Energy-saving of air-cooling heat exchangers operating under wet conditions with the help of superhydrophobic coating

Abstract

The condensate retention and bridging on the airside of the heat exchanger, such as the evaporator of the heat pump and air-conditioning system, can adversely increase the pressure drop penalty and energy consumption of the heat transfer systems. The objective of this study is to minimize the airside pressure drop of the rectangular plain heat exchangers using superhydrophobic coating which promotes continuous condensate shedding through coalescence induced droplet jumping. The experiments are carried out for different inlet air temperatures (23 °C and 27 °C), relative humidities (50%, 70%, and 90%) and the fin base temperature is fixed to be 7 °C. While the frontal air velocity is varied from 0.5 to 2.5 m/s, and the fin spacing ranges from 1 mm to 4 mm. The results showed that the heat transfer rate between untreated and superhydrophobic heat exchanger is almost similar; whereas a 30–55% increase in heat transfer is observed when inlet air temperature increased from 23 °C to 27 °C and an increase of 20–50% and 60–100% in heat transfer is noticed when relative humidity increased from 50% to 70% and 90%, respectively. Due to the effective condensate removal and the early arrival of steady state, the airside pressure drop for the superhydrophobic heat exchanger is almost two times lower than that of the untreated one. The reduction in airside pressure drop led to appreciable energy saving of the heat transfer system, and it is found that 30–60% saving can be achieved especially at higher relative humidities (70% or 90%) and frontal air velocities (more than 1 m/s).