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A study on improvement of wettability on heating surface and boiling heat transfer enhancement by thermal spray coating

热喷涂改善受热面润湿性及强化沸腾传热的研究

基本信息

批准号：
17560187
负责人：
ASANO Hitoshi
金额：
$ 2.18万
依托单位：
Kobe University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2006
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-17560187/
关键词：
Nucleate boiling Heat transfer enhancement Thermal spray coating Pool boiling Forced convective boiling Wall superheat at onset of boiling Critical heat flux Neutron radiography 核沸騰熱伝達沸騰開始過熱度ボイド率

项目摘要

Two-phase flow cooling system utilizing latent heat is required to obtain higher cooling heat flux from electro or power equipments. In this case, enhancement of boiling heat transfer, reduction in wall superheat at the onset of boiling, and increase critical heat flux are desired. In the investigator's previous work on pool boiling experiments, it was shown that constant heat transfer enhancement could be obtained by vacuum plasma spray coating over the experimental heat flux range, and wall superheat at the onset of boiling could be reduced. However, critical heat flux on thermal spray coating was almost the same as that on smooth surface. Moreover, from a microgravity experiment during a parabolic trajectory flight of airplane, it was shown that thermal spray coating produced almost the same boiling heat transfer enhancement as that under normal gravity. It could be said that the surface has high wettability due to complex microscopic sub-channels in coatings.In this study, pool boi … More ling and forced convective boiling heat transfer on thermal spray coatings were evaluated for some coatings with different material and structure. In the pool boiling experiments, a horizontal tube test section was covered by a cylinder with a clearance of 1 to 2 mm in order to clarify the effect of vapor bubble that is hard to depart, and the effect of the cover on the boiling heat transfer was considered. As the result, it was shown that heat transfer was improved by the cover, the effect for smooth surface was larger than for thermal spray coating, and the critical heat flux was decreased by the cover for both surfaces.On the other hand, for the forced convective boiling experiment, aluminum and copper narrow channels with the conduit width of 20 mm and height of 2 mm were used. For the aluminum test section, vertical upward flows under inlet subcool condition were examined, and wall superheat at the onset of boiling and steady condition were evaluated. Moreover, void fraction distributions in the narrow channel were measured by neutron radiography method. As the results, the thermal spray surface made the wall superheat at the onset of boiling lower and the critical heat flux higher.For copper coating on copper plate, it was shown from horizontal boiling flow experiments that the coating surface produced 2 to 4 times higher heat transfer coefficient. The enhancement factor increased with increasing heat flux. Hysteresis in heating procedure existed in boiling heat transfer characteristics. Higher heating velocity lead to higher heat transfer coefficient. Less

为了获得较高的冷却热流密度，电力设备需要采用潜热两相流冷却系统。在这种情况下，需要强化沸腾传热，减少沸腾开始时的壁厚，并增加临界热通量。在研究人员以前的工作池沸腾实验，它表明，恒定的传热增强可以通过真空等离子喷涂涂层在实验的热通量范围内获得，并可以减少沸腾开始时的壁厚。而热喷涂层的临界热流密度与光滑表面的临界热流密度基本相同。此外，在微重力条件下，飞机抛物线轨迹飞行实验表明，热喷涂涂层具有与正常重力条件下几乎相同的沸腾传热强化效果。可以说，由于涂层中复杂的微观子通道，表面具有高润湿性。 ...更多信息对不同材料和结构的热喷涂涂层进行了沸腾和强制对流沸腾传热的实验研究。在池沸腾实验中，为了考察难以分离的汽泡对沸腾换热的影响，在水平管实验段上加盖1 ~ 2 mm的圆柱体，考察了加盖对沸腾换热的影响。结果表明，在光滑表面上，覆盖层的传热效果比热喷涂层的效果好，覆盖层降低了两种表面上的临界热流密度。另一方面，在强制对流沸腾实验中，采用了铝和铜窄通道，通道宽度为20 mm，高度为2 mm。对于铝试验段，检查了入口过冷条件下的垂直向上流动，并评估了沸腾开始和稳定条件下的壁面过热度。此外，窄通道中的空隙率分布的中子照相方法进行了测量。结果表明，热喷涂表面使沸腾起始时的壁面粗糙度降低，临界热流密度提高;对于铜板表面的铜涂层，水平沸腾实验表明，涂层表面的传热系数提高了2 ~ 4倍。增强因子随热流密度的增大而增大。沸腾传热特性存在加热过程滞后现象。加热速度越大，传热系数越大。少