Understanding the transient behavior of the dew point evaporative cooler from the first and second law of thermodynamics

Owing to its high energy efficiency without using greenhouse gases, dew point evaporative cooling offers a desired solution for thermal management of electronic and electrical devices. This paper elucidates the transient behavior of a dew point evaporative cooler and its significant influence on the dynamic cooling performance. A large time constant (400 s) of the product air temperature was observed under a zero-state response, leading to a pronounced deviation of the time-average cooling performance below its steady state by 13.8%–26.4% over a long period (2500 s). To capture this phenomenon, a modified transient lumped parameter model and a new partial differential exergy model were developed. An air mixing process in the dry channel was identified to account for the slow cooler's transient responses. A detailed exergy analysis revealed that the specific exergy destruction at the dry channel entrance was above 400 W/kg, owing to the air mixing. This finding demonstrates that the transient behavior should be judiciously considered in the cooler design and optimization, together with the steady-state performance. Accordingly, a detailed sensitivity analysis of the cooler's objective variables is proposed to gain insights into the future improvement of the dew point evaporative cooler.