Flow visualization of natural convection in vertical channels with opposing buoyancy forces

Natural convection inside an asymmetrically, isothermally heated vertical channel with opposing buoyancy forces was studied with flow visualization and laser interferometry. Opposing buoyancy forces occur inside the channel when the hot wall is warmer than the ambient temperature and the cold wall is cooler than the ambient. These opposing buoyancy forces can cause flow instability inside the channel. The flow- and temperature-fields are of interest for validation of numerical modelling. The flow-field was obtained with flow visualization using a laser sheet and a Dräger tube, which supplied the aerosol. The temperature-field was obtained using a Mach-Zehnder interferometer. Experiments were carried out over a range of temperature ratios between −0.25 and −0.75 using aspect ratios between 13.2 and 26.4. These conditions provided a modified Rayleigh number range of approximately 5-215. Flow- and temperature-field photographs were taken ranging from steady laminar to unsteady turbulent flow.