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

需要利用潜热的两相流量冷却系统来从电气或动力设备获得更高的冷却热通量。在这种情况下，需要增强沸腾的传热，沸腾开始时壁过热的减少以及临界热通量增加。在研究者先前在池沸腾实验方面的工作中，显示出可通过真空血浆喷雾涂层在实验性热通量范围内获得恒定的传热增强，并且可以减少沸腾发作时的壁过热。但是，热喷雾涂层上的临界热通量几乎与光滑表面上的临界通量相同。此外，从飞机的抛物线轨迹轨迹飞行中的微重力实验中，显示热喷雾涂层几乎产生与正常重力下的沸腾传热增强。可以说，由于涂料中复杂的显微镜亚渠道，表面具有很高的润湿性。在这项研究中，对一些具有不同材料和结构的涂层进行了评估，评估了一些涂料上的ling和强迫对流和对流的沸腾传热。在池沸腾的实验中，水平管测试部分被圆柱体覆盖，清除为1至2 mm，以阐明很难分散的蒸气气泡的影响，并且考虑了盖子对沸腾热传递的影响。结果，结果表明，盖子可以改善热传递，光滑表面的效果大于热喷涂涂层的效果，并且两个表面的盖子都会降低临界热通量。另一方面，对于强制的对流沸腾实验，铝和铜狭窄的通道，使用了20 mm和2 mm的高度。对于铝制测试部分，检查了在入口亚冷的条件下的垂直向上流，并评估沸腾和稳定条件时的壁过热。此外，通过中子射线照相法测量了窄通道中的空隙分数分布。作为结果，热喷雾表面在沸腾的沸腾开始时使壁过热和更高的临界热通量。对于铜板上的铜涂层，从水平沸腾的流动实验中显示，涂层表面产生了2至4倍的热传递系数。增强因子随热通量增加而增加。沸腾的传热特征中存在加热程序中的滞后。较高的加热速度导致更高的传热系数。较少的