New models for heat flux splitting at the boundary of a porous medium: three energy equations for nanofluid flow under local thermal nonequilibrium conditions

2014 ◽  
Vol 92 (11) ◽  
pp. 1312-1319 ◽  
Author(s):  
M. Nazari ◽  
M.J. Maghrebi ◽  
T. Armaghani ◽  
Ali J. Chamkha
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Porous Medium ◽  
Solid Phase ◽  
Solid Matrix ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Thermal Nonequilibrium ◽  
Local Thermal Nonequilibrium ◽  
Energy Equations

One of the challenging points in the simulation of a nanofluid flowing through a porous medium is modeling the surface heat flux in the presence of nanoparticles and internal solid matrix. The question is how much energy is absorbed by the solid phase, fluid phase, and particles at the surface of imposing heat flux? To reach a suitable answer, a local thermal nonequilibrium approach (including three energy equations) is presented in this paper and three heat flux models are proposed for the first time. The proposed models are compared and analyzed. The effects of interstitial heat transfer coefficients on the heat transfer in a porous channel are completely studied. The fluid temperature distributions and heat transfer rate obtained by homogenous and nonhomogenous approaches (for the proposed models) are completely studied and compared. The results show that the nonhomogeneous approach experiences larger Nusselt number than the homogeneous one for all the recommended heat flux models.

A Local Thermal Nonequilibrium Analysis of Silicon Carbide Ceramic Foam as a Solar Volumetric Receiver

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
Y. Sano ◽  
S. Iwase ◽  
A. Nakayama
Keyword(s):  
Heat Transfer ◽  
Silicon Carbide ◽  
Pore Diameter ◽  
Solid Phase ◽  
Flow Direction ◽  
Ceramic Foam ◽  
Thermal Nonequilibrium ◽  
Silicon Carbide Ceramic ◽  
Local Thermal Nonequilibrium ◽  
Solar Receiver

A volumetric solar receiver receives the concentrated radiation generated by a large number of heliostats. Heat transfer takes place from the receiver solid phase to the air as it passes through the porous receiver. Such combined heat transfer within the receiver, associated radiation, convection and conduction, are investigated using a local thermal nonequilibrium model. The Rosseland approximation is applied to account for the radiative heat transfer through the solar receiver, while the low Mach approximation is exploited to investigate the compressible flow through the receiver. Analytic solutions are obtained for the developments of air and ceramic temperatures as well as the pressure along the flow direction. The results show that the pore diameter must be larger than its critical value to achieve high receiver efficiency. Subsequently, there exists an optimal pore diameter for achieving the maximum receiver efficiency under the equal pumping power. The solutions serve as a useful tool for designing a novel volumetric solar receiver of silicon carbide ceramic foam.

scholarly journals HEAT TRANSFER FOR FILN BOILING OF A LIQUID ON A VERTICAL HEATED WALL IN A POROUS MEDIUM

2021 ◽  
Vol 43 (1) ◽  
pp. 20-29
Author(s):  
A.A. Avramenko ◽  
M.M. Kovetskaya ◽  
E.A. Kondratieva ◽  
T.V. Sorokina
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Porous Medium ◽  
Fluid Flow ◽  
Wall Temperature ◽  
Heated Wall ◽  
Film Boiling ◽  
Transfer Coefficients ◽  
Constant Wall Temperature ◽  
Heat Transfer Coefficients

The paper presents results of the modelling of heat transfer at film boiling of a liquid in a porous medium on a vertical heated wall. Such processes are observed at cooling of high-temperature surfaces of heat pipes, microstructural radiators etc. Heating conditions at the wall were the constant wall temperature or heat flux. An analytical solution was obtained for the problem of fluid flow and heat transfer using the porous medium model in the Darcy-Brinkman. It was shown that heat transfer at film boiling in a porous medium was less intensive than in the absence of a porous medium (free fluid flow) and further decreased with the decreasing permeability of the porous medium. A sharp decrease in heat transfer was observed for the Darcy numbers lower than five. The analytical predictions of heat transfer coefficients qualitatively agreed with the data [14] though demonstrated lower values of heat transfer coefficients for the conditions of the constant wall temperature and constant wall heat flux.

Heat Transfer in a Porous Electrode of Fuel Cells

2005 ◽  
Vol 128 (5) ◽  
pp. 434-443 ◽  
Author(s):  
J. J. Hwang
Keyword(s):  
Heat Transfer ◽  
Diffusion Layer ◽  
Wall Temperature ◽  
Solid Phase ◽  
Porous Electrode ◽  
Catalyst Layer ◽  
Fluid Phase ◽  
Stanton Number ◽  
Thermal Nonequilibrium ◽  
Local Thermal Nonequilibrium

The thermal-fluid behaviors in a porous electrode of a proton exchange membrane fuel cell (PEMFC) in contact with an interdigitated gas distributor are investigated numerically. The porous electrode consists of a catalyst layer and a diffusion layer. The heat transfer in the catalyst layer is coupled with species transports via a macroscopic electrochemical model. In the diffusion layer, the energy equations based on the local thermal nonequilibrium (LTNE) are derived to resolve the temperature difference between the solid phase and the fluid phase. Parametric studies include the Reynolds number and the Stanton number (St). Results show that the wall temperature decreases with increasing Stanton number. The maximum wall temperatures occur at the downstream end of the module, while the locations of local minimum wall temperature depend on the Stanton numbers. Moreover, the solid phase and the fluid phase in the diffusion layer are thermally insulated as St⪡1. The diffusion layer becomes local thermal nonequilibrium as the Stanton number around unity. The porous electrode is local thermal equilibrium for St⪢1. Finally, the species concentrations inside the catalyst and diffusion layers are also provided.

Turbulent Heat and Momentum Transports in an Infinite Rod Array

1987 ◽  
Vol 109 (3) ◽  
pp. 599-605 ◽  
Author(s):  
An-Shik Yang ◽  
Ching-Chang Chieng
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Equation Model ◽  
Temperature Fields ◽  
Turbulent Heat ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Anisotropic Factor ◽  
Flow Through ◽  
Rod Array

An anisotropic factor is carefully selected from eleven distributions and adopted to the k–ε two-equation model of turbulence to obtain detailed velocity and temperature fields for steady-state, fully developed turbulent flow through infinite triangular/square rod array. The present study covers the ranges of pitch-to-diameter ratio from 1.123 to 1.5, and Reynolds number from 2.4 × 104 to 106. Velocity and wall shear stress are calculated and compared to experimental data. Normalized fluid temperature, friction factor, and heat transfer coefficient are also computed. The correlations of friction factor and heat transfer coefficients for flow inside circular pipe and flow through finite rod arrays are compared with the results for flow through infinite rod arrays.

scholarly journals Darcy-Brinkman free convection about a wedge and a cone subjected to a mixed thermal boundary condition

1992 ◽  
Vol 15 (4) ◽  
pp. 789-794 ◽  
Author(s):  
G. Ramanaiah ◽  
V. Kumaran
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Porous Medium ◽  
Heat Transfer Coefficient ◽  
Free Convection ◽  
Transformation Group ◽  
Darcy Number ◽  
Thermal Boundary Condition ◽  
High Porosity

The Darcy-Brinkman free convection near a wedge and a cone in a porous medium with high porosity has been considered. The surfaces are subjected to a mixed thermal boundary condition characterized by a parameterm;m=0,1,∞correspond to the cases of prescribed temperature, prescribed heat flux and prescribed heat transfer coefficient respectively. It is shown that the solutions for differentmare dependent and a transformation group has been found, through which one can get solution for anymprovided solution for a particular value ofmis known. The effects of Darcy number on skin friction and rate of heat transfer are analyzed.

scholarly journals Operating temperatures of oil-lubricated medium-speed gears: Numerical models and experimental results

2003 ◽  
Vol 217 (2) ◽  
pp. 87-106 ◽  
Author(s):  
H Long ◽  
A A Lord ◽  
D T Gethin ◽  
B J Roylance
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Rotational Speed ◽  
High Speed ◽  
Applied Load ◽  
Frictional Heat ◽  
Transfer Coefficients ◽  
Gear Teeth ◽  
Heat Transfer Coefficients

This paper investigates the effects of gear geometry, rotational speed and applied load, as well as lubrication conditions on surface temperature of high-speed gear teeth. The analytical approach and procedure for estimating frictional heat flux and heat transfer coefficients of gear teeth in high-speed operational conditions was developed and accounts for the effect of oil mist as a cooling medium. Numerical simulations of tooth temperature based on finite element analysis were established to investigate temperature distributions and variations over a range of applied load and rotational speed, which compared well with experimental measurements. A sensitivity analysis of surface temperature to gear configuration, frictional heat flux, heat transfer coefficients, and oil and ambient temperatures was conducted and the major parameters influencing surface temperature were evaluated.

Oscillatory Heat Transfer in a Pipe Subjected to a Laminar Reciprocating Flow

1996 ◽  
Vol 118 (3) ◽  
pp. 592-597 ◽  
Author(s):  
T. S. Zhao ◽  
P. Cheng
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Nusselt Number ◽  
Numerical Study ◽  
Temperature Cycle ◽  
Uniform Heat Flux ◽  
Fluid Temperature ◽  
Cycle Space ◽  
Reciprocating Flow

An experimental and numerical study has been carried out for laminar forced convection in a long pipe heated by uniform heat flux and subjected to a reciprocating flow of air. Transient fluid temperature variations in the two mixing chambers connected to both ends of the heated section were measured. These measurements were used as the thermal boundary conditions for the numerical simulation of the hydrodynamically and thermally developing reciprocating flow in the heated pipe. The coupled governing equations for time-dependent convective heat transfer in the fluid flow and conduction in the wall of the heated tube were solved numerically. The numerical results for time-resolved centerline fuid temperature, cycle-averaged wall temperature, and the space-cycle averaged Nusselt number are shown to be in good agreement with the experimental data. Based on the experimental data, a correlation equation is obtained for the cycle-space averaged Nusselt number in terms of appropriate dimensionless parameters for a laminar reciprocating flow of air in a long pipe with constant heat flux.

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