Experimental investigation of a serial-parallel configuration helium pulsating heat pipe

Abstract

Cryogenic pulsating heat pipe with the features of exceptional heat transfer performance and easy manufacturing is a good candidate to effectively transfer the cooling power energy in the conduction-cooled superconducting magnet system. In this work, a new type of serial-parallel 24-turn configuration pulsating heat pipe with helium as working fluid has been investigated experimentally under various working conditions by changing heat loads, inclination angles, and filling ratios. Experimental results demonstrate that for this pulsating heat pipe, working in vertical orientation is more appropriate. Additionally, the optimum filling ratio changes with the heat load input. The maximum effective thermal conductivity is 12357 W/(m∙K), obtained at the inclination angle of 90° and the filling ratio of 66.1%. The new configuration demonstrates high thermal performance well above the critical point of helium. At the filling ratio of 94.2% and the vertical position, this pulsating heat pipe can transport up to 25 W heat load without reaching dry-out occurrence. The influences of the number of turns and tube structure are discussed by comparing the serial-parallel 24-turn helium pulsating heat pipe with the 4-turn helium pulsating heat pipe and the serial 24-turn helium pulsating heat pipe with the same dimensions we tested previously. The result shows that the serial-parallel 24-turn helium pulsating heat pipe is more efficient concerning heat transfer capacity and thermal resistance. Increasing the number of turns can reduce the temperature gradient of the helium pulsating heat pipe, and changing the tube structure from series to series–parallel can greatly improve the heat transfer limit of the helium pulsating heat pipe. Moreover, another novel parallel 24-turn helium pulsating heat pipe is proposed. According to the theoretical analysis, The parallel 24-turn helium pulsating heat pipe could reach a higher maximum effective thermal conductivity, whereas the serial-parallel 24-turn helium pulsating heat pipe is outstanding in heat transfer capacity.