Plume Dynamics in Convective Air Flows by Combined PIT/PIV

Abstract

Tracer particles of thermochromic liquid crystals, which change their color according to the surrounding temperature, enable simultaneous temperature and velocity field measurements and allow for studies of dynamic processes in convective flows (Dabiri, 2009). As opposed to previous studies, which focus on flows of liquids, we employ these tracers for measurements in air flows. We present the cornerstones of the combined PIV / PIT measurement technique, which we advanced to flow measurements in air. The technique is applied to mixed convection in a cuboidal sample, where it is used to capture thermal structures close above the heating plate. Four different parameter combinations of Ra, Re and Ar are considered. The fingerprints of the thermal plumes, which emerge from the thermal boundary layer, are well resolved in the measurement plane. Using an image rate of 4 Hz, the plume dynamics were captured time resolved as well. The probability density functions of the temperatures in the measurement plane reveal a bimodal distribution, which allows for a discrimination of the thermal background from the plumes. The velocity PDFs reveal a flow reversal in the measurement plane between Ar = 1.8 and Ar = 3.1.