﻿ 水冷式射频组织焊接电极的多物理场仿真与实验研究
 上海理工大学学报  2023, Vol. 45 Issue (6): 653-660 PDF

Multiphysics simulation and experiment of water-cooled radiofrequency tissue welding electrodes
CHEN Tong, TU Liangyong, CHEN Liuxiao, TU Mingyu, MAO Lin, SONG Chengli
School of Health Science and Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
Abstract: To reduce thermal damage caused by high temperature during radiofrequency tissue welding, a novel water-cooled radiofrequency tissue welding electrode was designed. COMSOL Multiphysics was used to simulate in vitro welding process of porcine small bowel. Welding temperature and effect on biological tissue were analyzed through welding and bursting pressure experiments. Results showed simulation with temperature threshold method could solve reversible water evaporation problem in the existing model. Maximum and average welding temperatures of water-cooled electrodes were 139.8 ℃ and 112.5 ℃, respectively, which were significantly controlled compared to typical metal electrodes under the same conditions. Tissue welded by water-cooled electrodes reached bursting pressure of 63.6±13.7 mmHg and welding requirement was satisfied. Temperature predicted by simulation model fit well with experimental results, and water-cooled electrodes demonstrated effectiveness in welding tissue and controlling welding temperature.
Key words: radiofrequency current     tissue welding     water-cooled electrode     temperature     multiphysics simulation

1 材料与方法 1.1 射频组织焊接基本原理

 $\nabla \cdot \left( {\sigma \nabla V} \right) = 0$ (1)

 $J = \sigma { E}$ (2)

 $\rho c\frac{{\partial T}}{{\partial t}} = k{\nabla ^2}T - \rho c{\boldsymbol{u}} \cdot \nabla T + {Q_{\rm{b}}} + {Q_{\rm{m}}} + {Q_{\rm{j}}}$ (3)

 $\left\{ \begin{gathered} \alpha (t) = {\alpha _0} + \frac{1}{{{t_{\rm_{d,h}}}}}\int_0^t {(T > {T_{\rm_{d,h}}}){\rm d}t} \\ \alpha (t) = 1,(T > {T_{\rm_{n,h}}}) \\ \end{gathered} \right.$ (4)

1.2 焊接电极结构

 图 1 电极结构 Fig. 1 Electrode structures

1.3 有限元建模与仿真

1.3.1 有限元模型

 图 2 有限元模型及边界条件 Fig. 2 Finite element model and boundary conditions

 $\sigma \left( T \right) = {\sigma _{{\rm{ref}}}}\left[ {1 + 0.02 \times \left( {T - {T_{{\rm{ref}}}}} \right)} \right]$ (5)
 $k\left( T \right) = {k_{{\rm{ref}}}}{\text{ + 0}}{\text{.001 17}} \times \left( {T - {T_{{\rm{ref}}}}} \right)$ (6)

Chen等[13]和Yang等[21]认为生物组织的比热容有两部分来源：30%的干组织和70%的水分。仿真时总比热容由式（7）表示，其中ct为干组织比热容，cw为水比热容，cl为水的汽化潜热；构成比例与生物组织含水量W(T)密切相关；W(T)使用Yang等[22]的经验公式（8）计算。标准状态下cw为4200 J/(kg·K)，cl为2260 kJ/kg，生物组织含水量、总比热容与温度的函数关系分别如图3(a)图3(b)所示，图3(b)表明生物组织水分蒸发所等效的汽化潜热吸收量对总比热容c影响极大。

 图 3 生物组织温度特性 Fig. 3 Temperature characteristics of biological tissue
 $c\left( T \right) = [1 - W(T)]{c_{\rm_t}} + W(T){c_{\rm_w}} + \left|\frac{{{\rm d}W(T)}}{{{\rm d}T}}\right|{c_{\rm_l}}$ (7)
 $W\left( T \right) = \frac{{1.166}}{{1 + {{\rm e}^{0.417\times\left[ {\left( {T - 273.15} \right) - 103} \right]}}}}\times 70\text{%} + 0.1\text{%}$ (8)

1.3.2 网格及求解器设置

 图 4 有限元网格 Fig. 4 Finite element meshes

1.4 焊接实验与爆破压实验

 图 5 实验平台 Fig. 5 Experimental platforms
2 结果与讨论 2.1 流动速度

 图 6 流速仿真结果 Fig. 6 Simulation results of flow velocity
2.2 电流密度与温度

 图 7 电流密度仿真结果 Fig. 7 Simulation results of electric current density

 图 8 温度仿真结果 Fig. 8 Simulation results fo temperature

 图 9 焊接结果及温度曲线 Fig. 9 Welding results and temperature curves
2.3 爆破压

3 结　论

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