Thermal characteristics of an alumunum closed-loop pulsating heat pipe charged with ammonia

Abstract

Pulsating heat pipe is a two-phase heat transfer device that uses pulsating motion to transfer heat from a source and passively move it to a condenser or radiator. In the recent past, many researches have been carried out on Pulsating Heat Pipes (PHPs) to enhance heat transfer through passive two-phase heat transfer mechanism. Although a complete theoretical understanding of operational characteristics of this device is not yet achieved, there are many emerging applications, ranging from electronics thermal management to compact heat exchangers. For a better theoretical understanding, it is vital to generate experimental data under various operating boundary conditions. In this background, this study aims for thermal analysis of a closed loop pulsating heat pipe based on heat input, inclination, fill ratio. So, a closed loop pulsating heat pipe is designed and fabricated with Aluminium. This closed loop Aluminium PHP with ammonia as working fluid is experimentally investigated for variable varying inclination and fill ratios. The experimental apparatus consists of a 8.862m long 3mm inner diameter closed loop Aluminum pipe meandering back and forth into an electrically heated block of Aluminum. One end of the PHPs is inserted inside the heater and the other end of it is placed in air. Heat transfer characteristics of PHPs are determined experimentally, based on the heat transfer principles. Response curves in terms of heat transfer rate, heat transfer coefficient and thermal resistance are obtained for different inclinations and liquid ammonia fill ratios. The overall heat transfer coefficient and thermal resistance of the system is determined to show the heat transfer capability of the PHP. The results show that, the performance of the heat pipe varies substantially for different inclinations and fill ratios.