A Numerical Analysis of the Local Anomalies in a Natural-Draft Cooling Tower

Abstract

This paper presents experimental and numerical analyses of the aero-thermodynamic characteristics of a natural-draft cooling tower. The influence of local technical faults in the fill and rain region on the cooling tower's performance was estimated. Measurements of the air velocity and the temperature above the droplet eliminators showed a noticeable non-uniformity of both parameters. This is caused by a non-uniform airflow resistance and heat-transfer rate within the fill and rain region. Based on these measurements, a commercial CFD model was customized with additional relations describing the heat- and mass-transfer, as well as the airflow resistance in individual regions of the cooling tower. The results of a 3D numerical simulation of the cooling tower are the temperature and velocity distributions within the entire cooling tower. A comparison of nominal and actual cooling tower operation shows regions with unfavorable air temperatures or velocities. Thus, the inefficiently operating areas of the cooling tower's cross-section can be identified. These areas cause non-homogeneous aero-thermodynamic characteristics and have an influence on the integral characteristics of the cooling tower. A sample calculation of an actual cooling tower shows the usefulness of the method when it comes to improving the cooling tower's performance. The improvement can be achieved by modifying the fill resistance and water distribution.