Turbulent heat transfer in a flat channel with stable and unstable stratification in the flow

Abstract

This report presents an experimental study of turbulent mixed-convection 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/2 h about 44). The study covered Re from 3 × 10 3 to 8 × 10 4 and Gr q from 2 × 10 7 to 9 × 10 10. None of the available descriptions for the thermal gravity effect was in a satisfactory agreement with the test points. General relations are suggested to predict the local heat transfer in air for stable density stratification (upper wall heated), unstable stratification (bottom wall heated) and for two-side heating. Different characteristic buoyancy parameters were stated for stable and for unstable stratification, as well as a higher heat transfer rate from the upper wall for two-side heating, as compared to stable stratification for one-side heating.