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

Abstract

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.

Effect of vent aspect ratio on unsteady laminar buoyant flow through rectangular vents in large enclosures

“…This is the only flow reversal that occurs in this flow regime. Such a phenomenon has also seen by Myrum [17]. He conducted an experimental study to find the effect of vent size and Ra on natural convection heat transfer from a heated disk.…”

“…Although a direct comparison cannot be made of the current study and Myrum's Myrum [17], the time history of heat transfer along with numerical flow visualization reveal mode III. At the time of this change in direction near s = 8 as discussed above, the exchange flow rate decreases drastically with corresponding decrease in heat transfer across the vent as seen in Figs.…”

“…Myrum [17] conducted heat transfer experiments using water in a top-vented enclosure heated by a disk on the enclosure floor. He observed four modes of flow, which were unstable and oscillated randomly from one to the next.…”

Transient Flow of Air through Rectangular Vents in a Horizontal Partition

“…Such a phenomenon was also seen by Myrum (1990). He conducted an experimental study to find the effect of vent size and Ra on natural convection heat transfer from a heated disk.…”

“…Tan and Jaluria (1992) and Jaluria et al (1993) studied the cases where the vent flow was governed by both pressure and density differences across the vent. Myrum (1990) conducted heat transfer experiments using water in a top-vented enclosure heated by a disk on the enclosure floor. He observed four modes of flow, which were unstable and oscillated randomly from one to the next.…”