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Old   March 14, 2017, 00:57
Default Flow Simulation
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Prince Hossain
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Hi guys!!
I want to run a simulation on a duct of non frost fridge. Would someone please suggest me how many iteration i will do for a static setup. i want to calculate the average flow and temperature distribution in the duct.
Thanks
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Old   March 14, 2017, 01:46
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Uwe Pilz
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I see two ways to come to an answer:
1) Let a simulation run and look after some simulated time whether the total thermical engergy still changes .
2) Calculate the Prandl number for your case. This gives you an idea how fast things change.
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Old   March 14, 2017, 06:06
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i didn't catch it properly. will you please elaborate
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Old   March 14, 2017, 12:42
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I recommend:

- calculate the Reynold number for the outer flow. For that you need some idea of the velocity U_{\infty}.
- calculate the Prandt number for the outer flow. You need the kinematic viscosity and the thermal diffusivity for that, which you may get from tables. For air is Pr~0.7 and for water at 20 deg Pr~7.
- calculate the Nußelt number

Nu \sim 0.037 Re ^{0.8} Pr ^{0.43}

With the help of the Nußelt number you may calculate the maximal thermal flow (at starting temperature difference). Using the the heat capacity you may calculate how long it lasts to exchange all the energy. The real time will be longer, depending on what remaining difference you accept. But you get at least an idea in which range this time will be.
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einer Logarithmentafel enthalten ist (Carl Friedrich Gauß)
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Old   March 15, 2017, 05:32
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thank you so much for your answer. i am on it
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