Study on Circulation Flow in Closed Loop Pulsating Heat Pipe

This research utilized 6 mm outer diameter and 3 mm inner diameter glass tubes to manufacture 9 turns Closed-Loop Pulsating Heat Pipe (CLPHP) with,a total length of 1980mm. For achieving the loop circulation easily, a water cooling system kept at 35 degrees C was used as the condenser. The experiment was conducted to evaluate the thermal resistance under different fluid filling ratios (20%, 30%, 40%, 50%, 60%, 70% and 80%), and at a series change of heat inputs (40W, 80W, 120W, 160W, 200W). Through a digital video camera, the visualization experiment was carried out to observe the circulation flow period in the PHP. A styrofoam ball was designed to put into the tube for a better observation and a correct estimation of fluid flow direction. Circulation times and circulation period were observed and calculated. The results showed that PHP reached fully circulation under the filling ratio of 60%, 70%, and 80%, at an input power of 200W. The circulation can be categorized into clockwise circulation, counterclockwise circulation and transition circulation status. The CLPHP thermal resistance was observed to be the least in circulation flow situation.