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首页> 外文期刊>International Journal of Heat and Mass Transfer >Boiling behaviors and critical heat flux on a horizontal and vertical plate in saturated pool boiling with and without ZnO nanofluid
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Boiling behaviors and critical heat flux on a horizontal and vertical plate in saturated pool boiling with and without ZnO nanofluid

机译：含和不含ZnO纳米流体的饱和池沸腾中水平和垂直板上的沸腾行为和临界热通量

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When considering critical heat flux (CHF), a difficult compromise has to be made between economy and safety in many types of thermal systems such as nuclear power plants. Much research work has been carried out to increase CHF values using nano-fluids and to change the characteristics of the heating surface. In this work, the pool boiling experiments were carried out with and without ZnO nano-fluid (0.01 vol.%) on a SS-304 sample in atmospheric and saturated water conditions. The experimental test loop provides the evolution of the heat flux and wall temperature from nucleate boiling to film regime, without breaking and/or damaging the sample. Thus, it was possible to carry out several consecutive tests with the same sample in the same or different fluid conditions. Three different types of test conditions were used: (a) tests with de-ionized water (DIW), (b) tests with nano-fluid (NF) and (c) tests in DIW with a sample with an initial ZnO nano-particle coating (NFC). It was found that during the tests with nano-fluid, a very sizeable layer of nano-particle deposit was formed (～70 μm thick after five tests). The nature of the deposit phenomenon is highly transitory, and its performance changes during each test. On the other hand, the increase in CHF is probably due to the characteristics of the heating sample surface (porosity, capillary wicking, roughness and wettability) resulting from the deposit of nano-particles and not to the nano-fluids themselves. Indeed, we obtain the same level of CHF for the tests with an initial nano-particle deposit on the sample and the nano-fluid tests. Finally, for the tests with NF and NFC we found that the heat flux in the film regime is much higher than that in DIW conditions, of the order of up to 10 times due to the surface characteristics with nano-particles deposited.
机译：在考虑临界热通量（CHF）时，必须在许多类型的热力系统（例如核电厂）的经济性和安全性之间做出艰难的折衷。已经进行了许多研究工作，以使用纳米流体来增加CHF值并改变加热表面的特性。在这项工作中，在大气和饱和水条件下，在有和没有ZnO纳米流体（0.01％（体积））的情况下进行了池沸腾实验。实验测试回路可提供从核沸腾到薄膜状态的热通量和壁温的演变，而不会破坏和/或损坏样品。因此，有可能在相同或不同的流体条件下对同一样品进行几次连续测试。使用了三种不同类型的测试条件：（a）去离子水（DIW）测试，（b）纳米流体（NF）测试和（c）带有初始ZnO纳米颗粒的样品在DIW中测试涂层（NFC）。发现在用纳米流体进行测试的过程中，形成了非常大的纳米颗粒沉积层（五次测试后约70μm厚）。沉积现象的性质是高度暂时的，并且在每次测试期间其性能都会发生变化。另一方面，CHF的增加可能是由于加热样品表面的特性（孔隙度，毛细作用，粗糙度和润湿性）所致，这是由于纳米颗粒的沉积而不是由于纳米流体本身造成的。确实，在样品上进行了初始纳米颗粒沉积和纳米流体测试后，我们为测试获得了相同水平的CHF。最后，对于NF和NFC的测试，我们发现，由于沉积了纳米粒子的表面特性，薄膜状态下的热通量要比DIW条件下的热通量高得多，最高可达10倍。

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