Experimental studies on boiling heat transfer and friction characteristics in evaporator with double-layer micro/nano porous wick

Abstract

High-performance boiling devices are widely adopted in various scientific and industrial applications. In this paper, in order to achieve the synergy between liquid supply and vapor escape in boiling heat transfer, the multi-scale double-layer porous wick evaporators were fabricated by sintering two different sizes of copper particles with surface modification through nano-structures. The boiling heat transfer and pressure drop characteristics were studied experimentally. The S-shaped flow boiling curves are shown with three heat transfer regimes, corresponding to pool boiling, secondary boiling and vapor convection heat transfer, respectively. The secondary boiling can enhance the heat transfer coefficient (HTC) around twice. The maximum critical heat flux (CHF) of 578 W/cm2 can be achieved in the evaporator with the smooth surface of copper particles of 57 μm in diameter. Because the liquid and vapor flow separately, according to the concept of process decomposition, the ultra-low pressure drop about 1 kPa is achieved in the double-layer porous wick, even to zero in some cases. The nano-structures on the copper particle surface can provide more nucleation sites, thus enhance HTC up to 250 kW/m2K, but the corresponding the pressure drop is increased to 10 kPa. This study is helpful to reveal the flow boiling mechanism in porous wick evaporators with multiscale structures, and provide a guideline for fabrication of high-performance porous wick evaporators.