Heat and mass transfer mechanisms of a self-sustained thermally driven oscillating liquid-vapour meniscus

Self-sustained thermally-induced oscillations of a meniscus in a two-phase system, consisting of a liquid plug and a vapour bubble in a capillary tube, are studied. This system represents the simplest 'unit-cell' version of a pulsating heat pipe (PHP). An experimental setup has been built to visualise and record the meniscus oscillations and the thin liquid film that is laid on the wall when the meniscus leaves the evaporator. The pressure and temperature of the vapour are also simultaneously measured. When the temperature difference between the heat source and the heat sink increases, different meniscus dynamics, having excellent repeatability, is observed. The experimental results clearly demonstrate that evaporation of the liquid film is responsible for these patterns. The different components of evaporation and condensation processes are critically analysed. Two different modes of evaporation are observed inside the system: one at the triple-line and one at the liquid-vapour interface. Considering that no comprehensive model of PHP system is available, the conclusions and directions provided in this study are important for building a broader understanding.