شبیه‌سازی عددی تغییرشکل و تجزیه قطره در میدان الکتریکی

نوع مقاله : مقاله پژوهشی

نویسندگان

1 پژوهشگاه هوافضا، تهران، ایران

2 پژوهشکده سامان ههای حمل و نقل فضایی، پژوهشگاه فضایی ایران، تهران، ایران

3 مجتمع برق و الکترونیک، دانشگاه صنعتی مالک اشتر، تهران، ایران

چکیده

قطره‌ی مایع معلق در یک سیال دیگر در بسیاری از فرآیندهای طبیعی رخ می‌دهد. به کارگیری میدان الکتریکی چشم اندازی نوید بخشی را برای کنترل حرکت، تغییر شکل، تجزیه و هدایت قطره فراهم می‌کند. تحقیق حاضر به شبیه سازیِ پاسخ دینامیکی قطره‌ای معلق در سیالی دیگر، واقع در فضای میانِ دو الکترودِ رسانای دارای اختلاف پتانسیل الکتریکی می‌پردازد. در این راستا تاثیر پتانسیل الکتریکی، هدایت الکتریکی و گذردهی نسبی مورد بررسی قرار گرفته است. مطابق نتایج، افزایش پتانسیل الکتریکی و نسبت هدایت الکتریکی روندی افزایشی را برای تغییر شکل قطره به دنبال دارند، در حالی که افزایش گذردهی نسبی روندی کاهشی-افزایشی را برای تغییر شکل قطره به نمایش می‌گذارد. بررسی الگوی جریان سیال در داخل قطره نشان می‌دهد که قرارگیری قطره در میدان الکتریکیِ خارجی ضمن ایجاد قطبیت الکتریکی در قطره موجب القای میدانی الکتریکی در داخل آن می‌شود که به پیدایش گردابه هایی در درون قطره منتهی می‌شود. بزرگی یا کوچکی هدایت الکتریکی و گذردهی الکتریکی نسبت به یکدیگر کاملا بر ناحیه‌ی تجمع بارهای الکتریکی در سطح قطره تاثیر می‌گذارند که این تعیین کننده‌ی جهت چرخش گردابه‌های درونی قطره می‌باشد. افزایش پتانسیل الکتریکی و به تبع آن تقویت شدت میدان الکتریکی با افزایش تجمع بار الکتریکی در سطح قطره زمینه‌ی تغییر شکل قطره و سپس تجزیه و شکست آن را فراهم می‌سازد. در این حالت قطبیدگی الکتریکی ضمن ایجاد کشیدگی در قطره باعث خروج جت و ساطع شدن ریز قطراتی از آن می‌شود که استمرار این فرآیند با تقلیل جرم در هسته ی قطره اصلی به استهلاک نهایی قطره منجر می‌شود.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Numerical Simulation of Drop Deformation and Breakup in an Electric Field

نویسندگان [English]

  • H. Dastourani 1
  • M.R. Jahannama 2
  • A. Eslami Majd 3
1 Aerospace Research Institute, Tehran, Iran
2 Space Transportation Research Institute, Iranian Space Research Center, Tehran, Iran
3 Electrical and Electronics Department, Malek Ashtar University of Technology, Tehran, Iran
چکیده [English]

Liquid drop suspension in another fluid occurs in many natural processes. Applying electric field has shown a promising outlook for the control of motion, deformation, breakup and guidance of the drops. In this study, the dynamic response of a liquid drop suspended in another fluid across two conducting electrodes held at different electrical potentials has been simulated. In this regard, the effects of electric potential, electrical conductivity and relative permittivity have been studied. According to results, an increase in electric potential and conductivity leads to increasing trend in drop deformation whereas this trend converts into an ascending-descending pattern due to increase in electrical permittivity. An insight into the flow patterns inside and outside the drop shows that the positioning of a liquid drop in an external electric field in addition to drop polarization results in an electric field induced within the drop which causes the creation of vortices inside the drop. Magnitude of electrical conductivity and permittivity factors compared to each other apparently affect the accumulation area of electrical charges on the drop surface which in turn determines the circulating direction of vortices within the drop. Increasing electric field intensity due to an increase in electrical potential or change in magnitude of other physical properties would fortify the electric charge on the drop surface escalating drop deformation towards drop breakup. In this condition, the electrical polarization in addition to drop prolation causes jet exit from which a continuous line of droplets is emerged until the total dissipation of the drop.

کلیدواژه‌ها [English]

  • Drop deformation
  • Electrical conductivity
  • Electrohydrodynamics
  • Numerical simulation
  • Relative permittivity

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نشریه مهندسی مکانیک امیرکبیر
دوره 50، شماره 4
مهر و آبان 1397
صفحه 767-784

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