Study on heat transfer characteristics of ethane pulsating heat pipe in middle-low temperature region

A series of experiments were conducted to identify the thermal performance of an ethane pulsating heat pipe (EPHP) in middle-low temperature region (-90 degrees C to 0 degrees C). The copper EPHP with an inner diameter of 2 mm was bent to 10 turns, and the lengths of the evaporation section, condensation section, and adiabatic section were 150 mm, 150 mm, and 100 mm, respectively. Tests of the EPHP were performed with different heat inputs (HIs), inclination angles (IAs), filling ratios (FRs) and operating temperatures, so as to understand the effect of various operational parameters on the heat transfer performance. The experimental results showed that the optimal FR for the best EPHP performance was immune to the operating temperature and HI, and always remained about 30%. As the temperature of condensation section decreased from 0 degrees C to 90 degrees C, there existed the optimal temperature of -80 degrees C corresponding to the lowest thermal resistance. At different operating temperatures and HIs, the best performance of the EPHP could be achieved at about 30 degrees IA. The lower the working temperature was, the easier it was to start the EPHP at 0 degrees IA. Moreover, it was found that at relatively high HI (30-50W), the latent heat of vaporization (LHV) was the dominant property that determined the thermal performance of the EPHP. When the HI was less than 20 W, the effect of the LHV on heat transfer dwindled, and the heat transfer had a close relationship with the liquid specific heat.