Thermal analysis and optimization of indirect flat evaporative coolers

•Analyzing the energy and exergy performance of indirect flat evaporative coolers on the basis of a verified numerical model and experimental correlation.•Investigating the mechanism and theory of operation of indirect flat-panel evaporative coolers based on X-analysis.•Calculating the entropy production rate of the flat-plate heat exchanger of the cooler. Less attention and analysis have been given to cooling indirect evaporative coolers with different configurations and working air sources so far. This paper investigates the mechanism and theory of operation of indirect flat-panel evaporative coolers based on X-analysis. Then, based on the second law of thermodynamics analysis, the entropy production rate of the flat-plate heat exchanger of the cooler is calculated. As a result of this analysis, the optimal energy efficiency-evaporation efficiency and cooling capacity values are presented in terms of effective parameters in the design. It was concluded that dew point effectiveness and COP of the proposed system change monotonously with inlet mass flow rate, temperature and humidity ratio of primary air, respectively. The dew point effectiveness also varies monotonously with the mass flow rate ratio of secondary air to primary air. However, there exists an optimal mass flow rate ratio resulting in a maximum COP.