Modeling of a Rotary Dry Cooling Tower

A novel design of a rotary heat exchanger to be used as a dry cooling tower is described. The heat exchanger consists of a matrix of thin steel disks which rotate between a hot water bath and a forced draft air stream. On top of the water floats a 2 cm thick layer of oil which coats the rotating disks and thus eliminates evaporation. An analytical model of the heat exchanger was developed and validated with experimental measurements taken on a 1.5 m dia test section. The model was then used to determine the net effect of the oil on the heat transfer performance. Although the oil film that coats the disks presents an additional resistance to the transfer of heat, it also contributes to the heat capacity of the disks. It was found that the reduction in the overall heat transfer rate due to the presence of the oil is small, of the order of 5 to 10 percent.