微通道流动沸腾不稳定性和临界热流密度特性研究
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摘 要
微尺度条件下的沸腾换热与常规尺度传热有着显著的差异，随着现代科学技
术水平的不断提高，微型设备的散热要求越来越高，因此微尺度流动沸腾换热有
着广泛的应用前景，近年来已经成为国际传热学界研究的热点领域，本文对微细
通道内的流动沸腾不稳定性和 CHF 进行理论和实验研究，主要内容如下：
(1) 对微通道流动不稳定性进行实验研究，得出压降——流量特性曲线，该特
征曲线与理论分析完全吻合，都呈现“N”字形曲线，随着工质入口温度的升高，
压降——流量的“N”字形特性曲线变得越来越平坦，微通道中的沸腾不稳定性受
到抑制，气泡之间聚合演化形成的大气泡(其内部的压力较小)对微通道的阻力要小
于气泡急剧膨胀形成拉长气泡(其内部压力较大)对微通道的阻力。
(2) 发现去离子水为流动工质很容易发生不稳定性，且壁面温度波动振幅非常
大，而采用乙醇作为流动工质时，相对较难发生流动不稳定性，壁面温度波动的
振幅比较小。分析了壁温及压力周期性波动的振幅(壁面温度振幅达到 400 ℃)、周
期(10.5 s)、频率(0.095 Hz)，发现壁温与压力同相位但与质量流量相位角几乎相差
180 度。随着入口过冷度的减小，流动沸腾不稳定性逐渐减小，当入口温度达到
80 ℃时，以去离子水为流动工质，几乎不发生沸腾不稳定性；相较于去离子水以
乙醇为工质时更不容易发生沸腾不稳定性。
(3) 微通道稳定沸腾区域和不稳定沸腾区域的划分，微通道内直径为 812.6 μm，
当去离子水入口温度为 23、40 ℃时，qeff/G=0.202、0.116 kJ/kg；微通道内径为 652.5
μm，当去离子水入口温度为 23、40 ℃时，qeff/G=0.321、0.192 kJ/kg。微通道直径
越大，从稳定沸腾区域过渡到不稳定沸腾区域的 qeff/G 值越小，说明微通道越大越
不容易发生流动沸腾不稳定性定。
(4) 分析微细通道轴向导热对流动沸腾过程的影响，根据 Maranzana 等研究人
员提出的分析计算微通道轴向导热能力的关联式，依据本实验条件参数计算平均
M=3.31×10-6 远小于标准值 10-2，因此实验的分析计算中都不需要再考虑微通道轴
向导热的影响。
(5) 环状流阶段的 CHF，除了出口处热电偶 T7的温度很高外，其它位置的热
电偶温度都很低很均匀，但温度都高于对应压力下的饱和温度，这与环状流阶段
的以对流沸腾为主导的换热机制完全吻合。由于壁面的持续加热，沿流动方向环
状流型的液膜在蒸发作用下，液膜不断减薄最后出现局部干涸现象，从而触发了
环状流阶段的 CHF，在环状流与雾状流过渡的气、液、固三相接触线处的壁面得
不到新鲜液膜的润湿作用，此时就会出现相对较稳定的 CHF，此时的 CHF 值高于
不稳定沸腾阶段的 CHF 值。
(6) 在环状流型末端出现干涸时的气、液、固三相分界线处，建立表面张力、
惯性力、粘性力和蒸发动量力的力平衡关系式，即当蒸发动量力大于或等于表面
张力、惯性力和粘性力三项之和的时候，就认为在力的角度达到促发 CHF 的条件，
对该力的平衡关系进行处理得出了包含 We 数和 Ca 数的 CHF 关联式，最后经过实
验参数的回归分析得到该 CHF 关联式的系数值。
(7) 将实验参数代入根据力平衡原理得到的 CHF 关联式中，经过回归分析得
到系数值分别为 C1=3.6135×10-5，C2=-0.4908，C4=6.3155×10-4，所得关联式的预测
值都在±10%的偏差范围内，与实验数据吻合的良好。
关键词： 微细通道 流动沸腾 CHF 模型 不稳定性 液膜 干涸
力平衡原理
ABSTRACT
There are significant differences of boiling heat transfer. between micro-channels
and macro-channels. With the improvement of modern advanced technology, the
micro-device needs meeting the high demand of heat dissipation, thus flow boiling
heat transfer in micro-channels has extensive applied prospect. Flow boiling heat
transfer in micro-channels already becomes a hot academic field in the international
heat transfer society. Experimental and theory study on instability and critical heat
flux of flow boiling in micro-channels have been done in this paper. The main
contents of this paper are as following:
(1) Research the experiment of flow boiling instability in micro-channels, and
obtain the character curve of pressure-drop—mass flux which agrees well with
theoretical analysis and the curve appears the shape of “N”. The shape of character
curve of pressure-drop—mass flux becomes more and more smooth and the instability
of flow boiling in micro-channels is restrained with the inlet temperature of working
medium increasing. The resistance of flow of big bubbles (the inner pressure of
bubbles is small) which comes from evolution between bubbles is smaller than that of
elongated bubbles (the inner pressure of bubbles is large) through rapid explode.
(2) Finding the working medium instability occurs easily and the amplitude of
temperature of micro-channel’s wall is very large when the working medium is
deionized water. While the flow boiling instability occurs scarcely and the amplitude
of temperature of micro-channel’s wall is small when the alcohol is as working
medium. Analyze the periodic amplitude (when the amplitude of wall temperature
reaches 400 ℃) and period(10.5 s) and frequency(0.095Hz) of wall temperature and
pressure oscillation. Find that the wall temperature and pressure are in the same phase
but the phase angle is almost different from the mass flux and the phase differ 180
degrees. The flow boiling instability gradually became small with the inlet condensate
depression decreasing. Using deionized water as working medium ,we find that the
flow boiling instability almost didn’t appear when the inlet temperature reaches
80 ℃.Compared with deionized water , using the alcohol as working medium , flow
boiling instability hardly occur.
(3) Divide the stable boiling region of the micro-channel and unstable boiling
region. When the inner diameter of micro-channel is 812.6μm and inlet temperature of
deionized water are 23 and 40 °C respectively, qeff/G =0.202 and 0.116 kJ/kg; While
the inner diameter of micro-channel is 652.5 μm and the inlet temperature of
deionized water are 23 and 40 °C respectively, qeff/G= 0.321 and 0.192 kJ/kg. The
larger the diameter of the micro-channel, the transition from stable boiling region to
unstable boiling region qeff/G value is smaller, and the larger the micro-channel is, the
less possibility of flow boiling instability to occur.
(4) Analyze the impact of axial thermal conductivity in the micro-channel on the
flow boiling process. According to the axial heat conduction capability correlation of
micro-channels proposed by researchers such as Maranzana, based on the parameters
of the experimental conditions, calculate the average M=3.31×10-6 ,and it is far
smaller than the standard value of 10-2, the impacts of micro-channel axial heat
conduction are not considered in the experimental analysis calculations.
(5) When CHF is in annular flow, in addition to the outlet from the high
temperature of the thermocouple T7 at this stage, the other position of the
thermocouple temperature is low and uniformly, but the temperature is higher than the
saturation temperature corresponding to the pressure, which is consistent to heat
transfer mechanism led by convection boiling in annular flow stage. Due to the
continued heating of the wall surface, the liquid film along the direction of flow of the
annular flow in the evaporation effect, the film constantly last thin and partly dry up,
thereby triggering the critical heat flux(CHF) of annular flow stage, in the annular
flow and the mist flow transition stage the gas, liquid, solid three-phase contact line at
the wall is not the role of fresh liquid film wetting appears relatively stable CHF, the
CHF value in annular stage higher than that in the unstable boiling stage.
(6) At the three phases boundary line of gas, liquid, solid in the end of the
annular flow, establish the force balance relationship of surface tension, the force of
inertial force, the viscous force and evaporated momentum force, i.e. when the
evaporation momentum force is greater than or be equal to the sum of the surface
tension, inertial forces and viscous forces when considered reaching the priming
conditions of CHF in the angle of the force, and processing the force equilibrium
relationship obtained the CHF correlation which contained We number and Ca number,
and finally the coefficient values of the CHF correlation obtained through regression
analysis of the experimental parameters.
(7) Substitute the experimental parameters into CHF correlation obtained
according to the force balance principle ,the coefficient values were obtained by
regression analysis that C1=3.6135×10-5, C2=-0.4908, C4=6.3155×10-4, the resulting of
the correlation predictive value are within the deviation range of ±10%,and the results
coincide well with experimental data.
Key words: micro-channels, flow boiling, critical heat flux, model,
instability, liquid film, dry-out, force balance principle
目 录
中文摘要
ABSTRACT
第一章 绪 论………………………………………………………………………….1
§1.1 课题背景及意义 ............................................................................................ 1
§1.2 通道划分标准 ................................................................................................ 1
§1.3 微细通道内的流动沸腾 ................................................................................ 3
§1.3.1 微细通道内的沸腾起始点 .................................................................... 3
§1.3.2 微细通道内的流动沸腾不稳定性 ........................................................ 4
§1.3.3 微细通道内的流动沸腾换热特点 ........................................................ 4
§1.4 国内外对微细通道 CHF 的研究现状 .......................................................... 6
§1.4.1 通道内 CHF 的分类 .............................................................................. 6
§1.4.2 国内外对微细通道 CHF 的实验研究 .................................................. 7
§1.4.3 微细通道 CHF 的经验关联式 ............................................................ 10
§1.4.4 微细通道 CHF 的理论模型 ................................................................. 11
§1.5 本课题研究内容及工作 .............................................................................. 12
第二章 微细通道流动沸腾实验装置系统…………………………………………...13
§2.1 实验目的和内容 .......................................................................................... 13
§2.2 实验装置系统 .............................................................................................. 13
§2.3 实验段 .......................................................................................................... 15
§2.4 测量方法 ...................................................................................................... 18
§2.4.1 温度测量 .............................................................................................. 18
§2.4.2 压力测量 .............................................................................................. 19
§2.4.3 加热功率 .............................................................................................. 19
§2.4.4 质量流量 .............................................................................................. 19
§2.4.5 数据采集 .............................................................................................. 20
§2.5 实验操作步骤 .............................................................................................. 20
§2.6 实验数据处理 .............................................................................................. 21
§2.7 不确定度分析 .............................................................................................. 23
§2.8 本章小结 ...................................................................................................... 24
第三章 流动沸腾不稳定性研究……………………………………………………...25
§3.1 微通道内的沸腾不稳定性特征 .................................................................. 25
§3.1.1 微通道内的静态不稳定性特征 .......................................................... 25
§3.1.2 微通道内的动态不稳定性特征 .......................................................... 25
§3.1.3 微通道内部流动系统压力的研究 ...................................................... 25
§3.1.4 微通道流动系统外部驱动压力的研究 .............................................. 28
§3.2 微通道内沸腾不稳定性特征实验 .............................................................. 29
§3.2.1 微通道内压降——流量特征曲线 ...................................................... 29
§3.2.2 微通道内温度压力流量的不稳定性 .................................................. 34
§3.2.3 稳定沸腾区和不稳定沸腾区的划分 .................................................. 43
§3.3 本章小结 ...................................................................................................... 48
第四章 微细通道内 CHF实验研究…………………………………………………..50
§4.1 微细通道轴向导热分析 .............................................................................. 50
§4.2 微细通道内不同条件下两种 CHF 的壁温分布特点 ................................ 50
§4.2.1 微细通道内不稳定沸腾阶段的 CHF 的壁温分布 ............................ 50
§4.2.2 微细通道内环状流阶段 CHF 的壁温分布 ........................................ 52
§4.3 微细通道 CHF 与壁面过热度的关系 ........................................................ 53
§4.4 微细通道 CHF 与干度的关系 .................................................................... 56
§4.5 微细通道 CHF 与各种 CHF 关联式预测值的比较 ................................... 57
§4.6 本章小结 ...................................................................................................... 59
第五章 微细通道 CHF模型研究……………………………………………………..61
§5.1 建立微细通道流动沸腾 CHF 模型的基本条件 ........................................ 61
§5 .1.1 建立微细通道 CHF 模型的前提 ........................................................ 61
§5.1.2 建立微细通道 CHF 模型的基本假设 ................................................ 62
§5.1.3 微细通道内各种作用力的研究 .......................................................... 62
§5.2 建立微细通道流动沸腾 CHF 模型 ............................................................ 66
§5.2.1 微细通道 CHF 模型的无量纲数组 .................................................... 66
§5.2.2 微细通道 CHF 模型的受力分析 ........................................................ 67
§5.2.3 微细通道 CHF 模型中接触角的分析 ................................................ 70
§5.3 微细通道 CHF 与模型预测关联式的关系 ................................................ 71
§5.4 本章小结 ...................................................................................................... 72
第六章 总 结………………………………………………………………………...74
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作者：赵德峰
分类：高等教育资料
价格：15积分
属性：94 页
大小：4.32MB
格式：PDF
时间：2025-01-09
