基于静态与动态电导率的组织不可逆电穿孔电-热耦合场及消融效果分析

不可逆电穿孔肿瘤消融治疗前对组织内部电-热耦合场的分析计算是实现肿瘤组织有效消融的关键所在,但目前对于多针系统下考虑组织电导率动态变化的真实组织内部电–热耦合场分布还缺乏系统研究。为此,首先通过二维有限元模型,量化分析了静态电导率与动态电导率模型下组织电场分布与电导率分布的差异。随后,根据患者肿瘤医学影像,重建了包含肿瘤的肾脏组织三维模型,研究了多脉冲下电–热耦合场分布及消融效果。研究结果表明,相同脉冲参数下,动态电导率模型得到的消融尺寸在垂直于电场方向上始终大于静态电导率模型;平行于电场方向上,随着场强的增大,动态电导率模型的消融尺寸出现先小于后大于静态电导率模型的现象,且动态电导率模型计算得到的消融面积(或体积)均更大;动态电导率模型下的组织温度分布同样显著区别于静态电导率模型。因此,采用动态电导率模型进行术前的治疗参数确定有利于达到最佳的肿瘤消融效果,并最大限度地降低对正常组织的损伤。

特高压环氧浸纸−SF_(6)气体复合绝缘穿墙套管界面电荷积累过程和直流电场分布特性仿真

特高压直流穿墙套管作为换流站中连接阀厅和直流场的唯一通道,是承载系统全电压、全电流的核心设备,掌握穿墙套管在直流电压下的电荷积累特性和暂态电场变化规律对保障其运行可靠性具有重要意义。为此以±1100 kV直流环氧浸纸–SF_(6)气体复合绝缘穿墙套管为研究对象,建立基于介质内部和分界面上电荷驰豫过程的复合绝缘系统电场模型,提出一种气体饱和电流密度的简化计算方法,以解决求解复杂仿真模型时对流扩散方程收敛较为困难的问题,利用该模型研究环氧浸纸–SF_(6)气体复合绝缘穿墙套管直流电场过渡过程和界面电荷积累现象,并结合三维电磁–热–流场数值计算,获得环氧浸纸–SF_(6)气体复合绝缘穿墙套管的三维温度场分布,分析环氧浸纸–SF_(6)气体复合绝缘穿墙套管在实际运行工况下的电–热耦合场分布规律。相关结论可为环氧浸纸–SF_(6)气体复合绝缘穿墙套管的结构优化设计、寿命评估和故障分析提供理论依据。

Experiment and numerical simulation on flow and heat transfer in all-glass evacuated tube solar collectors

The experimental study of natural convection in allglass evacuated tube solar collectors is performed through the experimental platform of the solar-assisted fuel cell system.The experimental facility includes solar collectors with different length and diameter tubes, different coating materials, and with / without guide plates, respectively. Threedimensional mathematical models on natural and forced convections in the solar collectors are established and the experimental data is validated by field synergy and entransy principles. The results of natural convection show that the water temperature increases and thermal efficiency decreases gradually with the evacuated tube length. The thermal efficiency increases when absorption rates increase from 0. 95 to 1. 0 and emission rates decrease from 0. 16 to 0. 06. The thermal efficiency of solar collectors is increased after being equipped with the guide plate, which is attributed to the disappearance of the mixed flowand the enhancement of the heat transfer at the bottom of the evacuated tube. The results of forced convertion indicate that the Reynolds, Nusselt and entransy increments of the horizontal double collectors are higher than those of the vertical single collector while the entransy dissipation is lower than that of the vertical single collector. It is concluded that the solar collectors with guide plates are suitable for natural convection while the double horizontal collectors are suitable for forced convection in the thermal field of solar-assisted fuel cell systems with lowand medium temperatures.