Influences of height to diameter ratios of dry-cooling tower upon thermo-flow characteristics of indirect dry cooling system

Abstract

Ambient winds may reduce the cooling efficiency of a nature draft dry-cooling tower, so it is of benefit to the design and operation of indirect dry cooling system to determine the preferred tower shape to restrain the adverse impacts of ambient winds. Based on the dry-cooling tower with vertically arranged heat exchanger bundles around the circumference, air-side flow and heat transfer models are developed for three typical height to diameter ratios of tower. The velocity, pressure and temperature fields of cooling air in the absence and presence of ambient winds are presented, and the mass flow rate, heat rejection and outlet water temperature of each sector and air-cooled heat exchangers are calculated. The results show that the dry-cooling tower with a low height to diameter ratio is superior to that with a high ratio in thermo-flow performances of indirect dry cooling system at high wind speeds on condition that the air-cooled heat exchangers have the same heat transfer surface areas. At low wind speeds, the mass flow rate and heat rejection of air-cooled heat exchanger vary little with height to diameter ratios of tower due to almost the same buoyancy forces. It is recommended to take a low height to diameter ratio of tower, especially at strong ambient winds for better thermo-flow performances of indirect dry cooling system.