Flow boiling patterns of refrigerant 134A in a minichannel with meandering flow passage

摘要

High-speed video photography was employed to capture the flow boiling patterns of R-134a in a horizontal minichannel. The channel had 20 transverse ribs which provided a meandering path for the refrigerant. The video pictures were taken at the speed of 2000 frames per second. The vapor quality, mass flux, saturation temperature, and heat flux were, respectively, 0.04-0.91, 100-200 kg/m~2s, 20-30℃, and 14 kW/m~2. Large bubbles, surrounded by numerous smaller bubbles, were observed upstream of the minichannel. The flow boiling occurred near the confined bubble flow regime and the narrow-channel effect was partially observed. The meandering flow passage created flow mixing, which stretched and divided the larger bubbles into smaller bubbles. Downstream, the length scale decreased due to mixing, and the flow became homogenized. Dry-out was observed at higher values of vapor quality. Flow separation occurred, forming small recirculation zones adjacent to the rib's tip. The flow oscillated randomly with unclear frequency.