Heat transfer enhancement by filling metal porous medium in central area of tubes

摘要

Given that the fluid within the tubes of some industrial heat exchangers is under a state of fully developed laminar flow with a constant Nu number, increasing the surface area for heat transfer will significantly increase the flow resistance. In this paper, we filled metal porous medium with high thermal conductivity, high porosity and high filling radius in the central area of fully developed laminar flow within the tube, and established corresponding numerical models for fluid flow and heat transfer. Numerical simulation results indicate that after filling the tube with metal porous medium, the temperature profiles within the porous medium area are very uniform, and the temperature difference between the tube wall and the fluid decreases significantly which correspondingly results in a notable increase of Nu number; meanwhile, the characteristic of flow field redistribution occurs within the enhanced tube, but the total flow resistance composed of the Darcy resistance and inertial resistance of the porous medium area and the shear stress caused by velocity gradient and fluid viscosity of the non-porous medium area near the wall increase; correspondingly, the performance evaluation criteria (PEC) value is thus applied to evaluate the effect of the heat tranfer enhancement method. For a tube of 9 mm in radius, the PEC values are all above 1 when the filling radius of the metal porous medium is larger than 7 mm.