Performance Analyses of Counter-Flow Closed Wet Cooling Towers Based on a Simplified Calculation Method

Abstract

Abstract:As one of the most widely used units in water cooling systems, the closed wet cooling towers (CWCTs) have two typical counter-flow constructions, in which the spray water flows from the top to the bottom, and the moist air and cooling water flow in the opposite direction vertically (parallel) or horizontally (cross), respectively. This study aims to present a simplified calculation method for conveniently and accurately analyzing the thermal performance of the two types of counter-flow CWCTs, viz. the parallel counter-flow CWCT (PCFCWCT) and the cross counter-flow CWCT (CCFCWCT). A simplified cooling capacity model that just includes two characteristic parameters is developed. The Levenberg-Marquardt method is employed to determine the model parameters by curve fitting of experimental data. Based on the proposed model, the predicted outlet temperatures of the process water are compared with the measurements of a PCFCWCT and a CCFCWCT, respectively, reported in the literature. The results indicate that the predicted values agree well with the experimental data in previous studies. The maximum absolute errors in predicting the process water outlet temperatures are 0.20 and 0.24 • C for the PCFCWCT and CCFCWCT, respectively. These results indicate that the simplified method is reliable for performance prediction of counter-flow CWCTs. Although the flow patterns of the two towers are different, the variation trends of thermal performance are similar to each other under various operating conditions. The inlet air wet-bulb temperature, inlet cooling water temperature, air flow rate, and cooling water flow rate are crucial for determining the cooling capacity of a counter-flow CWCT, while the cooling tower effectiveness is mainly determined by the flow rates of air and cooling water. Compared with the CCFCWCT, the PCFCWCT is much more applicable in a large-scale cooling water system, and the superiority would be amplified when the scale of water distribution system increases. Without multiple iterative calculations and extensive experimental data, the simplified method could be used to effectively analyze the thermal performance of counter-flow CWCTs in operation. It is useful for optimization operation of counter-flow CWCTs such that to improve the energy efficiency of the overall cooling water system.

Modeling and Optimization of a CoolingTower-Assisted Heat Pump System

“…The cooling tower model follows our recent work [19], which is a modification of the work conducted by Pascal Stabat and Dominique Marchio [20]. The cooling capacity of a closed wet cooling tower under the counter-flow condition is simply given by [19]: Figure 1.…”

“…The cooling capacity of a closed wet cooling tower under the counter-flow condition is simply given by [19]: Figure 1. Schematic diagram of the CTAHP system under cooling conditions.…”

“…The cooling capacity of a closed wet cooling tower under the counter-flow condition is simply given by [19]: The speeds of pumps and fan can be controlled to improve the whole system's performance. The power consumptions of the condenser water pump and fan are influenced by the mass flow rates of the condenser water and air, which are given, respectively, by [18,21]:…”

“…The temperature difference between the inlet and outlet condenser water of tower is usually not greater than 5 • C, which can be expressed as [19]:…”

“…Spray water pump power consumption of 0.150 kW could provide a large enough spray water flow to ensure the external surfaces of the heat exchanger in the tower was fully wetted by the spray water. When the spray water moistened all the surfaces, the effect of the variation of spray water flow rate on the thermal performance of the cooling tower unit could be neglected [19,28]. Thus, the power consumption of the spray pump was selected as 0.150 kW for the following analysis.…”