Natural Convection From a Heat Source in a Top-Vented Enclosure

Natural convection from a heated disk situated at the bottom of a top-vented enclosure was studied experimentally. The experiments were performed in water (Pr ≅ 5) for parametric variations of the vent opening size, inner enclosure height, and disk-to-enclosure-wall tempearture difference (Rayleigh number). For comparison purposes, baseline data were obtained for an unvented enclosure and for the “infinite” case (no enclosure). The heat transfer data were supplemented by cross-vent temperature measurements and by flow visualization using the thymol-blue electrochemical technique. The experiments demonstrated that, for the range of parameters considered, the average Nusselt numbers could be correlated using a single correlation to within 8 percent. It was also found that the presence of the enclosure (vented or unvented) acted to reduce the Nusselt number, especially at the lower Rayleigh numbers. Flow visualization experiments revealed an unstable flow pattern in the vicinity of the vent that fluctuated in a nonperiodic manner between four basic modes. Temperature measurements revealed asymmetric mean cross-vent temperature profiles, with the mean temperature level increasing with decreasing vent size. The intensity of the temperature fluctuations in the vent opening also increased with decreasing vent size.