Effects of acoustic vibration on microheater-induced vapor bubble incipience in a microchannel

A simultaneous temperature measurement and high-speed visualization study has been carried out to investigate the effects of acoustic vibration on vapor bubble dynamics and flow boiling in a single microchannel which is formed by bonding a bottom Pyrex glass wall with a top PDMS (polydimethylsiloxane) wall. A single platinum serpentine microheater, fabricated on the Pyrex glass substrate and integrated into the microchannel, is used to generate vapor bubbles and measure local wall temperature simultaneously. The temperature variations and flow pattern maps in terms of acoustic frequency and acoustic signal amplitude are presented, respectively. It is found that the acoustic vibration can induce bubble incipience with a relatively low heating power. The frequency, acoustic signal amplitude and flow rate are important factors affecting vapor bubble incipience. A lower acoustic signal amplitude can promote bubble incipience to happen easily but no obvious effect when further increasing the acoustic amplitude to a relatively high level. A low flow rate can advance bubble incipience, while a very high flow rate can hinder bubble incipience under the same acoustic and heating conditions. The experimental results are instructive for the design of novel microfluid and MEMS (microelectromechanical systems) devices, such as lab-on-a-chip or thermal management devices.