Nucleation and bubble evolution in subcooled liquid under pulse heating

摘要

The transient heating of liquid using a local heat source is widely used in practice including MEMS and laser medicine technologies. In particular the laser heating of liquid through the optical fiber has become a widespread method for obliteration of varicose veins (endovenous laser ablation, EVLA) and treatment of cysts of various localization. In this research there is proposed to use the electrically heated transparent microheater based on ITO film to simulate the laser-induced heating of the subcooled liquid through the optical fiber. The paper reports the experimental results on the nucleation and evolution of vapor bubbles in subcooled water induced by pulsed heating of the microheater. The experiments were performed at the initial liquid temperature of 27, 38, and 51 °C, with heating power in the pulse of 3.6 - 41W and pulse duration of 100-2000 ms using high-speed visualization and infrared thermography. The boiling and convection onsets, the rates of growth and condensation of vapor bubbles, and their maximum sizes depending on the heating power and the liquid initial temperature were measured. The development of convection before the boiling onset was shown to significantly affect the nucleation and further evolution of bubbles. It was found that at the stage of bubbles condensation, the shape of the interfacial surface significantly deviates from the spherically symmetric one, and the maximum condensation rate is observed at some distance from the heated surface. Using infrared thermography and numerical simulation, the time dependences of the ITO microheater and sapphire surface temperature for various heating power and initial liquid temperatures were obtained. On the basis of the temperature dependences and experimentally measured times of boiling onset, the nucleation temperatures were determined.