论文总字数：25575字

摘 要

低温泵是一种可以运输液氮、液氢等低温流体的离心泵，广泛应用于石油、化工、空分等行业中，将低温介质通过过流部件运送到指定高度或压力的地方。因为输送的低温流体其物性受温度影响很大，所以低温泵工作过程中极易发生空化现象。空化现象会导致机械产生机械振动、发出噪音，降低低温泵的工作效率、工作寿命和使用安全性。本文采用CFD数值模拟的方法，选用Zwart空化模型和RNG k-ω湍流模型，对泵内压降和水力损失、泵内压降和蜗壳内壁温度耦合作用下低温泵内流体流动情况进行了研究：

（1）研究了不同流量下低温泵的空化特性曲线。结果表明低温泵的扬程随汽蚀余量的减小而减小，随流量的减小而增大。当进入空化临界状态时，扬程快速下降。当流量为0.6Q时，受水力损失影响，扬程增长幅度较小。

（2）研究了不同进口压力下低温泵内压力分布图、温度分布图和空泡体积分数分布图。在额定流量下，随着入口压力的降低，空化区域增大，空泡区域的温度降低，叶轮内的低压区域增大。在一定范围内，随着流量不断减小，叶轮内的压力逐渐增大，空化区域逐渐减小。随着流量不断减小，泵内出现涡状流，影响了流道内流体的流动。

（3）研究了不同流量下低温泵的内特性曲线。结果表明，低温泵的扬程随汽蚀余量的减小而减小，低温泵的效率随汽蚀余量的减小而减小。当空化进入临界状态，扬程快速下降，效率也快速下降。发生空化时吸热，因此叶轮内空化区域温度降低。

（4）研究了不同工况下低温泵内压力分布图、温度分布图和空泡体积分数分布图。结果表明，当入口压力为0.078MPa、蜗壳内壁温度大于128K时，蜗壳内压力分布变化明显；蜗壳内壁温度小于128K时，压力分布没有明显变化。不同入口压力下，蜗壳内温度变化不大。泵内高温区域集中在蜗舌和蜗壳附近，这也是空化区域，空泡气体分数随蜗壳内壁温度增大而增大。研究结果对提高低温泵的抗空化性能具有一定帮助。

关键词：低温泵 空化 多诱因 数值模拟

Research on the internal flow of cryopumps under the coupling effect of multiple gasification inducements

Abstract

The cryopump is a kind of centrifugal pump which can transport liquid nitrogen, liquid hydrogen and other Cryogenic fluids. It is widely used in petroleum, chemical industry, air separation and other industries. It can transport cryogenic media to a place of designated height or pressure through flow passage parts. Because the physical properties of the delivered cryogenic fluid are greatly affected by the temperature, the cavitation phenomenon is very easy to occur during the operation of the cryogenic pump. Cavitation will cause mechanical vibration and noise, and reduce the working efficiency, working life and use safety of cryopump. In this dissertation, using CFD numerical simulation method, Zwart cavitation model and RNG k-ω turbulence model, the fluid flow in the cryopump under the coupling effect of pressure drop and hydraulic loss in the pump, pressure drop in the pump and temperature in the inner wall of the volute is studied.

(1) The cavitation characteristic curve of cryopump with different flow rate was studied. The results show that the head of cryopump decreases with the decrease of NPSH and increases with the decrease of flow rate. When entering the critical state of cavitation, the head drops rapidly. When the mass flow rate is 0.6q, the increase range of head is small due to the influence of hydraulic loss.

(2) The pressure distribution, temperature distribution and vapor volume fraction distribution in cryopump under different inlet pressures were studied. At the rated flow rate, with the decrease of the inlet pressure, the cavitation area increases, the temperature of the cavitation area decreases, and the low pressure area in the impeller increases. In a certain range, with the flow decreasing, the pressure in the impeller increases gradually, and the cavitation area decreases gradually. With the decrease of flow rate, vortex flow appears in the pump, which affects the flow of fluid in the channel.

(3) The internal characteristic curve of cryopump with different flow rate was studied. The results show that the head of cryopump decreases with the decrease of NPSH, and the efficiency of cryopump decreases with the decrease of NPSH. When cavitation enters the critical state, the head decreases rapidly, and the efficiency also decreases rapidly. When cavitation occurs, it absorbs heat, so the temperature of cavitation area in impeller decreases.

(4) The pressure distribution, temperature distribution and vapor volume fraction distribution in cryopump under different working conditions were studied. The results show that when the inlet pressure is 0.078Mpa and the inner wall temperature of the volute is above 128K, the pressure distribution in the volute changes obviously; when the inner wall temperature of the volute is less than 128K, the pressure distribution does not change obviously. Under different inlet pressure, the temperature in the volute changes little. The high temperature region in the pump is concentrated near the volute tongue and volute inner wall, which is also the cavitation region. The vapor volume fraction increases with the increase of the inner wall temperature of volute inner wall. The results are helpful to improve the cavitation resistance of cryopump.

Keywords: cryopump; cavitation, multiple inducements; numerical simulation

目录

摘 要 I

第一章 绪论 1

1.1 研究背景和意义 1

1.1.1 低温泵研究的背景 1

1.1.2 低温泵研究的意义 1

1.2 国内外研究现状 2

1.2.1 理论数值研究 2

1.2.2 试验研究 3

1.3 低温泵的研究趋势 3

第二章 数值计算方法 5

2.1 几何模型的建立 5

2.1.1 三维建模软件介绍 5

2.1.2 几何模型的建立 5

2.2 网格划分 6

2.2.1 网格的分类 6

2.2.2 几何模型的网格划分 6

2.3 Zwart空化模型 7

2.4 湍流模型 7

2.4.1 湍流模型的比较 7

2.4.2 RNG k-ε模型 8

2.5热力学效应 8

2.6边界条件设置与模拟方案 9

2.7 本章小结 10

第三章 泵内压降和水力损失对低温泵空化流动的影响 11

3.1 进口压力影响下的低温泵数值模拟过程概述 11

3.2 空化特性曲线的绘制与对比分析 11

3.2.1 临界空化压力介绍 11

3.2.2 不同流量下低温泵的空化特性曲线 12

3.3 低温泵空化流动下流场参数的分析 12

3.3.1 低温泵空化流动下压力的分析 13

3.3.2 低温泵空化流动下温度的分析 15

3.3.3 低温泵空化流动下空泡体积分数的分析 16

3.4 本章小结 17

第四章 泵内压降和蜗壳内壁温度对低温泵流动的影响 19

4.1 出口流量影响下的低温泵数值模拟过程概述 19

4.2 不同流量下低温泵空化的外特性分析 19

4.2.1 不同工况下低温泵扬程的分析 19

请支付后下载全文，论文总字数：25575字