The augmentation of the heat recovery by using evaporative cooling in HVAC applications: Experimental study

Abstract

An experimental study was conducted to investigate the impact of evaporative cooling on heat recovery within HVAC systems. This study involved the development of a specialized test rig comprising two air passages connected by a wickless heat pipe heat exchanger (wickless HPHE). Additionally, an evaporative cooling pad was integrated into the cold air return duct. The evaporative cooling process effectively lowered the temperature of the cold air, which was subsequently directed through the wickless HPHE condenser. This occurred at a variable mass flow rate ratio, in contrast to the constant mass flow rate of warm air passing through the wickless HPHE evaporator section. The study encompassed a range of mass flowrate ratios, specifically 1, 1.5, and 2. The thermosiphon heat pipe was charged with acetone at a 60 % filling ratio. The results clearly demonstrated that evaporative cooling played a pivotal role in enhancing the heat exchanger's performance. Notably, the temperature differential observed in the wickless HPHE evaporator surpassed that in the HPHE condenser, primarily due to the influence of evaporative cooling. The highest temperature difference recorded in the HPHE evaporator was 17.8 °C, indicative of the most substantial heat recovery achieved. Importantly, the effect of evaporative cooling significantly improved the performance of the wickless HPHE by more than 48 %.