Numerical Study of Condensation Heat Transfer of Steam with Non-condensable Gas

doi:10.12382/bgxb.2022.0225

Abstract

Abstract:

In order to study the performance of a high-pressure heat exchanger in an underwater semi-closed cycle power system, we establish a numerical model to analyze the condensation process of steam containing a significant proportion of non-condensable gas under high pressure. The model is verified through a specific experiment, and we conduct simulations of the gas flow channel in the heat exchanger under different working conditions, taking gravity into consideration. The results show that due to the gravity, the liquid film thicknesses at the top and bottom of the pipe are not uniform, resulting in swirling flow within the gas phase. These two effects lead to uneven heat transfer characteristics in the pipe. Additionally, the flow velocity increases with the decreasing pipe diameter, causing a rise in the Reynolds number and a thinning of the bottom liquid film. This contributes to heat transfer. The increased flow velocity also reduces the effect of gravity, reducing the disparity in heat transfer intensity between the top and bottom sections of the pipe. Under the working conditions in this paper, even with a reduced total heat transfer area, reducing the pipe diameter remains conducive to the improvement of the total heat transfer power. The maximum temperature error between the experimental and simulated results is 19.5%. The conclusions contribute to the design of high-pressure heat exchangers in underwater semi-closed cycle power systems.

Key words: condensation heat transfer, non-condensable gas, steam condensation, computational fluid dynamics

GUO Qing, LUO Kai, GENG Shaohang, QIN Kan. Numerical Study of Condensation Heat Transfer of Steam with Non-condensable Gas[J]. Acta Armamentarii, 2023, 44(7): 2080-2091.

Figures/Tables 21

Fig.1 Schematic diagram of a semi-closed cycle power system

Table 1 Combustion products of the HAP tri-component propellant

组分	质量分数/%	特性
CO	0.26	不溶于水
CO₂	20.47	不溶于水
H₂	0.12	不溶于水
N₂	5.48	不溶于水
HCl	8.44	可溶于水
H₂O	65.18	可凝结

Fig.2 Schematic diagram of a double-pipe heat exchanger

Table 2 Working conditions of the research mentioned above

研究者	研究类型	工质种类	压力/MPa
Kuhn^[7]	试验研究	空气、氦气	0.1~0.5
Lee等^[8]	试验研究	氮气	0.1~0.13
Ren等^[9]	试验研究	空气	0.1~0.4
马喜振^[10]	试验研究	氮气、氩气	0.2~5.6
Park等^[11]	试验研究	空气	0.19~0.49
Ji等^[12]	试验研究	未注明	0.02~0.07
Groff等^[15]	数值研究	空气	0.1
Bian等^[16]	数值研究	空气	0.1~0.4
耿少航等^[19]	数值研究	CO₂	10

Fig.3 Casing heat exchanger test equipment

Fig.4 Schematic diagram of the heat exchanger

Fig.5 Flow domain of the heat exchanger pipe

Table 3 Boundary conditions for simulations

参数	数值
入口质量流量/(g·s^-1)	10
入口温度/K	575
入口水蒸气过热度/K	2.5
出口压力/MPa	10
壁面温度/K	545
工质种类	水蒸气、CO₂
CO₂质量分数	0.3

Table 4 Operation parameters of the experiment

参数	数值
燃气通道入口压力/MPa	10
燃气通道入口温度/K	1100
燃气通道出口温度/K	340
冷却水通道入口压力/MPa	5
冷却水通道入口温度/K	280
冷却水通道出口温度/K	600
燃气通道入口水蒸气体积分数/%	7

Fig.6 Flow domain of the high-temperature heat exchanger

Fig.7 Comparison of temperature distribution between simulation and experimental results

Table 5 Mesh setting parameters in grid independence study

工况	网格数	近壁面第1层网格厚度/mm	径向网格增长率	平均y⁺
网格1	242万	0.012	1.2	1.09
网格2	389万	0.010	1.2	0.92
网格3	627万	0.008	1.2	0.86

Fig.8 Film thickness and heat transfer coefficient of the grid independence study

Fig.9 Velocity distrubutions at z=1.0m, 1.2m, 1.4m and 1.6m of the heat exchanger pipe

Fig.10 Water film thickness and water volume fraction-streamline contours at z=1.0m, 1.2m, 1.4m and 1.6m of the heat exchanger pipe

Fig.11 Heat flux and heat transfer coefficient distributions along the axial direction of the heat exchanger pipe

Fig.12 Bulk temperature and heat flux under conditions of different pipe diameters

Fig.13 Velocity distubutions at z=1.2m with different pipe diameters

Fig.14 Film thickness with different pipe diameters

Fig.15 Relationship between average gas Reynolds number and wall heat flux with different pipe diameters

Fig.16 Total heat transfer power of pipes with different diameters

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