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cfd simulation of solar water heater using cfx 13.0

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Old   December 20, 2011, 18:15
Default cfd simulation of solar water heater using cfx 13.0
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avinash madhavan
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hi.
i want to simulate a thermosiphon solar water heater . i have attached the picture of a model.i have only considered a fluid domain.
since the model is being tested indoors i do not want to consider the radiation effect. so there is only natural convection and conduction.
the source of energy is a 1000 watt spot light. i have entered this as the source of heat flux in set up. is that right?
the only other available data is the mass flow rate at the inlet which is 0.01 kg/s. and the temperature of water at inlet is 20 degree celicis.
can anyone suggest how to proceed..
because i run the simulation and i wanted to get the temperature of water at the outlet. which i didn't get
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Old   December 20, 2011, 18:19
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Glenn Horrocks
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I have moved this post to a new thread - please do not hijack other threads, start a new thread.

Have you read the FAQ?
http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F
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Old   December 20, 2011, 18:28
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i am new to this site. i couldnt find how to post a new thread.
thanks
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Old   December 20, 2011, 18:32
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if any one can help me with this query i would be very thankful.
i have been struggling with this problem for a while.
thanks
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Old   December 20, 2011, 19:04
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I already have replied - have you read the FAQ? Your question seems to be "Why is my simulation inaccurate?" and this has been asked so much that we have done a FAQ on it. I will not assist you in further details until you have covered the basics in the FAQ.
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Old   December 21, 2011, 08:15
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hi ghorrocks.
i went through the FAQ's. i am new to the software . i presume my boundary conditions are right. but my mesh is not so fine. i have inserted inflation and edge sizing. is there any wat i can improve the mesh quality..
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Old   December 21, 2011, 10:33
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Your mesh isnt good enough, it needs to improved all over. Also your geometry is different from the original picture. The flow field will be different so you'll get different results.
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Old   December 21, 2011, 11:35
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avinash madhavan
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hi.
i am considering the fluid domain only..i have not taken into account the copper channel in which the fluid flow..
can yu give me any suggestions on how to improve the mesh as i am new to this software.. i tried inserting inflations on the boundaries..
any help will be appreciated
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avinash madhavan
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Old   December 21, 2011, 18:05
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Do the meshing tutorials for meshing skills.

You will need a MUCH finer mesh than this to get anything close to reality. Also you will need to move your inlets and outlets further away from the active region. And I reckon your assumption that you can model the fluid domain without the solid domain is probably wrong too.
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Old   December 21, 2011, 18:18
Default cfd simulation of solar water heater using cfx 13.0
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avinash madhavan
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as i told you i am new to this software, using my knowledge i have tried to improve the mesh using edge sizing and inserting inflation. will that be ok to get a proper mesh or should i go for some other options.
thanks
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Old   December 21, 2011, 18:39
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The FAQ I pointed you to explains what you need to do.

If you are unsure whether your mesh (or anything else for that matter) is good enough, then do a sensitivity study. Do two meshes which are significantly different (eg 1mm average edge length compared to 0.5mm average edge length, in 3D this will be a mesh about 8 times bigger) and compare the results. Keep refining the mesh until the results converge to a tolerance you are happy with.
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Old   December 23, 2011, 05:26
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The problem set up in CFD is not correct from whatever data u have supplied. If u are simulating natural convection flow then inlet mass flow should not inlfuence the flow of waterthrough the pipes. Watershould flow by itelf(buoyancy flow). In ur case i understant u have one inlet and one outlet...and such case inletmass flow pushes the waterto outlet. This becomes a forced circulation flow...even when u have small mass flow at inlet.

You will have to redesign ur experimental set up also .
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Old   January 4, 2012, 13:06
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avinash madhavan
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hi. i have tested the model both indoors and outdoors. i have got an outlet water temperature of 40 degrees when inlet water temperature was 20 degree.. i think my mesh is not so accurate. i have inserted body sizing face sizing and edge sizing. the total no of elements was 1260,550.. can any body help me on how i can improve my mesh as i have only a few boundary conditions to specify. i have used a buyoncy effect in this case.
thanks
happy new year to everyone
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Old   January 9, 2012, 12:20
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is it possible to obtain the value of overall heat loss coefficient in cfd post .
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Old   January 9, 2012, 18:11
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Yes. You can integrate expressions or variables over surfaces and you can evaluate the overall heat loss from that.
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