低温液体传输中夹带固态颗粒的流动特性研究

针对低温液体传输中夹带固态颗粒的流动属于低浓度固液两相流,且存在流道和部件动静干涉的特点,建立了低温流体传输管路中的固液两相流模型,并模拟研究了低温液体传输中夹带固态颗粒时不同传输压力、传输速度以及固体颗粒浓度下,传输管路的压力场、速度场以及固体颗粒的分布。     

竖直管道内冰浆流体流动特性的数值模拟

为研究竖直管道内冰浆流体流动特性,采用基于颗粒动力学理论的两相流双流体模型,通过CFD模拟研究了竖直管道内冰浆流体的等温流动过程。结果表明,在竖直管道内冰浆湍流输送过程中,流速沿管道中心轴线处近似呈对称分布。当冰浆流速较低时,管道截面处冰粒子的速度分布梯度较小,浓度分布趋于均匀,而随着冰浆流速升高,冰粒子的流场及浓度场均呈现出一定的梯级分布:管道近壁面处冰粒子浓度较低,而管道中心处冰粒子浓度较高,并在略偏于管道中心轴线位置处冰粒子浓度达到峰值。竖直管道内冰浆流体的流向变化对速度分布影响较弱,但对冰粒子浓度分布会产生一定影响,进而使得冰浆流体的管道压降在不同流向时存在着一定差异。     

流体性质对固液两相流离心泵的性能影响研究

运用数值计算软件Fluent6.2,以山西省某火电厂固液两相流泵离心泵为实例,对泵内流场进行数值计算,研究流体性质如介质粘度、介质浓度等对固液两相流离心泵性能的影响.在此基础上分析其运行效率低、局部磨蚀严重现象的原因.以期为火电厂固液两相流离心泵的设计及改造提供可靠依据.     

一种用于精确分级的受阻沉降器

从固液两相流理论出发介绍了受阻沉降器的基本原理,讨论了松散度、物料特性等因素对流体速度的影响,研究了影响流态和分级效果的结构因素,介绍了在石英砂分级中的实际应用。     

电磁流量计测量固液两相流质体流量时测量段流速的选择

测量固液两相流体中固体颗粒分布不均匀时的流量将会产生较大误差。当固液两相流体的物理性质和固体颗粒几何尺寸一定时，选择适当的流速将可以减少这类流量测量误差和使测量仪表长久可靠地运行。     

电磁流量计测量固流两相流质体流量时测量段流速的选择

测量固液两相流体中固体颗粒分布不均匀时的流量将会产生较大误差。当固液两相流体的物理性质和固体颗粒几何尺寸一定时，选择适当的流速将可以减少这类流量测量误差和使测量仪表长久可靠地运行。     

金属在液固两相流中的冲刷腐蚀

液固两相流体的冲刷腐蚀行为较单相流体更为复杂,在相同液相介质的情况下,其冲刷腐蚀对材料的破坏程度更为严重。综述了国内外对液固两相流的冲刷腐蚀体系开展的研究,对冲刷腐蚀的过程有了进一步的认识,对冲刷腐蚀的影响规律和危害性进行了论述,从而为材料的选用提供一定的参考依据。     

基于两相流理论的稀疏和致密颗粒流统一模型

统一描述不同浓度的固、液两相流动具有重要意义。该文充分考虑不同流态下颗粒体的本构关系、颗粒体与流体的相间作用以及流体紊动影响,应用两相流模型对统一描述稀疏和致密颗粒流问题进行了探索。经与实验结果比较,该两相流模型对不同粒径的稀疏和致密颗粒体的运动过程均能准确刻画。模拟结果表明,不同粒径稀疏颗粒体与流体的相间作用差异较大,其中细颗粒体受到的沉积作用更弱,更容易在周围流体中保持悬浮状态,因而前端运动距离更长。流体紊动粘性对涡旋结构的发展有较大的影响,考虑紊动时流体倾向于向前运动,进而促进了稀疏颗粒体的发展。致密颗粒体堆积表面附近受到的流体拖曳力较大,其在较长时间内促进了细颗粒体的向外发展,对粗颗粒体的运动则主要起到了阻碍作用。致密细颗粒体中的流体动压作用更为明显,流体正压促进了初始颗粒体前端的发展,流体负压则影响着颗粒体堆积形态的塑造。     

冰浆冰蓄冷方法发展现状分析

该文详细地介绍了冰浆在食品保鲜、奶制品加工、制冷以及矿井降温等不同领域的应用前景,与其他制冷方法相比,研究发现冰浆蓄冷制冷法具有流动性强、蓄冷能力强和无污染等其他制冷方式无法代替的优势。通过对比目前比较成熟的冰浆制取技术方法,分析了过冷法、接触法、刮削法、真空法等几种不同冰浆制取技术各自的优缺点,详细的介绍了流化床法制取冰浆的优缺点。通过该研究发现流化床法制取冰浆技术是1种传热效率高、不发生冰堵的具有较大应用潜力的冰浆制取方法。但是流化床法制取冰浆技术还不成熟,需要进行系统的研究。     

纸浆绝干纤维计量系统标定与误差分析

介绍基于测量液固两相流体（纸浆）体积流量与固相浓度和间接计量纸浆固相质量流量的纸浆纸干纤维计量系统的误差分析及标定方法。     

Effects of storage on flow and heat transfer characteristics of ice slurry

The effect of storage on flow and heat transfer characteristics of ice slurry was investigated experimentally. After ice slurry had been stored in the storage tank, variations in ice particle size were measured using a microscope, and diameter distribution and average diameter determined. The ice packing factor, Reynolds number and storage time were varied as experimental parameters. The pressure drop and heat transfer coefficient were measured when the ice slurry flowed in the horizontal tube. For laminar flow, the ratios of pipe friction and heat transfer coefficient decreased with storage time. For more than 12 h storage time, the ice slurry could not flow in the tube. The adhesion between ice particles seemed to cause a blockage in the tube. On the other hand, for turbulent flow, the pipe friction and ice slurry heat transfer coefficients were similar to that of the ethanol solution, and the storage effect was insignificant.     

Experimental investigation of ice slurry heat transfer in horizontal tube

Heat transfer of ice slurry flow based on ethanol–water mixture in a circular horizontal tube has been experimentally investigated. The secondary fluid was prepared by mixing ethanol and water to obtain initial alcohol concentration of 10.3% (initial freezing temperature -4.4 °C). The heat transfer tests were conducted to cover laminar and slightly turbulent flow with ice mass fraction varying from 0% to 22% depending on test performed. Measured heat transfer coefficients of ice slurry are found to be higher than those for single phase fluid, especially for laminar flow conditions and high ice mass fractions where the heat transfer is increased with a factor 2 in comparison to the single phase flow. In addition, experimentally determined heat transfer coefficients of ice slurry flow were compared to the analytical results, based on the correlation by Sieder and Tate for laminar single phase regime, by Dittus–Boelter for turbulent single phase regime and empirical correlation by Christensen and Kauffeld derived for laminar/turbulent ice slurry flow in circular horizontal tubes. It was found that the classical correlation proposed by Sieder and Tate for laminar forced convection in smooth straight circular ducts cannot be used for heat transfer prediction of ice slurry flow since it strongly underestimates measured values, while, for the turbulent flow regime the simple Dittus–Boelter relation predicts the heat transfer coefficient of ice slurry flow with high accuracy but only up to an ice mass fraction of 10% and Re_cf > 2300 regardless of imposed heat flux. For higher ice mass fractions and regardless of the flow regime, the correlation proposed by Christensen and Kauffeld gives good agreement with experimental results.     

动态冰浆的应用及制取方法的现状及展望

近二十年来,动态冰浆作为一种新型蓄冷介质,具有换热系数高、冷却速率高、可泵送和可流动的优点,已被广泛的应用到各个领域中。冰浆的作用主要是充当载冷剂,对食品、建筑物等进行冷却降温。冰浆制取技术也成为冰浆课题研究中的关键部分,本文对冰浆的性能研究以及在各个领域的应用进行了总结,概括分析了目前已有的冰浆制取方法,并且对未来制取方法和应用领域的发展方向进行了展望。     

Thermal and hydrodynamic considerations of ice slurry in heat exchangers

This article focuses on the behavior in heat exchangers of an ice slurry composed of fine ice particles inside an ethanol–water solution. The heat transfer and friction characteristics were studied in two double pipe heat exchangers, one with a smooth surface and another with an improved surface. Heat transfer coefficients and pressure drops were experimentally investigated for the slurry flowing in the internal tube with ice mass fractions ranging from 0 to 30% and with flow velocities between 0.3 and 1.9 m s^?1. For some flow velocities, the results showed that an increase in the ice fractions caused a change in the slurry flow structure influencing the evolution of the pressure drops and the heat transfer coefficients. Critical ice fraction values were determined corresponding to a change flow structure from laminar to turbulent motion revealed by the evolution of the friction factor.     

Effect of initial aqueous solution concentration on rheological behavior of ice slurry

Ice slurry displays many advantages as a phase-change material because the latent heat of ice particles can be used and their heat exchange area is large. In this study, the effect of initial concentration on the rheological behavior of ice slurry was investigated experimentally. Ice slurry flowed upward and downward to keep it homogeneous in the tube, and pressure drop was measured to explain the rheological behavior of the ice slurry. The ice packing factor, Reynolds number, and initial aqueous solution concentration were varied as parameters. The ice slurry flow characteristics exhibit a pseudo-plastic fluid tendency for 5 and 10 wt% of the initial concentration. Ice slurry generated from 2 wt% ethanol solution behaves as a Newtonian fluid.     

Thermo-hydraulic behavior of ice slurry in an offset strip-fin plate heat exchanger

Ice slurry is a promising alternative to conventional single-phase coolants in indirect refrigeration systems. In this paper, an experimental analysis of an offset strip-fin heat exchanger operating with ice slurry as working fluid is presented. The pressure drop and thermal performance have been determined. In order to obtain the partial thermal resistance in the ice slurry side an empirical correlation for the secondary fluid side was determined by applying the Wilson plot method in a set of tests performed previously. An empirical correlation in terms of the Colburn j-factor to describe the thermal behavior of the heat exchanger with ice slurry was obtained. On the other hand, the direct pressure drop measurements operating with different flow rates and ice fractions are shown and compared with values obtained with single-phase fluids. Pressure drop instabilities have been observed for flow rates lower than the nominal value provided by the manufacturer.     

Heat transfer characteristics of the ice slurry at melting process in a tube flow

The heat transfer characteristics were experimentally investigated for ice slurry made from 6.5% ethylene glycol–water solution flow in a 13.84 mm internal diameter, 1500 mm long horizontal copper tube. The ice slurry was heated by hot water circulated at the annulus gap of the test section. Experiments of the melting process were conducted with changing the ice slurry mass flux and the ice fraction from 800 to 3500 kg/m² s and 0–25%, respectively. During the experiment, it was found that the measured heat transfer rates increase with the mass flow rate and ice fraction; however, the effect of ice fraction appears not to be significant at high mass flow rate. At the region of low mass flow rates, a sharp increase in the heat transfer coefficient was observed when the ice fraction was more than 10%.     

Superheating of ice slurry in melting heat exchangers

One of the main components of an ice slurry system is the melting heat exchanger, in which ice slurry absorbs heat resulting in the melting of ice crystals. Design calculations of melting heat exchangers are mainly based on heat transfer and pressure drop data, but recent experimental studies have shown that superheating of ice slurry should also be considered. This paper presents ice slurry melting experiments with a tube-in-tube heat transfer coil. The experimental results indicate that operating conditions such as ice slurry velocity, heat flux, solute concentration, ice fraction, and ice crystal size determine the degree of superheating. The various influences are explained by considering the melting process as a two-stage process consisting of the heat transfer between wall and liquid and the combined heat and mass transfer between liquid and crystals. Bigger ice crystals and higher solute concentrations decrease the rate of the second stage and therefore increase the degree of superheating.     

冰浆存储期间冰晶演化研究进展

冰浆作为一种优良的蓄冷和载冷介质,其存储过程冰晶的演化规律与冰浆制备系统优化以及冰浆流动换热过程密切相关。概述了冰浆的形成机理,以此为基础,从控制冰晶生长和冰晶动态分布这两方面,阐明冰晶演化研究在内外取得的研究进展与发展现状。最后提出进一步研究建议。