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.

Thermal Interaction at the Interface Between a Porous Medium and an Impermeable Wall

2001 ◽  
Vol 123 (3) ◽  
pp. 527-533 ◽  
Author(s):  
Sung Jin Kim ◽  
Duckjong Kim
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Porous Medium ◽  
Heat Sink ◽  
Thermal Boundary Condition ◽  
Local Thermal Equilibrium ◽  
Porous Channel ◽  
Microchannel Heat Sink ◽  
Impermeable Wall

The present work investigates a heat transfer phenomenon at the interface between a porous medium and an impermeable wall subject to a constant heat flux at the bottom. Currently, two possible thermal boundary conditions (which are called the First Approach and the Second Approach) at the interface are used interchangeably for the thermal analysis of convection in a channel filled with a porous medium. The focus of this paper is to determine which of these thermal boundary conditions is more appropriate in accurately predicting the heat transfer characteristics in a porous channel. To this end, we numerically examine the heat transfer at the interface between a microchannel heat sink (an ideally organized porous medium) and a finite-thickness substrate. From the examination, it is clarified that the heat flux distribution at the interface is not uniform for an impermeable wall with finite thickness. This means that a non-uniform distribution of the heat flux (First Approach) is physically reasonable. When the First Approach is applied to the thermal boundary condition, an additional boundary condition based on the local thermal equilibrium assumption at the interface is used. This additional boundary condition is applicable except in the case of a very thin impermeable wall. Hence, for practical situations, the First Approach with a local thermal equilibrium assumption at the interface is suggested as an appropriate thermal boundary condition. In order to confirm our suggestion, convective flows both in a microchannel heat sink and in a sintered porous channel subject to a constant heat flux condition are analyzed by using the two Approaches separately as a thermal boundary condition at the interface. The analytically obtained thermal resistance of the microchannel heat sink and the numerically obtained overall Nusselt number for the sintered porous channel are shown to be in close agreement with available experimental results when our suggestion for the thermal boundary condition at the interface is applied.

An Investigation of Local Heat Transfer during Grinding Process—Effects of Porosity of Grinding Wheel

1979 ◽  
Vol 101 (2) ◽  
pp. 97-103 ◽  
Author(s):  
Y. Saito ◽  
N. Nishiwaki ◽  
Y. Ito
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Thermal Boundary Condition ◽  
Grinding Wheel ◽  
Grinding Process ◽  
Workpiece Surface

The thermal boundary condition around the workpiece surface is one of important factors to analyze the thermal deformation of a workpiece, which is in close relation to the machining, accuracy of grinding. The heat dissipation from the workpiece surface which is influenced by the flow pattern, may govern this thermal boundary condition. In consequence, it is necessary to clarify the convection heat transfer coefficient and the flow pattern of air and/or grinding fluid around surroundings of a rotating grinding wheel and of a workpiece. Here experiments were carried out in a surface grinding process to measure the flow velocity, wall pressure and local heat transfer by changing the porosity of the grinding wheel. The air blowing out from the grinding wheel which is effected by the porosity may be considered to have large influences on the local heat transfer coefficient, which is found to be neither symmetric nor uniform over the workpiece surface.

Nodal Topology in Compact Thermal Models

2007 ◽  
Author(s):  
D. H. Greisen ◽  
V. P. Manno
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Boundary Conditions ◽  
Transfer Coefficient ◽  
Area Ratio ◽  
System Level ◽  
Thermal Models ◽  
Single Boundary

Compact Thermal Models (CTMs) utilize a few connected thermal nodes to represent the thermal characteristics of electronic packages. These models are preferable to highly discretized models in preliminary design and system level analysis because of their computational efficiency. Surface heat flux non-uniformities often make it necessary to subdivide the package surfaces into multiple CTM nodes. This division is often quantified as the surface area ratio. This work assesses CTM performance sensitivity to area ratio changes and variation in heat transfer coefficient boundary conditions. CTMs for benchmark TQFP and BGA packages are developed using an admittance matrix approach. While optimum area ratios are identified, a direct correlation between these optimal values and the heat flux distributions computed from fully-discretized models was not obtained. CTM performance was found to be sensitive to changes in the heat transfer coefficient used to generate the CTM parameter values. A critical generating heat transfer coefficient was determined such that the resulting CTM, when optimized for a single boundary condition, was relatively accurate over the whole set of boundary conditions considered. This single boundary condition also provided an upper bound for error. This finding could be significant in future CTM development procedures.

Analysis of Heat Transfer and Entropy Generation in a Channel Partially Filled With N-Layer Porous Media

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Kun Yang ◽  
Hao Chen ◽  
Jiabing Wang
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Porous Medium ◽  
Porous Media ◽  
Entropy Generation ◽  
Entropy Generation Rate ◽  
Free Fluid ◽  
Bejan Number ◽  
Stress Jump

Convective heat transfer in a channel partially filled with porous medium has received a lot of attention due to its wide engineering applications. However, most researches focused on a channel partially filled with single layer porous medium. In this paper, we will analyze the heat transfer and entropy generation inside a channel partially filled with N-layer porous media. The flow and the heat transfer in the porous region are described by the Darcy–Brinkman model and the local thermal nonequilibrium model, respectively. At the porous-free fluid interface, the momentum and the heat transfer are described by the stress jump boundary condition and the heat flux jump boundary condition, respectively; while at the interface between two different porous layers, the momentum and the heat transfer are described by the stress continuity boundary condition and the heat flux continuity boundary condition, respectively. The analytical solutions for the velocity and temperature in the channel are derived and used to calculate the overall Nusselt number, the total entropy generation rate, the Bejan number, and the friction factor. Furthermore, the performances of the flow and heat transfer of a channel partially filled with third-layer porous media are studied.

Thermal Behavior of Double Glass Window Filled with Absorbing and Non-Absorbing Gas

2013 ◽  
Vol 805-806 ◽  
pp. 1603-1611 ◽  
Author(s):  
Chun Li Tang ◽  
Xiao Wei Zhang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Solar Radiation ◽  
Free Convection ◽  
Surface Heat Flux ◽  
Radiation Flux ◽  
Surface Heat ◽  
Solar Radiation Flux ◽  
Surface Heat Transfer Coefficient

This paper presents a radiant model based on the radiant resistance analysis theory and the results of numerical simulations of double glass window. The two-dimensional steady state model is formulated based upon the radiation and free convection heat transfer at different external and internal ambient conditions.The properties of glass which change with incident wavelength are also considered. Specifically, air and CO2 are used as the medium in the 8mm and 10mm cavity of the double glass window, respectively. Several parameters, including transmitted solar radiation flux, temperature distribution, surface heat transfer coefficient for free convection and total surface heat flux are calculated. The results show that transmitted solar radiation flux is slightly lower when filled with CO2 in the cavity than with air due to their absorption difference. Also, the temperature of gas closing to internal glass sheet and the total surface heat flux of internal glass sheet are decreased when filled with CO2 than with air, although the surface heat transfer coefficient is slightly higher when it is CO2. .The temperature variation curves show that less heat flows into the room when filled with CO2 than air in double glass window.

scholarly journals Method for Determining the Boundary Condition of Heat Transfer in Mold for Slab Casting

2021 ◽  
Vol 2101 (1) ◽  
pp. 012037
Author(s):  
Junli Guo ◽  
Jin Zou ◽  
Changlin Yang ◽  
Deping Lu ◽  
Lefei Sun
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Temperature Field ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Casting Speed ◽  
Cooling Condition ◽  
Average Heat Transfer Coefficient ◽  
Average Heat

Abstract The calculation of temperature field in the mold is important for the study of solidification process of liquid steel. In order to calculate the accurate temperature field of slab in the mod, the boundary condition of heat transfer in the mold should be determined before the calculation of slab temperature. In this paper, the relationship among the average heat transfer coefficient in the mold, the physical properties of steel, the cast condition and the cooling condition is derived according to the energy conservation equation and the Fourier law of heat conduction. Furthermore, the method for determining the parameters related to the formula of boundary heat flux is introduced. Results indicate that the average heat transfer coefficient in the mold ranges from 450 to 2000 W·(m2oC)−1 for conventional caster with a casting speed ranging from 0.8 and 1.8 m·min-1. The average heat transfer coefficient increases with the increase of casting speed. Besides, the casting speed has an effect on the parameters in the formula of calculating boundary heat flux, which indicates that the casting speed and the cooling condition should be taken into consideration for determining parameters related to the formula of calculating surface heat flux in the mold.

Single Phase Heat Transfer In Parallel Micro-Channel Heat Sink

2018 ◽  
pp. 11-16
Author(s):  
R. AL-Khafajy
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Test Section ◽  
Single Phase ◽  
Electric Heater ◽  
Micro Channel ◽  
Parallel Channels

A copper parallel channels test piece has built into the test section containing twenty five, one mm by one mm, parallel channels the channels were fifty mm long; the Heat-transfer coefficients for single-phase are reported. Micro- channel was Square shape and the test section has a glass top plate to permit visual observations. The data are taken while the rig is working .The test section is received the heat by an electric heater is associated normally with a boundary condition for constant heat flux. Because the important variation in the single-phase - heat-transfer coefficient in the inlet zone, the interceding copper and aluminum material is shown to make the test section close isothermal wall boundary condition. The heat conduction influence is taken into computation in the data analysis finally; the effective heat flux and the single-phase heat transfer coefficient are reported in this paper experiments and predictions. Key words— Single phase Heat transfer cofficients , Parallel channels ,Heat flux,Mass flux.

Experimental Study of Boiling Heat Transfer From a Sphere Embedded in a Liquid-Saturated Porous Medium

1990 ◽  
Vol 112 (3) ◽  
pp. 736-743 ◽  
Author(s):  
V. X. Tung ◽  
V. K. Dhir
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Particle Size ◽  
Porous Medium ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Maximum Heat ◽  
Maximum Heat Flux

Boiling heat transfer from a sphere embedded in a porous medium composed of nonheated glass particles was studied under steady-state and transient quenching conditions. In the experiments, the diameter of the nonheated glass particles forming the porous layers was varied parametrically. Freon-113 was used as the test liquid. Experimental results showed that the maximum heat flux increased monotonically with increasing glass particle diameter and approached an asymptotic value corresponding to the maximum heat flux obtained in a pool free of glass particles. It was also observed that the minimum heat flux was nearly insensitive to the particle size and the film boiling heat transfer coefficient increased slightly with decreasing particle size. In the nucleate boiling region, the heat transfer coefficient showed a much weaker dependence on wall superheat in the presence of particles. Transient data indicated that the surface temperature was not uniform during quenching. Therefore, different maximum heat fluxes were obtained depending on the location of the thermocouple whose temperature history was employed in recovering the transient boiling curve. However, for some applications, cooling rates predicted by imposing the steady-state boiling curve may not be in large error.

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