Enhanced Flow Boiling in Microchannels Using Auxiliary Channels and Multiple Micronozzles

Flow boiling in an array of five parallel microchannels (W=200 μm, H=250 μm, L=10 mm) can be dramatically enhanced using self-excited and self-sustained high frequency two-phase oscillations induced by two-nozzle configuration. However, the effect of the two-phase oscillations is confined to the downstream of the microchannels. In this study, four-nozzle microchannel configuration is developed with an aim to extend mixing to the entire channel. Flow boiling in the four-nozzle microchannel is experimentally studied with deionized water over a mass flux range of 120 to 600 kg/m² s. Overall average heat transfer coefficient (HTC) is significantly enhanced approximately 54.5% by extending the enhanced multi-channel mixing to the whole channel. It is equally important that the pressure drop can be further reduced by approximately 50%. Compared with previous two-nozzle design, four-nozzle configuration not only extends the mixing to the whole channel but also increase nucleation sites, which has been confirmed by visualization study to promote nucleation boiling.