بررسي آزمايشگاهي و مدلسازي انتقال حرارت نانو سيالات

Experimental study and heat transfer modeling of nanofluids

يك مدل تئوري با استفاده از ايده مقاومتها براي برآورد حدود بالا و پايين هدايت حرارتي سوسپانسيون هاي حاوي ذرات كروي (اعم از نانو سيالات يا سوسپانسيون ها حاوي ميكروذرات) پيشنهاد شده كه مقايسه نتايج مدل براي سوسپانسيون هاي حاوي ميكرو ذرات با نتايج مدل ماكسول كه براي اين نوع سوسپانسيون ها پيش بيني قابل قبولي دارد، درستي مدل را تائيد مي كند. مدل مورد نظر به گونه اي توسعه داده شده كه براي همه نانو سيالات (حاوي ذرات كروي يا غير كروي) نيز قابل كاربرد باشد. پروفايل سرعت و دماي نانو سيال، در جريان متلاطم توسعه يافته كامل، با سيال پايه مقايسه شده است. طبق نتايج به دست آمده، عامل تعيين كننده تغيير انتقال حرارت جابه جايي نانو سيالات در مقايسه با سيالات پايه، شكب پروفايل دما مي باشد. رد عين حال، شكل پروفايل سرعت نانو سيالات در شرايط متلاطم توسعه يافته مانند سيالات پايه است.

A resistance approach theoretical model was suggested to evaluate thermal conductivity of suspensions (including nanofluids and micro-suspensions) and its results compared to Mawell's theory - as an acceptable theory for thermal conductivity of micro-suspensions - proved its validity. The prevailing parameter in the proposed model is the distance between the particles that was equated to effective diameter in the case of micro-suspensions and was estimated through Brownian motion approach for nanofluids. The results of the model compared to our experimental data and other data published by different authors showed that in the most cases, the proposed model with effective diameter and Brownian mean free path as distance between particles will give lower and higher limits of nanofluids' thermal conductivity, respectively. The proposed resistance model was improved by inserting an adjustable parameter and its validity was proved by comparing the results with the experimental data. The velocity and temperature profiles of nanofluid were compared with those of the base fluid in fully developed turbulent flow conditions. It was shown that the change of convective heat transfer coefficient of nanofluid compared to that of the base fluid is related to its temperature profile. However, velocity profile of the nanofluid in fully developed turbulent flow is similar to that of the base fluid and pressure drop increment of the nanofluid may be solely related to change of its properties compared to that of the base fluid.