An Experimental Study on the Void Fraction for Gas-Liquid Two-Phase Flows in a Horizontal Pipe

The flow patterns and the void fraction related to a gas-liquid two-phase flow in a small channel are experimentally studied.The test channel is a transparent quartz glass circular channel with an inner diameter of 6.68 mm.The working fluids are air and water and their superficial velocities range from 0.014 to 8.127 m/s and from 0.0238 to 0.556 m/s,respectively.The void fraction is determined using the flow pattern images captured by a high-speed camera,while quick closing valves are used for verification.Four flow patterns are analyzed in experiments:slug flow,bubbly flow,annular flow and stratified flow.For intermittent flows(bubbly flow and slug flow),the cross-sectional void fraction is in a borderline condition while its probability distribution function(PDF)image displays a bimodal structure.For continuous flows(annular flow and stratified flow)the cross-sectional void fraction behaves as a fluctuating continuous curve while the(PDF)image displays a single peak structure.The volumetric void fraction data are also compared with available predictive formulas,and the results show that the agreement is very good.An effort is also provided to improve the so-called Gregory and Scott model using the available data.

Flow Behaviour Analysis and Experimental Investigation for Emitter Micro-channels

The existing research of the flow behavior in emitter micro-channels mainly focuses on the single-phase flow behavior.And the recent micro-particle image velocimetry（PIV） experimental research on the flow characteristics in various micro-channels mainly focuses on the single-phase fluid flow.However,using an original-size emitter prototype to perform the experiments on the two-phase flow characteristics of the labyrinth channels is seldom reported.In this paper,the practical flow of water,mixed with sand escaped from filtering,in the labyrinth channel,is investigated.And some research work on the clogging mechanism of the labyrinth channel＇s structure is conducted.Computational fluid dynamics（CFD） analysis has been performed on liquid-solid two-phase flow in labyrinth-channel emitters.Based on flow visualization technology-micro-PIV,the flow in labyrinth channel has been photographed and recorded.The path line graph and velocity vector graph are obtained through the post-treatment of experimental results.The graphs agree well with CFD analysis results,so CFD analysis can be used in optimal design of labyrinth-channel emitters.And the optimized anti-clogging structures of the rectangular channel and zigzag channel have been designed here.The CFD numerical simulation and the micro-PIV experiments analysis on labyrinth-channel emitter,make the ＂black box＂ of the flow behavior in the emitter channel broken.Furthermore,the proposed research promotes an advanced method to evaluate the emitter＇s performance and can be used to conducting the optimal design of the labyrinth-channel emitters.

Solid Particles Injection in Gas Turbulent Channel Flow

This paper represents a review of the recent researches that investigate the behavior of the gas turbulent flow laden with solid particles. The significant parameters that influence the interactions between the both phases, such as particle size, loading ratio and the gas velocity, have been extensively reviewed. Those parameters are presented in dimensionless numbers in which the applicability of studying its effect in terms of all circumstances of the gas turbulent channel flow at different condition is possible. The represented results show that the turbulence degree is proportional to the particle size. It was found that at the most flow conditions even at low mass ratio, the particle shape, density and size significantly alter the turbulence characteristics. However, the results demonstrate that the particle Reynolds number is a vital sign: the turbulence field becomes weaker if particle Reynolds number is lower than the critical limit and vies verse. The gas velocity has a strong effect on the particles settling along the channel flow and as a result, the pressure drop will be affected.

竖直互连小通道内流动沸腾传热强化机理分析

为推动流动沸腾技术在燃料电池散热领域的应用,该文以R141b为工质,对不同流速下的并联直通道及互连小通道内流动沸腾情况进行三维瞬态数值模拟。利用换热系数、基底温度及综合换热因子等参数对比各结构的换热性能,并探究互连小通道的换热强化机理。研究表明:换热趋势随气泡行为呈周期性变化,气泡脱离时的换热效果最佳;由连通口引发的二次流促进热量传递与壁温升高,使通道可提前2 ms满足成核条件,且气泡在10^(-4) m/s以上的二次流速作用下率先脱离;五连通通道的换热系数较并联直通道可提升19.6%~23.3%,继续增加连通口数,换热系数的相对增长率均不足3.5%;涡结构使压降随连通口数增加而增大,且增势并不减弱,八连通通道的压降较并联直通道增加29.5%~42%。可见,二次流在影响气泡行为、强化换热的同时也带来压力损失,综合换热性能与连通口数目不成正相关。

多通道平行流扁管-紧凑式翅片相变蓄热器蓄/放热性能

工业余热浪费严重、利用率较低且实际应用过程中受到时间和空间的限制,需要高效蓄热技术和装置来解决此类问题。提出一种将多通道平行流扁管与紧凑式翅片相结合的新型相变蓄热器,以水为载热流体,月桂酸为相变材料。实验研究了载热流体注入方式、流量、入口温度对蓄热器蓄/放热性能的影响,并分析小温差下蓄热器的传热特性。结果显示,该蓄热器相变材料填充率为82.5%,紧凑式翅片的采用极大强化了相变材料侧换热过程,蓄/放热性能优良。当载热流体入口温度分别为45℃和41℃时,相变材料约在270 min和75 min完成相变,最小蓄/放热温差可达2℃,最小温差时的平均蓄热比功率为25.18 W/kg,平均取热比功率为20.23 W/kg。

小型堆中窄矩形通道自然循环临界热流密度实验研究

针对窄矩形通道在换热过程中有较高功率密度的问题,本文为了解决在小型反应堆中的应用,采用所搭建的小型窄矩形自然循环通道,进行实验研究,并结合BP神经网络方法对实验数据进行预测,分析在不同参数工况下临界热流密度随不同参数的变化情况以及不同参数对临界热流密度的影响程度。研究结果表明:质量流量与系统压力对临界热流密度点的影响呈现正相关;出口干度对临界热流密度呈现负相关;且质量流量对临界热流密度的影响程度最大;压力对临界热流密度的影响程度最小。利用相关实验数据,基于影响因素大小,通过BP神经网络方式,建立了适合于自然循环窄通道小堆的模型。BP神经网络算法的预测值与实验值符合良好,误差为10%;Katto模型与实验数据相比误差较大,Zhang公式和拟合公式的误差较小,所建立的临界热流密度模型可作为窄矩形通道自然循环临界热流密度的计算公式。

Experimental study on the flow pattern and pressure gradient of air-water two-phase flow in a horizontal circular mini-channel

Experimental studies on the flow pattern and the pressure gradient of gas-liquid co-current two-phase flow in a mini-channel were conducted.The test section was a transparent circular channel of 1.6 mm inner diameter.The working fluids were air and water.The superficial velocities of gas and liquid were in the range of 0.025-66.300 m/s and 0.033-4.935 m/s,respectively.In the present work,the flow pattern and the pressure gradient data were obtained by analyzing the flow images captured by a high-speed camera,and by using the pressure transducer,respectively.As a result,it was found that (1) the obtained flow patterns were bubbly,plug,slug-annular,annular,and chum flows,(2) new experimental correlations on the bubble and plug lengths were proposed,whereas the lengths are the function of the homogeneous void fraction,(3) both gas and liquid superficial velocities affect proportionally to the pressure gradient,whereas it increases with the increase both of JG,JL.In addition,the obtained flow patterns are in a good agreement with that of the available flow pattern maps in the open literatures,such as,Triplett et al.(1999) and Chung and Kawaji (2004).

Analysis on Link Between the Macroscopic and Microscopic Air–Water Properties in Self-Aerated Flows

Self-aeration in high-speed free surface flows occurs commonly and is of interest to ocean engineering, hydraulic engineering, and environmental engineering. For two-phase air–water flows, macroscopic air–water flow properties develop gradually, accompanied by the change of microscopic air–water structures. In this article, representational experimental studies on macroscopic and microscopic characteristics of self-aerated open-channel flows are summarized and compared. The isolated effect of the flow Reynolds number and air quantity on the differences in air count rate and chord size are analyzed and discussed. The results show that the characterized flow depth y, affected by the turbulence transfer, is a specific criterion to distinguish the interior air–water structure development. Two distinct linear trends of self-aeration are found, depending on the y/yvariation with a breaking point at Cmean =0.50. The air count rate and size scale in self-aerated flows are affected by the air quantity of self-aerated flows, even with identical flow Reynolds numbers. Thus, a specific parameter is proposed to assess the air–water structures and a series of self-similarity relationships in self-aeration properties are obtained. The link between macroscopic and microscopic air–water properties results in significant scale effect on air–water structures in self-aerated flows.

Experiment on Boiling Heat Transfer of Refrigerant R134a in Mini-channels

The flow boiling heat transfer characteristics of refrigerant R134 a flowing inside two different kinds of minichannels are investigated. One channel is multi-port extruded with the hydraulic diameter of 0.63 mm,and the other one is rectangular with offset fins and a hydraulic diameter of 1.28 mm. The experiments are performed with a mass flow rate between 68 and 630 kg/(m^2·s),a heat flux between 9 and 64 kW/m^2,and a saturation pressure between 0.24 and 0.63 MPa,under the constant heat flux heating mode. It is found that the effect of mass flow rate on boiling heat transfer is related to heat flux,and that with the increase of heat flux,the effect can only be efficient in higher vapor quality region. The effects of heat flux and saturation pressure on boiling heat transfer are related to a threshold vapor quality,and the value will gradually decrease with the increase of heat flux or saturation pressure. Based on these analyses,a new correlation is proposed to predict the boiling heat transfer coefficient of refrigerant R134 a in the mini-channels under the experimental conditions.

RESEARCH ON THE EFFECT OF CYLINDER PARTICLES ON THE TURBULENT PROPERTIES IN PARTICULATE FLOWS

The fluid fluctuating velocity equations which include the term of cylinder particles were established. The turbulent intensity and Reynolds stress of fluid were obtained by averaging fluctuating velocity based on the solution of the fluctuating velocity equations. Above approach was used to solve the channel turbulent flows, and computational results were compared with the experimental ones for the case of single phase flow. The effects of volume fraction of particles, the ratio of particle length to diameter and the particle relaxation time on turbulent properties were illustrated by changing cylinder particle parameters. It is shown that particles play a restraining role to turbulent properties in the flows. The degree of restraint is directly proportional to the volume fraction of particle, the ratio of particle length to diameter and inversely proportional to particle relaxation time.

轴面流道类型对径向直叶片水轮机的性能影响

针对径向直叶片水轮机轴面流道做混流式和全径向式布置时对性能的影响进行研究。首先建立径向直叶片水轮机的理论模型,然后基于两种不同类型的轴面流道进行转轮设计,最后通过数值仿真对其外特性和内部流场进行分析对比。研究表明,两种方案均能适应超小流量和较宽的水头变化范围,采用混流式流道方案时最优数值预测效率为81.4%,较全径向式流道方案偏大1.8%,并具有较高的过流能力。经试验检验混流式流道方案的最优效率约74.2%,基本满足超小流量余能回收的需要。研究成果为超小流量余能回收水轮机的设计提供参考。

正方形小通道内气液两相流垂直向上流动特性

辅助高速摄影仪对正方形小通道内氮气-水两相流向上流动进行可视化观察,对流动特性进行了实验研究,获得了典型的流型图像。采用数字图像处理技术对流型图像进行了处理,检测得到气相的周长、面积,并通过提出的假想圆柱体模型计算和统计得到了截面含气率。将压降实验数据分析结果与典型的分相流、均相流压降模型预测值比较,结果表明,Chisholm关系式能较好地预测两相流的压降变化,Lee&Lee关系式和Dukler关系式可较好地预测低表观速度时的两相流压降。

氮气-水两相流流型平滑Wigner三谱切片时频特征

将平滑Wigner三谱切片理论应用到混沌序列(Lorenz)、分形序列(Conway)和周期序列(Sin),检验了抗噪、抑制交叉性和能量集中性能力。结果表明:平滑Wigner三谱切片方法在这三方面性能上具有明显的优势,可以应用到现场采集到的波动信号上。在此基础上,对水力直径为1.15mm的矩形小通道内氮气-水两相流型的差压信号进行了研究。通过对流型差压信号平滑Wigner三谱切片、等高线以及二次切片的分析揭示了不同流型的演化规律,同时也为其他不同介质的多相流动特性分析与流型辨识提供了一个新的思路。

小通道内两相流摩擦压降计算方法评价

从文献中收集了2902个小通道内的两相流摩擦压降实验数据，实验工质包括R123、R134a、R22、R236ea、R245fa、R404a、R407C、R410a、R507、CO2、水和空气，流道当量直径范围0．51—12mm，气-液相雷诺数范围10〈Re1〈37000，气相雷诺数范围3〈ReR〈4x10^5。基于这些实验数据，对11个小通道内的两相流摩擦压降计算模型和方法进行了评价。结果表明，在层流区域，Lockhart-Martinelli、Mishima-Hibild、Zhang-Mishima以及Lee．Mudawar方法相近，而Muller-Steinhagen-Heck方法在紊流区精度最高，平均误差为34．8％。基于Chisholm方法给出了小通道内的两相流摩擦压降修正计算关系式，计算表明，该关系式在层流和紊流范围内优于其他公式。

水平矩形小通道内气-液两相流摩擦压降的研究

本文以氮气和水为工质,在水平矩形小通道(d_h=0.99mm)中对两相流摩擦压降进行了实验研究.实验是在大气压力下进行的,氮气的折算流速的范围为0.017～33.3m/s,水的折算流速的范围为0.1～5m/s.实验对所得的219个数据点进行了分析,并同L&M关系式、L&L关系式、均相流模型以及均相流修正模型进行了比较,得出:(1)L&M关系式比均相流模型、均相流修正模型以及L&L关系式的偏差都小,能更好地预测两相流压降变化.(2)L&M关系式中的C在不同的流型(流型是由U_(GS)、U_(LS)以及d_h决定)具有不同的值,在同一U_(LS)下,C随X(U_(GS))的变化呈现一定的规律性,在X=7左右,C出现最大值,而此处恰好是块状流最激烈区域.但是C随U_(LS)没有一定的规律性.

小通道气液两相流电容测量方法研究

本文设计了一套用于小通道气液两相流的电容测量系统,并对内径为1.56 mm、2.65 mm和3.96 mm的玻璃管气液两相流进行了实验研究.文中首先对电容方法在小通道下的应用做了探索性尝试,设计了用于小通道气液两相流的电容传感器;然后利用所设计的电容传感器对小通道气液两相流弹状流电容动态数据进行采集、处理和分析;最后利用相关原理对气弹速度的测量进行了研究。研究结果表明所提出的电容方法可用于小通道气液两相流的分析研究中,是一种有效的小通道气液两相流参数检测手段,并为小通道两相流检测的研究提供了一定的借鉴.

水平矩形小通道内气—液两相流流动特性的研究

以氮气和水为工质，在水平矩形小通道（dh=0．99mm）中对两相流摩擦压降和流型进行了实验研究。实验在大气压力下进行，氮气的折算流速的范围为0．017～33．3m／s，水的折算流速的范围为0．1～5m／s。对实验所得的219个数据点进行分析，并与L＆M关系式、H＆S关系式（修正了C值的L＆M关系式）、均相流模型以及均相流修正模型进行了比较。得出：（1）L＆M关系式比均相流模型、均相流修正模型以及H＆S关系式的偏差都小，能更好地预测两相流压降变化。（2）L＆M关系式中的C在不同的流型（流型是由UGS、ULS以及dh决定）具有不同的值，在同一ULS下，C随X（UGS）的变化呈现一定的规律性，在X=7左右，C出现最大值，而此处恰好是块状流最激烈区域。但是C随ULS没有一定的规律性。同时，通过可视化方法（高速摄像仪）和压差波动相结合的方法初步确定了各个流型的范围。

矩形小通道内气液两相流垂直向上流动特性

以氮气和水为实验介质,利用高速摄像机对水力直径为1.15 mm的矩形小通道内的气液两相垂直向上流动特性进行可视化研究,依次得到泡状流、弹状流、搅拌流和环状流4种典型的流型图像。针对小通道内气泡之间相互无遮掩性的优势,运用图像处理技术对流型图像分形增强,检测气泡边缘并填充后根据提出的气相体积模型,得到两相流动的含气率。结合实验数据,根据分液相Reynolds数把流动分为层流区、过渡区和紊流区,并对Chisholm关系式进行修正,结果表明:修正后的压降模型能较好地预测本文实验结果。

微小槽道散热器流动与换热实验研究

以 0 .4mm× 2 .0mm× 2 0mm的微小矩形槽道蔟为实验段 ,对水和 6 6 %乙二醇水溶液在底部加热的微小槽道散热器中的流动与换热特性进行了实验研究 ,实验的Re数范围为 2～ 2 5 0 0。实验结果表明 :水和乙二醇水溶液工质在微槽散热器中的流动阻力系数随Re数的增大而减小 ;对流换热的Nu数均随着Re数的增大而增加 ;在相同Re数下 ,Pr数大的乙二醇水溶液工质的Nu数大于水的Nu数。在实验基础上 。

船用燃气轮机一次表面回热器的设计分析

提出了一种新型紧凑式回热器———一次表面回热器(PSR)的设计技术。结合船用ICR燃气轮机一次表面回热器的研发,简述PSR的结构特点及其设计计算的理论依据,并给出了设计算例。研究表明,一次表面回热器具有极高的紧凑性和卓越的换热性能,因而这种先进的热交换装置必将替代那些常规的热交换器,在船用动力装置及先进热工程设施中发挥重要作用。