低温输运管道预冷过程的气液两相数值分析

doi:10.11949/0438-1157.20201609

摘要/Abstract

摘要：

低温流体在输运管道中预冷时会出现复杂的气液两相流现象。本研究的数值仿真主要针对液氮在管道内沸腾过程中的传热特性、气泡的生成规律、临界热通量等进行分析。通过改变管道直径、入口液氮流量，讨论了不同时刻计算域内部的温度、热通量以及两相分布规律，最终得到研究范围内的临界热通量（CHF）特性。研究发现，流体温度突变时间随着管径的减小而提前，随着流量的增大而后延；壁面温度变化幅度随着管径的增大而增大；CHF值随着管径的减小而增加，随着入口流量的增加而减小。

关键词: 预冷, 沸腾, 汽化, 计算流体力学, 气液两相流

Abstract:

There are many applications about cryogenic multiphase flow in various industry situations. In this paper, the precooling flow of liquid nitrogen in a mini pipe was discussed with numerical simulation, some characteristics were displayed such as, bubbles formation, critical heat flux, and temperature profiles, etc. The employed mathematical and physical methods were verified with some experimental data in the previous literature. According to simulation results about precooling processes, the temperature drop of internal fluid happened early with the pipe diameter decreasing, and the temperature drop happened lately with the liquid nitrogen mass flow increasing. The amplitude of the wall temperature drop decreased with the pipe diameter decreasing. In the range of calculation conditions, the higher CHF values occurred with less inner diameter tubes and higher mass flow rate.

Key words: precooling, boiling, vaporization, CFD, gas-liquid flow

中图分类号:

TK 124

林恩承, 王文, 匡以武, 石玉美, 耑锐, 孙礼杰. 低温输运管道预冷过程的气液两相数值分析[J]. 化工学报, 2021, 72(S1): 153-160.

LIN Encheng, WANG Wen, KUANG Yiwu, SHI Yumei, ZHUAN Rui, SUN Lijie. Numerical analysis of cryogenic two-phase precooling flow in a mini pipe[J]. CIESC Journal, 2021, 72(S1): 153-160.

图/表 17

图1 管道几何模型

Fig.1 Geometric model

表1 计算工况

Table 1 Calculation condition

工况	质量流量/ (g/s)	管内径/ mm
1	1.6	12.7
2	1.6	11.7
3	1.6	10.7
4	3.2	12.7
5	4.8	12.7

图2 网格无关性曲线

Fig.2 Grid independent curves

图3 网格尺度分布模型

Fig.3 Grid distribution model

图4 监测点位置[9]

Fig.4 Location of monitoring points

表2 数值计算温度与文献［9］试验数据对比

Table 2 Comparison of calculated temperature with experimental data

时间/ s	监测点入口温度/ K	监测点流体温度/ K	监测点壁面温度/ K	质量流量/ (g/s)	过渡区时长/ s
0	77 /77	290 /290	295 /295	1.6	121 /149
100	77 /77	273 /285	278 /289
200	77 /77	200 /224	226 /242
300	77 /77	80 /86	145 /168
400	77 /77	80 /83	86 /113
500	77 /77	80 /82	85 /96
最大误差		0.12	0.31		0.23

表3 压降的计算结果与文献［9］试验数据对比

Table 3 Comparison of calculated pressure differences with experimental data

时间/ s	入口压力/ kPa
0	200 /200
40	186 /190
80	173 /177
120	160 /165
最大误差	0.03

图5 瞬态试验数据-数值分析数据对比

Fig.5 Comparison of transient experimental data and numerical analysis data

图6 不同时刻的流型

Fig.6 Flow pattern in precooling process

图7 预冷中气膜的演化过程

Fig.7 Evolution of nitrogen film

图8 不同时刻的壁温

Fig.8 Wall temperature at different times

图9 不同工况入口5.5 m处瞬态温度变化

Fig.9 Transient temperature change of 5.5 m under different working conditions

图10 不同工况瞬态压降变化

Fig.10 Transient pressure drop variation under different working conditions

图11 CHF值达到空泡份额82%的气相体积比云图

Fig.11 Volume fraction distribution when CHF occurs

图12 不同截面处氮气体积分布云图

Fig.12 Volume fraction nephogram of gas phase on different sections

图13 不同直径及不同质量流量时管道内部及壁面的沿程热通量变化

Fig.13 Variation of heat flux along pipe with different diameters and different mass flow rates

表4 不同工况下的CHF值

Table 4 CHF values under different working conditions

工况	热通量/(kW/m²)
1	32.5
2	35.7
3	38.9
4	30.2
5	28.3

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