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external cross flow problem

Question asked by Emre Kavlak on Apr 12, 2014
Latest reply on Apr 15, 2014 by Kyu-Hyung Kim

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I'd like to simulate a tube which has a water mass flow rate 0.21 kg/s and inlet temp is 340K. also there is a cross flow air over the tube externaly whose temp initialy is 288 K and velocity 20m/s. Thus I wanna see the fluid temp distribution thorugh the tube but i cant simulute that. I choose external flow analys and insert fluid subdomain as water in tube. also specify the tube material as aliminum. after i calculated i get the uniform 340K temp inside the tube. Pls can u help me about this ?

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Mark Keown Apr 13, 2014 4:44 PM
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Emre, I suapect that the drop in water temperature is so small you are just not seeing it. Try setting the results scale to a very narrow band (like 340K to 339.9K) and see if that will show the temperature gradient in the water.
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- Emre Kavlak @ Mark Keown on Apr 13, 2014 8:15 PM
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  hello mr Keown, I think problem is not about the scale. Fluid is at 340 K all over tube and there is no heat transfer between fluid and air. I attached the file above. Pls could you check it.
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  - Jared Conway @ Emre Kavlak on Apr 13, 2014 11:31 PM
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    What is your expected result?
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    - Emre Kavlak @ Jared Conway on Apr 14, 2014 9:29 AM
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      Expected result should be That decreasing temp distribution along the tube.i mean if inlet temp Of Fluid is 67 the outer temp should be less than it
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      - Jared Conway @ Emre Kavlak on Apr 15, 2014 2:11 AM
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        how much change are you expecting?
        
        also can you check your inputs, i think the flow rate was 0.3, not the 0.21 you specified. please also make sure to check the units.
        
        i would also recommend that you put goals at the inlet and outlet for velocity, pressure, mass flow rate...etc
        
        one in consistency with your description is that your external flow is actually going past your lids. so it is cooling on the outside of your lids in additino to the tube. is that really happening? you may want to setup a second box to control the flow. (similar to the tutorial on cross flow heat exchanger)
        
        and i don't believe you need the fluid subdomain. try it without it and see what happens. but you may need local initial conditions instead.
        
        nothing else was really glaring, so i would be more interested in your expectations.
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  - Mark Keown @ Emre Kavlak on Apr 13, 2014 11:59 PM
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    Is solve conduction in solids ticked in the setup? Just asking
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    - Emre Kavlak @ Mark Keown on Apr 14, 2014 9:32 AM
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      Yes i checked it Busolvedlem is NOT solve
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Kyu-Hyung Kim Apr 15, 2014 3:07 AM
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In this case, Convection is consider on tube outer suface.

In my calculation , 476.603W is going to surround by convection. So outlet water temperature is lower about 0.54degC than inlet Temperature. and Q_water=0.21[kg/s]*4188[J/kg*k]*0.54[k]=476.86W is approximately equal to convection heat trasnfer rate.

if you see unifom temperature of water, consider adiabatic boundary condition on tube outer surface.[wall-ideal wall]
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