自然循环流动不稳定条件下的传热特性实验研究
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摘要
为探究流动不稳定性机理,在低压自然循环系统中开展了一系列相关实验,分析了不同流量振荡模式下自然循环的沸腾传热机制及局部传热特性。实验表明:中、低热流密度下出现的较规则的周期性振荡由加热段内流动沸腾诱发,壁面过热度不会随流量振荡而大幅度变化;高热流密度下自然循环系统出现的周期性不规则振荡现象中,流动沸腾类型间的相互转变不是流量波动的唯一原因。大幅度的流量脉动可能在高热流密度下导致沸腾临界的发生,出口壁面出现间歇性干涸,局部传热系数下降的同时伴随壁温的短暂飞跃。随着热流密度的提高,自然循环系统可能出现持续性干涸。
A series of natural circulation experiments were carried out in order to explore the flow instability mechanism. The flow boiling mechanism and local heat transfer characteristics were analyzed for different natural circulation oscillation modes. The experimental results show that the periodic and regular oscillation is induced by flow boiling under low and/or medium heat flux. Meanwhile, the wall superheat varies within a small range when flow rate oscillates. Under high heat flux conditions, an irregular but periodic oscillation is observed in the experiment. The transition of different boiling regimes is not the unique reason for this oscillatory circulation mode. Large amplitude oscillation is likely to trigger transient critical boiling. Periodic dryout occurs near the outlet and gives rise to the decrease of local heat transfer coefficient and the fly-up of wall temperature. With the increase of heat flux, continuous dryout might take place in natural circulation system.
A series of natural circulation experiments were carried out in order to explore the flow instability mechanism. The flow boiling mechanism and local heat transfer characteristics were analyzed for different natural circulation oscillation modes. The experimental results show that the periodic and regular oscillation is induced by flow boiling under low and/or medium heat flux. Meanwhile, the wall superheat varies within a small range when flow rate oscillates. Under high heat flux conditions, an irregular but periodic oscillation is observed in the experiment. The transition of different boiling regimes is not the unique reason for this oscillatory circulation mode. Large amplitude oscillation is likely to trigger transient critical boiling. Periodic dryout occurs near the outlet and gives rise to the decrease of local heat transfer coefficient and the fly-up of wall temperature. With the increase of heat flux, continuous dryout might take place in natural circulation system.
引文
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[18] MISHIMA K, ISHII M. Flow regime transition criteria for upward two-phase flow in vertical tubes[J]. International Journal of Heat and Mass Transfer, 1984, 27: 723-737.
[2] 王强,高璞珍,王忠乙,等. 低压高过冷度下自然循环流动不稳定性实验研究[J]. 原子能科学技术,2018,52(5):822-828. WANG Qiang, GAO Puzhen, WANG Zhongyi, et al. Experimental investigation on flow instability under low pressure and high subcooling natural circulation conditions[J]. Atomic Energy Science and Technology, 2018, 52(5): 822-828(in Chinese).
[3] 杨瑞昌,王彦武,王飞,等. 自然循环过冷沸腾流动不稳定性的实验研究[J]. 核动力工程,2005,26(4):317-322. YANG Ruichang, WANG Yanwu, WANG Fei, et al. An experimental investigation on flow instability under natural circulation under subcooled conditions[J]. Nuclear Power Engineering, 2005, 26(4): 317-322(in Chinese).
[4] 陈听宽. 两相流与传热研究[M]. 西安:西安交通大学出版社,2004:69-70.
[5] ZHAO D W, SU G H, LIANG Z H, et al. Experimental research on transient critical heat flux in vertical tube under oscillatory flow condition[J]. International Journal of Multiphase Flow, 2011, 37: 1 235-1 244.
[6] OKAWA T, GOTO T, MINAMITANI J, et al. Liquid film dryout in a boiling channel under flow oscillation conditions[J]. International Journal of Heat and Mass Transfer, 2009, 52: 3 665-3 675.
[7] BARBER J, SEFIANE K, BRUTIN D, et al. Hydrodynamics and heat transfer during flow boiling instabilities in a single microchannel[J]. Applied Thermal Engineering, 2009, 29: 1 299-1 308.
[8] LEE S, DEVAHDHANUSH V S, MUDAWAR I. Investigation of subcooled and saturated boiling heat transfer mechanisms, instabilities, and transient flow regime maps for large length-to-diameter ratio micro-channel heat sinks[J]. International Journal of Heat and Mass Transfer, 2018, 123: 172-191.
[9] CHEN Xianbing, GAO Puzhen, TAN Sichao, et al. An experimental investigation of flow boiling instability in a natural circulation loop[J]. International Journal of Heat and Mass Transfer, 2018, 117: 1 125-1 134.
[10] MOFFAT R J. Describing the uncertainties in experimental results[J]. Experimental Thermal and Fluid Science, 1988, 1(1): 3-17.
[11] 杨瑞昌,唐虹,王彦武. 自然循环过冷沸腾流动不稳定性的研究[J]. 工程热物理学报,2004,25(3):435-438. YANG Ruichang, TANG Hong, WANG Yanwu. Study on flow instability in a natural circulation system with subcooled boiling[J]. Journal of Engineering Thermophysics, 2004, 25(3): 435-438(in Chinese).
[12] FURUYA M, INADA F, van der HAGEN T H J J. Flashing-induced density wave oscillations in a natural circulation BWR-mechanism of instability and stability map[J]. Nuclear Engineering and Design, 2005, 235: 1 557-1 569.
[13] ARITOMI M, CHIANG J H, MORI M. Geysering in parallel boiling channels[J]. Nuclear Engineering Design, 1993, 141: 111-121.
[14] MARCEL C P, ROHDE M, van der HAGEN T H J J. Experimental and numerical investigations on flashing-induced instabilities in a single channel[J]. Experimental Thermal and Fluid Science, 2009, 33: 1 197-1 208.
[15] KYUNG I S, LEE S Y. Periodic flow excursion in an open two-phase natural circulation loop[J]. Nuclear Engineering and Design, 1996, 162: 233-244.
[16] OZAWA M, UMEKAWA H, UOSHIOKA Y, et al. Dryout under oscillatory flow condition in vertical and horizontal tubes-experiments at low velocity and pressure conditions[J]. International Journal of Heat and Mass Transfer, 1993, 36: 4 076-4 078.
[17] 彭传新,陈炳德,卓文彬,等. 两相自然循环系统压降震荡流动不稳定性起始点研究[J]. 核动力工程,2017,38(2):32-37. PENG Chuanxin, CHEN Bingde, ZHUO Wenbin, et al. Research on onset of pressure drop oscillation flow instability in a two-phase natural circulation system[J]. Nuclear Power Engineering, 2017, 38(2): 32-37(in Chinese).
[18] MISHIMA K, ISHII M. Flow regime transition criteria for upward two-phase flow in vertical tubes[J]. International Journal of Heat and Mass Transfer, 1984, 27: 723-737.