Effect of the gap height between the vibration plate and heating surface on boiling heat transfer in a boiling bubble resonator

For boiling heat transfer, it is important to improve both the critical heat flux and heat transfer coefficient. In general, the heat transfer coefficient is improved by promoting the nucleation of boiling bubbles on the heating surface. However, this decreases the critical heat flux. To improve the heat transfer coefficient without decreasing the critical heat flux, we previously developed a technique using a boiling bubble resonator, which consists of a material attached close to the heating surface that vibrates in response to the growth and collapse of boiling bubbles. In this study, we used spacer plates to vary the gap height between the heating surface and boiling bubble resonator to maximize the boiling heat transfer. By optimizing the gap height, the wall superheat decreased by 7 and 25 K at 0.8 and 5.6 MW/m², respectively. The maximum heat flux was 5.8 MW/m² with the optimized gap height. In addition, we observed sound signals when the boiling bubble resonator was optimally vibrating. Moreover, jet flow from the gap appeared with the vibration of the boiling bubble resonator.