TURBULENT HEAT-TRANSFER IN A FLAT CHANNEL WITH STABLE AND UNSTABLE STRATIFICATION IN THE FLOW

This report presents an experimental study of turbulent mixed-convecti on heat exchange in a flat horizontal channel with a ratio of height h to width b of about 1:10, and with length about 4 m (x/2h about 44). The study covered Re from 3 x 10(3) to 8 x 10(4) and Gr(q) from 2 x 10 (7) to 9 x 10(10). None of the available descriptions for the thermal gravity effect was in a satisfactory agreement with the test points. G eneral relations are suggested to predict the local heat transfer in a ir for stable density stratification (upper wall heated), unstable str atification (bottom wall heated) and for two-side heating. Different c haracteristic buoyancy parameters were stated for stable and for unsta ble stratification, as well as a higher heat transfer rate from the up per wall for two-side heating, as compared to stable stratification fo r one-side heating.