بررسی انتقال حرارت سیالات غیرنیوتونی شبه‌پلاستیک در مبدل‌های حرارتی متخلخل

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشکده مهندسی، دانشگاه شهید چمران اهواز، اهواز، ایران

2 گروه مهندسی مکانیک، واحد دزفول، دانشگاه آزاد اسلامی، دزفول، ایران

چکیده

در این مقاله انتقال حرارت جابجایی طبیعی رایلی-بنارد سیالات غیرنیوتونی شبه‌پلاستیک در مبدل حرارتی لوله‌ای که دیواره‌ی سمت چپ آن از لایه‌ی متخلخل مشخص با ضخامت مشخص پوشیده شده است برای حالت ناپایدار و آرام به صورت عددی بررسی شده است. دیواره‌ی پایینی در دمای ثابت Th و دیواره‌ی بالایی در دمایTc که (Th>Tc) قرار دارد. دیواره‌ی سمت چپ و راست عایق هستند. معادلات حاکم بر مسئله پس از بی‌بعد شدن، به روش المان محدود به صورت همزمان حل شده است و سپس صحت نتایج در مقایسه با پژوهش‌های پیشین ارزیابی شده است. نتایج نشان می‌دهند که در رایلی‌های بزرگ ‌( 105Ra=) به دلیل غالب بودن انتقال حرارت جابه‌جایی طبیعی نسبت به انتقال حرارت هدایت، ناسلت متوسط با سرعت قابل توجهی افزایش می‌یابد. همچنین در اعداد دارسی کوچک (4-10=Da) میزان نفوذپذیری جریان بسیار کم است و ماهیت جریان به گونه‌ای تغییر می‌کند که باعث کاهش عملکرد حرارتی جریان جابجایی طبیعی می‌شود. نتایج نشان می‌دهد که با کاهش شاخص پاورلا دمای بی‌بعد کاهش یافته و کمترین دمای بی‌بعد برای کمترین شاخص پاورلا به دست می‌آید. از سوی دیگر، با افزایش شاخص پاورلا در یک رایلی ثابت و گذشت زمان، افزایش انتقال حرارت طبیعی اتفاق می‌افتد. همچنین عدد رایلی برای شروع جابه‌جایی طبیعی با افزایش شاخص پاورلا کاهش می‌یابد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Investigation of Heat Transfer of Non-Newtonian Pseudo-Plastic Fluids in Porous Heat Exchangers

نویسندگان [English]

  • Amin Reza Noghreabadi 1
  • kasra ayoubi ayoubloo 1
  • Reza Bahoosh Kazerooni 1
  • Mohammad Ghalambaz 2
1 Mechanical Engineering Department, Faculty of Engineering, Shahid Chamran of Ahvaz University, Ahvaz, IRAN
2 Assistant professor, Department of Mechanical Engineering, Dezful Branch, Islamic Azad University, Dezful, Iran
چکیده [English]

In this paper, the natural heat transfer of Rayleigh-Benard's non-Newtonian Pseudo-Plastics fluid in a tube heat exchanger with its left wall lined with a porous layer of a thickness l is considered numerically for an unstable state of laminar. The lower wall of the heat exchanger is at constant temperature Thand the upper wall at Tc temperature (Th>Tc). The walls are left and right insulated. The dimensionless governing equations are solved by the finite element method and the accuracy of the results is compared with previous studies. The results show that, in a large Rayleigh number, the average Nusselt number increases due to the fact that the natural heat transfer is more than conduction heat transfer. Also, in small Darcy numbers, the flow permeability is very low which causes reduce natural heat transfer convection. The results show that by decreasing the Power-law index, the non-dimensional temperature is reduced and the lowest non-dimensional temperature is obtained for the lowest Power-law index. On the other hand, with the increase of the Power-law index in a constant Rayleigh number and the passage of time, the increase of natural heat transfer occurs in the tube. Also, the Rayleigh number decreases with the increase of the Power-law index to start the natural convection in the heat exchanger.

کلیدواژه‌ها [English]

  • Rayleigh-Benard convection
  • Non-Newtonian fluid
  • pseudo-plastic
  • heat exchanger
  • Porous Layer
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