Direct Contact Evaporation Process for Recovery of Waste Heat

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The direct contact evaporation process of dispersed low boiling-point liquid within immiscible hot water is prospective for industrial use to recover waste heat from hot water. This study aims at pursuing heat transfer characteristics in a direct contact evaporation column.Boiling characteristics of refrigerant R113 injected as the dispersed phase into hot water flowing upwards in a vertical test column at atmospheric pressure are investigated by photographic observation of the flow pattern and by measurement of the local flow and heat transfer behavior with the aid of the multi probe void meter developed for this work.Heat transfer characteristics are strongly influenced by the boiling regime just near the nozzle. An increase in the inlet temperature of water and R113, and an increase in the nozzle Reynolds number promote the rate of evaporation and the bubble coalescence. As a result, the boiling regime near the nozzle changes from the unstable, stable, to column-like ones and the heat transfer is improved in this order. In the column-like regime where the highest performance is attained, heat transfer coefficient is influenced by the mass velocity of liquid R113 and the temperature driving force and not by the inlet temperature of R113 and the nozzle Reynolds number. Volumetric heat transfer coefficients, local and also average over the column, are correlated in terms of those two influencing parameters.