动态冰浆传热特性的研究

动态冰浆由于具有较强的蓄能和传热能力,日益受到人们的重视。文中建立了动态冰浆传热特性的数理模型,并利用已知的载流溶液和冰晶的物性参数,得到了动态冰浆在水平直管、等热流加热条件下的传热系数,根据计算结果,分析了传热系数随着冰浆浓度的变化的规律和冰浆流速和管径对动态冰浆传热性能的影响。     

90°弯管内冰浆流动特性数值模拟

基于欧拉法建立了冰浆流动的混合模型,对冰浆在90°弯管内的流动特性进行了数值模拟研究,获得了弯管内冰浆的流场和冰晶颗粒的运动轨迹,探讨了弯管管径、曲率半径及冰浆的流速、浓度参数对弯管内冰浆压降的影响,并对弯管压降的模拟结果与实验结果进行对比,两者吻合较好。结果表明:在计算参数范围内,弯管压降随冰浆流速、浓度及弯管曲率半径的增大而增大,随弯管管径的增大而减小;冰浆在弯管内流动形成二次流现象,两个漩涡区域出现在弯管截面两侧;漩涡导致部分冰晶颗粒的运动轨迹发生改变,并使其向弯管下方的负压区聚集,增大了冰晶颗粒的碰撞几率。     

冰浆流动换热特性的综述及模拟分析

综述冰浆输送过程和在换热器中的流动换热特性研究现状。目前对冰浆流动特性研究主要是为了解决输送冷流体过程中的压降、摩阻系数等问题,输送途径主要是直管、弯管,可控因变量包括含冰率、管道直径、冰浆粘度、流速、Re数等参数。此外,还对冰浆在水平直管中流动情况进行了数值模拟,提出了最值冰浆浓度和第一临界速度、第二临界速度等参数,并推测冰浆流动换热应从三段进行考虑。冰浆在换热器中的流动换热过程与管道输送相比,通道结构更复杂导致阻力损失变大、换热增强、相变程度大,同时还要考虑固体颗粒与流体之间的耦合作用,因此目前的研究主要停留在实验阶段,在实验基础上进行半经验公式的推导。基础性理论研究主要涉及两相流动、颗粒力学和相变潜热三方面。此外,对未来研究方向提出几点建议,尤其是应从微观颗粒受力和晶体结构角度探讨冰浆的流动换热情况,脱离原有单相流体研究方式,冰浆颗粒流动至少分三段研究。     

冰浆流动特性研究进展

冰浆是当前载冷和蓄冷材料领域的研究热点,有着良好的流动和换热性能。综述了冰浆在管道、泵等输配部件内的流动特性;探讨了含冰率、流速、初始溶液浓度等因素对冰浆流动形态、流变特性以及流动压降的影响;在总结冰浆流态转换规律的基础上,分析了冰浆的流变模型和其在不同部件中流动的压降特性。     

动态冰浆在多领域上的应用

为加深对动态冰浆的认识,文章介绍了动态冰浆的制取方式,着重讨论动态冰浆在建筑空调、食品加工、医疗保护以及其他场合的应用.通过与冷冻水及其它类型冰的比较分析,表明动态冰浆在蓄冷密度、流动性与传热性能等方面具有独特的技术优势.     

动态冰浆流动特性分析

阐述了动态冰浆流变性质的Bingham模型,并利用该模型计算了冰浆在层流和湍流状态下的摩擦因子,得到了冰浆在水平直管内流动的压降曲线,分别就层流和湍流情形分析了各种参数对流动压降的影响。     

驻波声场中圆柱形管道周围颗粒的运动特性

针对圆柱形管道外部的流体与颗粒介质运动问题,提出了结合圆柱周围声辐射力和声流Stokes力的研究方法。从柱体外部声流方程出发,得到影响涡流结构的无量纲参数Rem≥325.27时,外涡最大流速大于内涡最大流速。在此基础上,采用Nyborg的边界滑移速度理论,获得管道外部声流的极限滑移速度,推导得出圆柱附近的声辐射力公式。基于此公式,在理论上推导出颗粒速度为0、声辐射力和声流Stokes力平衡时,颗粒临界直径的表达式。通过对圆柱位于不同位置时,圆柱外部的颗粒运动进行仿真模拟,得到与理论公式相一致的结论:颗粒的临界直径的大小与声波频率有关,当颗粒直径小于临界直径时,声流Stokes力为主导,颗粒随声流运动,颗粒直径大于等于临界直径时,声辐射力为主导,颗粒在声辐射力作用下逐渐向声辐射力的节点聚集。理论与仿真结果表明该方法可用于分析管道外颗粒的分布状态,其研究结果有助于解决电站中换热器的管道结垢、热交换率降低等问题。     

磁流变液效应对远端流场的扰动

研究了磁流变效应对远离磁极的流道中流动的扰动问题。通过双腔型结构器件的动态力学响应以及混合流模式的流动分析,揭示了当磁流变液离开磁极后,由于剩磁的影响,磁极后方的管道中的流动将受影响,主要表现在流过管道的介质的体积比浓度将发生显著变化。     

过冷水法冰浆制取的实验设计与分析

动态冰蓄冷技术是目前蓄能技术重要的研究方向之一,其中冰浆制取方式是研究的关键课题。冰浆具有良好的流动性,大的相变潜热和快速的释冷特性,是常规载冷剂的潜在替代物。该文给出了过冷水法冰浆制取的实验装置,采用纯净水和自来水为试样,在不同的条件下进行了对比实验,并分析了管内冻结情况。     

血液粘度与人体疾病

 血液流变学是研究血液流动性和变形性的学科,是物理学与生命科学交叉渗透的新兴边缘学科,是处于生命科学前沿的一门学科。血液流变学分为宏观血液流变学、微观血液流变学和分子血液流变学。在血液流变学的临床指标中,血液粘度,包括全血粘度和血浆粘度是其基本指标或核心指标之一。流体在管道内流动时,若流速较低,流体质点流动平稳,没有宏观混杂,呈层流。流体作层流时,相接触的两流层间因速度差的存在,会相互产生摩擦力,即内摩擦力。由牛顿粘滞定律,内摩擦力F的大小与相邻流层的接触面积S成正比,与两流层接触处的速度梯度dv/dr成正比,即F=ηSdv/dr。     

Formation of Calcium Carbonate Sub‐Micron Particles in a High Shear Stress Three‐Phase Reactor

The production of precipitated calcium carbonate (PCC) was investigated experimentally under industrially relevant conditions, i.e. at high solid concentrations and increasing amount of solid product in the slurry. Temperature is an important parameter since it determines the crystal structure, the particle shape and, as a consequence, the viscosity of the slurry. Of course, the mass concentration of the raw material also has an important influence on the viscosity. From the particle size distributions of primary particles and agglomerates, it can be concluded that the nucleation process is governed by primary nucleation. Also, heterogeneous nucleation occurs on solid calcium hydroxide particles that are present in the slurry. Especially if the raw material contains impurities heterogeneous nucleation occurs and large and unwanted particles are formed. If the slurry is not stabilized, strong agglomeration occurs that can be influenced by the shear stress introduced to the slurry: a high shear stress which is linked to the viscosity of the slurry limits the upper particle diameter and leads to a steep particle size distribution of the product.     

固液两相流中微对流强化的机理分析与数值模拟

本文对分散型固液两相混合物层流管流中非均匀剪切力场导致的微对流现象以及由此引起的导热系数增强效应作了机理和影响因素分析,认为除速度分布、颗粒浓度和粒径以外,还存在颗粒形状、粒径分布,壁面热流方向、颗粒表面性质及其与载流介质间的相容性等多个影响因素.模拟计算表明,由微对流导致的对流换热强化与流体在管壁面上的表观导热系数强化具有相同的数量。     

Monitoring acoustic emission (AE) energy of abrasive particle impacts in a slurry flow loop using a statistical distribution model

Slurry erosion has been recognized as a serious problem in many industrial applications. In slurry flows, the estimation of the amount of incident kinetic energy that transmits from particles suspended in the fluid to the containment structures is a key aspect in evaluating its abrasive potential. This work represents a systematic investigation of particle impact energy measurement using acoustic emission (AE), as indicated by a sensor mounted on the outer surface of a sharp bend, in an arrangement that had been pre-calibrated using controlled single and multiple impacts. Particle size, free stream velocity, and nominal particle concentration were varied, and the amount of energy dissipated in the carbon steel bend was assessed using a slurry impingement flow loop test rig. Silica sand particles of mean particle size 225–650 μm were used for impingement on the bend with particle nominal concentrations between 1 and 5% while the free stream velocity was changed between 4.2 and 14 ms⁻¹.     

气体直接接触式制取冰浆实验研究

冰浆具有良好的流动性,有着广泛的用途。气体直接接触式换热具有换热系数高的优点,由于气流的速度可以更高,换热也就可以更充分,换热性能更好。本文利用氮气作为直接接触制冰系统的低温介质进行了制冰实验,分析了流量、流速、温度等因素对系统换热性能和冰堵的影响。     

Particle Mass Loading Effect on a Two-Phase Turbulent Downward Jet Flow

The particle mass loading effect on the flow structure of a two-phase turbulent jet flow was studied. A particle mass loading ratio ranging from 0 to 3.6 was used as the control parameter. The polystyrene solid particles used had nominal diameters of 210 and 780 μm. The flow Reynolds number, which was based on the pipe nozzle diameter and the fluid-phase centerline mean velocity, was 2 × 10⁴ in the current test. A two-color laser Doppler anemometer (LDA), combined with the amplitude discrimination method and the velocity filter method, was employed to measure the mean velocity distributions for the particle and fluid phases, and the turbulent intensities and Reynolds stresses of the flow. The two-phase jet flow field was measured from the initial pipe exit to 90 D downstream. Another one-component He? Ne laser LDA system was also applied to obtain the energy spectra and temporal correlations of the two-phase jet flow.     

Particle removal by a single cavitation bubble

In the paper,the behavior of the particle acted by the oscillating bubble is studied using a high-speed video camera.The bubble is generated using a very low voltage of 55 V.Images are captured at a speed of 15000 fps(frames per second).It is found that the velocity of the particle is dependent on the liquid viscosity,particle size,and tube diameter.Particle velocity decreases with the increase of the glycron-water mixture viscosity.A model is presented to predict the velocity and verified by experimental results.These observations may be beneficial for the application in medical treatment.     

An investigation on erosion behavior of HVOF sprayed WC-CoCr coatings

Present work is an investigation of slurry erosion behavior of WC-CoCr cermet coatings deposited with two different WC grain sizes. HVOF thermal spray process was employed due to its high velocity and low flame temperature characteristics resulting in quality coating. HVOF spraying was assisted with in-flight particle temperature and velocity measurement system to control its heating. Slurry erosion testing was performed using a pot-type slurry erosion tester to evaluate slurry erosion resistance of the coatings. Two parameters were considered for testing viz. erodent particle size and slurry concentration. Surface morphology was examined using SEM images and phase identification was done by XRD. The erosion behavior and mechanism of material removal was studied and discussed based on microstructural examination. It was observed that WC-CoCr cermet coating deposited with fine grain WC exhibits higher slurry erosion resistance under all testing conditions as compared to conventional cermet coating.