An Experimental Investigation into the Effect of Surfactants on Air-Water Two-Phase Flow in Minichannels

The complex interfacial phenomena involved in two-phase gas-liquid flow have defied mathematical simplification and modeling. However, these systems are used in heat exchangers, condensers, chemical processing plants, nuclear reactor systems, and fuel cells. The present work considers a 1 mm-square minichannel and adiabatic flows corresponding to practical PEM fuel cell conditions. Pressure drop data is collected over mass fluxes of 4.0–12.0 kg/m²s for air and 0.5–21.6 kg/m²s for water, corresponding to superficial gas and liquid velocities of 3.19–10.06 m/s and 0.0005–0.022 m/s, respectively. The experiments are repeated with water-surfactant mixtures of different concentrations in order to quantify the surface tension effects, as it is recognized that surface tension is an important parameter for two-phase flow in minichannels. The accuracy of various two-phase pressure drop models is evaluated, and a new model for laminar-laminar two-phase flow pressure drop is developed.     

电弧炉用氧技术的多相流数值模拟研究

对150 t电弧炉冶炼过程中单支氧枪供氧流量分别为500,1 450,1 800,2 000 m<'3>/h时氧气射流冲击熔池进行了三维三相流数值模拟.模拟研究表明,随着供氧流量的增加,熔池中钢液和渣液的流动速度、裸露钢液面面积及射流的冲击深度均增大.由数值模拟和水模得到的供氧流量与射流冲击深度的规律得到了很好的吻合....     

Modeling of Bubble Growth Under an Impinging Free Planar Water Jet

Developing a wall heat flux-partitioning model (WHFP) would reduce the empiricism commonly encountered in modeling of jet impinging boiling (JIB). An integral and necessary part of any WHFP model is a method to predict the area fraction on the heated surface influenced by bubble generation. Addressing such need, a scenario identification procedure (SIP) has been developed to predict bubble growth termination (BGT) during JIB. Two conditions have been considered in determining the most probable BGT scenario for JIB configuration: (1) the thermal equilibrium of the bubble with the surrounding liquid bulk, and (2) the dynamic equilibrium of forces acting on the bubble. If the bubble diameter corresponding to thermal equilibrium is reached first, then most probably the bubble will locally collapse. If the bubble diameter associated with dynamic equilibrium is reached first then bubble departure and sliding along the heated surface are expected to take place. The BGT predictions obtained using the developed SIP has been validated using visual observations of nucleate JIB on a horizontal flat surface. The planar free water jet velocity, degree of water subcooling, and surface superheat were varied between 0.4 m/s and 1.7 m/s, 10°C and 28°C, and 0°C and 30°C, respectively. Bubble dynamics was observed over a span of the heated surface from jet stagnation 10 ten jet widths. Experimental results show that the proposed SIP is capable of predicting both the prevailing BGT scenario and the maximum bubble diameter reasonably well. As mentioned before, these are very important elements in developing a WHFP model for JIB.     

Large-Eddy Simulations and Heat-Flux Modeling in a Turbulent Impinging Jet

This article documents the results of an investigation into aspects of the simulation and modeling of turbulent jets that impinge orthogonally on a target surface. The focus is on the case of a jet which issues from a circular pipe into stagnant surrounding at the relatively high value of Reynolds number of 23,000 (based on nozzle diameter and bulk velocity) for which experimental data are available. Large-eddy simulations were performed to obtain details of the mean flows and the turbulence fields including distributions of all components of the turbulent heat fluxes. The outcome of these simulations were used to assess three alternative models for the turbulent heat fluxes which differ from the conventional Fourier's Law by not being based on the assumption of proportionality between the eddy and thermal diffusivities via a constant Prandtl number. It was found that only one of the models considered succeeds in representing the effects on the heat fluxes of the complex strain field associated with the stagnation region and the subsequent development into the wall-jet region. The reasons for this outcome are discussed.     

Experimental Investigation and RELAP5 Modeling of Two-Phase Flow in Horizontal Rectangular Channel

The investigation of steam, water, and air flow characteristics in horizontal channel is a part of major investigations program at the Lithuanian Energy Institute. The objective of this program is to identify condensation effects on two-phase flow stability and to predict conditions when rapid condensation could be induced in two-phase condensable flow. This article presents investigation of steam–water and air multiphase flow in nearly horizontal rectangular channel. The experimental data for pressure drop and interfacial and wall shear stresses in the channel with uniform distribution of void fraction are presented in this paper. Overall channel dimensions are length = 1.2 m, width = 0.02 m, height = 0.1 m; however, the test section was about 0.84 m in length. Three different flow types were analyzed at atmospheric pressure: (1) single-phase air flow (height of the channel was reduced to 0.075 m); (2) non-condensable air–water two-phase flow at void fraction of 0.75; (3) two-phase steam–water flow at almost saturation conditions, and void fraction of 0.75. RELAP5 Mod3.3 code was selected to model test cases. Modeling results and experimental measurements show good agreement with each other. The developed model will be used for calculating different cases of the process.     

Experimental Investigation on Thermal Protection of High Temperature and High Velocity Jet Impinging a Cross-Shaped plate

Abstract

This paper investigated the heat transfer of high temperature jet impinging a cross-shaped plate. An experimental mockup was designed and used to produce high temperature (～500?°C) impinging gas jet with stable high speed (～56?m/s) at the nozzle exit. A one-dimensional theoretical model was proposed to predict the temperature increment of the back-side surface(s) that opposed to the impinging surface, by simplifying and assuming the heat transfer process can be governed by convection. Three materials were selected due to its potential high heat transfer resistance, speedy installation and long duration under severe impinging conditions. For each material, four types of thermal insulation structures were designed and subjected for testing. The following conclusions from comparison of the results of the model predictions with experimental data can be drawn. The proposed simplified one-dimensional model can be used to predict heat transfer at the back-side under high temperature and high-speed impinging. The optimal case among the 12 thermal protecting designs was obtained, majorly due to low back temperature and less material consumption.     

利用双像高速摄影研究柴油机燃油束撞击雾化及燃烧特性

利用双像高速摄影技术研究直喷式柴油机燃油束撞击雾化及燃烧过程。对轴针式喷油嘴在缸内的燃油束撞击挡块反弹雾化混合过程的火焰扩展过程进行了分析研究 ,结果表明 ,燃油束撞击反弹方向和喷油压力对油气混合气形成和燃烧过程有很大影响。     

高压甲烷气体碰壁射流扩散与卷吸特性的试验

在定容装置上利用高速摄影纹影法开展了不同冲击高度和冲击角度下的甲烷高压碰壁射流扩散和卷吸特性试验.通过纹影照片得到了不同冲击高度和冲击角度下的射流贯穿距离随时间变化的规律,计算得到了射流卷吸空气质量随时间变化的规律.结果表明:碰壁射流发展分两个阶段,碰壁之前贯穿距离和卷吸空气质量与自由射流基本相同;碰壁之后,由于壁面阻力的作用,其贯穿距离和卷吸空气质量的增加速率低于自由射流.随着冲击高度的增加,碰壁射流贯穿距离和卷吸空气质量增大;随着冲击角度的减小,碰壁射流贯穿距离和卷吸空气质量增大.最后对Poreh碰壁射流贯穿距离和卷吸空气质量经验公式进行修改,使其适用于一般碰壁射流贯穿距离和卷吸空气质量的特性计算.     

Numerical Analysis of Film Boiling in Liquid Jet Impingement

A numerical approach is presented for computing film boiling in liquid jet impingement on a high-temperature plate. The conservation equations of mass, momentum and energy are numerically solved in the liquid, vapor, and air phases. The sharp-interface level-set formulation is employed to track the liquid-air interface, as well as the liquid-vapor interface with phase change. A simplified analytical model for a thin vapor film, whose thickness is several orders of magnitude smaller than the liquid layer, is incorporated into the level-set formulation. The multiscale approach is tested through the computations of film boiling in a circular water jet.     

蒸汽水下喷注噪声的实验研究

通过实验探索了蒸汽在水下有限空间内喷注时喷注噪声的辐射规律,发现噪声声压级和频谱同水温有着直接的关系。在此基础上,本文进行了降噪实验,发现导流筒对降噪效果显著,同时发现临界流量对噪声的影响明显,在达到临界流量时,喷注噪声的声压级将大幅度降低。     

Experimental Investigation of Two-Phase Pressure Drop in a Microchannel

Experimental results of two-phase pressure drop in a horizontal circular microchannel are reported in this paper. A test tube was made of fused silica having an internal diameter of 781 μm with a total length of 261 mm and a heated length of 191 mm. The outer surface of the test tube was coated with an electrically conductive thin layer of ITO (indium tin oxide) for direct heating of the test section. Refrigerants R134a and R245fa were used as the working fluids, and mass flux during the experiments was varied between 100 and 650 kg/m²-s. Experiments were performed at two different system pressures corresponding to saturation temperatures of 25°C and 30°C for R134a and at three different system pressures corresponding to saturation temperatures of 30°C, 35°C, and 40°C for R245fa. Two-phase frictional pressure drop characteristics with variation of mass flux, vapor fraction, saturation temperature, and heat flux were explored in detail. Finally, the prediction capability of some well-known correlations available in the literature, some developed for macrochannels and others especially developed for microchannels, was assessed.     

台阶式溢流坝消力池时均压强特性试验研究

Experimental research was conducted on the stepped chute which connected with horizontal stilling basin directly. New date was presented on the pressure head alone the floor of the stilling basin and the characteristics of hydraulic jump. The experiment data indicated that the maximum pressure head was in the impact area of the stilling basin floor next to the chute. Smaller step size and steeper chute angle would cause bigger pressure head. The minimum value of the pressure head was found behind the impact area.     

Gas Absorption by Wavy Falling Liquid Film Formed on Inner Surface of Vertical lubes

An experimental study on gas absorption into falling liquid film formed on inner surface of vertical tubes has been carried out in order to clarify fundamental characteristics of the gas absorption and enhancement by surface waves. The water supplied into the test tubes is periodically disturbed by fluctuating a silicon tube before the test section with a speaker and the wavy films absorb the oxygen filled in the tubes. Imposing the periodic disturbance enhances the gas absorption and the enhancement has a maximum at around 20-30 Hz, where the gas absorption is 20-30% higher. Mass transfer coefficients obtained with five tubes agree well with those obtained with single tube. Two-dimensional numerical simulations have also been conducted for gas absorption by wavy film and the enhancement mechanism of the gas absorption is discussed.     

Modeling of Thin Liquid Film in Grooved Heat Pipes

Axially grooved heat pipes are devices used mainly to dissipate heat flow through the latent heat of phase change of a fluid at a saturation state. Part of the heat injected at the evaporator flows through a micro-region where the meniscus remains hung at the top of each groove. This article presents a steady-state model built to study the heat and mass transfers in this zone. A parametric study has been performed on aluminum/ammonia heat pipes, mainly used for satellite thermal control, and it led to interesting results, especially regarding the incidence of the radius of curvature of the meniscus and the influence of temperatures on the transfers occurring in the problem.     

射流表面波理论的研究进展

在过去的20年中,喷雾科学与技术有了长足的发展,应用领域不断扩大。目前,喷雾学已经成为国际性的研究领域。其发展主要表现在数学模型的进展、数值计算分析的不断完善和光学测试技术的改进与开发,重要性日益显著。本文论述了利用线性稳定性理论和非线性稳定性理论对典型的圆射流、平面液膜射流和环状液膜射流碎裂过程的研究进展。     

燃烧室壁面形状对撞壁射流气体混合过程的影响

本文研究了燃烧室壁面形状对撞壁射流气体沿壁发展过程的影响，实验发现：射流气体撞壁后主要沿壁面发展；近壁区域会形成浓混合气层，并且混合很慢，本文提出了两种方法，１）在壁面设置矩形凹槽，并且利用环境的气流运动加快射流气体的混合。２）在壁面上设置条形障碍物，使射流气体脱离壁面形成空间流动，另外，本文也模拟了ＯＳＫＡ－Ｄ燃烧系统中燃油撞壁后的发展过程。     

Thermal Analysis of an Impinging Jet on a Plate With and Without a Porous Layer

This work shows numerical results for a jet impinging against a flat plane covered with a layer of a porous material, which is maintained at a higher temperature than the incoming fluid. Parameters such as permeability and thickness of the porous layer and thermal conductivity ration are varied in order to analyze their effects on the local distribution of Nu. The macroscopic equations for mass, momentum, and energy are obtained based on a volume-average concept. The numerical technique employed for discretizing the governing equations was the control volume method with a boundary-fitted nonorthogonal coordinate system. The SIMPLE algorithm was used to handle the pressure-velocity coupling. Results indicate that inclusion of a porous layer decreases the peak in Nu avoiding excessive heating or cooling at the stagnation point. Also found was that the integral heat flux from the wall is enhanced for certain range of values of layer thickness, porosity, and thermal conductivity ratio.     

Experimental Studies of Heat Transfer by Slot Jet and Single/Triple Row of Round Jets Impinging on Semicylindrical Concave Surfaces

Experimental results for average heat transfer coefficients have been obtained for a slot jet, a single row of round jets, and a triple row of round jets impinging onto a concave semicylindrical surface. Average Nusselt numbers have been expressed as functions of Reynolds number, Prandtl number, and non-dimensional geometric parameters of jet-target configuration.     

Investigation of a Confined Laminar Impinging Jet on a Plate with a Porous Layer Using the Preconditioned Density-Based Algorithm

The preconditioned density-based algorithm and two-domain approach were used to investigate the fluid flow and heat transfer characteristics of a confined laminar impinging jet on a plate covered with porous layer. In the porous zone, the momentum equations were formulated by the Darcy-Brinkman-Forchheimer model; the thermal nonequilibrium model was adopted for the energy equation. At the porous/fluid interface, the applicability and influence of different hydrodynamic and thermal interfacial conditions were analyzed for the problem. The governing equations were solved by the preconditioned density-based finite-volume method, with preconditioning matrix for equations of porous domain adopted, aiming to eliminate the equation stiffness of porous seepage flows. The effects of Reynolds number, porosity, Darcy number, thermal conductivity ratio, Biot number, and porous layer thickness on the flow pattern and local heat transfer performance were studied. Results indicate that the Reynolds number and porosity don't strongly influence the flow pattern of porous channel, while the Darcy number and porous layer thickness have obvious influence on the flow pattern. The heat transfer performance are greatly influenced by the parameters studied.     

二维流化床内射流深度的试验研究

研究二维流化床内的水平射流和垂直向上射流。利用图象处理技术得到了水平射流的水平深度和垂直向上深度以及垂直向上射流的射流深度。通过多元线性最小二乘回归,得到了射流深度的关联式。研究了流化数、射流速度、颗粒平均粒径和静态床层高度对射流深度的影响。试验结果表明,流化数和射流速度的增加,射流深度将增加;颗粒粒径增加,射流深度将减小;静态床层高度变化时,射流深度基本不变。发现射流深度决定于射流与乳化相气体和颗粒的动量交换。对水平射流的垂直向上深度和垂直向上射流的射流深度进行了比较。