The development of a falling cloud heat exchanger—Air and particle flow and heat transfer

Abstract

Air and particle flow and heat transfer tests for steel and alumina particles were carried out on the Falling Cloud Heat Exchanger rig at the University of Aston in Birmingham. The rig was operated up to extremes of air flow and temperature conditions. Initial tests revealed that the formation of eddy currents in the vicinity of the air entry section reduced the effective heating length and the thermal ratings of the rig. Further tests were, therefore, conducted under constant air flow conditions. The heat-transfer coefficient for steel particles was found to be greater than that for alumina. But the higher specific heat and specific surface area resulted in alumina recovering more heat per unit mass of the particles. There was some evidence of the heat-transfer coefficient increasing directly with particle concentration in the heat column. It was more pronounced for alumina. The overall effects of this need investigation. The effects of particle material and particularly the particle change due to contaminated hot gases are discussed. Suggestions for further work together with pilot plant design considerations and progress are mentioned. Included also, are the possible applications of the Falling Cloud Heat Exchanger in industries producing dusty or corrosive effluent gases.