Force analysis and bubble dynamics during flow boiling in silicon nanowire microchannels

Abstract

In microchannel flow boiling, bubble nucleation, growth and flow regime development are highly influenced by channel cross-section and physical phenomena underlying this flow boiling mechanism are far from being well-established. Relative effects of different forces acting on wall-liquid and liquid-vapor interface of a confined bubble play an important role in heat transfer performances. Therefore, fundamental investigations are necessary to develop enhanced microchannel heat transfer surfaces. Force analysis of nucleating bubble and bubble dynamics in flow boiling silicon nanowire microchannels have been performed based on theoretical, experimental and visualization studies. The relative effects of different forces on flow regimes, instabilities and heat transfer performances of flow boiling in silicon nanowire microchannels have been identified. Inertia, surface tension, shear, buoyancy, and evaporation momentum forces have significant importance at liquid-vapor interface as discussed earlier by other researchers. However, no comparative study has been done for different surface properties till date. Detail analyses of these forces including contact angle effect, channel dimension effect, heat flux effect and mass flux effect in flow boiling microchannels have been conducted in this study. A comparative study between silicon nanowire and plainwall microchannels has been performed based on force analysis in the flow boiling microchannels. Compared to plainwall microchannels, enhanced surface rewetting and CHF are owing to higher surface tension force at liquid-vapor interface and Capillary dominance resulting from silicon nanowires. Whereas, low Weber number in silicon nanowire helps maintaining uniform and stable thin film and improves heat transfer performances. Moreover, results from these studies are compared with the literatures and great agreements have been observed.