Analysis of modified counter-flow cooling towers

Abstract

Evaporative air cooling for human comfort and other applications, whenever possible and feasible, is less expensive than conventional air conditioning. A cooling tower is used in the centralised evaporative air cooling system. In the present study, the counter-flow cooling tower is modified to pre-cool the air at the tower inlet, either by the water after the cooling load, or the tower exit air. These two modified cooling towers are modelled and their thermal performances are compared with the conventional counter-flow cooling tower. For generality, the results are presented in terms of number of transfer units (NTU), a dimensionless number for a cooling tower indicating its size. The modified cooling towers are found to be better than the conventional one in lowering the tower approaches below about 2°C. These cooling towers seem to be distinctly advantageous when operating at low approaches, small ranges and large wet-bulb depressions, thus making them quite useful in evaporative air cooling applications.