Flow boiling in microchannel with synthetic jet in cross-flow

Abstract

Flow boiling heat transfer in a microchannel with a micro synthetic jet powered by liquid/vapor phase change was studied. The synthetic jet had no moving parts and used the motion of the interfacial layer between vapor and liquid to propel liquid. Bubbles were generated on a micro heater in a chamber, 3.5 mm in radius and 220 µm tall, which was connected to the microchannel through a 300 µm nozzle opening. Periodic growth and collapse of bubbles in the chamber powered the synthetic jet. Using high-speed photography and a microscope, the sequence of bubble growth and collapse in the chamber, bubble nucleation in the microchannel, and their interaction with the synthetic jet were captured and analyzed. The jet velocity was estimated using image processing and its momentum coefficient was used to characterize the strength of the synthetic jet. The results showed that the synthetic jet enhanced nucleate flow boiling heat transfer in the microchannel by up to 20%. dry-out spots formed over the heated surface for high heat fluxes were mitigated by the synthetic jet as it assisted rewetting the surface and maintaining the integrity of the thin liquid film adjacent to the heated surface.