自调节液位控制装置在电厂的应用

火力发电厂的锅炉和汽轮发电机组系统中存在许多汽液两相流装置，要求水位的控制越稳越好，水位控制平稳。龙凤热电厂应用西安大恒节能技术有限公司生产的“汽液两相流自调节液位控制装置”进行改造，该装置控制机构简单，水位控制相当平稳。通过改造既有利于安全生产，另一方面更有利于经济运行，节约了发电成本，同时提高了经济性。     

高压加热器疏水采用汽液两相流的经济性分析

探讨了江西新余发电有限责任公司2号机高加疏水系统改造前后的运行状况,简介汽液两相流自调节装置的原理,并对系统改造前后的经济性进行了定量计算。     

新型液气两相流自调节疏水器在电厂中的应用

发电厂回热加热器因疏水器的工作可靠性差而长期处于无水位运行,韶关发电厂在疏水器改造中应用了新型汽液两相流自调节疏水器,改造实践证明该种疏水器工作可靠,维护方便,节能效果明显。     

汽液两相流调节器在回热系统中的应用研究

本文介绍了汽液两相流调节器的工作原理,对此调节器的特性进行了分析,并结合应用实例阐述了汽液两相流调节器在实际应用中的优越性。     

基于反问题理论的汽液两相上升流流型预测与实验研究

汽液两相流流型的测量在两相流研究中占有重要地位。应用均相流模型建立了圆管内汽液两相上升流压力分布,基于反问题理论反演了汽液两相的物性参数,将反演结果与流型图结合,精确地预测了管内流型,计算结果与实验结果进行了对比,误差小于5%。提出的反演流型的方法,可以推广到水平管、螺旋管,为工程上的汽液两相流设备安全性分析、稳定性分析等提供了一种简单可靠的技术方法。     

进水温度对汽液两相流激波升压特性影响的实验研究

采用实验方法研究了进水温度对汽液两相流激波升压特性的影响。实验采用供热机组的工业抽汽;由蒸汽喷嘴,混合腔及相应的阀门和管道组成汽液两相流激波升压装置,实验发现存在一个临界进水温度,当水温度大于该临界值后,汽液两相流激波升压装置的升压特性将严重下降。     

汽液两相流疏水器故障分析

本文介绍了汽液两相流疏水器工作原理和过程,运行过程中由于低压加热器汽液两相流疏水器故障导致水位大幅波动,不能维持正常水位,阐述了低加水位大幅波动的现象和原因分析以及解决的方法.     

加热器疏水调阀后管道的研究与应用

为研究汽液两相流管道的流动特性及选型方法,以加热器疏水调阀后汽液两相流动典型代表为例,对汽液两相流的产生机理、危害及其应对策略进行了研究分析,并以工程热力学、流体力学及汽液两相流的均相流模型为主要理论基础,结合核电工程实际,介绍了一种简单、实用的加热器疏水调阀后管道计算选型的方法,填补了设计工作中的"模糊地带",为后续项目设计工作提供参考。     

汽—液两相流通过孔板的阻力计算方法

本文根据汽-液两相流一维分相流动模型.提出了计算汽-液两相流通过孔板的局部阻力系数和局都阻力的计算方法.为适应工程计算的需要,作者还提供了相应的线算图.     

高加疏水改造

分析了胜利发电厂I期两台机组高加疏水改造前后的运行工况,介绍了汽液两相流自调整装置的原理,并对系统改造后的经济性进行了定量计算。     

Study of a Vertical Boiling Flow in Rectangular Mini-Channels

Mini-channel heat exchangers with boiling flows present optimal performances: they are highly efficient and compact and require low fluid mass. However, classical correlations for two-phase flow in macro-channels fail in predicting the heat transfer coefficient and the eventual premature dry-out in mini-channels. Therefore, new studies are needed to provide better knowledge on flow boiling phenomena in small, confined spaces. The proposed paper presents an experimental study of vertical flow boiling in mini-channels. The pressure drop and the heat transfer coefficient in the test section have been measured for a variety of conditions. Different heat flux, inlet vapor quality, and mass flow rate values have been tested. A critical dry-out vapor quality depending on the mass flow rate has been found. Nevertheless, the superficial velocity appears to be much more appropriate than the vapor quality or the mass flow rate for the dry-out occurrence prediction. A clean dependence with a single critical velocity value has been found.     

CO2跨临界循环吸热过程换热性能理论分析

通过对两相流型和干涸现象进行分析，发现CO2在吸热沸腾过程中，环状流是主要的流型，液滴夹带和沉降是支持环状流最可能的机理。与其他制冷剂相比，CO2出现环状流以及发生干涸时的干度值要低得多。并且干涸前和干涸后的传热特点，以及关联式形式存在很大差别，应该区分对待。因此，研究能淮确描述CO2流动沸腾换热关联式，为CO2跨临界制冷循环蒸发器的优化设计提供理论依据，是非常必要的。     

单面加热竖直窄通道内环状流沸腾传热特性

基于汽芯的动量方程和液膜的质量和动量方程,建立了单面均匀热流竖直窄通道内环状流沸腾传热模型,利用数值法对方程组进行求解,得出了环状流区域的液膜厚度,并进一步预测了环状流两相沸腾传热系数。研究表明:模型预测的两相沸腾传热系数比Mahmound关联式计算值偏小;将不同工况下的291组环状流两相沸腾传热系数实验值与模型预测值进行对比,平均绝对误差为12.7%。     

Thermal and hydraulic analysis of a brazed aluminum evaporator

This paper presents an analytical/computer model to predict the performance of a brazed aluminum evaporator operating under dehumidifying conditions. The evaporator uses small hydraulic diameter, flat multi-channel tubes and louver fins. The in-tube refrigerant flow was divided into three regions including the two-phase, liquid deficient and superheat regions. For each region, correlations were selected from the open literature to calculate the local heat transfer and pressure drop. The effects of refrigerant pressure drop along tube and pressure losses at the tube entrance and exit were accounted for in the heat transfer calculations. The air-side fins were assumed to operate at the fully wet condition and the sensible heat transfer coefficient of the wet fins was assumed to be equal to that of the dry fins. The overall heat transfer coefficient was calculated using the enthalpy driving potential method. The total heat transfer rate and refrigerant pressure drop depend on the ratio of the number of tubes in the first and second passes. Parametric studies were done to illustrate selection of the preferred number of tubes per pass. The average refrigerant side heat transfer coefficient is sensitive to the dry-out vapor quality. However, the total heat transfer rate is relatively insensitive to the dry-out vapor quality. As the air inlet humidity increases, the latent and total heat transfer rates increase, but the sensible heat transfer rate decreases. The program was used to design an R-404A evaporator, for which a prototype was built and tested. The program over-predicted the evaporator capacity by 8%. The over-prediction is believed due to flow mal-distribution in the branch tubes.     

Correlation to Predict the Maximum Heat Flux of a Vertical Closed-Loop Pulsating Heat Pipe

The objective of this study is to experimentally investigate the effect of various parameters on the maximum heat flux of a vertical closed-loop pulsating heat pipe (CLPHP) and the inside phenomena that cause maximum heat flux to occur. A correlation to predict the maximum heat flux using the obtained results was also established. Quantitative and qualitative experiments were conducted and analyzed. A copper CLPHP and a transparent high-temperature glass capillary tube CLPHP were used in the quantitative and qualitative experiments. From the study, it was found that when the internal diameter and number of meandering turns increased, the maximum heat flux increased. However, when the evaporator section length increased, the maximum heat flux decreased. The maximum heat flux of a CLPHP occurs due to the dry-out of liquid film at the evaporator section. This occurs after a two-phase working fluid circulation changes flow pattern from countercurrent slug flow to co-current annular flow, because the vapor velocity increases beyond a critical value. A correlation to predict the maximum heat flux obtained from this study was developed.     

Modelling of fin-and-tube evaporators considering non-uniform in-tube heat transfer

This paper is devoted to the presentation of a new model for fin-and-tube evaporators, focusing on the solid core simulation and its integration with a quasi-homogeneous two-phase flow model for the in-tube refrigerant flow. Special attention is given to separated in-tube flow patterns (stratified, stratified-wavy), because of their importance in liquid overfeed and domestic refrigerator evaporators and the impact on the solid core temperature distribution. The paper presents the solid core formulation and numerical method, the in-tube two-phase flow model, and describes the proposed integration algorithm between them. A selected single-tube baseline case is analysed in full detail, showing the impact of stratified flow on the fin-and-tube temperature distributions. Additional studies are finally presented analysing different flow transitions (single phase to stratified flow, stratified-wavy flow to annular flow, annular flow to partial dry-out) and several operating parameters (flow regime, tube material, tube thickness). Special attention is given to the influence of the flow pattern on the fin-and-tube core temperature profiles.     

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.     

Intermittent heat transportation by discharge of accumulated vapor

A heat transporting cycle already proposed by the authors was composed of the following processes: (A) accumulation of high-pressure vapor in an evaporator vessel, (B) discharge of the accumulated vapor from the evaporator followed by the condensation of a part of the vapor in the downstream condenser and the returning vapor–liquid two-phase flow from the condenser toward the evaporator, (C) return of the liquid to the evaporator after stopping of the flow through a check valve. In the present study, the flow and heat transport performances of a downward heat transport closed loop utilizing the above-mentioned cycle was investigated experimentally by using a setup of 3 and 5 m in height. The inner tube diameter was 10 mm. In the riser tube, high-speed upward two-phase flow with disturbance waves appeared. Experimental flow conditions and pressure drop for this annular flow were compared with the correlations of Fukano and Lockhart–Martinelli. In some cases the operation ceased due to the blockage of this two-phase flow by the tall condensate liquid column formed in the riser. A precise investigation showed that the vapor generation by flash evaporation in the evaporator during the period (B) played a very important role in avoiding this blockage effect.     

Analysis of heat transfer with liquid-vapor phase change in a forced-flow fluid moving through porous media

This study focuses on the experimental analysis of transient-regime heat transfer with liquidvapor phase change in a fluid as it flows through a porous media composed of small bronze spheres. Three distinct zones can be observed: liquid, two-phase and superheated vapor. The boundaries between these zones are determined using temperature and pressure fields. An N-shaped profile is observed for the temperature values along the main flow axis. The first local maximum value on the temperature curve corresponds to the boundary between the liquid zone and the two-phase zone. When a local minimum temperature exists, it corresponds to the boundary between the two-phase and the vapor zones. A finite element numerical simulation is used to predict the saturation field, which is numerically determined from the boundaries of the two-phase zone and of the experimental temperature field. The liquid and vapor pressure fields are then deduced for all three phase zones of the porous medium.