Natural convection in a vertical channel vented to the ambient through an aperture in the channel wall

Abstract

Natural convection in a one-sided-heated, vertical channel in the presence of a vent opening in the unheated wall was studied both experimentally and numerically. The experiments were performed in water ( Pr ≅ 5) for parametric variations of the interwall spacing, vent opening size, vent axial position, and wall-toambient temperature difference (Rayleigh number). For comparison purposes, baseline data were also obtained for unvented channels. The heat transfer data were supplemented by cross-channel temperature distribution measurements and by flow visualization performed using the thymol blue electrochemical technique. The numerical solutions provided information on both the local and average Nusselt numbers, cross-channel temperature profiles, and the rates of fluid flow through the opening at the bottom of the channel and through the vent. Both the experiments and the numerical solutions demonstrated that the average Nusselt numbers for the channel are insensitive to both the vent opening size and the vent axial position, for the range of operating conditions investigated. The numerical solutions showed that although the mass flow rate entering the channel through the opening at the bottom decreases in response to the presence of the vent, the total mass flow rate drawn into the channel is very little affected. The local Nusselt number distributions exhibited sharp, vent-related peaks. Excellent agreement prevailed between the experimentally and numerically determined cross-channel temperature profiles. For certain operating conditions, the flow visualization experiments revealed the existence of a recirculation zone inside the channel, adjacent to the lower edge of the vent opening.