微纳尺度毛细芯吸液特性

摘要

为提高相变传热中毛细芯的吸液性能，以4种粒度(da=556 nm~73.8μm)的球形铜粉并添加不同体积分数的Na2CO3(φ=0%~40%)，用粉末烧结的方法制备不同规格的毛细芯，采用红外热成像法测定液体在其内部的爬升高度，用高速摄影捕捉液滴被吸入的运动过程，以此为基础对微纳尺度毛细芯的吸液特性进行研究。结果表明：不同的颗粒直径及掺盐比可使毛细芯内部结构产生明显的差异，从而显著影响毛细芯的毛细特性和液体在其内部的爬升高度。当φ=0%时，与da=556 nm的毛细芯相比，da=73.8μm的毛细芯中液体的爬升高度增加约373 mm；而对da=24.1μm的毛细芯，最佳掺盐比φ=30%，液体所达到的最大爬升高度约518 mm，相比φ=0%的毛细芯，液体爬升高度提升45%。液滴被吸入的运动过程表明，由于纳米级毛细芯的毛细吸力较大，在液滴吸入初期可使其产生较大的变形，但由于渗透率较小导致完全吸入液滴所用时间较长，可见毛细芯吸液过程是毛细吸力和渗透率协同作用的结果，可通过调节金属粉末直径和掺盐比获得最优性能。%In order to improve capillary performances of wicks used in phase change heat transfer progress, different samples were prepared by sintering spherical copper particles (da=556 nm~73.8μm) with different volume fractions of Na2CO3 (φ=0%−40%). Capillary performances of wicks were investigated by using the infrared thermal imaging method to locate the liquid meniscus, and a high speed camera to record the suction process of liquid droplets. The results show that the volume fractions of Na2CO3 and Cu powder diameters influence both capillary performance and liquid capillary rise height by changing the internal structures of wicks. Asφ=0%, liquid capillary rise height increases about 373 mm in wicks withda=73.8μm, than that in 556 nm wicks. For 24.1μm wicks, the bestφis 30% and the corresponding max liquid capillary rise height is about 518 mm. The height can be increased by 45% than that of wick with theφ=0%. Compared to micro scale wicks, nano wicks have larger capillary pressure that makes a larger deformation of a liquid droplet at the beginning of the suction process. But the suction time is longer because of the lower permeability. Capillary performances of wicks can be considered as the best balance of capillary pressure and permeability, so the optimal performance can be obtained by adjusting the volume fractions of Na2CO3 and Cu powder diameters.