Microfluidic technology has been widely applied in different fields such as environmental monitoring. The performance of the microfluidic devices largely depends on the manipulation of the bubble or droplet at the microscale level, especially their motion in the microchannels. Consequently, the flow boiling phenomenon that mainly occurs when the microchannel wall is heated exhibits remarkable heat transfer enhancement advantages. Different boiling conditions with different structures exist. Among them, T-junction branching structures have been widely used to facilitate the formation and breakup of bubbles. Unfortunately, the mechanism of bubble motion in flow boiling conditions with T-shaped branching microchannels is sparsely explored despite its potential application of improving and optimizing the microfluidic devices.
To date, numerous studies on the bubble dynamics in adiabatic conditions within T-shaped branching microchannels, both theoretically and experimentally, have been widely explored in literature. Nevertheless, despite the significant progress, the underlying mechanism behind the bubble motion in flow boiling conditions remain scanty. On this account, Dr. Zhe Yan and Professor Zhenhai Pan from Shanghai Jiao Tong University conducted a numerical investigation on the saturated boiling of an isolated vapor bubble traveling through a heated T-shaped branching microchannel. Their main objective was to obtain more insights into the dynamics and phase change heat transfer of the isolated vapor bubble. The work is currently published in the International Journal of Heat and Mass Transfer.
In this approach, the research team started their studies by presenting a detailed bubble motion process in a heated T-shaped branched microchannel, which was divided into three main parts: heated branching channel (HBC), adiabatic main channel (AMC), and heated maim channel (HMC). Next, the fluid flow velocity was altered to explore the influence of the inlet Reynolds number on the bubble dynamics and phase change heat transfer characteristics. The heat and mass exchange on the interface was simulated by a saturated-interface volume phase change mode, while the evolution of the liquid-vapor interface was obtained through the volume of fluid method. The numerical model was validated with the existing experimental data.
The authors observed that very low wall heat flux significantly influenced the bubble dynamics and heat transfer characteristics due to the evaporation effects. As the bubble traveled through the heated main channel, it grew and changed its profile from asymmetrical to symmetrical relative central axis of the channel. Thus, the heat transfer coefficient of the channel increased. Moreover, the breaking up of the bubble into two resulted in a higher heat transfer coefficient than the heated main channel, attributed to the significant role of the bubble breakage process in influencing the heat transfer characteristics of the heated branching channel. Furthermore, the breakup regime changed the inlet Reynolds number from 77 to 612 even though the overall heat transfer enhancement decreased with an increase in the Reynolds number.
In summary, the study reported in their investigation the isolated vapor bubble traveling through a heated T-shaped branching microchannel. The influence of the inlet Reynolds number on the bubble dynamics and heat characteristics was revealed, and the overall heat transfer characteristics decreased with increasing Reynolds number. Compared to the heated main channel, the heat transfer coefficient of the heated branching channel was significantly higher due to the effects of the breaking regime. Altogether, the study results provided new insights into understanding the bubble motion of T-shaped branching microchannel. In a statement to Advances in Engineering, the authors noted that the results would advance the development of high-performance microfluidic devices for different applications.
Yan, Z., & Pan, Z. (2020). Dynamics and phase change heat transfer of an isolated vapor bubble traveling through a heated T-shaped branching microchannel. International Journal of Heat and Mass Transfer, 160, 120186.