液固流态化动态过程中相间作用力的数值模拟及实验验证

doi:10.11949/0438-1157.20200368

摘要/Abstract

摘要：

选择恰当的相间作用力模型是液固流态化动态特性CFD建模的关键。首先采用Richardson-Zaki关联式验证了稳态操作条件下整体固含率的实验结果，然后在基于颗粒动理学理论的欧拉-欧拉双流体模型中比较了Wen-Yu、Gidaspow、Syamlal-O’Brien、Dallavalle和TGS 5个曳力计算公式对液固流化床收缩和膨胀特性的数值模拟结果，进而探讨了Moraga等提出的升力模型影响行为及主要相间作用力影响机制。与实验测量数据比较结果表明：收缩过程中Syamlal-O’Brien和TGS曳力模型对响应时间预测较为准确，TGS曳力模型对整体固含率的预测精度较高；膨胀过程中TGS曳力模型对响应时间和整体固含率的预测优于其他模型。整体而言，基于静止颗粒群绕流直接模拟得到的TGS曳力模型忽略了颗粒-颗粒相互作用，与液固散式体系中颗粒动力学特性相符合。升力模型对动态特性模拟结果影响较小，CFD模拟时根据选择体系可予以适当忽略。

关键词: 计算流体力学, 实验验证, 流化床, 液固两相流, 动态特性, 相间作用力

Abstract:

Choosing the appropriate interphase force model is the key to CFD modeling of liquid-solid fluidization dynamic characteristics. Measured overall solids holdups are validated by Richardson-Zaki correlation under steady-state operating conditions. Then five drag formulas including Wen-Yu, Gidaspow, Syamlal-O??Brien, Dallavalle and TGS are assessed in the contraction and expansion processes by using Euler-Euler two-fluid model with the kinetic theory of granular flow. Furthermore, the influence of the classical lift model suggested by Moraga et al. on CFD predictions and the influence mechanism of main inter-phase forces are discussed. The results compared with the experimental data show that the response time of bed contraction process predicted by Syamlal- O??Brien or TGS drag model is more accurate than those by the others. Moreover, TGS drag model shows the most reasonable prediction in overall solids holdup. For the bed expansion process, TGS drag model gives more reliable prediction in the response time and overall solids holdup than the other models. The main reason behind the best hydrodynamic performance with TGS drag model in this study is that the modeling basis of TGS drag model is consistent with the dynamic behaviors of particles in liquid-solid system. The lift model has little influence on the CFD results, and thus it can be ignored in the modelling of inter-phase force for the dynamic characteristics according to the homogeneous liquid-solid fluidized system investigated in this study.

Key words: CFD, experimental validation, fluidized-bed, liquid-solid two-phase flow, dynamic characteristics, inter-phase forces

中图分类号:

TQ 021.1

张仪,李兵,白玉龙,张锴. 液固流态化动态过程中相间作用力的数值模拟及实验验证[J]. 化工学报, 2020, 71(11): 5129-5139.

Yi ZHANG,Bing LI,Yulong BAI,Kai ZHANG. Numerical simulation and experimental validation of inter-phase forces in dynamic process of liquid-solid fluidization[J]. CIESC Journal, 2020, 71(11): 5129-5139.

图/表 12

图1 液固流态化实验装置

Fig.1 Schematic diagram of experimental setup of liquid-solid fluidization

图2 稳定流化状态下整体固含率实验值验证

Fig.2 Validation of experimental overall solids holdup in steady fluidization

表1 边界条件与初始化设置

Table 1 Boundary conditions and initialization settings

Description	Contraction		Expansion
Description	case 1	case 2	case 3	case 4
experiments
bed height before sudden change in operating velocity, h₀/mm	530	675	400	505
liquid concentration before sudden change in operating velocity, ε_l_,0	0.717	0.778	0.625	0.703
liquid operating velocity before the sudden change, u₀/(mm·s^-1)	41	54	25	38
liquid operating velocity after the sudden change, u₁/(mm·s^-1)	25	38	41	54
liquid temperature/℃	20 — 23
simulations
inlet boundary condition	uniform velocity inlet
liquid inlet velocity, u₁/(mm·s^-1)	25	38	41	54
outlet boundary condition	pressure outlet, 1.013×10⁵Pa
wall boundary condition	no slip for liquid phase, free slip for solid phase
initial bed height, h₀/mm	530	675	400	505
initial liquid velocity in the bed(u_l_,in = u₀/ε_l_,0), u_l,_in/(mm·s^-1)	57	69	40	54

图3 边界条件与初始化设置

Fig.3 Schematic diagram of boundary conditions and initialization settings

图4 液固流化床的收缩过程

Fig.4 Contraction process of liquid-solid fluidized bed (from u0 = 41 mm·s-1 to u1 = 25 mm·s-1)

图5 液固流化床动态收缩时的床层高度分布

Fig.5 Distributions of bed height in contraction process of liquid-solid fluidized bed

表2 床层收缩过程终止时的整体固含率实验值和模拟值

Table 2 Experimental and simulated results of overall solids holdups after contraction process of liquid-solid fluidized bed

Case	Experimental result	Simulated result/error
Case	Experimental result	Wen-Yu	Gidaspow	Syamlal-O’Brien	Dallavalle	TGS
case 1 (h₀= 530 mm, u₀= 41 mm·s^-1, u₁= 25 mm·s^-1)	0.375	0.425/13.2%	0.421/12.2%	0.4436/16.2%	0.400/6.6%	0.380/1.3%
case 2 (h₀= 675 mm, u₀= 54 mm·s^-1, u₁= 38 mm·s^-1)	0.297	0.341/14.7%	0.316/6.4%	0.327/10.1%	0.321/8.0%	0.300/0.9%

图6 升力模型对床层收缩特性的影响

Fig.6 Effect of lift force model on contraction processes

图7 液固流化床的膨胀过程

Fig.7 Expansion process of liquid-solid fluidized bed (from u0 = 25 mm·s-1 to u1 = 41 mm·s-1)

图8 液固流化床动态膨胀时的床层高度分布

Fig.8 Distributions of bed height in expansion process of liquid-solid fluidized bed

表3 床层膨胀过程终止时的整体固含率实验值和模拟值

Table 3 Experimental and simulated result of overall solids holdups after expansion process of liquid-solid fluidized bed

Case

Experimental result

Simulated result/error

Wen-Yu

Gidaspow

Syamlal-

O’Brien

Dallavalle

TGS

case 3 (h₀= 400 mm, u₀= 25 mm·s^-1, u₁= 41 mm·s^-1)

case 4 (h₀= 505 mm, u₀= 38 mm·s^-1, u₁= 54 mm·s^-1)

图9 升力模型对床层膨胀特性的影响

Fig.9 Effect of lift force model on expansion processes

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