Experimental Study on Hydrogen Pulsating Heat Pipes under Different Number of Turns

The number of turns is an important geometric parameter of the pulsating heat pipe. Currently, there is no criterion for selecting the number of turns. To study the effects of the number of turns, two hydrogen closed-loop pulsating heat pipes were tested with 2 turns and 5 turns, respectively. Other parameters were kept the same. To eliminate the influence of the condenser temperature, the condenser temperature was maintained at 19 K under different heat loads. The experiments were carried out at three filling ratios, 28%, 34% and 50%, with a heat load between 0 and 5.5 W. The results show that thermal conductivities of both PHPs are in the range of 10,000 to 70,000 W/(m.K), and the thermal resistances are in the range of 0.2 to 0.8 K/W. The effective thermal conductivity of the 2-turn PHP is higher than that of the 5-turn PHP at each filling ratio. But the thermal resistance of the 2-turn PHP is larger than that of the 5-turn PHP due to the smaller heat transfer area. If the 2-turn PHP is scaled 2.5 times, which is a total of 5 turns, it will outperform the 5-turn PHP in terms of low thermal resistance and high effective conductivity.