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[therm] A_heat + B_heat not equal to (A+B) heat !!!
 
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debabrata.podder
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Joined: 21 Feb 2013
Posts: 51
Location: NIT Meghalaya, India

PostPosted: Fri Oct 11, 2013 6:52 pm  Reply with quote

Dear experts, I am heating up a body (by heating up every elements in that volume) having volume V by HGEN. Now I am dividing the volume into V_A and V_B, where V=V_A + V_B and V_A = 30% of V, V_B = 70 % of V. Total amount of heat is Q. Now if I apply 0.3Q into volume V_A and 0.7Q into volume V_B, then I am getting (Q_A + Q_B) is not equal to Q !! The Q is much higher than the (Q_A+Q_B) !!! Why ? Is there anything wrong !!

Thanks in advance.

Regards-
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Debabrata Podder(PhD)
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edward.carman
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Joined: 21 Oct 2008
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Location: Johannesburg, South Africa

PostPosted: Sun Oct 13, 2013 11:33 pm  Reply with quote

As described in the theory reference in the manual, HGEN defines the heat generation rate per unit volume. Total heat is then Q*V.

If you split your volume, you still need to apply Q to each sub-volume, giving Q*V_A+Q*V_B = Q*0.3V + Q*0.7V = Q*V.

In your case, you've applied 0.3Q*V_A + 0.7*V_B = 0.58Q*V
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debabrata.podder
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PostPosted: Tue Oct 15, 2013 3:21 pm  Reply with quote

Thanks for your time Mr. Carman. But here Q, Q_A and Q_B are total heat contents not the heat per unit_volume !!! And this Q_A and Q_B is equal to Q*(V_A/V) and Q*(V_B/V) respectively.
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Martin Liddle
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PostPosted: Tue Oct 15, 2013 4:46 pm  Reply with quote

On 15/10/2013 23:21, debabrata.podder wrote:
Quote:
Same Q can not be applied both on V_A( which is 0.3V) and V_B( which is 0.7V) !!! So how to deal with this you think !!! So is there anything wrong with "the heat is distrib_uted to their respective volume proportions " !!!

Obviously there is something wrong but I think you can be confident that
the problem is in your code. Try a simple test problem and you will
find it works perfectly.

--
Martin Liddle, Tynemouth Computer Services,
Chesterfield, Derbyshire, UK.
www.tynecomp.co.uk

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keith.technologies
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Joined: 05 Feb 2009
Posts: 100

PostPosted: Tue Oct 15, 2013 5:51 pm  Reply with quote

Are you doing a steady state or transient analysis ?

Keith DiRienz
FEA Technologies

At 03:21 PM 10/15/2013, you wrote:

Quote:
It should match, QA = Q_A*V_A + Q_B*V_B; But it is coming as 0.58 QV.
Same Q can not be applied both on V_A( which is 0.3V) and V_B( which is 0.7V) !!! So how to deal with this you think !!! So is there anything wrong with "the heat is distrib_uted to their respective volume proportions " !!!


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debabrata.podder
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Joined: 21 Feb 2013
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PostPosted: Tue Oct 15, 2013 5:57 pm  Reply with quote

Thanks, Mr. Liddle & Mr. DiRienz for your time. It is transient_analysis and Q, Q_A, Q_B are the total heat amount, not heat per unit_volume.

Thanks-
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Debabrata Podder(PhD)
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himanshu.goyal
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Joined: 09 Sep 2013
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PostPosted: Tue Oct 15, 2013 6:03 pm  Reply with quote

It is 0.3*0.3+0.7*0.7=0.58


Q is heat gen/volume but instead it is going in @ same ratio - if you read through your code - that is what you are doing.






On Tue, Oct 15, 2013 at 6:46 PM, Martin Liddle <xansys05@tynecomp.co.uk (xansys05@tynecomp.co.uk)> wrote:
Quote:
On 15/10/2013 23:21, debabrata.podder wrote:
Quote:
  Same Q can not be applied both on V_A( which is 0.3V) and V_B( which is 0.7V) !!! So how to deal with this you think !!! So is there anything wrong with "the heat is distrib_uted to their respective volume proportions " !!!


Obviously there is something wrong but I think you can be confident that
the problem is in your code.  Try a simple test problem and you will
find it works perfectly.

--
Martin Liddle, Tynemouth Computer Services,
Chesterfield, Derbyshire, UK.
www.tynecomp.co.uk

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