Numerical Simulation of Adiabatic Two-Phase Flow in Micro-Channels

Compact and efficient heat exchangers are needed to obtain energy efficient processes. An optimal design and operation of such systems require improving the physical understanding of the complex two-phase flow phenomena. The complexity of the evaporation process has been widely acknowledged, and several descriptions have been proposed with special focus on the micro region between the bubble interface and the heated wall [1,2,3]. In the case of evaporation in micro channels and as a consequence of the large interfacial area to volume ratio, some factors such as surface tension, frictional pressure drop, nucleation, etc. are playing an important role, and thus cannot be neglected. The prediction of the behavior of micro-scale two-phase evaporation is still limited. While experimental studies [4] have provided valuable insight of the phenomena, due to limitations in the experimental conditions all aspects of the micro scale boiling flow are not completely understood. In this sense, a computational approach can help to complement experimental studies. However the simulation of micro scale flow has several challenging aspects such as the tracking of the bubble interface, introduction of the surface tension effects, subscale modeling of the micro region, and the like. The goal of this work is to discuss the development of a computational model for studying micro scale evaporation phenomena and bubble dynamics in micro scale boiling and flowing. The model is based on a continuum surface force (CSF) model which belongs to the family of diffuse interface methods. A particular aspect of this work is the subgrid modeling of the micro scale region and its coupling to the macro scale flow. The mathematical model is solved using a spectral element method which provides a good balance between accuracy and computational cost.