Acoustic Radiation, Cavitation Collapses, and Dryout in a Capillary Oscillating Heat Pipe

In an oscillation heat pipe (OHP), when two-phase flow oscillates to the condensation region, saturated vapor bubbles/slugs are subjected to a sudden temperature reduction or immediate subcooling. Rapid condensation ruptures vapor bubbles and generates cavitation erosions on the tube interior surface. In this article, a thorough study is performed to understand discrepancy of variation tendency between acoustic radiation and OHP temperature difference that both are operating temperature-dependent. On this basis, three temperature zones were identified: (1) low operating temperature zone with strong cavitation collapse and acoustic radiations, (2) optimal temperature zone with the minimum temperature difference and weakening cavitation collapses, and, (3) high-temperature zone where dryout and oscillation failures develop. At the optimal operating temperature, high-frequent oscillations reduce subcooling of two-phase flow, alleviating the impact of cavitation collapses and ceasing acoustic radiations. At high operating temperature, liquid surface tension dramatically reduces and dynamic contact angle significantly increases. Both the factors tend to lower the critical diameter necessary to maintain pressure difference and oscillating two-phase slug flow. When the critical diameter reduces to be less than the OHP tube diameter, liquid slugs are not able to seal the OHP capillary tubes, leading to dryout or insufficient heat and mass transfer.