Thermal performance analysis of closed wet cooling towers under both unsaturated and supersaturated conditions

A closed wet cooling tower (CWCT) can be regarded as a cooling tower with the packing replaced by a bank of tubes. The heat and mass transfer in CWCT has been little investigated under supersaturated condition. The governing equations for heat and mass transfer in CWCT under both unsaturated and supersaturated conditions were derived based on Poppe method. Based on a sectional method, two analytical models were proposed and a program was coded to investigate the thermal performance by automatically selecting the corresponding governing equations whether the air was supersaturated or not. The results show that the air temperature, humidity ratio and enthalpy distributions under both unsaturated and supersaturated conditions could be accurately predicted with the analytical models. Then the effect of degree of saturation of inlet air on the heat transfer rate and process-water outlet temperature was presented, and little difference was found between the unsaturated and supersaturated conditions if the outlet air was supersaturated.