Investigation of nanoparticles diameter on free convection of Aluminum Oxide-Water nanofluid by single phase and two phase models

محورهای موضوعی : فصلنامه شبیه سازی و تحلیل تکنولوژی های نوین در مهندسی مکانیک

میثم اسفندیاری ¹ (دانشجو)
بابک مهماندوست ² ()
آرش کریمی پور ³ (هیأت علمی)

تاریخ دریافت : 1394/09/30 تاریخ پذیرش : 1394/11/05 تاریخ انتشار : 1395/02/01

کلید واژه: Nanofluid, Free Convection, Thermophoresis, Brownian Motion, numerical study,

چکیده مقاله :

In this research, effect of nanoparticles dimeter on free convection of aluminum oxide-water was investigated in a cavity by single phase and two phase models. The range of Rayleigh number is considered 105-107 in volume fractions of 0.01 to 0.03 for nanoparticles with various diameters (25, 33, 50 and 100 nm). Given that the two phase nature of nanofluids, necessity of modeling by this method is increasing. Single phase approach (in contrary of two phase) for nanofluids is based on that the behaviors of each two solid phase (nanoparticles) and liquid phase (base fluid) are completely similar. In this study, Eulerian-Eulerian approach and mixture model was used given that Brownian motion and thermophoresis effects. Brownian motion and thermophoresis creates under influences of volume fraction gradient and temperature gradient, respectively that cause to creating slip between nanoparticles and base fluid; thus, kind of non-uniformity creates on behavior between nanoparticles and base fluid. This non-uniformity leads to significant effects on results of two phase modeling that creates better agreement to single phase modeling with experimental results. Results indicate that heat transfer decreases with increasing diameter and volume fraction of nanoparticles. Also, effect of nanoparticle diameter on flow and heat transfer is tangible.

چکیده انگلیسی:

در این پژوهش، اثر قطرنانوذرات در جابجایی آزاد نانوسیال آب- اکسید آلومینیوم در یک محفظه با مدل دو فازی و تک‌فازی بررسی شده است. محدوده عدد رایلی 105 تا 107 در کسر حجمی‌های 01/0 تا 03/0 برای نانوذرات با قطر-های گوناگون (25، 33، 50 و 100) نانومتر در نظر گرفته شده است. با توجه به طبیعت دو‌فازی بودن نانوسیال‌ها، نیاز به مدلسازی با استفاده از این در حال افزایش است. فرض تک‌فازی (بر خلاف دو فازی) برای نانوسیال‌ها بر این اساس است که رفتار‌های هر دو فازجامد (نانوذرات) و فاز مایع (سیال پایه) کاملاً مشابه هستند. در این مطالعه، از دیدگاه اویلری- اویلری و مدل مخلوط با توجه به اثرات حرکت براونی و ترموفرسیس استفاده شده است. حرکت براونی و ترموفرسیس به ترتیب تحت اثرات گرادیان کسر حجمی و گرادیان دما بوجود می‌آیند که سبب بوجود آمدن لغزش میان نانوذرات و سیال پایه می‌شوند؛ بنابراین، نوعی ناهمگنی در رفتار میان نانوذرات و سیال پایه بوجود می‌آید. این ناهمگنی منجر به اثرات قابل توجهی در نتایج مدل‌سازی دو‌فازی می‌شود که تطابق بهتری نسبت به مدل‌سازی تک‌فازی با نتایج تجربی ایجاد می‌کند. نتایج نشان می‌دهند که با افزایش قطر و مقدار کسر حجمی نانوذرات انتقال حرات کاهش می‌یابد. همچنین، اثر قطر نانوذرات بر جریان و انتقال حرارت محسوس است.

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