Enhanced thermal efficiency in crossflow evaporative cooling systems: A comparative study of materials and flow patterns

The performance of crossflow evaporative cooling systems can be significantly influenced by a well-designed airflow and water distribution pattern, along with highly absorbent heat and mass exchange materials in the wet channels. This study presents a comprehensive numerical and experimental analysis of three different design variants of crossflow evaporative heat and mass exchangers: (i). DV1: Aluminum-cotton cloth channels with a zig-zag airflow pattern, (ii). DV2: Polypropylene-nonwoven fabric channels with a center-line airflow pattern, and (iii). DV3: Polypropylene-nonwoven fabric channels with an extreme-side airflow pattern. The aim is to examine the thermal and mass transfer properties of different geometric and operational configurations of HMX, especially those incorporating cost-effective and high-efficiency materials, and their effect on system performance. Initially, a detailed numerical analysis is performed to determine the heat and mass characteristics of the three design variants, evaluating the air temperature, relative humidity, and evaporation rates on a unit channel basis. Based on the numerical assessment, prototypes for each design are developed with unit channel (a dry sub-channel overlapped with two wet sub-channels) of size 8000 mm3 for detailed experimentation under a wide range of actual operating conditions. The results at the unit channel revealed that the overall performance of DV2 and DV3 is better compared to DV1, mainly due to the high wettability maintained by the non-woven fabric in the wet channels. Moreover, DV2 and DV3 achieved a maximum air temperature reduction of about 7 °C and 6.7 °C, respectively. The maximum cooling capacity and COP achieved 398.62 W and 4.2, respectively, whereas the wet-bulb and dew-point effectiveness varied from 0.11 to 0.3, and 0.08 to 0.23, respectively. Thus, it is apparent that appropriate material selection with high wettability and suitable air-water flow patterns can significantly enhance evaporative cooling to ensure efficient thermal comfort.