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A Study on De-Freeze-Off of Layered Air-Water in a Circular Tube

圆管内分层气水解冻研究

基本信息

批准号：
01460113
负责人：
FUKUSAKO Shoichiro
金额：
$ 4.1万
依托单位：
Hokkaido University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1991
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-01460113/
关键词：
Freezing Heat Transfer Layered Flow Freeze-Off Condition Freeze Injury Freeze Destruction Phase Change Convection Heat Transfer Turbulent Pipe Flow 強制対流熱伝達二相流れ凍結管内閉塞

项目摘要

An experimental investigation has been performed to determine the efficient method to prevent the freeze-off which should be observed in a horizontal cooled circular tube. The experiments were carried out under a variety of conditions of airflow rate, water flow rate, cooled air temperature, inlet water temperature, and initial water level. Extensive photographical and visual observations of the developing ice layer along the tube wall were conducted along with the experimental determination of the characteristics of the freezing heat transfer. The effect of the flow separation induced by an orifice situated at the entrance section of an uniformly cooled circular tube was extensively determined.A. Free Convection Heat Transfer of Air-Water Layers(1) Initially cooled water in the tube flows downward along the tube wall. Next a secondary eddy is formed due to density inversion in the water, and it flows upward along the tube wall, while the initial downward flowing eddy becomes weaker.(2 … More ) The water at the air-water interface is supercooled by the density inversion, and this supercooled water gradually spreads to the tube bottom by free convection.(3) The local heat flux increases with the cooling rate, but the rate of increase is quite small during the experiment.B. Characteristics of Freezing Heat Transfer of Layered Air-Water Flow(1) The freeze-off region and steady-state region can be apparently classified by the equation, THETA_c = 1.92 x 10^<-1>Re_W0.35.(2) In the freeze-off region, there are three kinds of ice forms. Furthermore, in the steady-state region, there are two kinds of ice forms and no ice region.(3) Ice layer along the upper tube wall grows because of the splashing of the ripples at the air-water interface, which may be caused mainly by the developed ice layer and the ice transition (ice test formed).C. Effect of Flow Separation on the Freezing Heat Transfer and Freeze-Off(1) The flow separation increases the time from the start of experimental run to the onset of freeze-off condition. The time of freeze-off takes the maximum at d/D=1/2.(2) The ice-deposit formed in the separated region just downstream of an orifice is concave when d/D is less than 3/4.(3) The ice-deposit thickness along the length of the tube decreases and the station of the rapid expansion of flow passage tends to move upstream as the water-flow velocity increases.(4) The time of freeze-off decreases with a decrease in the tube diameter. Less

本文对水平冷却圆管中的冻结现象进行了实验研究，以确定防止冻结的有效方法。实验在不同的空气流量、水流量、冷却空气温度、入口水温和初始水位条件下进行。对沿着管壁发展的冰层进行了广泛的摄影和视觉观察，沿着进行了冻结传热特性的实验测定。本文对均匀冷却圆管进口段节流孔引起的流动分离效应进行了广泛的测定。空气-水层的自由对流换热（1）管内初始冷却水沿着管壁向下流动。其次，由于水的密度反转而形成二次涡流，二次涡流沿管壁沿着向上流动，而初始向下流动的涡流变弱。（二） ...更多信息）空气-水界面处的水通过密度反转而过冷，并且这种过冷水通过自由对流逐渐扩散到管底部。(3)局部热流密度随冷却速率的增加而增加，但增加的幅度很小.（1）冻结区和稳态区可明显地用公式THETA_c = 1.92 × 10 ~（-3）<-1>Re_W ~（0.35）来区分。(2)在封冻区，有三种冰型。此外，在稳态区，有两种冰的形式和无冰区。(3)由于气水界面处波纹的飞溅，沿上管壁的冰层沿着生长，这可能主要是由冰层的发育和冰的过渡（形成冰试验）引起的。流动分离对冻结传热和冻结的影响（1）流动分离增加了从实验开始到冻结条件开始的时间。冻结时间在d/D=1/2时最大。(2)当d/D小于3/4时，在孔口下游分离区形成的冰沉积是凹形的。(3)随着水流速度的增加，冰厚沿着管长方向逐渐减小，流道快速扩张的位置有向上游移动的趋势。(4)冻结时间随管径的减小而减小。少