An Evaporation Based Micro-Synthetic Jet in Microchannel and its Applications

An approach to create synthetic jets at micro-scales using periodic bubble growth and collapse was presented and studied over a range of operating frequencies (0.1 to 2.5 Hz) and heating powers (3 to 4.5 Watt). The microfluidic device uses an interfacial layer between vapor and liquid phases which substitutes the requirement for a physical flexible membrane and any other moving parts. The bubble explosion and implosion in the chamber was triggered by periodically powering a micro-heater, which in turn generated the synthetic jet. High-speed camera photography and a microscope were used to capture sequential images of bubble nucleation, growth and collapse in the chamber. In order to characterize the synthetic jet, a momentum coefficient was used. It was found that its average value exceeds unity for a large range of operating frequencies suggesting that this synthetic jet can improve the performance of a range of micro-system performance, such as micro-mixing in microfluidic devices. Subsequently, two potential applications of the introduced synthetic jet for heat transfer enhancement and micro-propulsion were studied. In doing so, first, the influence of the synthetic jet on flow boiling heat transfer in a microchannel was considered. The results showed that the synthetic jet enhanced nucleate flow boiling heat transfer in the microchannel by up to 20% by mitigating dry-out spots over the heated surface and enhancing thin film evaporation. Then in the following section, its application for micro-propulsion was studied. In this method, the interfacial layer movement between the vapor and liquid phases during the bubble growth, propelled the liquid through the micro-nozzle located at the chamber exit. The synthetic jet velocity at the nozzle exit was then numerically simulated using the SST k-ω turbulence model. Comparing the operating power of different types of micro-thrusters showed that the approach is one of the lowest powered micro-thrusters