EFFECT OF RIBS/FINS AND ASPECT RATIO ON FLOW BOILING CHARACTERISTICS IN CONVENTIONAL CHANNELS

Abstract

In this work, experiments are conducted with conventional rectangular channels of two different aspect ratios (AR=w/d) for the horizontal boiling flow conditions at atmospheric pressure. Distilled water was used as the working substance. The heat transfer coefficients (HTC) were measured for mass fluxes and heat fluxes ranging from 85.94 kg/m2-s to 343.77 kg/m2-s and 10 kW/m2 to 100 kW/m2 respectively and at inlet subcooled temperatures of 303K, 313K and 323K. Visualization of the boiling phenomenon was done using a high-speed camera for the two channels under similar conditions. The results show that the AR has a dominant effect on the HTC. At low heat flux values, higher HTC was noticed for the channel of higher AR (AR= 1.25) whereas, at high heat flux conditions, the HTC is higher for the channel of lower AR (AR= 0.2). With an increase in inlet subcooled temperature, the HTC decreased for both channels due to increased thermal boundary layer thickness and reduced bubble formation. Further, the channel of AR=1.25 with ribs/fins performed better than the smooth channel due to the high bubble nucleation rate.