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QTRAN, what is it?

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Old   October 27, 2003, 03:40
Default QTRAN, what is it?
  #1
Giovanni
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Hello guy,

I'm doing a transient analysis and I'm monitoring heat balance in the .info file.

QTRAN is too high and I don't know why, because I do not know what it is. User guide is not clear. Could you help me?

Thank you very much. Giovanni
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Old   October 27, 2003, 09:48
Default Re: QTRAN, what is it?
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Richard
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QTRAN is the rate of change of enthalpy in the solution domain during the time-step, i.e the rate of change of the volume integral of (density)*(specific enthalpy). Hence the units are (kg/m^3)*(J/kg)*(m^3)/s -> W.

But how can you say it is too high if you don't know what it is?
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Old   October 27, 2003, 11:53
Default Re: QTRAN, what is it?
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Giovanni
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Thank you Richard,

the analysis is of the warm-up of a passenger compartment.

In the heat balance: ENIN = 6.7016E+03 ENOUT = 6.7011E+03 QTRAN = 2.2430E+06

TOTAL HEAT BALANCE = 2.2430E+06 WATTS

It seem to me that the analysis is going uncorrectly!

What do you think? Giovanni
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Old   October 27, 2003, 12:32
Default Re: QTRAN, what is it?
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Richard
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I couldn't say whether such a high QTRAN value is wrong - it depends on the boundary conditions. ENIN and ENOUT are for open boundaries only; you will have HTIN and HTOUT for closed boundaries (walls). You may also have other heat sources (perhaps radiation in a passenger compartment). There's a list of the various terms on p17-5 of the v3.15 User Guide.

The important term is HDIFF. This tells you what the enthalpy imbalance is for this material; in effect this is the error in the enthalpy equation, due usually to incomplete convergence and discretization error. It should be small compared to all the significant terms of the enthalpy equation. If HDIFF is large it will mean QTRAN is wrong too.
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Old   October 28, 2003, 03:48
Default Re: QTRAN, what is it?
  #5
Giovanni
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Thanks Richard,

I'm according to you, but the problem is that I have neglected radiation and so I don't have any significant and evident heat sources, there is not conjugate heat transfer.

I will check the model again!

Giovanni

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