冰浆在管网中的流动特性分析

发布时间：2018-01-28 12:39

本文关键词： 冰浆压降临界速度含冰率　出处：《天津商业大学》2014年硕士论文　论文类型：学位论文

【摘要】：蓄冷技术在制冷空调领域应用广泛，冰浆作为蓄冷介质，因其颗粒较小、流动性好、融冰速度快成为国内外学者的研究重点。在已有的刮片式制取冰浆装置基础上，重点分析了冰浆在管网内的流动特性，流阻情况以及冰浆安全运输时的临界速度等。本文的研究工作主要集中在以下几个方面： 1）冰浆物性分析：分析了冰浆中冰晶和水溶液的物性，得出冰浆密度、导热系数、比热的计算公式，分析得出冰浆的热物性同时受冰晶颗粒和水溶液二者共同的影响。 2）冰浆管内流动数值模拟：采用Fluent中的双流体欧拉模型得出冰粒子在管内的分布云图，分析发现水平管道内粒子分布从顶部到底部呈规律性变化，在相同截面处，流速越小、管径越大，分层越明显，造成分层的主要原因是粒子碰撞以及浮力的作用。然后通过模拟分析了冰浆在管内流动的临界速度以及压降值随各参数（冰粒子直径、管道直径、入口含冰率、添加剂浓度等）的变化情况。 a）冰浆在管内安全运输的顶部冰粒子最大容纳率（冰粒子体积含冰率）为0.501，，临界速度随着粒子直径、含冰率、盐浓度、管直径的增大而增大； b）冰浆水平管内流动的单位压降随着流速、含冰率的增大而增大，随着管直径以及粒子直径的增大而减小。将上述Fluent模型计算的压降值与Bingham模型理论值进行比较分析，发现二者最大差别在15%左右，验证了采用Fluent模型的正确性。 3）冰浆管内流动特性实验：本实验采用三个循环系统（制冷剂循环系统、冰浆制取系统以及冰浆管内流动循环系统）。通过可视化玻璃管观察冰浆在不同流速、不同含冰率下的流动状态，发现冰浆在较高流速下混合均匀，在较低流速下会出现类似絮网状结构，产生的原因是由于扰动的减小会造成冰粒子的凝聚。分析实验数据得到：冰浆压降随着流速的变化在较低盐浓度时呈阶梯状上升，较高盐浓度时呈抛物线型上升。最后将实验得到的冰浆管内流动压降随着含冰率的变化规律与模拟结果进行对比，发现实验值与模拟值变化趋势一致，而且实验值高于模拟值，二者最大差值发生在管直径32mm管内且为5%。由于在实验过程中，随着体积含冰率的降低盐浓度也会逐渐减低，两者都会增大冰浆压降的下降速率，所以实验条件下的压降下降速率比同等条件下模拟值要大。 4）由于在初始含冰率下测得的盐浓度会随着冰粒子的融化而降低，根据氯碱手册中1%-5%的氯化钠浓度理论值拟合出该范围内氯化钠密度随浓度变化的关系式，然后得出随着冰粒子融化处于不同含冰率下的盐浓度计算式。
[Abstract]:Cold storage technology is widely used in the field of refrigeration and air conditioning, ice slurry as a cold storage medium, because of its small particles, good fluidity. On the basis of the existing scraper ice slurry device, the flow characteristics of ice slurry in pipe network are analyzed. Flow resistance and critical velocity of ice slurry in safe transportation. The research work of this paper mainly focuses on the following aspects: 1) physical properties of ice slurry: the physical properties of ice crystal and aqueous solution in ice slurry were analyzed, and the calculation formulas of density, heat conductivity and specific heat of ice slurry were obtained. It is concluded that the thermal properties of ice slurry are affected by both ice grain and aqueous solution. 2) numerical simulation of ice slurry flow: the two-fluid Euler model in Fluent is used to get the distribution of ice particles in the pipe. It is found that the particle distribution in the horizontal pipe changes regularly from the top to the bottom. At the same section, the smaller the velocity is, the larger the diameter of the pipe is, and the more obvious the stratification is. The main causes of stratification are particle collision and buoyancy. Then the critical velocity and pressure drop of ice slurry flow in pipe are analyzed with the parameters (ice particle diameter pipe diameter and ice content at the inlet). Change in the concentration of additives, etc. A) the maximum ice particle holding ratio (ice particle volume ice content) at the top of the ice slurry transported safely in the pipe is 0.501, and the critical velocity increases with the increase of particle diameter, ice content, salt concentration and pipe diameter. B) the unit pressure drop of ice slurry flow increases with the increase of flow velocity and ice content, and decreases with the increase of tube diameter and particle diameter. The pressure drop calculated by the above Fluent model is compared with the theoretical value of the Bingham model, and the maximum difference between them is found to be about 15%. The correctness of the Fluent model is verified. 3) experiment of flow characteristics in ice slurry pipe: this experiment adopts three circulating systems (refrigerant circulation system). The ice slurry production system and the flow circulation system in the ice slurry pipe were observed by visual glass tube. The mixture of ice slurry was found to be uniform at higher flow rate and at different velocity of flow and different ice content. At a lower velocity, a similar floc network will appear. The reason is that the decrease of disturbance will lead to the condensation of ice particles. The experimental data show that the pressure drop of ice slurry increases with the change of flow velocity in the form of ladder when the concentration of salt is lower. When the salt concentration is high, the flow pressure drop in the ice slurry pipe is increased in parabola shape. Finally, the experimental results are compared with the simulation results, and it is found that the experimental value is consistent with the simulated value. And the experimental value is higher than the simulated value, the maximum difference between the two occurs in the diameter of 32mm tube and is 5. Because in the experiment process, the salt concentration will gradually decrease with the decrease of the volume ice content. Both of them will increase the falling rate of ice slurry pressure drop, so the pressure drop rate under the experimental condition is larger than that under the same condition. 4) the salt concentration measured at the initial ice content will decrease with the melting of the ice particles. According to the theoretical value of 1 ~ 5% sodium chloride concentration in the manual of chlor-alkali, the relationship between the density of sodium chloride and the concentration of sodium chloride in this range is fitted, and the formula for calculating the salt concentration under different ice content with the melting of ice particles is obtained.
【学位授予单位】：天津商业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TB64

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