Natural Convection in a Rectangular Porous Cavity With Constant Heat Flux on One Vertical Wall

1984 ◽  
Vol 106 (1) ◽  
pp. 152-157 ◽  
Author(s):  
V. Prasad ◽  
F. A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Solutions ◽  
Vertical Wall ◽  
Local Heat ◽  
Constant Heat Flux ◽  
Heated Wall ◽  
Width Ratio ◽  
Constant Heat ◽  
Nusselt Numbers

Numerical solutions for two-dimensional, steady, free convection are presented for a rectangular cavity with constant heat flux on one vertical wall, the other vertical wall being isothermally cooled. The horizontal walls are insulated. Results are presented in terms of streamlines and isotherms, local and average Nusselt numbers at the heated wall, and the local heat flux at the cooled wall. Flow patterns are observed to be quite different from those in the case of a cavity with both vertical walls at constant temperatures. Specifically, symmetry in the flow field is absent and any increase in applied heat flux is not accompanied by linearly proportional increase in the temperature on the heated wall. Also, for low Prandtl number, the heat transfer rate based upon the mean temperature difference is higher as compared to experimental results for the isothermal case. Heat transfer results, further, indicate that the average Nusselt number is correlated by a relation of the form Nu = constant Ra*mAn, where Ra* is the Rayleigh number and A the height-to-width ratio of the cavity.

Natural Convection Local Heat Transfer on Constant-Heat-Flux Inclined Surfaces

1969 ◽  
Vol 91 (4) ◽  
pp. 511-516 ◽  
Author(s):  
G. C. Vliet
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Natural Convection ◽  
Plate Theory ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Transfer Data ◽  
Inclined Surfaces

Experimental local heat transfer data are presented for natural convection on constant-heat-flux inclined surfaces using water and air. The data extend to Grz* Pr = 1016, cover angles from the vertical to 30 deg with the horizontal, and include the laminar, transition, and turbulent regimes. In the laminar regime the data correlate well with vertical plate theory when the gravitational component parallel to the surface is used. Transition is strongly affected by inclination, the transition Grz* Pr decreasing from near 1013 for vertical surfaces to approximately 108 for a surface at 30 deg to the horizontal. The turbulent local heat transfer data correlate using the actual gravity rather than the parallel component, and indicates a change in the Grz* Pr exponent from near 0 22 for a vertical surface to approximately 1/4 as the inclination decreases. The turbulent data can be correlated quite well by Nuz = 0.30(Grz* Pr)0.24.

Passive Solar Massive Wall Systems With Fins Attached on the Heated Wall and Without Glazing

2000 ◽  
Vol 122 (1) ◽  
pp. 30-34 ◽  
Author(s):  
E. Bilgen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heated Surface ◽  
Constant Heat Flux ◽  
Heated Wall ◽  
Concrete Wall ◽  
Constant Heat ◽  
Conduction Heat Transfer ◽  
Finned Surface ◽  
Passive Solar

Natural convection, radiation and conduction heat transfer in passive solar massive wall systems with fins attached to the heated surface and without glazing is experimentally studied. The system was 0.78 m high, 0.40 m wide, and 0.10 m thick concrete wall with 0.025 m long, 0.004 m thick horizontal fins made as an integral part of it and placed at 0.01 m intervals. A heat source was used to impose a constant heat flux which could be varied from about 200 to 800 W/m2. Temperatures at various points and heat flux by convection at the back were measured. Using periodicity hypothesis and various assumptions, the wall with fins was also analyzed theoretically. The results indicate that for the case considered, about 35 percent of the heat flux imposed on the finned surface goes through the system and is dissipated at the back. [S0199-6231(00)00701-2]

Non-Darcy Natural Convection in a Saturated Horizontal Porous Annulus

1988 ◽  
Vol 110 (1) ◽  
pp. 133-139 ◽  
Author(s):  
K. Muralidhar ◽  
F. A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Computational Study ◽  
Viscous Friction ◽  
Fluid Phase ◽  
Outer Wall ◽  
Constant Heat Flux ◽  
Darcy Flow ◽  
Constant Heat ◽  
Nusselt Numbers

A computational study of free convective flow and heat transfer in a saturated porous horizontal annulus is reported. Both isothermal and constant heat flux boundary conditions have been considered on the inner walls while the outer wall is held at a constant temperature. The calculation of the flow field involves consideration of non-Darcy effects, such as inertial and viscous forces, and also the variation of porosity near the walls. While the literature shows that Darcy flow model is inadequate in predicting average Nusselt numbers, the present study examines whether non-Darcy effects, and in particular the presence of the boundary, could play a significant role in explaining this discrepancy. Average Nusselt numbers have been obtained for Rayleigh–Darcy numbers from 20 to 4000 for the case of isothermal boundaries, and 20 to 20,000 for the case of constant heat flux on the inner wall. Radius ratio has been varied from 1.1 to 3. Over this range of parameters, inertia and viscous friction in the fluid phase have been found to produce a small effect on the Darcy flow. The effect of including variable porosity near a boundary is seen to produce channeling near the wall which in turn substantially increases the heat transfer coefficient.

Conjugate Heat Transfer Study of Turbulent Slot Impinging Jet

2015 ◽  
Vol 7 (4) ◽  
Author(s):  
A. Madhusudana Achari ◽  
Manab Kumar Das
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Nusselt Number ◽  
Conjugate Heat Transfer ◽  
Local Heat ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Impingement Plate ◽  
Local Heat Flux

Conjugate heat transfer in a two-dimensional, steady, incompressible, confined, turbulent slot jet impinging normally on a flat plate of finite thickness is one of the important problems as it mimics closely with industrial applications. The standard high Reynolds number two-equation k–ε eddy viscosity model has been used as the turbulence model. The turbulence intensity and the Reynolds number considered at the inlet are 2% and 15,000, respectively. The bottom face of the impingement plate is maintained at a constant temperature higher than the jet exit temperature and subjected with constant heat flux for the two cases considered in the study. The confinement plate is considered to be adiabatic. A parametric study has been done by analyzing the effect of nozzle-to-plate distance (4–8), Prandtl number of the fluid (0.1–100), thermal conductivity ratio of solid to fluid (1–1000), and impingement plate thickness (1–10) on distribution of solid–fluid interface temperature, bottom surface temperature (for constant heat flux case), local Nusselt number, and local heat flux. Effort has been given to relate the heat transfer behavior with the flow field. The crossover of distribution of local Nusselt number and local heat flux in a specified region when plotted for different nozzle-to-plate distances has been discussed. It is found that the Nusselt number distribution for different thermal conductivity ratios of solid-to-fluid and impingement plate thicknesses superimposed with each other indicating that the Nusselt number as a fluid flow property remains independent of solid plate properties.

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