化工学报 ›› 2021, Vol. 72 ›› Issue (S1): 227-235.doi: 10.11949/0438-1157.20210154

• 流体力学与传递现象 • 上一篇    下一篇

微波强化液桥式螺旋降膜蒸发器数值模拟

张亚爽(),李洪,从海峰,韩红明,李鑫钢,高鑫()   

  1. 天津大学化工学院,精馏技术国家工程研究中心,天津 300072
  • 收稿日期:2021-01-25 修回日期:2021-03-01 出版日期:2021-06-20 发布日期:2021-06-20
  • 通讯作者: 高鑫 E-mail:yashuangreal@163.com;gaoxin@tju.edu.cn
  • 作者简介:张亚爽(1996—),女,硕士研究生,yashuangreal@163.com
  • 基金资助:
    国家自然科学基金面上项目(21878219)

Numerical simulation of microwave-enhanced spiral liquid-bridge falling film evaporator

ZHANG Yashuang(),LI Hong,CONG Haifeng,HAN Hongming,LI Xingang,GAO Xin()   

  1. School of Chemical Engineering and Technology, National Engineering Research Center of Distillation Technology, Tianjin University, Tianjin 300072, China
  • Received:2021-01-25 Revised:2021-03-01 Published:2021-06-20 Online:2021-06-20
  • Contact: GAO Xin E-mail:yashuangreal@163.com;gaoxin@tju.edu.cn

摘要:

微波加热薄膜蒸发技术在促进极性/非极性混合物分离领域潜力巨大,但仍面临着能源利用效率低和加热不均的挑战,而电场分布不均是其根本原因,但影响电场分布的因素十分复杂且不可控,因此,从蒸发器结构及流体流动形式视角出发可为解决微波能高效利用的瓶颈提供新思路。为此本文提出了液桥式螺旋降膜蒸发器,通过COMSOL建立三维模型并模拟计算了微波能强化蒸发器上的螺旋降膜流动与蒸发过程,以蒸发率和温度变异系数作为评价指标,探究液膜厚度、螺距、蒸发器直径、流量以及时间对微波能利用效率的影响规律,研究结果表明该种结构在一定微波入射功率下,液膜蒸发率可达29.26%,温度变异系数降至0.0867,为微波能强化蒸发分离装置的设计提供了依据。

关键词: 微波, 过程强化, 螺旋降膜, 蒸发分离, 数值模拟, 优化设计

Abstract:

Microwave-enhanced thin film evaporation promoting the separation of mixture with the difference in polarity still faces the challenges of low energy efficiency and uneven heating, where electric field distribution is generally seen as a significantly related factor. However, considering that the factors affecting the electric field distribution are very complicated and uncontrollable, it is advisable to solve the bottleneck of efficient utilization of microwave energy from the perspective of evaporator structure and fluid flow pattern design. For this reason, a liquid-bridge spiral falling film evaporator is proposed in this study. The three-dimensional model is established first by COMSOL and then to simulate the process of water spiral falling film flow and evaporation on the designed evaporator. Evaporation efficiency and coefficient of temperature variation (COV) are used as evaluation indicators to explore the influence of liquid film thickness, the width of the spiral channel, evaporator diameter, flowrate and time on microwave energy utilization efficiency. The results show that at a certain microwave input power, the evaporation efficiency of the liquid film finally reaches 29.26% and the corresponding COV is reduced to 0.0867, which will provide foundation for the design of microwave-enhanced evaporation and separation devices.

Key words: microwave, process intensification, spiral falling film, evaporation separation, numerical simulation, optimal design

中图分类号: 

  • TQ 025.1

图1

液桥式螺旋降膜结构的示意图和几何参数"

图2

微波强化螺旋降膜蒸发设备"

表1

基本参数设置"

参数数值
水的介电常数[17],ε′water88.15-0.414T+0.131e-2T2-0.046e-4T3
水的介电损耗[17],ε″water28.472-0.971T+1.555e-2T2-1.205e-4T3+4.638e-7T4-1.387e-9T5+2.82e-12T6
初始温度,T025 K
弹簧截面固定宽度,B0.12 mm
蒸发潜热,?Hwater2257.6 kJ/kg
玻璃的相对介电常数4.2
空气的相对介电常数1
蒸发率测量时间30 min

图3

微波辅助螺旋降膜蒸发器的网格划分(a)与质量评价(b)"

图4

微波加热装置"

图5

不同流量下降膜管出口温度与加热时间关系"

图6

液膜厚度对α和COV的影响"

图7

螺距对α和COV的影响"

图8

螺距对流体上电场分布的影响"

图9

蒸发器外径对α和COV的影响"

图10

液膜流量对α和COV的影响"

图11

加热时间对α和COV的影响"

图12

螺旋降膜蒸发器场分布"

图13

不同高度水平截面上COV的变化"

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