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Numerical simulation of saturated steam condensation heat exchange in a vertical channel |
| LIU Qian1, GUI Nan1, YANG Xingtuan1, TU Jiyuan1,2, JIANG Shengyao1 |
1. Key Laboratory of Advanced Reactor Engineering and Safety of Ministry of Education, Collaborative Innovation Center of Advanced Nuclear Energy Technology, Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, China;
2. School of Engineering, RMIT University, Melbourne VIC 3083, Australia |
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Abstract [Objective] Condensing heat exchange is a crucial process in the primary circuit of small modular reactors and passive safety systems that rely on natural circulation as the driving force. With the higher requirements for heat exchange efficiency and reactor safety, in-depth research and an understanding of the condensation heat exchange process are needed. Therefore, numerical simulations of the condensing heat exchange process have attracted increasingly more interest. However, due to the complex phase change, the condensing heat exchange process is difficult to model using analytical equations. Traditional numerical simulation methods use the empirical equations summarized in experiments, and their universalities are controversial. In contrast, the lattice Boltzmann method is a mesoscopic-level numerical simulation method that tracks particle clusters and uses probability density functions to describe their distribution, resulting in a simple and clear structure that appropriately ignores the details of molecular motion. Moreover, it allows direct iterative solving of the probability density distribution function without relying on empirical equations. In previous studies, the feasibility of using the lattice Boltzmann pseudopotential model in condensation process simulation was verified. Subsequently, numerous researchers have used this model to analyze the condensation mechanism.[Methods] This study is based on the lattice Boltzmann method and uses a dual distribution function to simulate the condensation process of stationary saturated vapor within a vertical channel. To analyze the fluid flow characteristics, a pseudopotential model is used to simulate the density field variations during the vapor condensation. Additionally, a temperature distribution function is employed to simulate the temperature field changes during the vapor condensation, allowing for an examination of heat transfer efficiency. Throughout the simulation, we analyze the effects of channel width and the hydrophilicity and hydrophobicity of wall conditions on the condensate flow and heat transfer rate.[Results] The results showed that:1) When saturated vapor encountered a hydrophilic wall, it first condensed to form a thin liquid film covering the entire wall surface and then formed a steady liquid film from the top of the vertical channel, gradually expanding downward. Due to the pressure difference caused by the vapor condensation, the saturated vapor flowed down into the channel from the inlet at the top of the channel. 2) Under hydrophilic wall conditions, decreasing the channel width from 500 to 150 decreased the steady-state average mass flow rate at the inlet by approximately 20% and decreased the steady-state average heat flux density on the wall by approximately 6.5%. 3) The simulation results under different hydrophobic and hydrophilic characteristics were consistent with the theoretical analysis, indicating that the stronger the wall hydrophobicity was, the later the starting time of droplet nucleation and the lower the starting point of the vertical liquid film. On the ordinary hydrophobic wall surface, the droplet condensation was difficult to sustain, and after this surface was covered by a liquid film, the heat transfer rate was slower compared to the hydrophilic wall surface. Before the liquid film slipped out of the computational domain, the maximum average wall heat flux at an angle of 127° was approximately 75.8% of that at an angle of 51°.[Conclusions] The lattice Boltzmann pseudopotential model can simulate the condensation process of stationary saturated vapor within a vertical channel. During the simulation process, the effects of channel width and the hydrophilicity and hydrophobicity of wall conditions on condensate flow and heat flux density are important. In general, wider channel widths lead to higher wall heat flux density, and a higher inlet mass flow rate of steam is achieved at a steady state for saturated vapor initially in a stationary state within the channel. However, ordinary hydrophobic wall surfaces cannot sustain droplet condensation and do not demonstrate enhanced heat transfer. These findings have certain reference values for designing and optimizing heat transfer systems involving condensation in vertical channels.
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| Keywords
condensation heat transfer
lattice Boltzmann method
steam velocity
contact angle
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Issue Date: 22 July 2023
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[1] 李常伟. 非能动余热排出换热器换热特性研究及换热模型验证[D]. 哈尔滨:哈尔滨工程大学, 2013. LI C W. Study the heat transfer characteristics and verify the heat exchanger model of passive residual heat removal heat exchanger[D]. Harbin:Harbin Engineering University, 2013. (in Chinese)
[2] WANG M J, ZHAO H, ZHANG Y P, et al. Research on the designed emergency passive residual heat removal system during the station blackout scenario for CPR1000[J]. Annals of Nuclear Energy, 2012, 45:86-93.
[3] MARCEL C P, FURCI H F, DELMASTRO D F, et al. Phenomenology involved in self-pressurized, natural circulation, low thermo-dynamic quality, nuclear reactors:The thermal-hydraulics of the CAREM-25 reactor[J]. Nuclear Engineering and Design, 2013, 254:218-227.
[4] BHOWMIK P K, SCHLEGEL J P, REVANKAR S. State-of-the-art and review of condensation heat transfer for small modular reactor passive safety:Experimental studies[J]. International Journal of Heat and Mass Transfer, 2022, 192:122936.
[5] 黄潇立, 陈泽亮, 桂南, 等. 石墨烯强化沸腾传热研究进展及应用综述[J]. 清华大学学报(自然科学版), 2022, 62(10):1681-1690. HUANG X L, CHEN Z L, GUI N, et al. Review of graphene enhanced boiling heat transfer[J]. Journal of Tsinghua University (Science and Technology), 2022, 62(10):1681-1690. (in Chinese)
[6] 马喜振, 贾海军, 刘洋. 竖直管道内强迫循环下非凝性气体对蒸汽冷凝的影响[J]. 清华大学学报(自然科学版), 2017, 57(5):530-536. MA X Z, JIA H J, LIU Y. Effect of non-condensable gases on steam condensation in a vertical pipe with forced convection[J]. Journal of Tsinghua University (Science and Technology), 2017, 57(5):530-536. (in Chinese)
[7] LI Q, LUO K H, KANG Q J, et al. Lattice Boltzmann methods for multiphase flow and phase-change heat transfer[J]. Progress in Energy and Combustion Science, 2016, 52:62-105.
[8] LIU X L, CHENG P. Lattice Boltzmann simulation of steady laminar film condensation on a vertical hydrophilic subcooled flat plate[J]. International Journal of Heat and Mass Transfer, 2013, 62:507-514.
[9] MUKHERJEE A, BASU D N, MONDAL P K, et al. Characterization of condensation on nanostructured surfaces and associated thermal hydraulics using a thermal lattice Boltzmann method[J]. Physical Review E, 2022, 105(4):045308.
[10] LIU L J, LIANG G J, ZHAO H Q, et al. Effect of surface micromorphology and hydrophobicity on condensation efficiency of droplets using the lattice Boltzmann method[J]. Thermal Science, 2022, 26(4B):3505-3515.
[11] CAI J J, CHEN J T, DENG W, et al. Towards efficient and sustaining condensation via hierarchical meshed surfaces:A 3D LBM study[J]. International Communications in Heat and Mass Transfer, 2022, 132:105919.
[12] GONG S, CHENG P. Numerical investigation of droplet motion and coalescence by an improved lattice Boltzmann model for phase transitions and multiphase flows[J]. Computers & Fluids, 2012, 53:93-104.
[13] YUAN P, SCHAEFER L. Equations of state in a lattice Boltzmann model[J]. Physics of Fluids, 2006, 18(4):042101.
[14] SHAN X W, CHEN H D. Lattice Boltzmann model for simulating flows with multiple phases and components[J]. Physical Review E, 1993, 47(3):1815-1819.
[15] GONG S, CHENG P. A lattice Boltzmann method for simulation of liquid-vapor phase-change heat transfer[J]. International Journal of Heat and Mass Transfer, 2012, 55(17-18):4923-4927.
[16] VASYLIV Y, LEE D, TOWER T, et al. Modeling condensation on structured surfaces using lattice Boltzmann method[J]. International Journal of Heat and Mass Transfer, 2019, 136:196-212.
[17] GUO Z L, ZHENG C G, SHI B C. Non-equilibrium extra-polation method for velocity and pressure boundary conditions in the lattice Boltzmann method[J]. Chinese Physics, 2002, 11(4):366-374.
[18] LI Q, LUO K H, KANG Q J, et al. Contact angles in the pseudopotential lattice Boltzmann modeling of wetting[J]. Physical Review E, 2014, 90(5):053301.
[19] 杨世铭, 陶文铨. 传热学:3版[M]. 北京:高等教育出版社, 1998. YANG S M, TAO W Q. Heat transfer:3rd ed[M]. Beijing:Higher Education Press, 1998. (in Chinese)
[20] 施明恒, 甘永平, 马重芳. 沸腾和凝结[M]. 北京:高等教育出版社, 1995. SHI M H, GAN Y P, MA C F. Boiling and Condensation Heat Transfer[M]. Beijing:Higher Education Press, 1995. (in Chinese) |
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2023,
Vol. 63
