Buoyant Pulsating Exchange Flow Through a Vent

Abstract

Buoyancy-driven bidirectional pulsating exchange flow through a vent in a horizontal partition is studied experimentally using a brine/water system. The associated transient and pulsating exchange flows were studied by densimetric measurements, flow visualization, and laser Doppler velocimetry (LDV) measurements for three different vent length-to-diameter ratios: 0.106, 0.0376, and 0.008. A time scale, based on the rate of decay of the density difference between the two compartments, is developed that collapses all experimental data regarding the decay of density in the top compartment into one curve. Flow visualization was used to understand the flow features contributing to the pulsating flow and to provide a quantitative measure of the major pulsation frequency. Interfacial instability between brine and water at the vent was found to contribute to the pulsation. The pulsation frequencies and their decay were determined from the power spectrum of LDV measurements. For the small length-to-diameter ratios (0.008 and 0.0376) there are two different frequencies that decay at different rates, suggesting multiple flow processes that contribute to flow pulsations.

The Effects of Partition Thickness on Buoyant Exchange Flow Through a Horizontal Opening

“…However, they employed an axisymmetric model in which the geometry consisted of a cylinder of aspect ratio 2.0. Their results fall between the experimental data presented by Epstein [3] and those of Conover et al [4], and are also in excellent agreement with Epstein's theoretical predictions. Their results also indicated the presence of two dominant pulsation frequencies in the flow exchange.…”

“…At t ¼ 0 the temperature of the water in the upper chamber was set at 295 K and the temperature of the lower chamber was set at 320 K. This temperature matches that used by Spall and Anderson [8] and results in a density differential sufficient to create an unstable system. Resulting relevant dimensionless parameters include the density ratio Dr=r ¼ 0:9%, Gr ¼ 2.1610 7 , a densimetric Reynolds number Re ¼ 4,560, and Ra ¼ 5.2610 6 , values which are in the range of those used by Conover et al [4]. The fluid was assumed initially quiescent and therefore the velocity components were initialized to zero.…”

“…Conover et al [4] performed a detailed analysis of the pulsating flow exchange for small vent aspect ratios, L=D ( 1, using fresh water and brine as the working fluids. They determined that the flow rate is a function of aspect ratio for densimetric Reynolds numbers in the range of 1,940 Re 4,650.…”

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

“…An intermediate regime was also identified having combined characteristics of turbulent diffusion and Bernoulli flow. Brine-Water analog was also studied experimentally by Conover and Kumar [11] and Conover et al [12] studied experimentally the buoyant countercurrent exchange flow through a vented horizontal partition using a two-component laser Doppler velocimeter. Detailed measurements of velocity were made a small distance above a circular tube with an aspect ratio of 1.…”

Transient Flow of Air through Rectangular Vents in a Horizontal Partition

“…Brine-water analog was also studied experimentally by Conover and Kumar (1993), and Conover et al (1995) studied experimentally the buoyant countercurrent exchange flow through a vented horizontal partition using a two-component laser doppler velocimeter. Detailed measurements of velocity were made at a small distance above a circular tube with an aspect ratio of one.…”