An analytical and experimentall investigation of natural convection heat transfer in vertical channels with a single obstruction

Abstract

An experimental and numerical investigation was made of laminar natural convection flow of air in a vertical channel with a single obstruction. In the experimental study, optical techniques were used to obtain measurement of both quantitative data (heat fluxes and temperatures) and qualitative data (flow visualization). Only uniform wall temperature (UWT) boundary conditions were investigated experimentally. In the numerical study, a general purpose, finite element computer code called NACHOS was used. Thermal boundary conditions, uniform wall temperature (UWT), and uniform heat flux (UHF) were investigated numerically. The experimental and numerical results were in close agreement. The results indicate that for UWT boundary conditions the presence of an obstruction reduces the average Nusselt number by 5% at a Rayleigh number of 10 4 to about 40% at a Rayleigh number of 10. It is also noted that the location of the obstruction along the wall affects the rate of heat transfer. Moving the obstruction away from the entrance towards the exit reduces the average heat transfer rate for the channel. For UHF boundary conditions, the maximum temperature (which occurs at the intersection of the top edge of the obstruction and the wall) is only 4% higher than the maximum temperature for an unobstructed channel (which occurs at the exit of the channel).