Numerical investigation of swirl effects on a short natural draft dry cooling tower under windless and crosswind conditions

Abstract

Swirling motions have been proven to improve the thermal performance of short natural draft dry cooling towers by reducing the cold air inflow and increasing the draft speed. However, crosswind influences on the favourable swirl effects have not been investigated. To fill this gap, 3-Dimensional simulations of a short natural draft dry cooling tower are carried out. Three different locations of the swirl generator, with solid body rotation, are compared under windless and crosswind conditions. The results show that, with no wind present, introducing swirling motions right above the heat exchangers is found to be the optimal location for improving around 40% of the reduced thermal performance, which is casued by cold air inflow penetration. On the other hand, as the swirl intensity further increases after the cold air inflow is eliminated, locating it at the tower outlet performs the best on the air draft speed enhancement, and thus further increases approximately 17% of the heat transfer rate at the angular frequency input of 2s-1. In the presence of crosswind and windbreak walls, air flows through the heat exchangers and tower non-uniformly. By mounting the swirl generator right above the heat exchangers, the uniform index of the heat flux can be improved by 5% with 1s-1 angular frequency input. More importantly, inducing swirls at the tower outlet is still the optimal choice for increasing the air draft speed through the tower. With 2s-1 angular frequency input, the thermal performance of the tower can be enhanced by 11~17% in accordance with the crosswind speed.