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内循环流化床颗粒流动特性的直接数值模拟 总被引:1,自引:0,他引:1
内循环流化床是一种新型式的流化床,采用多风室非均匀布风实现床料颗粒的大尺度循环流动,从而增强了颗粒的横向混合。内循环流化床已应用于城市生活垃圾的焚烧制能,其燃烧速度、燃尽率及污染物排放优于传统的链条炉或鼓泡床。但是,目前设计的内循环流化床普遍较小,还不能满足城市垃圾的处理要求.根本原因在于对床内的气-固流动特性,特别是颗粒的运动规律没有深入的认识。内循环流化床内的气一固流动属于稠密的两相流,通过试验手段,如PIV、PDA也很难获得床内单个颗粒的运动特征。因此,采用前言的DEM(Discrete Element Method)模型对二维内循环流化床内的颗粒流动进行直接数值模拟.模拟结果表明非均匀布风内循环流化床内确实存在颗粒的大尺度循环流动。图4表1参5 相似文献
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《International Journal of Heat and Mass Transfer》2006,49(19-20):3338-3342
A new particle image technique was developed to analyze the dispersion of tracer particles in an internally circulating fluidized bed (ICFB). The movement course and the concentration distribution of tracer particles in the bed were imaged and the degree of inhomogeneity of tracer particles was analyzed. The lateral and axial dispersion coefficients of particles were calculated for various zones in ICFB. Results indicate that the lateral diffusion coefficient in the fluidized bed with uneven air distribution is significantly higher than that in uniform bubbling beds with even air distribution. The dispersion coefficients are different along bed length and height. 相似文献
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以旋涡流化床悬浮空浮空间喷入二次风形成一强放流场和气固悬浮流动为物理模型,试验研究了床面夹带到悬浮空间颗粒群的运动行为及气固两相浓度场的匹配,指出在气相强旋湍流的作用下,在近壁区形成一稳定的高浓度的颗粒悬浮层,颗粒在炉内的平均停留时间延长,气固滑移速度增大,两相混合强并充分接触,良好的空气动力结构对提高炭粒在悬浮空间的燃尽度,降低场析可燃物质损失十分有利,本文研究结果,对降低常规鼓泡床及抛煤机链条炉内的飞灰可燃物损失,提高悬浮空间的气流横向混合速率有重要参考价值。 相似文献
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为模拟存在滞水区的河道内水流运动开展了水槽试验,采用粒子图像测速仪(PIV)测得不同雷诺数下无植被滞水区、不同密度刚性非淹没植被滞水区的流场,分析了滞水区内的环流结构及横断面上流速分布规律。结果表明,植被对滞水区的水流结构有较大影响,植被密度较大时,滞水区中无环流结构,横断面上流速符合双曲正切函数分布;无植被及植被密度较小时,滞水区中有明显环流结构,横断面上仅剪切层部分区域流速符合双曲正切函数分布。对滞水区内部流速采用线性分布公式拟合,说明植被密度较大时,雷诺应力是主导切应力,滞水区横断面上力的平衡机理与充分发展的剪切层一致;无植被及植被密度较小时,空间脉动产生的分散应力及二次环流产生的影响增大,致使滞水区内部流速分布发生改变。 相似文献
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针对循环流化床结合煤粉燃烧技术,建立了炉内气固运动特性的三维数学模型,研究分析了煤粉不同喷入位置及不同二次风速度对炉内气固运动特性的影响.结果表明:在不同二次风速下,煤粉燃烧器布置位置距布风板2600 mm和2000 mm时,颗粒速度波动大,流动不稳定,不能在悬浮段形成局部颗粒流浓度;布置位置为距布风板2300 mm时,流动状态较稳定,而且能够在悬浮段形成高浓度颗粒流.因此在采用联合燃烧技术的循环流化床中,保持流化风速为2 m/s时,煤粉燃烧器布置位置在距布风板2300 mm时,能使煤颗粒在炉膛整个上升过程中处于高温燃烧氛围. 相似文献
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Akira Nishimura Seiichi Deguchi Hitoki Matsuda Masanobu Hasatani Arun S. Mujumdar 《亚洲传热研究》2002,31(4):307-319
A pulsating fluidized bed is operated with two sequential durations designated as an on‐period with injecting fluidization gas and an off‐period without it. The heat transfer coefficient between a vertically immersed heater and bed in a pulsating fluidized bed is measured under various pulse cycles and fluidized particles. The obtained results are compared with those in a normal fluidized bed with continuous fluidization air injection. The relationship between heat transfer coefficients and bubble characteristics, evaluated using a digital video camera, has also been investigated. For certain fluidized particles and operating pulse cycles, the fluidization of particles and the increment of heat transfer coefficients can be obtained under a mean air velocity based on a pulse cycle duration smaller than the minimum fluidization air velocity in a normal fluidized bed. Under the pulse cycles where a static bed through the whole bed is formed in the off‐period duration, the improved heat transfer rate over that in a normal fluidized bed can be measured. This may be attributed to large bubble formation. As heat transfer in the pulsating fluidized bed is obstructed with increasing time to keep a static bed due to the excessive off‐period duration, it is indicated that there is an optimum off‐period duration based on the heat transfer rate. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(4): 307–319, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10038 相似文献
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Yu.S. Teplitsky V.A. Borodulya E.F. Nogotov 《International Journal of Heat and Mass Transfer》2003,46(22):4335-4343
A phenomenological model of axial solids mixing in a circulating fluidized bed is formulated. The model allows for main specific features of the process: ascending motion of particles in the core zone and their descending motion in the annular zone (inner circulation of solids); substantial changes of particle concentration, sizes of core and annular zones over the bed height; net circulation of solids and the effect of the bottom bed on the process. The validity of initial postulates is confirmed by comparison of calculated and experimental curves of mixing. 相似文献