Enhanced heat transfer and reduced pressure drop using stepped fin microchannels

Experiments on flow boiling were conducted in straight and stepped fin microchannels. The test vehicles were made from copper with a footprint area of 25mm × 25mm. The microchannels were formed by wire cut Electro Discharge Machining process and have surface roughness (Ra) of about 2.0 μm. Tests were performed on channels having nominal width of 300 μm and a nominal aspect ratio of 4 over different mass velocity range and inlet temperature of 90°C. It was observed that the two phase pressure drop across the stepped fin microchannel heat sink was significantly lower as compared to its straight counterpart. Moreover the pressure drop and wall temperature fluctuations were seen reduced in the stepped fin microchannel heat sink. It was also noted that the stepped fin microchannel heat sink had a better heat transfer performance than the straight microchannel heat sink, under similar operating conditions. This phenomenon in stepped fin microchannel heat sink is explained based on its improved flow boiling stability that reduces the pressure drop oscillations, temperature oscillations and hence partial dry out, by allowing the bubbles to expand span wise and hence flow downstream with less resistance.