Numerical Simulation of a Rain Shower Affected by Waste Energy Released from a Cooling Tower Complex in a Calm Environment

Abstract

An axisymmetric cloud model is used to investigate the evolution of convective cells and associated rain showers that develop due to the sensible and latent heat released into a calm atmosphere from an industrial cooling complex. The simulated convection is in fair agreement with observations for a particular cloud developingover a large cooling system. Sensitivity experiments were run for two different soundings to quantify how the convection and rainfall depend on the magnitude of the waste energy loss, the area of the source region, and other parameters. The major findings were the following:1 ) Without a sustained waste heat input the model convection ceased. The model convection became progressively more intense and developed more rain when the rate of total waste energy heat released from thepower station was increased. Doubling the total waste energy amount from its control case value caused a 15-fold increase in 3-h rainfall values. However, reducing the control case value of total waste energy release by 20% led to much weaker convection without rain.2) The triggering of cumulus clouds was reduced when the waste energy was released in terms of latent heat rather than sensible heat. As the relative contribution of sensible heat increased, so did the intensity of the circulation and the rainfall.3) The cloud formation depended on the area of the heat source: a wider source tended to delay and to weaken the convection. Specifically, when the area was doubled the simulated cloud appeared 2.5 min laterand the total accumulated rain after 3 h was reduced by 88%. Moreover, the maximum total kinetic energy was reduced by 26%.4) The model results were only slightly sensitive to the radial distribution of the sensible and latent heatfluxes within the source region.