Microbubble Formation Dynamics Under High Heat Flux on Heaters with Different Aspect Ratios

Abstract

Extensive studies of vapor bubble in water on microbubble growth and collapse process on microheaters with heat fluxes of 1.2, 1.4, and 1.6 GW/m 2 are performed. The 4 μs heat pulse is applied to 30 × 30 μ m 2 , 30 × 60 μ m 2 , and 20 × 60 μ m 2 heaters for undergone the nucleate boiling. Sequential images during the micro bubble growth process are recorded by the microscopic flow visualization method coupled with phase-averaged technique. The analysis of the top view images show that the increase of aspect ratio of rectangular shape heater changes the bubble shape into ellipsoid with larger ratio of axes, slower rates of bubble growth and collapse, longer bubble lifetime, later time to reach maximum size but play small roles on incipience nucleation, and vapor formation temperature. While the change of high heat flux shifts the incipience time at nucleation temperature, time to vapor sheet formation, time to reach maximum size and thus the bubble lifetime. With side view of bubble images, not only histories of extension of bubble in height but also histories of the contact angle can be provided. Therefore, the correlations of contact angle/surface tension force and boundary moving speed of bubble boundary as well as the determination of major driving mechanism in bubble growth/collapse process can be identified.