基于单液滴蒸发的离心喷雾干燥数值模拟

doi:10.16085/j.issn.1000-6613.2023-0656

摘要/Abstract

摘要：

为了分析离心式喷雾干燥塔内物理场分布和液滴运动规律，采用欧拉-拉格朗日法，耦合单液滴干燥模型，建立了喷雾干燥过程的三维稳态数学模型。以70%（湿基）麦芽糊精溶液为原料液，在中试喷雾干燥系统上进行实验，测定了塔内温度分布。结果表明，模拟的塔内特征点温度与实验结果吻合良好，平均相对误差为1.84%，验证了模拟结果的准确性和可靠性。考察塔内连续相传递过程发现，三维物理场分布不是轴对称的，塔中心区域具有较高的温度、较低的水蒸气含量和较大的气流速度。分析液滴运动轨迹和干燥过程发现，较大的液滴干燥时间较长，较小的液滴干燥时间短但由于发生回旋返混停留时间较长。模拟研究了进风温度、雾化盘转速和进风角度对塔内物理场分布和液滴干燥行为的影响，分析了喷雾干燥过程的传质传热机理。

关键词: 喷雾干燥, 数值模拟, 单液滴干燥动力学, 运动轨迹, 传质传热

Abstract:

In order to analyze the physical field distribution and droplet movement pattern inside centrifugal spray dryer, a three-dimensional steady-state mathematical model of the spray drying process was established by using the Euler-Lagrange method coupling the single-droplet drying model. Experiments were conducted on a pilot-scale centrifugal spray drying system using 70% (wet basis) maltodextrin solution as the feedstock, and the temperature distribution inside the dryer was measured. The results showed that the simulated temperatures at characteristic points agreed well with the experimental values with 1.84% of average relative error, demonstrating the accuracy and reliability of the simulation results. Examination of continuous phase transfer process revealed that the three-dimensional physical field showed a cylindrically asymmetric distribution, having higher temperatures, lower water vapor contents, and greater airflow velocities at the center area of the tower. Analysis of droplet movement trajectory and drying process found that larger droplets had longer drying times, while smaller droplets had shorter drying times but longer residual time due to the occurrence of swirling and backflow. The effects of inlet air temperature, atomization disc rotation speed, and inlet air angle on the physical field distribution and droplet drying behavior inside the tower were studied by simulation, and the mass and heat transfer mechanism of spray drying process were analyzed.

Key words: spray drying, numerical simulation, single-droplet drying kinetics, motion trajectory, mass and heat transfer

中图分类号:

TQ028.5

祝妍妮, 王维, 孙闫晨昊, 魏岗, 张大为. 基于单液滴蒸发的离心喷雾干燥数值模拟[J]. 化工进展, 2024, 43(4): 1700-1710.

ZHU Yanni, WANG Wei, SUN Yanchenhao, WEI Gang, ZHANG Dawei. Numerical simulation of centrifugal spray drying based on single-droplet evaporation[J]. Chemical Industry and Engineering Progress, 2024, 43(4): 1700-1710.

图/表 16

图1 喷雾干燥塔物理模型

图2 喷雾干燥系统流程图1—空气过滤器；2—鼓风机；3—电加热器；4—雾化器；5—干燥塔；6—控制单元；7—进料泵；8—原料罐；9—冷却风机；10—旋风分离器；11—引风机

图3 喷雾干燥塔内测温点分布

图4 旋转雾化盘和液滴速度方向

表1 塔内温度模拟值与实验测量值对比

截面/mm	A			B			C
截面/mm	实验值/K	模拟值/K	相对误差/%	实验值/K	模拟值/K	相对误差/%	实验值/K	模拟值/K	相对误差/%
250	357.8	352.0	1.62	355.3	351.9	0.96	401.0	429.9	4.85
450	362.3	356.6	1.57	364.0	354.4	2.64	392.6	406.6	3.57
650	356.5	359.3	0.79	366.2	357.5	2.38	385.4	391.9	1.69
850	353.2	361.8	2.43	364.9	356.8	2.22	376.4	382.9	1.73
1050	354.4	362.4	2.26	360.6	361.1	0.14	373.6	376.6	0.8
1200	356.7	362.6	1.65	368.8	364.8	1.08	370.6	373.6	0.81

图5 塔内温度分布图

图6 塔内水蒸气含量分布图

图7 塔内速度分布图

图8 干燥过程中液滴运动轨迹

图9 不同粒径液滴运动轨迹

图10 液滴干燥过程

图11 不同进风温度对干燥过程的影响

表2 不同转速时的液滴参数

雾化盘转速 /r·min^-1	切向速度u_t/m·s^-1	径向速度u_r/m·s^-1	液滴平均直径D_vs/µm
24000	60.32	1.69	76.45
27000	67.86	1.83	69.33
30000	75.40	1.96	63.53

图12 不同雾化盘转速的温度分布云图

图13 不同雾化盘转速的液滴运动轨迹俯视图

图14 不同进风角度的温度分布云图

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