall temperature with respect to the radial coordinate does not change its sign). Outlined in this paper is an analytical form of non-monotone distribution of the wall temperature, which provided a new analytical solution for the turbulent Nusselt number including earlier known equations as a specific particular case. The solution is based on the integral method, which proved to be more precise than known Dorfman’s approach. Chosen for validation of the proposed method were turbulent heat transfer experiments of Northrop and Owen (1988). Predictions presented include analytical studies using inverse and direct problem solutions as well as numerical simulations using polynomial approximations of the experimental wall temperature distributions.

Effect of Aqueous Suspension of Graphene-Oxide Nanoparticles on Thermal Fluid Flow Transport in Circular Tube

2015 ◽  
Vol 23 (01) ◽  
pp. 1550005 ◽  
Author(s):  
Shuichi Torii ◽  
Hajime Yoshino
Keyword(s):  
Heat Transfer ◽  
Graphene Oxide ◽  
Heat Transfer Enhancement ◽  
Volume Fraction ◽  
Aqueous Suspension ◽  
Constant Heat Flux ◽  
Turbulent Heat Transfer ◽  
Working Fluid ◽  
Turbulent Heat ◽  
Transfer Enhancement

Experimental study is performed on the turbulent heat transfer behavior of aqueous suspensions of nanoparticles flowing through a horizontal circular pipe heated under constant heat flux condition. Consideration is given to the effects of nanoparticle concentration and Reynolds number on heat transfer enhancement. It is found that (i) heat transfer enhancement is caused by suspending nanoparticles, so that maximum value of the Nusselt number is over twice than that of the pure working fluid, (ii) graphene-oxide-nanofluid developed here is non-Newtonian fluid, and (iii) but the pressure drop for graphene-oxide-nanofluid is almost the same as that of the pure working fluid, because volume fraction of particles is less than 1.0%.

Splattering and Heat Transfer During Impingement of a Turbulent Liquid Jet

1992 ◽  
Vol 114 (2) ◽  
pp. 362-372 ◽  
Author(s):  
J. H. Lienhard ◽  
X. Liu ◽  
L. A. Gabour
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heated Surface ◽  
Film Surface ◽  
Turbulent Heat Transfer ◽  
Liquid Jet ◽  
Turbulent Heat ◽  
Disturbance Analysis ◽  
Momentum Integral ◽  
Surface Disturbances

Splattering and heat transfer due to impingement of an unsubmerged, fully turbulent liquid jet is investigated experimentally and analytically. Heat transfer measurements were made along a uniformly heated surface onto which a jet impacted, and a Phase Doppler Particle Analyzer was used to measure the size, velocity, and concentration of the droplets splattered after impingement. Splattering is found to occur in proportion to the magnitude of surface disturbances to the incoming jet, and it is observed to occur only within a certain radial range, rather than along the entire film surface. A nondimensional group developed from inviscid capillary disturbance analysis of the circular jet successfully scales the splattering data, yielding predictive results for the onset of splattering and for the mass splattered. A momentum integral analysis incorporating the splattering results is used to formulate a prediction of local Nusselt number. Both the prediction and the experimental data reveal that the Nusselt number is enhanced for radial locations immediately following splattering, but falls below the nonsplattering Nusselt number at larger radii. The turbulent heat transfer enhancement upstream of splattering is also characterized.

Local Heat Transfer in a Rotating Two-Pass Triangular Duct With Smooth Walls

1994 ◽  
Author(s):  
Sandip Dutta ◽  
Je-Chin Han ◽  
Yuming Zhang ◽  
C. Pang Lee
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Cross Section ◽  
Rotation Number ◽  
Secondary Flows ◽  
Rate Of Change ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

Earlier heat transfer studies with orthogonal rotation were conducted mostly on ducts of square cross-section. This paper reports a different cross-section, a triangular duct. Unlike a square cross-section, the triangular shape provides more restriction to the formation of the secondary flows. Moreover, the studied orientation of the right triangular duct avoids formation of symmetric vortex structures in the cross flow plane. This paper presents turbulent heat transfer characteristics of a two-pass smooth walled triangular duct. One pass is for radial outward flow and the other for radial inward flow. With rotation the radial outward and inward flow directions show different surface heat transfer characteristics. Like a square duct, differences between the trailing and the leading Nusselt number ratios for the triangular duct increase with rotation number. However, the rate of change of Nusselt number ratios with rotation number varies for the two duct geometries. Standard k-ε model predictions for a radial outward flow situation show that the Nusselt number ratio variations with Reynolds number are not drastic for the same rotation number.

Turbulent Thermal Fluid Flow Transport Phenomena of Aqueous Suspensions of Nano-Particles

2009 ◽  
Author(s):  
Shuichi Torii
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Pressure Loss ◽  
Volume Fraction ◽  
Nano Particles ◽  
Turbulent Heat Transfer ◽  
Working Fluid ◽  
Turbulent Heat ◽  
Flow Transport ◽  
Thermal Fluid Flow

The aim of the present study is to investigate the thermal fluid flow transport phenomenon of nanofluids in the heated horizontal circular tube. Consideration is given to the effects of volume fraction of the nanoparticle and Reynolds number on the turbulent heat transfer and pressure loss. Diamond, alumina (Al2O3) and oxide copper (CuO) are employed here as nanoparticles. It is found that (i) the viscosity of nanofluids increases with an increase in the volume fraction of nanoparticles dispersed in the working fluid, (ii) the pressure loss of nanofluids increases slightly in comparison with that of pure fluid and (iii) enhancement heat transfer performance is caused by suspending nanoparticles except for the case of large particle aggregation.

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