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131.
Wojciech P. Adamczyk ;Adam Klimanek ;Ryszard A. Biatecki ;Gabriel Wecel ;Pawel Kozolub ;Tomasz Czakiert 《Particuology》2014,(4):129-137
Particle transport phenomena in small-scale circulating fiuidized beds (CFB) can be simulated using the Euler-Euler, discrete element method, and Euler-Lagrange approaches. In this work, a hybrid Euler-Lagrange model known as the dense discrete phase model (DDPM), which has common roots with the multiphase particle-in-cell model, was applied in simulating particle transport within a mid-sized experimental CFB facility. Implementation of the DDPM into the commercial ANSYS Fluent CFD package is relatively young in comparison with the granular Eulerian model. For that reason, validation of the DDPM approach against experimental data is still required and is addressed in this paper. Additional difficulties encountered in modeling fluidization processes are connected with long calculation times. To reduce times, the complete boiler models are simplified to include just the combustion chamber. Such simplifications introduce errors in the predicted solid distribution in the boiler. To investigate the conse- quences of model reduction, simulations were made using the simplified and complete pilot geometries and compared with experimental data. All simulations were performed using the ANSYSFLUENT 14.0 package. A set of user defined functions were used in the hybrid DDPM and Euler-Euler approaches to recirculate solid particles. 相似文献
132.
Miguel Angel Sanchez Quintanill Manuel Jests Espin Jose Manuel Valverde 《Particuology》2014,(1):54-63
Geldart-A fluidized beds of fine particles experience a jamming transition between a fluid-like state and a solid-like state at a certain superficial gas velocity, that depends on the relative strength of interparticle attractive forces with respect to particle weight, lnterparticle forces provide the bed with a certain tensile strength in the jammed state. In the work presented here we analyze the behavior of a fluidized bed of magnetic particles subjected to an externally applied magnetic field, which contributes to enhance interparticle forces. The importance of the magnetic contribution to interparticle forces is measured by the changes in the tensile strength and the superficial gas velocity at the jamming transition. The link of the field orientation with the microstructure of the bed is discussed, 相似文献
133.
多孔物质气固反应动力学研究 总被引:1,自引:0,他引:1
利用自主研制的微型流化床反应分析仪(MFBRA)在等温条件下测试了高比表面活性炭氧化反应,并根据基于固体转化的热分析动力学方法及考虑气体在微孔内扩散与反应的应用化工动力学方法求算了动力学参数.在内外扩散抑制最小化的实验条件下,粒径小于5μm的活性炭在700-1000℃的燃烧反应动力学研究表明,根据微型流化床中实验数据,采用等温热分析动力学方法求算得内扩散控制区活化能约为95kJ/mol;弓l入化工动力学方法中的随机孔模型对低温区等温燃烧数据拟合,可得孔结构参数在0.17m^-3左右,反应活化能为178kJ/mol,约为内扩散反应活化能的两倍,最为接近本征的碳燃烧反应活化能. 相似文献
134.
重力再循环供液是指蒸发器依靠制冷剂自身的重力送入蒸发器,在供液高度大于蒸发器对制冷剂的阻力情况下,部分制冷剂液体在蒸发器和气液分离器所形成的回路中再循环。由于再循环作用不需要外加动力,并强化管内制冷剂的沸腾换热,蒸发器的效率得以明显提高。文中介绍了重力再循环供液制冷系统和蒸发器的结构,提出采用J.Chawla关系式和Shah关联式相结合的方法预测再循环蒸发器制冷剂侧的换热系数。采用空气侧热平衡法,对直接膨胀供液和重力再循环供液制冷系统分别进行了多蒸发温度下的性能测试。表明重力再循环供液制冷系统比直接膨胀供液制冷系统的制冷量平均增加26%,COP平均增加18%,蒸发温度平均升高1.1℃,传热系数是直接供液的1.57倍。J.Chawla关系式和Shah关联式相结合预测再循环蒸发器制冷剂侧的换热系数,其曲线结构与实验值近似,平均误差不大于20.6%。文章还对各热工参数的变化原因进行了分析。 相似文献
135.
136.
物理学是以实验为基础的自然科学,而物理实验对于建立物理基本概念和理论及加强对基本概念和基本理论的理解有着不可取代的作用.因此,加强学生实验教学显得尤为重要,但实验教学能否成功,规范的操作又是关键. 相似文献
137.
138.
Experimentalists, numerical modellers and reactor modellers need to work together, not only just for validation of numerical codes, but also to shed fundamental light on each other's problems and underlying assumptions. Several examples are given, Experimental gas axial dispersion data provide a means of choosing the most appropriate boundary condition (no slip, partial slip or full slip) for particles at the wall of fluidized beds. CFD simulations help to identify how close "two-dimensional" experimental columns are to being truly two-dimensional and to representing three-dimensional columns. CFD also can be used to provide a more rational means of establishing assumptions needed in the modelling of two-phase fluidized bed reactors, for example how to deal with cases where there is a change in molar flow (and hence volumetric flow) as a result of chemical reactions. 相似文献
139.
While circulating fluidized bed (CFB) reactor has many advantages over the more conventional turbulent fluidized bed (TFB) reactor, it does at least have one significant shortcoming-the rather dilute solids volume concentration in CFB reactor gives rise to less ideal reaction intensity. On the other hand, while having higher reaction intensity, TFB reactor has one fatal drawback of particle back-mixing, making it not suitable for certain reactions such as catalytic reaction where the catalyst requires frequent regeneration. This paper describes some key issues in the development of a circulating turbulent fluidized bed (CTFB) reactor that combines the advantages of both TFB and CFB, that is, to have the high reaction intensity as in TFB but and also to have a suppressed solids back-mixing as in CFB due to a continuous net upflow of solids flux through the bed. Experimental results show enough evidence to suggest that a new fluidization regime is formed, the characteristics of which appears to be distinct from those observed in a regular TFB and from those in either the bottom or the upper sections of regular CFB and/or high-density CFB (HDCFB). Fundamentally, the difference is that particle-particle interaction (collision) dominates the motion of particles in CTFB and TFB, while gas-particle interaction (drag force) is the key element that determines the two phase flow in CFB including HDCFB. 相似文献
140.