Molecular dynamics of boiling heat transfer under passive liquid driven mechanism based on capillary flow in rough nanochannels

Abstract

The boiling under capillary flow greatly affects the heat transfer performance of the passive two-phase heat dissipation devices. In this study, sinusoidal structures with various amplitudes (3.615 Å, 7.23 Å and 10.845 Å) and periods ($\frac{1}{5}\times 624\AA$, $\frac{2}{15}\times 624\AA$ and $\frac{1}{10}\times 624\AA$) are constructed to characterize rough microchannels. The capillary flow and boiling under capillary flow in various nanochannels are investigated separately by molecular dynamics simulations. The results show that adding rough elements to wall surface reduces the maximum velocity of the liquid at least 22.9 % compared to the smooth surface. The rough elements can effectively enhance the local heat transfer efficiency and trigger the flow boiling. At the same time, the expansion of the bubble leads to the blockage and prevents the liquid supply, leading to deterioration of heat transfer. Increasing the roughness by increasing the amplitude of the sinusoidal structure will increase the heat transfer coefficient but decrease the total heat absorption. A better approach is to increase roughness by decreasing the period of sinusoidal structure, which has a favorable effect on both heat transfer coefficient and total heat absorption. The rough surface leads to an increase in the concentration of liquid atoms near the wall, enhancing the effectiveness of heat transfer.