Experimental investigation on the effect of the condenser length on the thermal performance of a micro pulsating heat pipe

The effect of the condenser length on the thermal performance of a micro pulsating heat pipe (MPHP) is experimentally investigated under various condenser temperatures. Using MEMS techniques, silicon-based MPHP with 10 turns and a hydraulic diameter of 667 μm is fabricated. The length of the evaporator section and the total length of the MPHP are fixed at 20 mm and 100 mm, respectively. Ethanol is used as the working fluid at the filling ratio of 50%. The thermal performances of the MPHPs for the condenser lengths of 10, 20, 30, 40 and 50 mm are evaluated while the condenser temperature varies from 0 °C up to 80 °C in increments of 10 °C. Flow characteristics of the MPHP are also investigated through high-speed photography. The thermal resistance of the MPHP varies up to 15 times depending on the length and the temperature of the condenser section. When the condenser temperature is relatively low, the evaporator temperature of the MPHP decreases as the condenser length becomes shorter. However, when the condenser temperature is relatively high, the evaporator temperature decreases as the condenser length becomes longer. The MPHP has the optimum condenser length for which the evaporator temperature is the lowest because of the interplay of opposing effects: the heat exchange area and the liquid supply to evaporator section.