纳米颗粒及其接触角对沸腾传热系数的影响

Effects of Contact Angles of Nanoparticles on the Boiling Heat Transfer Coefficients

选取具有不同接触角的SiO_2纳米流体进行沸腾实验,探究纳米颗粒接触角对沸腾传热系数的影响。通过观察沸腾过程中气泡大小及沸腾实验后加热面上的沉积层形态,分析纳米颗粒接触角对沸腾气泡和沉积层形态的影响,进而揭示了纳米颗粒表面的润湿性对沸腾传热系数的影响机理。结果表明:纳米颗粒的接触角会影响纳米流体沸腾时气泡的稳定性和加热面上纳米沉积层的形态,不同表面形态具有不同的换热效果;中等亲水的纳米颗粒能吸附在气泡的气液界面上,使沸腾传热系数增大;加热面上沉积的中等亲水纳米颗粒会增大加热面粗糙度,产生更多的汽化核心,使沸腾传热系数增大。

To study the effects of contact angles of various nanoparticles on the boiling heat transfer coefficients,a boiling experiment was conducted using SiO2 nanofluids with different contact angles.By observing the sizes of the bubbles formed during boiling process and the morphology of the layers deposited on heated surface after boiling experiment,the effects of nanoparticles and their contact angles on the sizes of boiling bubbles and the morphology of deposited layers were studied,thus to further reveal the influence mechanism of the wettability of nanoparticles on the boiling heat transfer coefficients.Results show that the contact angles of nanoparticles would affect the stability of the bubbles formed in boiling process and the morphology of the layers deposited on heated surface,and different surface morphologies present different heat transfer effectiveness.Medium hydrophilic nanoparticles can be adsorbed on the gas-liquid interface of bubbles,producing enhanced heat transfer coefficients;whereas the medium hydrophilic nanoparticles deposited on the heated surface may increase the surface roughness,when more nucleation sites would be produced,resulting in improved heat transfer coefficients.