气液两相流动及沸腾传热流体模化分析

基于制冷剂类物质热物性表与水和水蒸气热力性质图表,计算并比较了R12、R22、R123、R134a在相同气液密度比条件下模化水热力过程的能力;应用相似原理与量纲理论分析了流体模化方法在研究气液两相流动特性、高温高压传热过程、临界热流密度现象以及近临界和超临界传热方面的优势与方法.结果表明:制冷剂类物质具有良好的热力性质,其中R134a在相同气液密度比条件下的压力值仅约为水的1/5,而且其臭氧消耗潜能值为0,是环境友好的理想模化流体.提出并探讨了从本质上革新准则数以及基于模型探索新的模化条件和发展新的准则关系式的流体模化技术发展思路.     

气液两相流相空间复杂网络非线性动力学特性分析

气液两相流动作为一个具有混沌特征的非线性动力学系统,其流型演化动力学特性尚未取得清楚的认识。以垂直上升管内空气-水两相流为研究对象,在实验获取气液两相流流型压差波动时间序列的基础上,将空气-水两相流的压差波动时间序列映射到流型相空间复杂网络对其非线性动力学特性进行了分析。通过分析发现在相空间不稳定周期轨的吸引特性作用下,不同流型的相空间复杂网络现呈出明显不同的网络结构,并且网络密度的演化趋势与流型的转化过程相吻合,较好地反映了垂直上升管内空气-水两相流的非线性动力学特性。     

液幕状气液两相流流动特性的实验研究

提出了一种名为“液幕状气液两相流”的新流型。对液幕状气液两相流的流动特性进行了实验研究,着重研究液幕状气液两相流的床层高度和阻力特性以及气相和液相流动速度之间的关系,得到了当量床层高度、实际床层高度以及液幕床层阻力系数计算的关联式。这些关联式为液幕状气液两相流的研究提供了基础性的科学实验数据。     

窄通道内流动沸腾强化换热研究进展

窄通道具有结构紧凑、传热效率高等优点。随着科技发展,窄通道已经成为强化换热的常用结构形式之一,被广泛应用于各种换热设备。由于窄通道内间隙内气泡的尺寸受限,气泡在发展过程中会受到挤压而发生变形,带走大量的潜热,引起汽液界面的扰动,换热性能较常规通道有很大区别。本文综述了窄通道内的主要流型及转变准则;介绍了几何与工况参数变化对窄通道内换热效果影响的传热实验研究;分析了窄通道中传热机理以及两相摩擦压降机理,并对关联式进行了总结与评述;对窄通道内强化换热的机理与进一步强化换热的方法进行归纳总结;结合目前实验与理论研究总结了现存问题,为窄通道内流动沸腾强化换热的进一步研究提供了参考。     

气液两相泡状流动中的压力分析

利用相平均和含气率α权重时间平均推导了气液两相泡状流的动量方程，分析了动量方程中的压力项，并对T型管中的气液两相泡状流进行了数值模拟，确定其含气率和压力的分布规律。图2参7     

紧凑式两相换热器中管式换热元件沸腾传热实验研究

以烃类物质（丙烷和正戊烷）作为工质,进行了紧凑式换热器中带有加工配置表面的管式换热元件池沸腾实验研究。其中,单管实验温度工况为２５３Ｋ￣２９３Ｋ（饱和工质）。实验中所采用的换热元件为重入式结构加工配置表面的强化传热管和光管以及低助管。针对由４５根光管或带有加工配置表面的管子所构成的叉排管束进行了实验研究,实验工质为丙烷和正戊烷,实验温度分别为两种工质在２６３Ｋ和３０８Ｋ之间的饱和和温度。并将所得实     

氧气顶吹转炉中的两相流流动

氧气顶吹转炉中的二次燃烧现象是一个非常复杂的现象,在本文中提出了两个三难数学模型去解释这个过程中的传输现象。第一个模型处理单相流,第二个模型把泡沫渣和炉气作为两个分离相来考虑。双方程湍流模型用于处理流体的湍流性能,本文作了一些简单的假设,利用这个模型预示了气体浓度和气体浓度脉动,这个模型同样预报了炉气的流动方式、温度场和湍流火焰形状。本文还讨论了二次喷嘴角度对二次燃烧的影响。这个模型可以用于优化二次氧枪设计。     

近临界压力区两相流沸腾传热特性的研究

本文介绍了近临界压力大容量机组的两相流的沸腾传热特性的研究。通过试验研究,采用内螺纹管能使传热特性得到改善,并进行了预测计算,可供有关技术人员参考。     

多孔微通道流动沸腾换热特性的实验研究

本文通过实验的方法对烧结的多孔微通道和铜基微通道的沸腾换热性能和流动不稳定进行研究.实验工质选用去离子水,采用的铜粉粒径分别为30μm、50μm、90 μm,烧结底厚为200 μm和400 μm.采取控制变量的方式,研究改变入口温度、铜粉粒径大小、入口流量对多孔微通道和铜基微通道换热性能的影响.研究表明:多孔微通道最优的厚度粒径比在2～5之间,在此区间的多孔微通道可以提高沸腾传热的性能.其中厚度粒径比为2和4的多孔微通道的最大换热系数是铜基微通道的换热系数的5倍.多孔微通道相对于铜基微通道有更好的换热能力,有着较低的壁面温度.     

Effect of aspect ratio on saturated boiling flow in microchannels with nonuniform heat flux

Microchannel two‐phase flow is an effective cooling method used in microelectronics, in which the heat flux density is unevenly distributed usually. The paper is focused on numerical study the effect of aspect ratio on the flow boiling of microchannels with nonuniform heat flux. The heat source is a three‐dimensional (3D) integrated circuit. 3D microchannel model and volume of fluid method are coupled in numerical simulation. The results show that the aspect ratio has no relationship with the two‐phase pressure drop of the microchannel. It has a certain influence on the distribution of bubble shape. In terms of the heat transfer coefficient, the aspect ratio has a certain influence on a section of the inlet. Due to the nucleate boiling, the convective heat transfer in the remaining areas is the dominant factor and the average heat transfer coefficient is mainly determined by the heat flux at the bottom of the channel.     

Flow Pattern and Heat Transfer Behavior of Boiling Two—Phase flow in Inclined Pipes

Movable Electrical Conducting Probe (MECP), a kind of simple and reliable measuring transducer, used for predicting full-flow-path flow pattern in a boiling vapor/liquid two-phase flow is introduced in this paper. When the test pipe is set at different inclination angles, several kinds of flow patterns, such as bubble, slug, churn, intermittent, and annular flows, may be observed in accordance with the locations of MECP. By means of flow pattern analysis, flow field numerical calculations have been carried out, and heat transfer coefficient correlations along full-flow-path derived. The results show that heat transfer performance of boiling two-phase flow could be significantly augmented as expected in some flow pattern zones.The results of the investigation, measuring techniques and conclusions contained in this paper would be a useful reference in foundational research for prediction of flow pattern and heat transfer behavior in boiling two-phase flow, as well as for turbine vane liquid-cooling design.     

表面微结构对流动沸腾中核沸腾抑制因子的影响

用两根内表面微结构不同的水平光滑管环状流区流动沸腾换热实验数据，采用叠加模型分别建立了流动沸腾换热关系式，并比较它们的抑制因子。结果表明，表面微结构对抑制因子有显的影响；当表面的平均凹腔半径较大时，抑制因子明显增大。表明表面微结构改变对流动沸腾换热能起到较好的强化作用。     

狭缝中流动沸腾传热过冷沸腾起始点的实验研究

以间隙为1．0mm和1．5mm的环形狭缝通道中流动沸腾传热的实验数据为基础，分析了影响过冷沸腾起始点热负荷的主要因素，给出了计算环形狭缝通道中流动沸腾传热过冷沸腾起始点的经验关联式，并将计算结果与实验值进行了比较。该关联式可以用来预测实验范围内的过冷沸腾起始点的热负荷。     

二相流基本方程的封闭问题及水气二相流数学模型

讨论了平均二相流基本方程的封闭问题。在此基础上 ,从建立数学模型的角度 ,提出将水利工程中的水气二相流划分为稀疏气泡流区、气相连续流区和掺气形成区 (稠密气泡流 )三个区 ;根据已有的方程封闭的研究成果 ,提出了可用于稀疏气泡流计算的双流体模型。     

竖直矩形窄通道内流动沸腾局部换热特性实验研究

为了明确竖直矩形窄通道内各阶段流动沸腾的换热特性,优化换热器性能,以去离子水为工质,对尺寸为720 mm×250 mm×3.5 mm的单面电加热竖直矩形窄通道内的流动沸腾换热进行实验研究,分析了质流密度、进口温度、热流密度对流动沸腾局部换热特性的影响。并在已有流动沸腾传热关联式的基础上,对实验数据进行非线性回归分析,得到适用于实验工况下的新流动沸腾传热关联式。结果表明：质流密度增大对流动沸腾段换热特性有强化作用,对核态沸腾段换热特性有削弱作用;热流密度对核态沸腾影响剧烈,但对流动沸腾的影响不明显;入口温度越高,流体会越早进入过冷沸腾阶段,但对局部传热系数的影响不明显;新流动沸腾传热关联式与实验值的平均相对误差为23.87%,其中74.19%的预测值在±25%内,83.87%的预测值在±50%以内,能很好地预测本实验工况下矩形窄通道内流动沸腾的局部传热系数。     

Subcooled flow boiling heat transfer in narrow passages

Subcooled flow boiling heat transfer coefficients for refrigerants R11 and HCFC123 in smooth copper tubes of small diameter have been investigated experimentally. The parameter ranges examined are: tube diameters of 0.92 and 1.95 mm; heat fluxes 11-170 kW m⁻²; mass fluxes 110-1840 kg m⁻² s⁻¹. The range of liquid Reynolds numbers encompassed by the data set is 450 to 12,000.The data in the subcooled and saturated regions are well represented by the simple addition of convective and nucleate boiling heat transfer contributions

     

Investigation of flow boiling in horizontal tubes: Part I—A new diabatic two-phase flow pattern map

Several important modifications to the flow pattern map of Kattan-Thome-Favrat [J. Heat Transfer 120(1) (1998) 140-147] made, resulting in a significantly new version of the map. Based on the dynamic void fraction measurements described in [Int. J. Multiphase Flow 30 (2004) 125-137], the stratified-wavy region has been subdivided into three subzones: slug, slug/stratified-wavy and stratified-wavy. Furthermore, annular-to-dryout and dryout-to-mist flow transition curves have been added and integrated into the new flow pattern map, identified by distinct trends of the heat transfer coefficient as a function of vapor quality and by flow pattern observations to determine (and then predict) the inception and completion of dryout in horizontal tubes.     

Heat transfer and pressure drop penalization terms (exergy losses) during flow boiling of refrigerants

Heat transfer coefficient and pressure drop correlations are used to analyse the boiling heat transfer performance potentials in plain evaporator tubes of several conventional refrigerants and two newer fluorinated propene isomers possessing low global warming potentials. These correlations are used to calculate two penalization quantities expressed in terms of the refrigerant saturation temperature drop due to pressure drop and the driving temperature difference. These penalization terms are combined into a single Performance Evaluation Criterion dubbed Total Temperature Penalization (TTP). Using the two penalization terms and the TTP, several refrigerants, including the newer alternatives R1234yf (CF₃CF=CH₂) and R1234ze(E) (CF₃CH=CHF ) , are evaluated for their boiling heat transfer performance potentials in plain evaporator tubes. Furthermore, the usefulness of the technique is illustrated through several examples of the optimization of evaporator tube length. Copyright © 2012 John Wiley & Sons, Ltd.