IJE TRANSACTIONS C: Aspects Vol. 30, No. 12 (December 2017) 1919-1924    Article in Press

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A. Shahriari, N. Jahantigh and F. Rakani
( Received: May 26, 2017 – Accepted in Revised Form: September 08, 2017 )

Abstract    The influence of temperature, mean nanoparticle size and the nanoparticle concentration on the dynamic viscosities of nanofluids are investigated in an analytical method followed by introduction of modified equations for calculating the nanofluidsí viscosities. A new correlation is developed for effective viscosity based on the previous model where the Brownian movement of the nanoparticles is considered as the key mechanism. In previous studies, the proposed models were not appropriate for nanoparticles larger than 36 nm. They were also focused on low concentrations of nanoparticles up to 5%. The possibility of homogeneous dispersion of the nanoparticles and the Stokes law are observed here. This new model is explained in terms of temperature, mean nanoparticle diameter, nanoparticle volume concentration and both the nanoparticle and base fluid thermophysical characteristics for the effective viscosity of nanofluids. A combined correction factor is introduced to take into account the simplification for a free stream boundary condition outside the boundary layer. A good agreement is observed between the effective viscosity obtained in this new model and those of recorded experiments conducted for different nanofluids. The results show that the present model is valid for large volume concentration (0% < φ <11%), mean nanoparticle size (13 nm < dp < 95 nm), temperature variations (290 K Normal 0 false false false EN-US X-NONE FA


Keywords    Effective Viscosity: Mean Nanoparticle Diameter: Nanofluid: Thermo physical Properties: Volume Concentration


چکیده    در کار حاضر تأثیر متغیرهای درجه حرارت، اندازه متوسط نانوذره و غلظت نانوذره روی ویسکوزیته دینامیکی نانوسیال بررسی شده است که بر یک روش تحلیلی معادلات اصلاح‌شده ویسکوزیته نانوسالات مبتنی است. مدل جدید بر اساس مدل‌های قبلی که اثر حرکت براونی را به‌عنوان یک پارامتر کلیدی مدنظر قرار می‌دادند، توسعه یافته است. نتایج نشان داد که استفاده از مدل‌های قبلی برای نانوذرات بزرگ‌تر از 36 نانومتر مناسب نیست. هم‌چنین مطالعات قبلی تنها در حجم کسری کم نانوذرات تا 5%متمرکز شده است. در کار حاضر امکان پراکندگی همگن نانوذرات و قانون استوکس برای نانوذرات لحاظ شده است. در مدل جدید اثر دما، قطر متوسط نانوذرات، غلظت نانوذره و نیز ویژگی‌های ترموفیزیکی نانوذره و سیال پایه برای ویسکوزیته مؤثر نانوسیال در نظر گرفته شده است. یک ضریب تصحیح ترکیبی برای لحاظ کردن ساده‌سازی شرط مرزی جریان آزاد در خارج از لایه مرزی معرفی شده است. توافق خوب نتایج بین ویسکوزیته مؤثر به‌دست‌آمده از مدل جدید و نتایج آزمایشگاهی برای نانوسیالات مختلف مشاهده شده است. نتایج نشان می‌دهد که مدل حاضر برای محدوده وسیعی از کسر حجمی (0% < φ <11%)، اندازه متوسط نانوذرات (13 nm < dp < 95 nm)، تغییرات دمایی نانوسیال (290 K < T < 350 K) و انواع مختلفی از نانوذرات معتبر است.


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