Numerical simulation of boiling behavior in vertical microchannels

High heat flux electronic devices put forward new requirements for heat dissipation, and boiling heat transfer technology is widely used because of its higher heat dissipation capacity. In this study, the volume of fluid method was employed, along with the incorporation of the Lee phase-change mass transfer model, to investigate two-phase flow and heat transfer in vertical upward rectangular microchannels. The heat flux was varied within the range of 10-40kW/m(2), while the mass flux was varied within the range of 200-600kg/m(2) s. With the increase in heat flux, bubble flow, slug flow, churn flow, and annular flow were found successively. A phase diagram was established to predict the flow pattern transition during the boiling process. When the flow pattern changes to the churn and the annular flow, the active nucleation site density increases obviously with the Boiling number (Bo). A new correlation was proposed for two-phase flow boiling heat transfer, suitable for vertical upward channels in microscale fluids. The friction factor obtained using the Darcy friction factor equation agrees well with the simulation results at a high-pressure drop. The instability in microchannels increases with the increase in heat flux, particularly in annular flow, resulting in more severe wall temperature fluctuations.