A numerical investigation of microtube length effect on convective boiling

Abstract The microtube length significantly influences the convective boiling process and associated heat transfer characteristics. Other than high heat transfer, low pressure drop is also desired to improve the energy efficiency of the pumping system. This work numerically investigates the microtube length effect on heat transfer and pressure drops of convective boiling with the volume of fluid (VOF) method. The simulation results of vapor formation, heat transfer coefficient, and pressure drop are shown with different microtube lengths L = 2–20 mm. The onset of boiling is around 2 mm away from the mass flux inlet. The subcooled boiling regime can be observed between 2 and 10 mm. Three distinct regimes, liquid single-phase flow, bubbly flow, and plug flow, are shown in the longer microtubes (L = 15 mm and 20 mm). It is found that shorter microtubes can lead to less bubble formation with higher heat transfer and lower pressure drop. The average heat transfer coefficient can achieve 2432 W/(m2K) with a lower quasi-steady total pressure drop Δp|total of 32.8 Pa inside a 2-mm-long microtube. This work offers a detailed study of the impact of microtube length on convective boiling, along with pertinent physical insights. It may serve as an indicator for future microscale heat transfer application designs.