Enhancement of the subcooled microchannel flow boiling heat transfer by the cylinder-induced vortices*

Microchannel flow boiling is gaining great attention due to its high heat dissipation with a small temperature difference, which is particularly beneficial in cooling systems. This work numerically studies the subcooled flow boiling heat transfer in microchannels enhanced by the cylinder-induced vortices. Simulations are conducted by an immersed boundary-lattice Boltzmann method. In this method, the boiling flow is solved by using the pseudopotential multiphase lattice Boltzmann model, the flow-induced vibration of the cylinder is modelled by a mass-spring-damping system, the heat transfer equation is solved by the finite difference method, and the boundary condition at the fluid-cylinder interface is handled by a feedback immersed boundary method. Three groups of simulations are examined: a clear channel, a channel with a stationary cylinder, and a channel with a flow-induced vibrating cylinder. Various parameters are varied, including Reynolds number, heat flux, surface wettability, and blockage ratio. In the case of flow over a fixed cylinder with a blockage ratio of 3.0, the induced vortex achieved an enhancement of about 20% in the rates of flow boiling heat transfer in the intermediate region of heat flux compared to the clear channel. Moreover, in the high heat flux region, there is a substantial improvement in heat transfer, exceeding 23.455%, 22.97%, and 25.881% for Reynolds numbers of 600, 800, and 1000, respectively. The presence of the induced vortex effectively delayed the onset of the dryout condition at the critical heat flux point. Additionally, decreasing the blockage ratio enhances the rates of heat transfer. When the vibrating cylinder is positioned near the wall with a low blockage ratio, notable enhancements in heat transfer in moderate range of heat flux. Therefore, this study provides an efficient solution for flow boiling problems without using any additional external power source for evaporative cooling systems of the high-powered applications.