基于亚格子尺度模型的液固流化床流动特性的数值模拟研究

发布时间：2019-01-08 19:19

【摘要】：液固两相流是多相流中一个重要的研究方向。液固流化床具有良好的混合、传热、传质等优点。然而由于目前对其理论研究工作较少,加之流化床内颗粒流体具有非线性和结构不均匀性等特点,因此亟需对液固流化床内两相流动的本质与机理进行深入讨论。本文采用数值模拟方法,基于亚格子尺度双流体模型加入壁面修正系数考虑壁面效应,结合双流体模型及颗粒动理学,建立液固提升管及液固喷动床的二维流动模型。研究不同工况下颗粒的流动特性,分析颗粒浓度、颗粒轴向速度等分布,从而得到床内颗粒流动规律。数值模拟液固提升管内流动行为,结果显示加入壁面修正的亚格子尺度模型网格适应性强,能够在粗网格计算中准确反映微观流动行为;在提升管发展段内,颗粒分布呈环-核结构,边壁出现明显的返混现象,加入壁面修正的亚格子尺度模型和EMMS模型相比,更加接近实验结果,意旨对亚格子模型进行了合理的模型验证。数值模拟液固喷动床内流动行为,得到了喷动床内喷射区、环隙区及喷泉区三大区域的流动状态;研究结果表明随液相入口速度增大、液相粘度增大,床层膨胀高度逐渐增加,颗粒浓度减小,颗粒及液相轴向速度增大;喷动床倒锥体锥角主要对床内环隙区产生影响,随锥角的减小,环隙区向喷射区流动的颗粒逐渐聚集,颗粒浓度减小、颗粒速度下降。模拟中将亚格子尺度模型基于其他曳力模型进行比较,可以明显捕捉喷动床喷射区域内颗粒浓度低,环隙区域内颗粒浓度高,固相颗粒在环隙区及喷射区内循环运动等特点。在喷射区、环隙区内亚格子模型模拟的颗粒浓度值偏大,而在喷泉区内模拟的颗粒浓度由边壁向中心呈逐渐减小趋势,以便证实该模型在液固喷动床中的适用性。
[Abstract]:Liquid-solid two-phase flow is an important research direction in multi-phase flow. Liquid-solid fluidized bed has the advantages of good mixing, heat transfer and mass transfer. However, due to the lack of theoretical research and the nonlinearity and non-uniformity of particle fluid in fluidized bed, the nature and mechanism of two-phase flow in liquid-solid fluidized bed need to be discussed in depth. In this paper, a two-dimensional flow model of liquid-solid riser and liquid-solid spouted bed is established by using numerical simulation method and considering wall effect by adding wall correction coefficient to sub-lattice scale two-fluid model and combining two-fluid model and particle dynamics. The flow characteristics of particles under different working conditions are studied, and the distribution of particle concentration and particle axial velocity are analyzed, and the flow law of particles in the bed is obtained. The numerical simulation results show that the sublattice model with wall modification is adaptive and can accurately reflect the microscopic flow behavior in coarse mesh calculation. In the development section of the riser, the particle distribution is ring-core structure and the side wall appears obvious backmixing phenomenon. Compared with the EMMS model, the modified sub-lattice model is closer to the experimental results. The sublattice model is verified reasonably by intention. The flow behavior in liquid-solid spouted bed is simulated numerically, and the flow states in the spray zone, annulus region and fountain region are obtained. The results show that with the increase of the inlet velocity of the liquid phase, the viscosity of the liquid phase increases, the expansion height of the bed increases gradually, the particle concentration decreases, and the axial velocity of the particle and liquid phase increases. The conical angle of the inverted cone of spouted bed mainly affects the annular gap in the bed. With the decrease of the cone angle, the particles flowing from the annulus to the jet zone gradually gather, the particle concentration decreases and the particle velocity decreases. By comparing sub-lattice model with other drag models, the characteristics of low particle concentration in spouted bed jet region, high particle concentration in annular zone and circulating movement of solid particles in annular and jet zone can be clearly captured. In the jet region, the particle concentration simulated by the sub-lattice model in the annular gap region is larger than that in the fountain region, and the particle concentration in the fountain region is gradually decreasing from the side wall to the center, in order to confirm the applicability of the model in the liquid-solid spouted bed.
【学位授予单位】：东北石油大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ051.13

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