Abstract
Predicted and test results of a packed cooling tower are presented in this paper. The geometrical form of the air-water interface may be described as a sheet conforming to the streamlined shape of the tower packing, in contrast with jets and drops encountered in other types of towers. Tower performance is expressed in terms of its effectiveness as an energy exchanger, as compared to the performance of an infinitely high tower. The effectiveness was found to vary from approximately 0.3 at low water rates and high air rates to 0.8 at high water rates and low air rates. Experimentally determined unit conductances for diffusion vary with the 0.48 power of the gas rate, for Reynolds numbers of from 7000 to 24,000, which is in substantial agreement with published thermal-convection data for similar shapes. The height of the transfer unit (HTU) was found to vary from 3.3 to 6.3 ft, depending predominantly upon the fraction of wetted packing area and the air rate. A simple method, analogous to that employed for counterflow heat-exchanger calculations, is presented for predicting tower performance analytically. This method is based upon the integration of the energy and material-balance equations together with the rate equations, subjected to the simplification that the unit over-all conductance for thermal convection may be approximated by the product of the air-water-vapor-mixture unit-heat capacity and the unit over-all conductance for mass transfer.
