摘要
以43%质量浓度的乙二醇水溶液为工质,针对5 mm×32 mm的加热面,采用孔径1 mm,孔间距和孔径比值为4(孔数为7),射距和孔径比值为5的一维阵列射流结构,对受限式射流过冷沸腾进行了可视化实验研究。结果发现,由于加热面朝下,沸腾气泡由于浮力紧贴壁面,而阵列射流引起的横流冲刷作用也不足以吹跑气泡,因此,在一定的热流密度下,当靠近加热表面的气液界面上的蒸发和受过冷液体冲击的气液界面上的凝结取得动态平衡时,将形成一定大小和分布规律的稳定气泡。随着热流密度的增加,气泡长大、合并,并最终形成覆盖整个壁面的"气垫",导致临界热流密度的发生。射流速度较小时,射流无法对加热面形成有效的直接冲击,气泡首先在整个加热面的中间形成;而在射流速度较大时,由于壁面射流的"对冲效应",气泡在两股射流的中间形成,因为那里的冷却最弱。
The nucleate bubble dynamics of confined jet impingement boiling of subcooled 43％ mass concentration aqueous ethylene glycol solution were visualized in a 1-D jet array configuration,with orifice diameter of 1mm,jet-to-jet pitch of 4mm,jet-to-wall distance of 5mm,and total jet number of 7.It was found that nucleate bubbles cannot lift off the wall via buoyancy force because of the downward heating surface in this study,and cannot be blown off either by the cross-flow within the jet impingement velocity range of this study.Steady bubbles will therefore be formed on the heating surface with their sizes corresponding to a certain heat flux level because of the dynamic equilibrium of the evaporation close to the wall and the condensation close the jet impingement.With the increasing of heat flux,the bubbles coalescence and finally form a vapor blanket to cause critical heat flux.For the small jet impingement velocity,the jet cannot impinge effectively to the wall and the bubble nucleates starts at the center of heater where the temperature is the highest,while for the high jet velocity,the bubble nucleation starts almost at the same time at the middle points of two jets where the flow is the weakest due to head-to-head collision of two adjacent wall jets.
出处
《低温工程》
CAS
CSCD
北大核心
2015年第2期44-50,共7页
Cryogenics
基金
国家自然科学基金项目(51376129)
上海市浦江人才计划(13PJD019)
上海航天技术研究院-上海交大航天先进技术联合研究中心资助项目(USCAST2012-03
USCAST2013-26)
关键词
受限式
射流冷却
乙二醇水溶液
沸腾
可视化研究
confined
jet impingement
aqueous ethylene glycol solution
boiling
visualization study
