油浸式变压器内部绕组的匝间纸绝缘受温度的影响会析出气泡,进而引发局部放电导致绝缘劣化。该文通过研究油纸界面的微观结构和气泡产生的物理过程,建立气泡演化的数值模型,结合气泡生长过程中的受力分析,得到了气泡在不同条件下的生长...油浸式变压器内部绕组的匝间纸绝缘受温度的影响会析出气泡,进而引发局部放电导致绝缘劣化。该文通过研究油纸界面的微观结构和气泡产生的物理过程,建立气泡演化的数值模型,结合气泡生长过程中的受力分析,得到了气泡在不同条件下的生长规律。首先,基于Rayleigh-Plesset方程建立油纸界面处由气泡内压强主导的气泡生长过程。其次,根据理想气体体积定律与Hertz-Knudsen界面蒸发冷凝方程量化界面处水蒸气进入气泡的质量通量,并在此基础上建立气泡内压的控制方程。最后,求解获得了升温时油纸系统中气泡的生长曲线,并根据气泡生长时的受力分析得到了气泡脱离半径进而计算出气泡初始逸出温度(initial temperature of bubble escape,ITBE)。计算的气泡脱离半径与实验结果具有较好的一致性,此外预测的ITBE与实验结果的最小平均相对误差为1.11%。模型结果表明,纸中水分质量分数越高,气泡生长速度越快。而绝缘纸微观结构的变化主要通过影响气泡初始半径和气泡在界面处所受表面张力的大小,从而影响气泡的形成过程。展开更多
The formation of bubbles generated in a bubble column with 190 mm I.D.from large orifices at high gas velocity was studied for air-deionized water system.The experiments were made with orifice diameters varying from 4...The formation of bubbles generated in a bubble column with 190 mm I.D.from large orifices at high gas velocity was studied for air-deionized water system.The experiments were made with orifice diameters varying from 4 mm to 21 mm and hole gas velocity in the range of 0.8—154.8 m·s-1.The bubble shape and bubble size were recorded by CCD camera,critical hole gas velocity for bubble deformation was derived from the transition of aspect ratio of bubbles.The results showed that bubbles were spherical when hole gas velocity was lower than 20 m·s-1.When hole gas velocity was higher than 50 m·s-1,the shape of bubbles changed to elliptical.A correlation equation was established for bubble size as a function of hole gas velocity and orifice diameter,and the equation predicted the bubble size well for orifice diameter larger than 3 mm and hole gas velocity from 10 m·s-1 to 80 m·s-1 in air-deionized water system.展开更多
The bubble forming and leaving mechanism for con tinuous bubbling in glass melt was assumed.And a mathematical description for continuous bubbling system was also established.The instaneous flow rate of air during bub...The bubble forming and leaving mechanism for con tinuous bubbling in glass melt was assumed.And a mathematical description for continuous bubbling system was also established.The instaneous flow rate of air during bubble formig is a main factor to the size of bubble.The bubble frequencedcpend on the physical properties of melt ,air flow rate and bubbling system.展开更多
文摘油浸式变压器内部绕组的匝间纸绝缘受温度的影响会析出气泡,进而引发局部放电导致绝缘劣化。该文通过研究油纸界面的微观结构和气泡产生的物理过程,建立气泡演化的数值模型,结合气泡生长过程中的受力分析,得到了气泡在不同条件下的生长规律。首先,基于Rayleigh-Plesset方程建立油纸界面处由气泡内压强主导的气泡生长过程。其次,根据理想气体体积定律与Hertz-Knudsen界面蒸发冷凝方程量化界面处水蒸气进入气泡的质量通量,并在此基础上建立气泡内压的控制方程。最后,求解获得了升温时油纸系统中气泡的生长曲线,并根据气泡生长时的受力分析得到了气泡脱离半径进而计算出气泡初始逸出温度(initial temperature of bubble escape,ITBE)。计算的气泡脱离半径与实验结果具有较好的一致性,此外预测的ITBE与实验结果的最小平均相对误差为1.11%。模型结果表明,纸中水分质量分数越高,气泡生长速度越快。而绝缘纸微观结构的变化主要通过影响气泡初始半径和气泡在界面处所受表面张力的大小,从而影响气泡的形成过程。
文摘The formation of bubbles generated in a bubble column with 190 mm I.D.from large orifices at high gas velocity was studied for air-deionized water system.The experiments were made with orifice diameters varying from 4 mm to 21 mm and hole gas velocity in the range of 0.8—154.8 m·s-1.The bubble shape and bubble size were recorded by CCD camera,critical hole gas velocity for bubble deformation was derived from the transition of aspect ratio of bubbles.The results showed that bubbles were spherical when hole gas velocity was lower than 20 m·s-1.When hole gas velocity was higher than 50 m·s-1,the shape of bubbles changed to elliptical.A correlation equation was established for bubble size as a function of hole gas velocity and orifice diameter,and the equation predicted the bubble size well for orifice diameter larger than 3 mm and hole gas velocity from 10 m·s-1 to 80 m·s-1 in air-deionized water system.
文摘The bubble forming and leaving mechanism for con tinuous bubbling in glass melt was assumed.And a mathematical description for continuous bubbling system was also established.The instaneous flow rate of air during bubble formig is a main factor to the size of bubble.The bubble frequencedcpend on the physical properties of melt ,air flow rate and bubbling system.
