Numerical investigation of a novel tubular dew-point evaporative cooler

Abstract

Dew-point evaporative cooling can efficiently bring down the air temperature to near dew point through water evaporation. Most dew-point evaporative coolers employing conventional plate type configurations have approached their limit and leveled off. To further improve the performance of dew-point evaporative cooling, a novel counter-flow tubular architecture is proposed in this paper. Based on the momentum, energy and mass balances, a rotating axisymmetric mathematical model is established for the new cooler. The heat and mass transfer process in the cooler is analyzed and compared with that of a conventional plate-type cooler. The cooling intensity, evaporation intensity and convective heat and mass transfer coefficient are discussed to elucidate the advanced cooling behavior of a tubular cooler. The results show that: (1) for ambient air with 30.0–38.0 ℃ temperature and 12.0–20.0 g/kg humidity, the product air temperature of a tube-type dew-point evaporative cooler is 1.6–3.0 ℃ lower than that of a plate-type, and the dew-point effectiveness is 0.18 higher; (2) the working air of the tubular cooler reaches humidity saturation at 0.05 m after entering the wet channel, which is significantly shorter than the plate structure by 0.25 m; (3) in the tubular wet channel, the channel length that achieves active cooling is longer than that of a plate-type cooler, and its convective heat and mass transfer coefficient are above 150 W/(m2·K) and 0.04 m/s respectively, i.e., 30 W/(m2·K) higher and 2.7 times to the plate-type cooler.