溢流式筛孔板热水塔内单气泡的可视化实验
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摘要
以煤气化渣水回收系统中的蒸发热水塔为研究对象,对热水塔内孔径为5 mm的塔板上单气泡的形成和运动特性进行了可视化实验,借助高速相机和图像处理方法得到了气泡整个生长周期的形变过程及运动特性。实验结果表明:气泡的生长周期分为3个阶段:形成区、上升区和振荡破碎区。气泡等效半径在形成区迅速增大,在上升区和振荡破碎区缓慢增加;气泡长径比在形成区呈衰减变化,而在振荡破碎区变化规律性较差;蒸汽气泡的y向形心运动速率先增大后平稳波动,氮气气泡的y向形心运动速率处于一直增加的状态,但在振荡破碎区的运动规律较差,蒸汽和混合气体气泡在冷凝过程中均出现了中空现象。对于混合气体气泡,氮气流量的增加导致气泡形成和破碎的时间变短,阻碍了蒸汽传热冷凝。
Based on the evaporating water tower of the circuit bottom ash sluicing system,the formation and movement of the single bubble emerging from an orifice with diameter of 5 mm in the middle of tray were investigated by visual experiments, with the water flow rate of 150, 200, 250 L/h, the steam flow rate of 5 kg/h, and nitrogen flow rate of 0.163 2 kg/h and 0.326 4 kg/h. The life time of bubbles was recorded by high speed camera and the characteristics of bubble deformation and movement were obtained by image processing software. The results show that the life time of bubble is divided into three parts on the basis of pictures: formation region, rising region and oscillation region. The bubble deformation and movement are obtained in each part. The equivalent radius of bubble increases rapidly in the first region because of the gas influx and grows more slowly in the latter two regions. The aspect ratio of bubble changes from large to small in the formation region, while it changes irregularly in the oscillation region. The vertical velocity of centroid of steam bubble increases at the beginning and then fluctuates. However, the vertical velocity of centroid of nitrogen bubble increases over time due to the lacking of mass transfer. The motion law of bubble in the oscillation region is hard to describe. The hollow phenomenon is found in both steam and mixture bubbles through the condensing process in the experiment. The effect of non-condensable gases to the transmission process is also discussed. With the increasing of the nitrogen flow rate, the time of formation and oscillation region decreases for the mixture gas bubble, leading to the deterioration of heat transfer in the tower. The result of this paper can be a theoretical guidance for evaporating hot water tower operation.
Based on the evaporating water tower of the circuit bottom ash sluicing system,the formation and movement of the single bubble emerging from an orifice with diameter of 5 mm in the middle of tray were investigated by visual experiments, with the water flow rate of 150, 200, 250 L/h, the steam flow rate of 5 kg/h, and nitrogen flow rate of 0.163 2 kg/h and 0.326 4 kg/h. The life time of bubbles was recorded by high speed camera and the characteristics of bubble deformation and movement were obtained by image processing software. The results show that the life time of bubble is divided into three parts on the basis of pictures: formation region, rising region and oscillation region. The bubble deformation and movement are obtained in each part. The equivalent radius of bubble increases rapidly in the first region because of the gas influx and grows more slowly in the latter two regions. The aspect ratio of bubble changes from large to small in the formation region, while it changes irregularly in the oscillation region. The vertical velocity of centroid of steam bubble increases at the beginning and then fluctuates. However, the vertical velocity of centroid of nitrogen bubble increases over time due to the lacking of mass transfer. The motion law of bubble in the oscillation region is hard to describe. The hollow phenomenon is found in both steam and mixture bubbles through the condensing process in the experiment. The effect of non-condensable gases to the transmission process is also discussed. With the increasing of the nitrogen flow rate, the time of formation and oscillation region decreases for the mixture gas bubble, leading to the deterioration of heat transfer in the tower. The result of this paper can be a theoretical guidance for evaporating hot water tower operation.
引文
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[15] JIANG B, LIU P, ZHANG L, et al. Hydrodynamics and mass-transfer analysis of a distillation ripple tray by computational fluid dynamics simulation[J]. Industrial & Engineering Chemistry Research, 2013, 52(49): 17618-17626.
[16] RAHIMI M R. Characteristics of gas-liquid contact on cross-current trays[J]. Separation Science and Technology, 2014, 49(17): 2772-2782.
[17] ZENG Q, CAI J, YIN H, et al. Numerical simulation of single bubble condensation in subcooled flow using OpenFOAM[J]. Progress in Nuclear Energy, 2015, 83: 336-346.
[18] CHEN Y M, MAYINGER F. Measurement of heat transfer at the phase interface of condensing bubbles[J]. International Journal of Multiphase Flow, 1992, 18(6): 877-890.
[19] WARRIER G R, BASU N, DHIR V K. Interfacial heat transfer during subcooled flow boiling[J]. International Journal of Heat and Mass Transfer, 2002, 45(19): 3947-3959.
[20] PAN L, TAN Z, CHEN D, et al. Numerical investigation of vapor bubble condensation characteristics of subcooled flow boiling in vertical rectangular channel[J]. Nuclear Engineering and Design, 2012, 248: 126-136.
[21] TIAN W, ISHIWATARI Y, IKEJIRI S, et al. Numerical simulation on direct contact condensation of single bubble in subcooled water using MPS method[C]//The 6th International Symposium on Multiphase Flow, Heat Mass Transfer and Energy Conversion. American: AIP Publishing, 2010: 933-938.
[22] ZENG Q, CAI J. Three-dimension simulation of bubble behavior under nonlinear oscillation[J]. Annals of Nuclear Energy, 2014, 63: 680-690.
[2] MARTíN M, MONTES F J, GALáN M A. Mass transfer from oscillating bubbles in bubble column reactors[J]. Chemical Engineering Journal, 2009, 151(1): 79-88.
[3] PAINMANAKUL P, LOUBIERE K, HEBRARD G, et al. Study of different membrane spargers used in waste water treatment: Characterisation and performance[J]. Chemical Engineering and Processing: Process Intensification, 2004, 43(11): 1347-1359.
[4] KODAMA Y, KAKUGAWA A, TAKAHASHI T, et al. Experimental study on microbubbles and their applicability to ships for skin friction reduction[J]. International Journal of Heat and Fluid Flow, 2000, 21(5): 582-588.
[5] 于广锁, 牛苗任, 王亦飞, 等. 气流床煤气化的技术现状和发展趋势[J]. 现代化工, 2004, 24(5): 23-26.
[6] ROBIN T T, SNYDER N W. Theoretical analysis of bubble dynamics for an artificially produced vapor bubble in a turbulent stream[J]. International Journal of Heat and Mass Transfer, 1970, 13(3): 523-536.
[7] 姜永浩, 陈雪莉, 许琳, 等. 固阀塔板上密集鼓泡区气泡的运动行为特征[J]. 华东理工大学学报(自然科学版), 2015, 41(6): 742-749.
[8] KAMEI S, HIRATA M. Condensing phenomena of a single vapor bubble into subcooled water[J]. Experimental Heat Transfer: An International Journal, 1990, 3(2): 173-182.
[9] HARADA T, NAGAKURA H, OKAWA T. Dependence of bubble behavior in subcooled boiling on surface wettability[J]. Nuclear Engineering and Design, 2010, 240(12): 3949-3955.
[10] TANG J, YAN C, SUN L. Effects of noncondensable gas and ultrasonic vibration on vapor bubble condensing and collapsing[J]. Experimental Thermal and Fluid Science, 2015, 61: 210-220.
[11] MORITA K, MATSUMOTO T, FUKUDA K, et al. Experimental verification of the fast reactor safety analysis code SIMMER-Ⅲ for transient bubble behavior with condensation[J]. Nuclear Engineering and Design, 2008, 238(1): 49-56.
[12] SUZUKI T, TOBITA Y, YAMANO H, et al. Development of multicomponent vaporization/condensation model for a reactor safety analysis code SIMMER-Ⅲ: Extended verification using multi-bubble condensation experiment[J]. Nuclear Engineering and Design, 2003, 220(3): 240-254.
[13] 屈晓航, 田茂诚, 张冠敏, 等. 含不凝气体蒸汽泡直接接触冷凝[J]. 化工学报, 2014, 65(12): 4749-4754.
[14] CLERX N, VAN DER GELD C W M. Experimental and analytical study of intermittency in direct contact condensation of steam in a cross-flow of water[C]//Proceedings of ECI International Conference on Boiling Heat Transfer. Florianopolis, Brazil: [s.n.], 2009: 1-8.
[15] JIANG B, LIU P, ZHANG L, et al. Hydrodynamics and mass-transfer analysis of a distillation ripple tray by computational fluid dynamics simulation[J]. Industrial & Engineering Chemistry Research, 2013, 52(49): 17618-17626.
[16] RAHIMI M R. Characteristics of gas-liquid contact on cross-current trays[J]. Separation Science and Technology, 2014, 49(17): 2772-2782.
[17] ZENG Q, CAI J, YIN H, et al. Numerical simulation of single bubble condensation in subcooled flow using OpenFOAM[J]. Progress in Nuclear Energy, 2015, 83: 336-346.
[18] CHEN Y M, MAYINGER F. Measurement of heat transfer at the phase interface of condensing bubbles[J]. International Journal of Multiphase Flow, 1992, 18(6): 877-890.
[19] WARRIER G R, BASU N, DHIR V K. Interfacial heat transfer during subcooled flow boiling[J]. International Journal of Heat and Mass Transfer, 2002, 45(19): 3947-3959.
[20] PAN L, TAN Z, CHEN D, et al. Numerical investigation of vapor bubble condensation characteristics of subcooled flow boiling in vertical rectangular channel[J]. Nuclear Engineering and Design, 2012, 248: 126-136.
[21] TIAN W, ISHIWATARI Y, IKEJIRI S, et al. Numerical simulation on direct contact condensation of single bubble in subcooled water using MPS method[C]//The 6th International Symposium on Multiphase Flow, Heat Mass Transfer and Energy Conversion. American: AIP Publishing, 2010: 933-938.
[22] ZENG Q, CAI J. Three-dimension simulation of bubble behavior under nonlinear oscillation[J]. Annals of Nuclear Energy, 2014, 63: 680-690.