Fractal Study On Convective Heat Transfer Coefficient In Porous Media

Porous media has good heat storage and heat exchanging performance and it is widely used inchemical industry, environmental protection, metallurgy, building materials, mining and many otherindustrial processes. Thus, efficient heat recovery and strengthening heat transfer in porous mediahas always been the hotspot in recent years. And to obtain the accurate and widely applicableconvective heat transfer coefficient in porous media has been the main task and the core of theresearch. Based on the research at home and abroad in recent years, it found that convective heattransfer coefficient in porous media is mainly obtained by experimental and numerical simulationmethod. Zheng Kuncan established the porous media pipe model and derived the convective heattransfer coefficient according to the fractal theory. It found that the criterion equation of the Nusseltnumber is closed to the form which fluid sweeps sphere.In order to get the accurate and widely applicable convective heat transfer coefficient of porousmedia and check if the inside flow of porous media is closer to the flow around a body, weestablished the porous media streaming and pore-throat model based on fractal theory and derivedthe convective heat transfer coefficient of the two models. The results were compared withtraditional―Wakao and Kaguei‖equation and the applicable scope was determined.For streaming model, fractal solution is in accordance with the traditional solution in the rangeof Reynolds number from103to105, Prandtl number from0.5to15, porosity from0.39to0.49andtemperature less than1200K and their maximum relative deviation is less than20%. For pore-throatmodel, fractal solution is in accordance with the traditional solution in the range of Reynoldsnumber from103to7.6×104, Prandtl number from0.5to55and their maximum relative deviationis less than20%. The influence of porosity and temperature is little. Besides, comparing the fractalsolution and the traditional solution, we found that fractal solution is higher than traditional solutionin low Reynolds number. With the increase of Reynolds number, the difference between fractalsolution and traditional solution first decrease then increase. Fractal solution is lower than traditionalsolution in high Reynolds number. In addition, seven sizes porous medium were selected and some classical traditional solutionwere compared and calculated with the fractal solution. Water was selected as the fluid and theeffects of equivalent diameter, porosity and Reynolds number were considered. We got the graph ofNusselt number and analyzed when these solutions can replace each other and how much is thedifference between them.