A general mathematical model for predicting the thermal performance of natural draft dry cooling towers and extending it to three aligned towers

Abstract

ABSTRACT Natural draft dry cooling towers (NDDCTs) are the most important cooling components in steam power plants in regions with lack of water. Thermal performance of these cooling towers is highly affected by the ambient temperature and wind velocity. There have been several studies in the last few decades to estimate or measure the performance of such towers in different ambient conditions. In this study, the thermal performance of four different NDDCTs (with an only similar parameter of tower’s outlet diameter to height ratio (D/H) of around 0.5) under various ambient conditions is investigated using a recently proposed theoretical method. Results showed that the towers behave in the same way under different ambient conditions. Having a reference condition and calculating three coefficients, a simple general mathematical model is created that can predict the tower’s thermal performance for a wide range of applicable wind velocities. It is shown that the selection of the reference condition has a high effect on the error generated by the model. The range of the best reference condition for using the mathematical model is obtained to be wind velocities between 3 and 4 m/s and initial temperature difference (ITD) of more than 20°C. The proposed model is validated against other reported NDDCTs (numerical models for 0.41 < D/H < 0.63). The maximum error in heat rejection was shown to be 13%. This mathematical model is also extended to predict the performance of a three aligned NDDCTs located in Shiraz/Iran, by introducing a correction factor.