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Multiphase flow of Nanofluids - Low Nusselt number problem

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Old   October 30, 2015, 02:20
Smile Multiphase flow of Nanofluids - Low Nusselt number problem
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Hello Everyone,

Am Aarthy, I am new to FLUENT.

I am modelling 2-D flow and heat transfer of nanofluids around an unconfined square cylinder for my M.Tech project. Initially, I tried a single phase flow using effective property models for properties of nanofluids. Those simualtions are fine and gave comparable results with the literature.

Now, I am trying to use multi-phase flow model. I am trying with mixture model in FLUENT. I tried with particle volume fraction as 0 (i.e., pure basefluid), and I got good values of Nu and drag coefficients which matched with literature.

When I increased the particle volume fraction, the values of Nu and C_D decreased. But, it is well known that, when particle volume fraction is increased, C_D and Nu will increase.

So I am stuck with this. Kindly, pls help me very urgent....
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Old   November 5, 2015, 01:30
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Hi Aarthy,

Firstly have you ever tried to monitor the conductivity values ? The mixture model defines the conductivity (k) with simple averaging (i.e. kmix=kf(1-phi)+phi*kp). For instance lets assume you are using Al2O3 nano particles with k~35 W/mK so the conductivity of Al2O3/water nanofluid with 0.01 volume fraction will be ~0.9-1.06 depending on temperature which is very high. Hence the Nu number will be decreased rapidly.
You can implement different conductivity model into Fluent by using UDF or manually or you can use different two-phase models. The thing is it is hard to define the proper thermal properties with mixture model. Also even if you manage to do it it won’t be so different than the single phase approach because of the small drift velocities between phases.
Anyways, good luck.

Last edited by ios; November 9, 2015 at 04:18.
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Old   November 17, 2015, 05:01
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Thank you ios... Thank you for your elaborate reply.. Can you pls help me by saying the step by step procedure of Eulerian-Eulerian method for my problem.. I will be very grateful to you.... You can contact me at aarthychubby123@gmail.com
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Old   January 6, 2016, 11:40
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Hi ios,

I tried as per ur suggestion. But I observe a decrease in drag and mean Nusselt number with increase in particle volume fraction. This is contradicting with literature.

Thank You.
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Old   January 6, 2016, 11:59
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Firstly stop contradicting with yourself then you can go for literature.
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Old   January 6, 2016, 12:03
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Quote:
Originally Posted by ios View Post
Firstly stop contradicting with yourself then you can go for literature.

I have mentioned that I have some doubts in the results.
You can see in the image which you have attached.
Those doubts are I observe increase in CD and NUM at lower Reynolds numbers. At higher Reynolds numbers I observed an opposite behavior. That is why I have posted now.
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