A BOUNDARY-LAYER ANALYSIS OF COMBINED HEAT AND MASS-TRANSFER BY NATURAL-CONVECTION FROM A CONCENTRATED SOURCE IN A SATURATED POROUS-MEDIUM

A boundary layer analysis was carried out to investigate the coupled p henomena of heat and mass transfer by natural convection from concentr ated heat and mass sources embedded in saturated porous media. Both li ne and point source problems were treated. The boundary layer equation s based on Darcy's law and Boussinesq approximation were solved by mea ns of similarity transformation to obtain the details of velocity, tem perature and concentration distributions above a concentrated heat sou rce. Two important parameters, namely the Lewis number Le and the buoy ancy ratio N were identified to conduct a series of numerical integrat ions. For the case of small Le, a substance diffuses further away from the plume centerline, such that the mass transfer influences both vel ocity and temperature profiles over a wide range. For large Le, on the other hand, the substance diffuses within a narrow range along the ce nterline. Naturally, the influence of mass transfer is limited to the level of the centerline velocity, so that a peaky velocity profile app ears for positive N whereas a velocity defect emerges along the center line for negative N. For such cases of large Let the temperature profi les are found to be fairly insensitive to Le.