管壳式蒸发器内制冷剂的均分特性研究

发布时间：2018-04-26 12:00

本文选题：干式管壳式蒸发器 + 分液装置　；参考：《南京师范大学》2015年硕士论文

【摘要】：干式管壳式蒸发器因其制冷剂需求量小、运行稳定等优点目前在制冷工业中应用广泛。目前制约其更大范围应用的一个瓶颈在于其换热性能仍不够理想,有研究认为各管间的制冷剂分配不均是导致其性能不能大幅提升的主要原因。本文分别通过理论分析、实验研究和数值模拟的方法对管壳式蒸发器内制冷剂的分液特性及分液对换热的影响进行了研究,并提出了改进方法。首先,本文首先提出了干式管壳式蒸发器内流量分配均匀度的评判标准,通过理论分析的方法得到了单管换热公式,研究了流量变化对换热的影响。结果表明,换热器内制冷剂存在的分配不均会对换热造成影响。流量分配均匀会带来换热的增强,湿周小于1的状况下流量分配对换热的影响更大。随后,本文建立了流体分配实验装置并开展了实验。由于受到实验条件的限制,文中对实验进行了简化和介质替代：分管数目为25个、实验介质为空气-水。实验的开展达到了以下两个目标：得到了流体分配的可视化结果；为同条件下的两相流的数值模拟提供了有效性证明。建立了与实际尺寸一致的干式管壳式蒸发器的三维模型并进行了数值计算。分析了换热器内分液不均的原因,认为各管程入口处的压力分布特点及分液装置内和管内的涡流区域是影响分流的重要因素。提出了改善分液装置内分液的方案,即将分液装置设计为为锥形分液装置。用简化后的模型对改进后的分液器进行了数值模拟研究,研究中为避免特殊流速对分液的影响,对流速进行了分析,认为1.5m/s的进口流速为适宜流速。在对13种不同锥形分液装置数值计算和分析的基础上,认为一种锥角位于流体入口中心线下方的锥形分液装置整体分液效果最好。针对该分液器,研究了不同的锥角高度h对流体分配的影响,结果表明,h=35mm时分液效果最好。本文的研究结果有望对干式壳管式蒸发器的性能改进提供参考。
[Abstract]:Dry shell evaporator is widely used in refrigeration industry because of its low refrigerant demand and stable operation. At present, a bottleneck of its wider application is that its heat transfer performance is still not ideal. It is considered that the uneven distribution of refrigerant among different tubes is the main reason why the performance can not be greatly improved. In this paper, theoretical analysis, experimental study and numerical simulation are used to study the characteristics of the refrigerant in the tube and shell evaporator and the effect of the separation of the liquid on the heat transfer, and the improved method is put forward. First of all, the criterion of uniformity of flow distribution in dry tube and shell evaporator is put forward in this paper. The formula of single tube heat transfer is obtained by theoretical analysis, and the influence of flow rate on heat transfer is studied. The results show that the uneven distribution of refrigerant in the heat exchanger will affect the heat transfer. Uniform flow distribution will increase heat transfer, and the effect of flow distribution on heat transfer is greater when wet cycle is less than 1. Then, the experimental device of fluid distribution is established and the experiment is carried out. Due to the limitation of the experimental conditions, the experiment is simplified and the medium is replaced: the number of tubes is 25, and the experimental medium is air-water. The experimental results are as follows: the visualization results of fluid distribution are obtained, and the validity of numerical simulation of two-phase flow under the same conditions is proved. A three-dimensional model of dry tube-shell evaporator is established and numerically calculated. Based on the analysis of the reasons for the uneven distribution of liquid in the heat exchanger, it is considered that the pressure distribution characteristics at the entrance of each tube and the eddy current region in the separation unit and the pipe are the important factors affecting the flow distribution. The scheme of improving the internal separation of liquid is put forward, that is to say, the separation device is designed as a conical separation device. In order to avoid the influence of special velocity on the separation of liquid, the velocity of flow is analyzed, and the inlet velocity of 1.5m/s is considered as the appropriate flow rate. On the basis of numerical calculation and analysis of 13 different conical liquid-separating devices, it is considered that a taper separation device with cone angle below the central line of the fluid inlet has the best overall liquid separation effect. The effect of different cone height h on the fluid distribution is studied. The results show that the solution is the best at 35mm. The results of this paper are expected to provide a reference for improving the performance of dry shell-tube evaporator.
【学位授予单位】：南京师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB64

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