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首页> 外文期刊>International Journal of Heat and Fluid Flow >Nanofluid Boiling: The Effect Of Surface Wettability
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Nanofluid Boiling: The Effect Of Surface Wettability

机译：纳米流体沸腾：表面润湿性的影响

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Nanofluid boiling has shown potential to increase boiling heat transfer, but the mechanisms responsible are poorly understood. One likely mechanism for nanofluid enhancement is an improvement in surface wettability. This study is targeted towards investigating whether or not nanofluids improve the critical heat flux (CHF) by altering the surface energy as has been observed for pure fluids. The surface of a heater was systematically altered by oxidizing its surface to varying degrees or by depositing metal onto the surface, and the surface energy was characterized by measuring the advancing three-phase contact angle. Boiling curves on these surfaces were measured for pure fluids and for water and ethanol based nanofluids with aluminum oxide nanoparticle concentrations from 0.001 g/L to 10 g/L Dilute suspensions of nanoparticles were found to degrade or have no effect on the boiling performance. Greater concentrations ( ≥ 0.5 g/L) led to modest (up to ～37%) increase in the CHF. Poorly wetting systems (e.g. water on polished copper) could be enhanced by the addition of nanoparticles, whereas better wetting systems (e.g. ethanol on glass) showed no improvement or a larger degradation. Furthermore, the addition of nanoparticles to water was found to improve wetting, but only when the surface was fouled by the particles. Interestingly, similar CHF enhancement was achieved without nanofluids using an oxidized surface, which was easily wetted with pure fluids. In fact, surface treatment alone resulted in similar CHF enhancement but at ～20 ℃ lower wall superheat than when using nanofluids.
机译：纳米流体的沸腾已显示出增加沸腾传热的潜力，但其机理尚不清楚。纳米流体增强的一种可能机制是表面润湿性的改善。这项研究的目的是调查纳米流体是否通过改变表面能来改善临界热通量（CHF），正如对纯流体所观察到的那样。通过改变其表面的氧化程度或在表面上沉积金属，系统地改变加热器的表面，并通过测量前进的三相接触角来表征表面能。测量了这些表面上的沸腾曲线，以测量纯流体以及氧化铝纳米颗粒浓度为0.001 g / L至10 g / L的水和乙醇基纳米流体，发现纳米颗粒的稀释悬浮液会降解或对沸腾性能没有影响。更高的浓度（≥0.5 g / L）导致CHF适度（高达〜37％）增加。纳米粒子的加入可增强润湿系统不良（例如，水在抛光铜上），而更好的润湿系统（例如在玻璃上的乙醇）则无改善或降解更大。此外，发现将纳米颗粒添加到水中可改善润湿性，但仅当表面被颗粒污染时才可。有趣的是，在不使用纳米流体的情况下，使用氧化表面也可实现类似的CHF增强，而氧化表面很容易被纯流体润湿。实际上，仅表面处理会导致类似的CHF增强，但比使用纳米流体时，在20℃的壁过热度低时。

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