Flow visualisation of natural convection around a heated vertical plate using background oriented schlieren

This study employed the background oriented schlieren (BOS) technique to visualise and quantify natural convection flow around a heated vertical plate. The BOS system comprised a camera, a heated plate, and a background image. The surface temperature of the vertical plate was set to 75, 100, 125, and 150°C, and natural convection was observed under ambient conditions. The recorded images were processed using a probabilistic optical flow algorithm to calculate pixel displacements and derive the velocity field, which was then calibrated by comparison with two-dimensional computational fluid dynamics (CFD) simulations of the same geometry and conditions. BOS successfully reproduced the velocity distribution in the high-temperature, high-speed core region, agreeing with CFD results within approximately 10% for peak velocity. However, in low-velocity and stagnant flow regions near the plate edges, minimal refractive index changes limited accurate velocity detection. These findings demonstrate the potential for extending BOS applications to thermal-fluid system monitoring and leak detection.