The performance and model of porous materials in the indirect evaporative cooling system: A review

Abstract

Evaporative cooling has been widely used due to its environment-friendly characteristic of cooling air by water evaporation. Nowadays, there are two common forms of evaporative cooling: indirect evaporative cooling (IEC) and dew point evaporative cooling (DPEC). While, the heat-moisture migration in the wet surface composed of porous materials is an important factor that affecting the heat and mass transfer of IEC. Therefore, the application of porous materials in IEC has been reviewed in this paper. Firstly, a comprehensive classification of the porous materials used in the IEC was introduced, which could be divided into porous ceramics and fibers. Porous ceramics had the function of storing water, and the fiber in the form of composite membranes was the current research hotspot. Then, by referring theoretical analysis and experimental research, the structural parameters (Porosity, Specific surface, Tortuosity) and characteristic parameters (Wicking height, Diffusivity, Evaporation rate) of porous materials were introduced in detail, which could be used as important indicators for selecting suitable porous materials. Since the heat and mass transfer process brought by the unique porous structure was quite complicated, the heat and mass transfer model of porous materials in IEC could be simplified. Based on the spray water flow, the theoretical research of the IEC mathematical model can be summarized into three situations. Among them, moderate water spray had the best cooling capacity for IEC, and could predict the temperature change of the water film surface well. Finally, four future research directions based on the characteristics of porous materials were also proposed in this paper. The aim of this paper is to provide a reference for the field of IEC.