Theoretical and experimental investigations on horizontal heat pipe heat exchangers using a composite wick structure for heat recovery in air-conditioning systems

Abstract

The literature review indicates that, though water has a good figure of merit, very limited information is available on the use of water as the working fluid in a horizontal heat pipe heat exchanger for air conditioning applications. This article investigates theoretical and experimental analyses of horizontal heat pipe heat exchangers for air conditioning applications using distilled water as the working fluid. This heat pipe heat exchanger study consists of 20 copper tubes of 9.5 mm outside diameter arranged in two rows with a 0.3 m evaporator length, a 0.3 m condenser length, a 0.05 m adiabatic length, and 12 fins per inch of aluminum plate fins. A comparative analysis is studied for two configurations of heat pipe heat exchangers. The first configuration of heat pipe heat exchanger consists of a single wick structure with two layers of 180 mesh of phosphor bronze wire mesh, and, in the second configuration, the heat pipe heat exchanger consists of a composite wick structure (two layers of 180 mesh and two layers of 60 mesh of phosphor bronze wire mesh). The investigations are performed only for sensible heat recovery between outdoor and return air. The experimental investigations are performed by varying the outdoor air dry bulb temperature in the range of 24°C to 40°C and return air dry bulb temperature in the range of 20°C to 24°C. The present study reveals that the amount of heat recovered by a heat pipe heat exchanger with a composite wick structure is 56% better than a heat pipe heat exchanger with a single wick structure at a higher velocity of 2.4 m/s and further improves to 88% at a lower velocity of 0.6 m/s.