Combined forced and free convection heat transfer in a semiporous open cavity (original) (raw)
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Laminar free and forced convection cooling of a semi permeable open cavity
Scientific research and essays
Heat transfer inside a semi porous two-dimensional rectangular open cavity was numerically investigated. The open cavity comprises two vertical walls closed to the bottom by an adiabatic horizontal wall. One vertical wall is a porous and an inflow of fluid occurs normal to it. The other wall transfers a uniform heat flux to the cavity. It shows how natural convection effects may enhance the forced convection inside the open cavity. The main motivation for the work is its application for electronic equipment where frequently the devices used for the electronic equipment cooling are based on natural and forced convection. Governing equations are expressed in Cartesian coordinates and numerically handled by a finite volume method. Results are presented for both local and average Nusselt numbers at the heated wall and for the isotherms and streamlines of the fluid flowing inside the open cavity as a function of Reynolds number ranging from 1 to 100, Grashof number ranging from 0 to 10+7...
2003
In this work, a experimental study of the natural convection heat transfer in a cavity with discrete heat sources flush mounted in one of the walls, simulating electronic components, is carried out. The inferior and superior walls are insulated and the temperature of the opposite wall to the one with heat sources is maintained constant, lower than the environment temperature. The influence of power dissipated by the sources, the cooling temperature, the aspect ratio and the inclination angle of the cavity with respect to the horizontal plane, on the flow and the heat transfer, have all been evaluated. Cubic cavities were built and experimental tests for measure of the temperature was realized by using thermocouples and a data acquisition system controlled by computer, being obtained the temperature fields inside the cavity, as well as the temperature distribution in the wall where the heat sources are mounted. The results were compared with respect to the maximum temperature in the ...
The conjugate natural convection heat transfer in a partially heated square porous enclosure had been studied numerically. The governing dimensionless equations are solved using COMSOL Multiphysics and Darcy model assumed to be used. The considering dimensionless parameters are modified Rayleigh number, finite wall thickness, thermal conductivity ratio and the heat source length. The results are presented in terms of streamlines, isotherms and local and average Nusselt number. The results indicate that; the heat transfer can be enhanced by increasing the modified Rayleigh number. When the heat source length increases, the local Nusselt number of fluid phase increases, while, a reverse behavior of the local Nusselt number along the heat source is found. As the Rayleigh number increase, the local Nusselt number for both fluid and solid phase increases, therefore, the heat transfer rate will be enhanced. On the other hand, when the thermal conductivity ratio increase, the local Nusselt number for the fluid phase increases, and the local Nusselt number along the heated wall decreases.
“Effects Of Heat Source Location On Natural Convection In A Square Cavity”
2012
Natural convection in a closed square cavity has occupied the centre stage in many fundamental heat transfer analysis which is of prime importance in certain technological applications. Infact buoyancy driven convection in a sealed cavity with differentially heated isothermal walls is a prototype of many industrial applications such as energy efficient buildings, operation and safety of nuclear reactor and convective heat transfer associated with electronic cooling equipment. The internal flow problems are considerably more complex than external ones. In electronic systems normally the heat generating bodies exist within the cavity. The effect of the presence of heat source on the mass flow rate and heat transfer is considered in present case for investigation. In order to verify the methodology of using fluent, the commercial software, the available problem in the literature is verified for parametric study on the location of heat source and its strength is considered for study. In present work, the given source is split into two parts and its effect on the flow rate and heat transfer is studied. An attempt is made for the best location of the heat source in the cavity so that it can be used in the electronic equipment generating heat.
International Journal of Heat and Mass Transfer, 2006
Natural convection flows in a square cavity filled with a porous matrix has been studied numerically using penalty finite element method for uniformly and non-uniformly heated bottom wall, and adiabatic top wall maintaining constant temperature of cold vertical walls. Darcy-Forchheimer model is used to simulate the momentum transfer in the porous medium. The numerical procedure is adopted in the present study yields consistent performance over a wide range of parameters (Rayleigh number Ra, 10 3 6 Ra 6 10 6 , Darcy number Da, 10 À5 6 Da 6 10 À3 , and Prandtl number Pr, 0.71 6 Pr 6 10) with respect to continuous and discontinuous thermal boundary conditions. Numerical results are presented in terms of stream functions, temperature profiles and Nusselt numbers. Non-uniform heating of the bottom wall produces greater heat transfer rate at the center of the bottom wall than uniform heating case for all Rayleigh numbers but average Nusselt number shows overall lower heat transfer rate for non-uniform heating case. It has been found that the heat transfer is primarily due to conduction for Da 6 10 À5 irrespective of Ra and Pr. The conductive heat transfer regime as a function of Ra has also been reported for Da P 10 À4 . Critical Rayleigh numbers for conduction dominant heat transfer cases have been obtained and for convection dominated regimes the power law correlations between average Nusselt number and Rayleigh numbers are presented.
Natural convection heat transfer in a porous rectangular partially active heated wall is numerically investigated using finite element method. Three different cases of heating and cooling zone had been taken in the consideration along the vertical walls while the others are considered to be adiabatic. The governing equations are obtained by the applying of Darcy Model and Boussinesq approximation. Finite element method is used to solve the dimensionless governing equations with the specified boundary conditions. The investigated parameters in the present study are the modified Rayleigh number (10 # Ra # 10), aspect ratio 3 (0.5 # A# 2), finite wall thickness (0.02 # D# = 0.5) and the thermal conductivity ratio (0.1# K # 10). The results r are presented in terms of streamlines, isotherms and Nusselt number. The results indicate that as the aspect ratio, finite wall thickness increase, Nusselt number decrease. Also, as the modified Rayleigh number increases, the Nusselt number will increase. Case 1 and 2 gave approximately the same effects of heat transfer rate while case 3 give lower rate of heat transfer rate.
Convective flow and heat transfer in a tall porous cavity side-cooled with temperature profile
International Journal of Heat and Mass Transfer, 2009
Natural convection in an air-filled (Prandtl number = 0.7) porous cavity with profiled side cooling and constant bottom heating is investigated over the Rayleigh number range of 1 Â 10 4 to 1 Â 10 8 at two Darcy numbers: 1 Â 10 À4 and 1 Â 10 À6 . The aspect ratio based on cavity height was varied from 0.5 to 0.1 to investigate penetration length according to linear or sinusoidal temperature profile. The general non-Darcy model adopted in this work was validated against experimental and theoretical results in the literature and Nusselt number was predicted within less than 3% in the worst case. The effect of left wall imposed temperature profile was investigated in detail. Different convective regimes were observed depending on the imposed profile. An active region was found to take place with the linear temperature profile and with extent proportional to Rayleigh number as predicted by scale analysis.
The present study is concerned numerically with the mixed convection in a square lid-driven cavity with moving upper surface filled with saturated porous material. Both upper and lower surfaces are being insulated while the vertical walls of the enclosure subjected to sinusoidal temperatures variation with different amplitude and phase angle in order to enhance the heat transfer. Steady state laminar regime is considered. The transport equations for continuity, momentum, energy are solved. The numerical results are reported for the effect of Richardson number (Ri), Darcy number (Da), Prandtl number (Pr), amplitude ratio (ε) and phase deviation angle (ϕ) on the iso-contours of streamline, and temperature. In addition, the predicted results for both local and average Nusselt numbers are presented and discussed for various parametric conditions. This study was done for 10
The effects of nonuniform heating and a finite wall thickness on natural convection in a square porous cavity based on the local thermal nonequilibrium (LTNE) model are studied numerically using the finite difference method (FDM). The finite-thickness horizontal wall of the cavity is heated either uniformly or nonuniformly, and the vertical walls are maintained at constant cold temperatures. The top horizontal insulated wall allows no heat transfer to the surrounding. The Darcy law is used along with the Boussinesq approximation for the flow. The results of this study are obtained for various parametric values of the Rayleigh number, thermal conductivity ratio, ratio of the wall thickness to its height, and the modified conductivity ratio. Comparisons with previously published work verify good agreement with the proposed method. The effects of the various parameters on the streamlines, isotherms, and the weighted-average heat transfer are shown graphically. It is shown that a thicker bottom solid wall clearly inhibits the temperature gradient which then leads to the thermal equilibrium case. Further, the overall heat transfer is highly affected by the presence of the solid wall. The results have possible applications in the heat-storage fluid-saturated porous systems and the applications of the high power heat transfer.