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September 15, 2013, 15:36 |
Post processing: Reporting of fluxes
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#1 |
Member
Vjoess
Join Date: Oct 2012
Posts: 54
Rep Power: 13 |
Hi
I carried out 2D analysis in which water transfers its heat energy to convert phase of material from solid to liquid. Water flows coaxialy through a container having phase change material. When i do reporting of fluxes/total heat transfer rate and select inlet and exit of water, there is some finite value which comes in net heat transfer. Incoming is not equal to outgoing which violates energy conservation. can anybody tell whats wrong? |
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September 15, 2013, 21:32 |
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#2 |
Senior Member
François Grégoire
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September 16, 2013, 02:32 |
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#3 |
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Vjoess
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September 16, 2013, 17:57 |
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#4 |
Senior Member
François Grégoire
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Location: Canada
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I guess there is a wall and its shadow counterpart on the boundary of the phase change material? You can see that the heat flux is the same on each side but with opposite sign, just unclick one of the fluxes and your energy balance should be right, unless you have bad energy convergence.
Last edited by macfly; September 16, 2013 at 20:33. |
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September 17, 2013, 07:52 |
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#5 | |
Member
Vjoess
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Quote:
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September 17, 2013, 09:21 |
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#6 |
Senior Member
François Grégoire
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Location: Canada
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select
- inlet - outlet - either all positive or all negative remaining boundaries it should balance |
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September 17, 2013, 14:54 |
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#7 |
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Vjoess
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September 17, 2013, 23:06 |
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#8 |
Senior Member
François Grégoire
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Look at the picture, it makes no sense if you select both -75 and 75 W fluxes in the energy balance. 75 W remains in the volume and energy balance across boundaries is ok: 100 - 75 - 25 = 0
I don't know what else to say. |
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September 18, 2013, 03:34 |
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#9 | |
Member
Vjoess
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Quote:
https://www.dropbox.com/sh/0oxd79vwf6nsly0/CtkIa4vU6R |
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September 18, 2013, 08:53 |
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#10 |
Senior Member
François Grégoire
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The net result of 401.2946 W looks like the 401.2 W across interface_1. Is it possible that interface_2 and part-fins are within the PCM? interface_1 is the only boundary between water and PCM? If yes, it looks ok.
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September 18, 2013, 10:22 |
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#11 | |
Member
Vjoess
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Quote:
Interface_1 is not the only boundary between water and PCM, there is another interface 2 the outer region which consists of outer wall of copper and copper fins, and then comes the PCM Last edited by dinesh; September 18, 2013 at 10:28. Reason: more explanation |
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September 18, 2013, 10:51 |
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#12 |
Senior Member
François Grégoire
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then the energy balance is just fine
draw a control volume around water only, and look what goes in and out : 377094.3 W - 376693.0 W - 401.2 = 0.1 W |
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September 18, 2013, 13:57 |
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#13 |
Member
Vjoess
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The why fluent window(image 3) shows a net heat transfer value=401. As per screenshot of fluent help (image 1)it says net value should be small/or zero
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September 18, 2013, 14:12 |
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#14 |
Senior Member
François Grégoire
Join Date: Jan 2010
Location: Canada
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There is no shadow wall in the Fluent user guide, it's not the same situation.
You have to put some thinking when doing energy balance, you cannot just select everything and abracadabra. Your case is really just like the picture I draw in post #8. here is the control volume I talked about in post #12 |
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