Experimental investigation of flow boiling characteristics in microchannels with the sinusoidal wavy sidewall

An improved microchannel heat sink with the sinusoidal wavy sidewall (SIN) is designed and fabricated by MEMS technique. The synchronous optical measurement system is established. The flow and heat transfer performance in SIN microchannels is experimentally studied using acetone as the working fluid. At mass fluxes of 251 kg/(m(2).s)-423 kg/(m(2).s) and heat fluxes of 0 kW/m(2)-601 kW/m(2), the pressure drops, boiling curves, and heat transfer coefficient are investigated and analyzed. The temperatures, pressure drops, and corresponding flow patterns in the stable state are emphatically examined. The experimental results show that, a continuously developing liquid film always exists near the sidewall, which not only timely supplies the liquid for nucleation tending to occur in the corner regions, but effectively prevents the microchannel dry-out. Consequently, the premature onset of nucleate boiling (ONB), the delayed critical heat flux (CHF), and about 100% enhancement of heat transfer coefficient can be achieved with SIN microchannels compared to the traditional rectangular (R) microchannels. In the stable state, all the dominant flow patterns at different positions are almost fixed, which result in stable heat transfer enhancement. The flow pattern transitions between single liquid/bubbly flow, bubbly/slug flow, bubbly/annular flow are observed at the channel midstream in the low/medium/high heat flux, respectively. It is noteworthy that all of the dominant flow patterns at the channel downstream are not vapor flow but annular flow with thin and continuous liquid film. In addition, the flow boiling instabilities characterized by the temperatures and pressure drops with obvious fluctuations are also illustrated.