A study on thermal performance of parallel connected pulsating heat pipe

A series of experiments were performed to investigate thermal performance of single, parallel connected and two turns pulsating heat pipe (PHP) using different working fluids. The copper capillary tube was used which has internal and external diameter 2.2 mm and 3.2 mm respectively. The PHP was filled with ethanol and deionized (DI) as working fluids with filling ratio 50%. Theoretical thermal resistance of parallel connected PHP was obtained using the experimental results of single turn PHP. DI water needs more input power to vaporize and startup than ethanol because boiling temperature and specific heat of DI water are larger than that of ethanol. At low input power, temperature of the PHP filled with DI water was not oscillated which means the device operates as thermosyphon. But temperature of the PHP filled with ethanol fluctuated at low input power which means liquid slug and vapor plug moves inside of the device. Thus, thermal resistance of the PHP filled with ethanol is lower than DI water which means ethanol is preferred as working fluid. Parallel connected pulsating heat pipe shows better thermal performance than two turns one from 42 W to 50 W for both working fluids because the effect of pressure drop is larger than the effect of increased perturbation.