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Suppression/Enhancement of Natural Convection by Use of Thermal Screen

使用隔热屏抑制/增强自然对流

基本信息

批准号：
01550186
负责人：
MASUOKA Takashi
金额：
$ 1.28万
依托单位：
Kyushu Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1990
项目状态：
已结题

项目摘要

An experimental and numerical study has been made concerning the effects of intermediate cooling or heating by use of thermal screen on both buoyant and Marangoni convection. A porous screen, which is called as a thermal screen in this study and is constituted with a row of heat pipes placed in a fluid layer, is adopted for the intermediate cooling or heating. Visual observations are made by using liquid crystal particles migrated into test liquid.First, the effects of thermal screen on natural convection in a fluid heated from below are examined. It is found that the thermal screen introduces a rather strong uniformity in horizontal temperature distributions which can modify the buoyancy forces and can substantially suppress the buoyant convection. In addition to this thermal effect of the screen, the Darcy resistance retards flow through the porous screen. Thus, convective patterns were found to occur in the form of either the retarded large-scale convection through the whole layer or the local convection confined to a space bounded by the porous screen depending on the temperature level and the permeability of the screen. Further, the numerical and experimental results show that the local convection entrains fluid of the other side of the screen with different temperatures, which can yield time-dependent periodic motions.Secondly, Marangoni convection induced by heating a thin wire on the free surface is examined. It is also found that the thermal screen can reduce horizontal temperature gradients particularly near the heated wire and the Marangoni convection is weakened. Again, it is noted that the Darcy resistance of the thermal screen can cause an effect of attenuation of flow.Then, it is concluded that the intermediate cooling or heating by the thermal screen can provide a very efficient method of control of both buoyant and Marangoni convection.

本文通过实验和数值模拟研究了热屏中间冷却或加热对浮力对流和Marangoni对流的影响。采用一种多孔屏，在本研究中称为热屏，它由一排放置在流体层中的热管组成，用于中间冷却或加热。首先，研究了热屏对自下而上加热的流体中自然对流的影响。结果表明，隔热屏能使水平温度分布具有较强的均匀性，从而改变浮力，并能有效地抑制浮力对流。除了筛网的这种热效应之外，达西阻力还阻碍了通过多孔筛网的流动。因此，对流模式被发现发生在通过整个层的延迟大规模对流或局部对流局限于由多孔屏幕取决于温度水平和渗透性的屏幕所界定的空间的形式。数值计算和实验结果表明，局部对流可以携带不同温度的屏壁另一侧的流体，产生与时间相关的周期性运动。其次，研究了自由表面加热细丝诱导的Marangoni对流。研究还发现，热屏可以减少水平温度梯度，特别是加热线附近的马兰戈尼对流减弱。再次指出，热屏的达西阻力可引起流动衰减的效应，然后得出结论，热屏的中间冷却或加热可提供一种非常有效的控制浮力对流和Marangoni对流的方法。