Heat transfer correlations and pressure drop dynamics of palm fibre wetting media for evaporative cooling at different air flow rates

Abstract

The thermal and flow resistance properties of wetting pads play a key role in how effective direct evaporative cooling (DEC) systems Perform. To make an informed decision, it's crucial to study the heat transfer properties and airflow resistance manifested in pressure drop for various types of wetting media. An experimental study was conducted to determine pressure drop and heat transfer correlation constants at three airflow rates for palm fruit mesocarp fibres (PFMF) wetting media. Heat transfer and pressure drop equations were fitted with generated data to obtain correlation constants. The wetting media were effective to lower the ambient temperature at an average depression of 6.6 to 8.2 °C and increase the relative humidity of the inlet air at an average value of 25.54 to 39.32%. PFMF had a low-pressure drop per unit length, ranging from 5.29 to 7.62 Pa/m, which makes it an appealing alternative to other wetting media. New correlation constants generated for pressure drop and heat transfer data fit well with high coefficient of determination (R2) values. The average cooling efficiency ranged from 56.43 to 65.27%, while the average Merkel number was 0.16 to 0.19. The Nusselt number increased with the Reynolds number and showed a laminar flow. Amaranths stored in DEC produced respiratory heat ranging from 290.86 to 336.53 mg/kg/h for all air velocities. Considering the respiratory rate within the range of cooler temperatures, it is recommended to use the DEC only for short periods or for pre-cooling of vegetable storage.