Investigation of spontaneous capillary flow and heat transfer characteristics in parallel microchannels based on phase-field model

Abstract

• The mechanism of liquid surface oscillation in capillary flow is revealed. • Effect of channel structure on capillary flow and heat transfer is discussed. • A novel heat sink based on parallel capillary microchannels is constructed. • Non-circular heat sink obtains better capillary flow and heat transfer performance. Passive heat dissipation based on capillary flow has excellent applications in the thermal management of electronic devices and spacecraft due to its advantages of spontaneity and high stability. However, the conflicting relationship between capillary pressure and permeability in conventional sintered capillary wick severely limits its heat dissipation limit, and the complex and tortuous flow path is the key limiting factor. In this study, a novel close-packed capillary microchannel is constructed to provide an unobstructed flow path, and based on the phase-field model, the capillary flow and heat transfer characteristics of capillary microchannels with different structures are investigated. First, for the single channel, the oscillatory mechanism of phase interface in the initial stage of capillary flow, which has received little attention before, is revealed, which is mainly caused by the reconstruction of the advancing meniscus. This provides more nuanced insights into the initiating mechanism of capillary flow. In the noncircular channel, due to the change in curvature of the liquid surface at the acute angle and the expansion of the adsorption layer on the wall surface, the capillary velocity and heat transfer capacity improve compared to circular channels of equal hydraulic diameter. In addition, the effects of channel diameter and wettability on capillary flow and heat transfer are discussed. Capillary microchannels with better wettability and larger diameter achieve better capillary flow and heat transfer capabilities. On this basis, the parallel capillary microchannels inside the block are analyzed, and the non-circular channels achieve a higher capillary velocity while ensuring capillary pressure. Furthermore, the design of the noncircular section obtains a smaller thermal resistance and greater heat transfer efficiency, where the triangular microchannels show the best results. For the same hydraulic diameter and total block area, the performance decreases continuously as the inner angle of the channel increases. These results provide new ideas and a theoretical basis for designing high-performance passive heat sinks based on capillary flow.