The effect of superheating on the performance of floating droplet direct contact heat exchangers

A mathematical model of a single evaporating, superheated droplet is formulated and studied numerically to determine instantaneous and average heat transfer rates to the droplet at various stages of evaporation. An explicit procedure for analyzing the entire heat exchanger is then developed based upon the application of a dimensional analysis derivation of a relationship for the heat flux from the single evaporating droplet. The results of the numerical model are used to define the parameters and determine the required constants. Two operating geothermal heat exchangers are designed using this procedure. The two sites both have a moderate temperature brine and both systems utilize pentane as the working fluid. The heat exchanger vessel pressures are varied, providing a range of superheats from 19 to 52 C. The average difference between the calculated and measured total heat flux is about 16%.