Experimental investigation of thermo-hydrodynamic behavior in a closed loop oscillating heat pipe

A simultaneous visualization and temperature measurement has been performed to investigate the interaction of bubble size distribution, bubble movement, temperature variation in a glass oscillating heat pipe (OHP) with an internal diameter of 2.5 mm. Ethanol was used as the working fluid with volumetric filling ratios of 50%, 60% and 70%. Fluid temperatures were recorded under four different heating power inputs of 38, 50, 75, and 110 W with thermocouples inserting into tube inside. The experimental results show that a higher heating power input or filling ratio usually leads to larger oscillation frequency and amplitude of bubble movement, contributing to better OHP performance. The quasi-sine oscillation wave of bubble movement was occasionally observed and its appearance also depends on the filling ratio and power input. Visual observation indicates that the bubble size distribution is associated with bubble movement and temperature variation, which is available to indirectly evaluate the OHP performance. This study provides a new approach to understand the thermo-hydrodynamic behavior of OHPs.