Computation fluid dynamics modelling of low cost, wind-driven fan pad evaporative cooling

The performance of evaporative cooling devices is driven by airflow properties. Evaporative cooling devices such as “EvaKuula” stand at about 1 m from the ground. The wind speeds at this height may not be enough to drive the EvaKuula fan, typically installed to move air through the device. We hypothesize that the desired cooling effect of the evaporative cooler can be achieved without the fan. We tested the hypothesis by examining mass, energy and momentum transfer between air and water in the context of milk freshness preservation. We used computational fluid dynamics (CFD) modeling under steady-state conditions. Experiments were also conducted to validate the model. Temperature and relative humidity predicted by the model agreed with the measured values with prediction errors below 10% for any time in the day. Results suggested that the temperature and relative humidity in the cooler at a given time of the day were not different under static and rotating fan conditions. However, by doubling the maximum speed (80 rpm) or increasing it further (160 rev/min), the exit velocity of the air increased but did not affect the temperature and humidity distribution in the cooler. Increase in the air exit velocity increased convective heat transfer, increasing the cooling rate. However, the cooling rate did not influence the final temperature of the air/water inside the cooler.