Thermo-hydrodynamic performance of tubular pulsating heat pipes with integral sintered powder wicks

The untraditional copper tubular pulsating heat pipes with integral inner-wall sintered powder wicks (PHPWWs) were fabricated to improve the thermal performance of the traditional pulsating heat pipes with no wicks (PHPWNWs). An experiment was performed to investigate the start-up and quasi-steady thermo-hydrodynamic characteristics of the PHPWWs and compare them with the PHPWNWs. The results indicate that, the wicks can improve the nucleation boiling in the evaporator to enhance the thermal driving force and provide additional capillary action to facilitate the liquid backflow to the evaporator. Consequently, differing from the PHPWNWs, the PHPWWs are able to work at the horizontal orientation, and their internal fluid flow motions 'abnormally' become smoother with decreasing inclination angle from 90 degrees to 0 degrees. In addition, PHPWWs has the lower start-up and quasi-steady-operation evaporator temperature as well as better thermal performance and gravity adaptability when compared with the PHPWNWs with similar inner and outer tube diameter. The operating principle of the PHPWW, especially the driving principle of the internal fluid, is determined by the cooperation and competition between those of the traditional PHPWNW and the conventional sintered wick heat pipe, which is affected by the inclination angle and particularly the tube inner diameter.