Breakup regime and heat transfer of a vapor bubble within T-shaped branching microchannel

Abstract

Understanding the transport characteristics and underlying mechanisms in microscale geometries is essential for microfluidic applications. While most fundamental studies in literatures focused on straight microchannels, the phase change process is still not fully understood for branching microchannels. In this study, a physically based high-fidelity numerical model is developed to investigate the breakup regime and phase change heat transfer of an isolated bubble within a T-shaped branching microchannel. The numerical model is first validated against both experimental data and numerical simulation in literatures, and a mesh independence study is performed to ensure the precision of the following simulations. Then, the influences of wall heat flux (50 W/m2 < q < 800 W/m2) and initial bubble size (0.64 < D* < 0.96) are investigated. Four distinct bubble breakup regimes can be recognized, namely non-breakup (NB) regime, “tunnel” breakup type one (TBⅠ) regime, “tunnel” breakup type two (TBⅡ) regime, and obstructed breakup (OB) regime. A phase diagram is plotted to describe the distribution of these regimes with respect to q and D*. The other important dynamic characteristics, such as two-phase flow structures, bubble deformation and growth are also investigated to help understanding the breakup process. In order to reveal the unique phase change heat transfer features within branching microchannel, the local heat transfer distribution and evolution are first quantitatively investigated on each channel wall, and then the influences of q and D* on the overall heat transfer performance are identified and compared with the single-phase heat transfer. The liquid film around the bubble and breakup dynamics are recognized as the key factors determining the phase change heat transfer performance within the microchannel and channel junction, respectively.