PRESSURE DROP MEASUREMENTS WITH BOILING IN DIVERGING MICROCHANNEL

Abstract

An experimental study of flow boiling through diverging microchannels has been carried out in this work, with the aim of exploring reduction in flow instabilities during boiling in diverging microchannels. Effect of mass flux, heat flux and divergence angle on two phase pressure drop has been studied using deionized water as the working fluid. The experiments are carried out on three test sections with divergence angle of 4, 8 and 12 deg with nearly constant hydraulic diameter (146, 154 and 157 μm respectively), for inlet mass flux and heat flux range of 117 - 1197 kg/m2-s and 2.5 to 19.7 W/cm2 respectively. Pressure drop with respect to mass flux is linear and non-linear in single and two phase regimes, respectively. There are up to three points in single/two-phase regime having the same pressure drop, which is similar to uniform cross section microchannel. However, unlike uniform cross section microchannel, the slope of demand curve at the point of onset of flow boiling is less steep in diverging microchannel; further, the slope is an inverse function of the divergence angle. Preliminary study suggests that diverging microchannel can reduce the flow instabilities.