Natural Convection Boundary Layers Adjacent to Heated Vertical Surfaces with Fluid Injection.

Abstract

The characteristics of boundary layers adjacent to heated vertical surfaces from which a fluid, different from that in the boundary layer, is being emitted, were studied. The values of the temperature, velocity, and concentration distributions were measured in boundary layers adjacent to heated polymethyl methacrylate (PMMA) and wood (Southern Pine) surfaces, and next to a sintered bronze plate through which propane was injected. The temperature and velocity were measured using thermocouple probes and flow visualization techniques, respectively. In order to measure the concentration of the vapor which issues from the surfaces, a heterodyne holographic interferometric technique was developed. The results of the heterodyne holographic interferometry measurements together with the data provided by the thermocouple measurements yielded the concentration of vapors in the boundary layer, for vapors emitted from PMMA, Southern Pine, or propane injected through the sintered bronze plate. The temperature, velocity, and concentration were measured as functions of position and time in the boundary layer. A model was also developed for calculating the temperature, velocity, and concentration distributions. The model was based on the conservation of mass, momentum, energy, and specie concentration and allows both the surface temperature and the velocity of the vapor leaving the surface to vary with position on the surface and time. The model also takes into account the variation of the properties with temperature. Solutions to the equations were obtained by a numerical procedure utilizing an explicit finite-difference method. A comparison was made between the measured and calculated temperature, velocity, and concentration distributions. The agreement between the calculated and measured values was generally good and was within the experimental uncertainty.