Experimental study on thermal performance of an anti-gravity pulsating heat pipe and its application on heat recovery utilization

Abstract

A series of experimental studies are conducted to investigate the thermal performance of a pulsating heat pipe (PHP) under anti-gravity operation. The working fluid in the PHP is methanol and the Bond number of these experiments ranges from 0.833 to 1.068. Via the comparison between the performance of the anti-gravity PHP and a gravity-assisted one under different working conditions, the effects of gravity, heat load, filling ratio, number of turns and length of each section on the thermal performance of the anti-gravity PHP are discussed and analyzed. The experimental results indicate that an anti-gravity PHP always experiences a longer start-up process, exhibits more intense quasi-steady temperature oscillations and has a greater thermal resistance, implying that gravity plays an important positive role in the thermal performance of the PHP. For a given heat load, increasing the number of turns and the length of each section of the anti-gravity PHP can both lead to more intense temperature oscillation among the PHP but result in better and worse thermal performance of the PHP, respectively. The optimum filling ratio for the heat transfer performance of the anti-gravity pulsating heat pipe is approximately 70%. In addition, with the increasing heat load, the effect of other operational parameters on the thermal performance of the anti-gravity PHP can be weakened. Accordingly, a conceptual apparatus for utilization of the anti-gravity PHP for waste heat recovery from the high-temperature exhaust to preheat the low-temperature fuel is developed and tested with the Bond number of 0.902. Compared to the conventional pure copper heat transfer medium, the anti-gravity PHP shows much better heat recovery capacity, which verifies the great potential of an anti-gravity PHP for heat recovery utilization.