饱和液氮中临界热流密度和最小膜态沸腾热流密度的实验研究

用直径为５０ｍｍ、厚度分别为１２，２０，３０ｍｍ的铜平板在液氮中进行了不同热面方位角（热面水平向下为０°，热面垂直为９０°）的淬冷沸腾实验研究。方位角对临界热流密度、最小膜态沸腾热流密度及其壁面过热度的影响较大。在一定的方位角下，临界热流密度随平板厚度的增加而增加，但厚度达到一定大小时，其值与厚度无关。最小膜态沸腾热流密度与厚度呈离散关系。平板厚度对临界沸腾密度和最小膜态沸腾热流密度所对应的表面过热度的影响较小     

加热方位对流动沸腾临界热流密度影响

为了研究重力场对流动沸腾临界热流密度的影响,搭建了两相沸腾换热实验系统。以蒸馏水为工质,采用单侧加热的窄缝通道,通过改变质量流速、入口过冷度和重力场与加热方位的夹角,考察不同加热方位临界热流密度特性和实验段流阻特性。分析了质量流速、入口过冷度、加热方位对流动沸腾临界热流密度的影响,并将实验数据与Ivey-Morris模型、Sudo模型和Wojtan模型的计算值进行了验证对比。结果表明:加热面呈0°放置时的临界热流密度最大,呈180°放置时最小,质量流速和入口过冷度的增大会加大临界热流密度。Sudo模型对本实验条件不适用;Ivey-Morris模型和Wojtan模型在加热面呈0°放置时与实验值符合情况良好,相对误差约在30%以内,其他加热方位时,计算值均大于实验值。     

CMC液体垂直向下流动沸腾临界热流实验

采用薄壁不锈钢管，用高粘幂律流体进行了垂直向下流动沸腾临界热流实验研究，建立了临界热流关联式。     

平板在过冷液氮中的淬冷沸腾传热的实验研究

用直径为５０ ｍ ｍ 、厚度为２０ ｍ ｍ 的平板实验研究了倾斜平板在过冷液氮中的淬冷沸腾传热, 方位角为０°（热面水平向下） 到９０°（热面垂直）, 液氮过冷度为０～１３ Ｋ。由实验结果得到, 在所有方位角情况下, 随着液氮过冷度的提高, 在热流密度曲线图上的热流密度曲线向右上方移动; 从最小膜态沸腾点向过渡膜态沸腾转变时, 有一热流密度迅速提高的突变过程, 过冷度越大, 这种突变过程表现得越突出。     

大小样品在液氮中的淬冷沸腾换热比较研究

分析了大小样品在液氮中的淬冷沸腾换热特性。大小样品的淬冷沸腾换热有着明显的差别，小样品的热流密度比大样品的明显高得多。小样品的淬冷沸腾有一起始段，其温降高达６０Ｋ。从实验结果还可以看到，小样品的Ｌｅｉｄｅｎｆｒｏｓｔ点和临界热流点对应的壁面过热度明显比大样品的高。最后还分析了样品直径对临界热流密度的影响。     

近临界热流密度区域低温液体活化核心密度预测

采用厚液层蒸发传热模型,对近临界热流密度区域活化核心密度进行预测.计算结果显示在离临界热流密度点相对较远的区域出现的线性规律与前人的发现具有很好的一致性,验证了所用方法的可行性;而在无量纲过热度约为0.89时,活化核心密度出现最大值,之后活化核心密度随过热度增大呈现下降趋势,将其归因为临界热流密度点附近的热条件、流动条件及活化核心重叠等因素对活化核心的抑制作用.     

一种高效复合多孔表面在液氮中沸腾传热的实验研究

本文对我们研制的一种复合多孔表面——烧结多孔U型翅片螺纹管表面,垂直置于液氮孔中,在常压下对其沸腾传热的性能进行了实验研究。结果表明,该复合多孔强化表面的沸腾传热系数是U型翅片螺纹管表面的3～6倍;是光滑表面的6～10倍。本文还拟合出该复合多孔强化传热表面的无因次沸腾传热准则关系式,拟合误差在±15％之内,具有实用意义。     

竖直多孔表面通道内液氮沸腾换热实验研究

在液氮自然循环流动时，对竖直多孔表面管管内沸腾换热及外管单面加热时竖直多孔表面套管内沸腾换热，进行了实验研究，分析并讨论了通道的当量半径、热流密度及含气率对沸腾换热的影响。     

液氮核态池沸腾CFD模拟和可视化实验

为探究低温流体池内核态沸腾机理,对液氮池内核态沸腾进行了计算流体力学(CFD)建模及实验研究。除了探究过热度和热流关系,重点分析过热度对气泡脱离直径和频率影响。根据实验观测,将核态沸腾过程分为3个阶段:低热流阶段;过渡沸腾阶段;完全核态沸腾(FDNB)阶段。基于得到的沸腾过程气泡直径及频率,构建了核态沸腾CFD数值模型,得到的过热度及热流密度关系,与实验测量得到的数据吻合。     

Convective heat transfer enhancement produced by secondary heat sources in a liquid nitrogen pool

This paper studies the influence of secondary heat sources on the convective heat transfer from a vertical cylindrical heater immersed in a LIN pool. Two types of secondary heat source have been used. In the first case, the heat leak through the vessel walls into the pool was varied without causing nucleation, so as to retain convective heat transfer. It was found that the convective flow loops induced in the pool produced a small enhancement of the heat transfer from the cylindrical heater. In the second case, a small horizontal heater loop was introduced into the pool below the cylindrical heater. The secondary heat flux used was such that boiling occurred at the loop to give rising bubbles surrounding the cylindrical heater. This produced a large enhancement of the convective heat transfer from the cylindrical heater. The enhancement ratio is presented as a function of the power supplied to the loop heater.     

Transient nucleate boiling of liquid nitrogen with a stepwise change of heat flux

Results of experimental and theoretical investigations of unsteady nucleate boiling of liquid nitrogen are presented. A strip of niobium foil placed along the axis of a tube served simultaneously as a heater and as a resistance thermometer. Noted deviations from correlations for the steady nucleate boiling are explained by a new methematical model, which considers the process of transient nucleate boiling as stochastic.     

Critical heat flux of binary mixtures in pool boiling and its correlation in terms of Marangoni number

Critical heat flux (CHF) in nucleate pool boiling of binary mixtures was newly measured with a horizontal platinum wire, 0.5 mm in diameter, and heated by DC, over the full range of concentrations. Seven mixtures were selected with the intent to cover various types of mixtures: methanol/water, ethanol/water, methanol/ethanol, ethanol/n-butanol, methanol/benzene, benzene/n-heptane and water/ethylene glycol, each in the saturated state at atmospheric pressure. Total 311 raw CHF data were obtained at 75 concentrations including pure components.Aqueous mixtures of methanol and ethanol revealed significant increase of CHF compared to either CHF linearly interpolated between pure components or CHF predicted from a single component correlation with use of the mixture properties. Three organic mixtures showed more or less the same level as an interpolated CHF, while the remaining two mixtures of methanol/benzene and water/ethylene glycol gave the reduced CHF by 20% and 50% at most, respectively. Marangoni number was introduced as a controlling variable to explain the observed increased, invariable, or reduced CHF, and an empirical correlation was developed.     

液氮流动沸腾数值模拟研究进展

对已有的针对低温流体的数值模拟进行了总结,比较了可用于液氮流动沸腾的数学模型,指出数值模拟液氮流动沸腾中尚待解决的问题,并对垂直环行管道中的液氮流动沸腾进行了数值模拟.     

液氢空间贮存过程膜态沸腾数值模拟

为实现液氢在空间中安全高效应用,针对微重力条件下液氢膜态沸腾现象,建立了加热细丝浸没在过冷液氢池中的数值计算模型.采用VOF方法捕捉相界面,相变模型选取Lee模型,利用文献中的实验数据验证了模型的准确性.从气泡运动行为和换热特性两方面开展研究,结果发现液体过冷度和重力水平是影响换热机理的两个重要因素.在高重力水平、低液...     

Enhancement of pool boiling

This review considers the many techniques that have been developed to enhance boiling heat transfer. After introducing the techniques, the applications to pool boiling are described. Comments are offered regarding commercial introduction of this technology and the generations of heat transfer technology; advanced enhancement represents 3rd generation heat transfer technology.     

低流量下阵列式微通道对流沸腾特性实验研究

设计了阵列式微通道热沉结构,进行了并R134a的沸腾流动换热实验。结果证明,在低干度区域由泡状流/弹状流/半环状流主导,主导换热机理为对流沸腾和蒸发,热交换系数随热流密度显著增加,随质量流量增大而略有增加。在高干度区域搅拌流/束状流主导沸腾流动,对流蒸发为主导换热机理,换热系数随流量增大而增大。该结构可以在低流量下提前紊流转捩;有效抑制压力波动,减小进出口压力差。实验观察发现搅拌流/束状流型,气液界面波失稳导致液膜破碎和卷携。液滴沉积会润湿局部蒸干壁面。当热流持续增大,液膜破碎并大量被卷携入气核后,壁面附着气膜且无法被润湿,形成反束状流型时,触发CHF。