A comparative study of flow boiling heat transfer in three different configurations of microchannels

In this work, an experimental investigation has been made to compare the flow boiling characteristics of deionized water in three different configurations of microchannels. The investigated channel configurations are uniform cross-section, diverging cross-section and segmented finned microchannels. In each configuration, an array consisting of twelve numbers of microchannels with rectangular cross-section has been fabricated on a copper block with footprint area of 25.7 × 12.02 mm2. Experiments have been conducted with subcooled liquid state at the entry with coolant mass and heat fluxes vary in the range 100-350 kg/m2 s and 10-350 kW/m2, respectively. Depending upon the heat flux and coolant flow rate different regimes of two phase boiling have been observed. The comparison of three configurations has been made in terms of heat transfer coefficient, pressure drop characteristics and affinity towards backflow or flow reversal in the channels. Bubbles dynamics and their role in flow reversal and flow instability have been discussed for all three types of channels. For entire operating conditions, segmented finned channels demonstrate the highest heat transfer coefficient with negligible higher pressure drop compared to other two configurations of channels. The performance of diverging cross-section channels is better than the uniform cross-section channels. However, they underperform compared with segmented finned channels. At higher heat flux, bubble clogging and flow reversal problem is worst in uniform cross-section channels. The problem is partially solved in diverging cross-section channels. Segmented channels completely relieve the problem of bubble clogging allowing smooth and easy passage of growing bubbles. Moreover flow reversal is not observed in segmented channels for entire operating range of heat flux and coolant mass flux.