HEAT-TRANSFER TO A LIQUID-SOLID MIXTURE IN A FLUME

Infrared thermography was used to study the thermal interaction between the particle-laden turbulent flow and a heated plate. Thermal streaks were observed on the heated plate, and the dimensionless mean distance LAMBDA+ between the streaks was found to increase with the Reynolds number. Introduction of polystyrene particles, within the uncertainty limits, did not change the value of LAMBDA+ in the flows with different particle volumetric loading Q(p)/Q(o). Particles generally accumulated in the warmer regions of the heated plate, i.e. in the low velocity streaks. The maximum amplitude of wall temperature fluctuations reached +/-40% of the difference between the average wall temperature and the fluid bulk temperature. Consequently, there are variations in the heat transfer coefficient of the same order. The addition of particles changed the temperature fluctuations level. The location of the maximum of the dimensionless average heat transfer coefficient alpha(p)/alpha(o) = f(Q(p)/Q(o)) depended on the Reynolds number and coincided with the location of the minimum non-dimensional RMS temperature fluctuation ratio, at the same Reynolds numbers. Many of the experimental observations are presented here on an ad hoc basis, since we do not have, at this stage, a theory which can adequately describe the wealth of experimental observations.