LDV study of a buoyant exchange flow through a vertical tube

The buoyant countercurrent exchange flow through a vertical tube in a horizontal partition of an enclosure was measured by densimetry and laser Doppler velocimetry. In this study, brine and water were used as the two fluids, and the length of diameter ratio of the vent tube was one. Unsteady mixing was observed inside the vent tube, and the less dense water rose in a plume from the vent into the brine in the upper compartment. An equation for exchange flow rate over time was developed based on densimetric measurements, and the flow coefficient was found to be a constant. A two-component forward-scatter laser Doppler velocimetry (LDV) system was configured to study the flow. A motorized X-Y positioning system was built to move the LDV measuring volume efficiently through a horizontal cross section of the water plume. Volumetric flow estimated from the integral of positive velocity measured throughout a plane cross section of the plume was about 1.77 times the exchange flow.