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Cooling rate at a certain temperature

Posted 12 janv. 2011, 05:25 UTC−5 7 Replies

Imre Felde
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Hi

I would be apprecited if you could help on the following issue:

I am dealing with temperature calculation of a 2d axissymmetric workpiece during cooling from 1000 C to 100 C. I would need the cooling rate at 700 C at the whole domain.

How could I do it?

thank you in advance!

7 Replies Last Post 14 janv. 2011, 15:31 UTC−5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 12 janv. 2011, 05:43 UTC−5
Hi

How do you define your cooling rate ?

is it the temperature derivative for a transient analysis ? this should be Tt = dT/dt in COMSOL notation

be sure your time derivatives is turned, that your physics do solve for T and that you are in a transient analysis

in v4.1 HT you have also the (ht.gradTphi, ht.gradTr, ht.gradTz) and ht.gradTmag

--
Good luck
Ivar
Hi How do you define your cooling rate ? is it the temperature derivative for a transient analysis ? this should be Tt = dT/dt in COMSOL notation be sure your time derivatives is turned, that your physics do solve for T and that you are in a transient analysis in v4.1 HT you have also the (ht.gradTphi, ht.gradTr, ht.gradTz) and ht.gradTmag -- Good luck Ivar
Imre Felde
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Posted: 1 decade ago 12 janv. 2011, 15:03 UTC−5
Hi Ivar,

Thank you for the quich reply!

Yes, I mean the cooling rate (CR) is the first derivative of temperaure, dT/dt [K/s]. I use Comol 3.4 release, transient heat transfer module. Are ht.gradTphi, ht.gradTr and ht.gradTz expressions available in v3.4?

If not so, could you please advise what sort of formula (expression, function) should I use to determine the cooling rate at 700 C (CR700) in the whole domain?

thank you again,
best

Imre
Hi Ivar, Thank you for the quich reply! Yes, I mean the cooling rate (CR) is the first derivative of temperaure, dT/dt [K/s]. I use Comol 3.4 release, transient heat transfer module. Are ht.gradTphi, ht.gradTr and ht.gradTz expressions available in v3.4? If not so, could you please advise what sort of formula (expression, function) should I use to determine the cooling rate at 700 C (CR700) in the whole domain? thank you again, best Imre
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 13 janv. 2011, 04:27 UTC−5
Hi

no, all prefixed_dot_ are v4 notations, in v3 it was suffix _ht

then I suppose that Tt should be defined as dT/dt (your version is old, I have forgotten in the mean time ;)

But in 3.5 I remember that the time derivatives were only calculated on demand, there is perhaps also a check box to select in the solver menu

--
Good luck
Ivar
Hi no, all prefixed_dot_ are v4 notations, in v3 it was suffix _ht then I suppose that Tt should be defined as dT/dt (your version is old, I have forgotten in the mean time ;) But in 3.5 I remember that the time derivatives were only calculated on demand, there is perhaps also a check box to select in the solver menu -- Good luck Ivar
Carol Platon
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Posted: 1 decade ago 13 janv. 2011, 11:49 UTC−5
if the casting is under equilibrium condition the cooling rate will be low and you must use implicit or explicit schem and not tansient integration
if the casting is under equilibrium condition the cooling rate will be low and you must use implicit or explicit schem and not tansient integration
Imre Felde
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Posted: 1 decade ago 14 janv. 2011, 08:13 UTC−5
Thank you very much for your responses.

I think my question was not clear, therefore I would like to ask some more help:

I am able to calculate the dT/dt (cooling rate, CR) in every time instance for the whole spatial domain by using the global expression ie: CR = diff(T,t).

However, I like to determine the CR given at 700 C (CR700). In other words, I would need the value of dT/dt when the temperature is T = 700 C for every points of the model .

So, what expression should be introduced to calculate CR700?

Thanks for your help in advance!
Thank you very much for your responses. I think my question was not clear, therefore I would like to ask some more help: I am able to calculate the dT/dt (cooling rate, CR) in every time instance for the whole spatial domain by using the global expression ie: CR = diff(T,t). However, I like to determine the CR given at 700 C (CR700). In other words, I would need the value of dT/dt when the temperature is T = 700 C for every points of the model . So, what expression should be introduced to calculate CR700? Thanks for your help in advance!
Carol Platon
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Posted: 1 decade ago 14 janv. 2011, 11:33 UTC−5
if you want to keep the temperature constant at 700C, i thimk it a state change: liquid to solid for exemple, so you must use heat latent, so dT/dt = 0 for few second.
if you want to keep the temperature constant at 700C, i thimk it a state change: liquid to solid for exemple, so you must use heat latent, so dT/dt = 0 for few second.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 14 janv. 2011, 15:31 UTC−5
Hi

I'm afraid that in 3.5 you need to go through matlab to have full control on the results.

In v4 you can easier use "filters" to limit the amount of data to i.e. a range of the bolean expression (T>LowerLimitOfT)*(T<HigherLimitOfT) and then plot Tt as variable. Then the question is to export this data, and if you need the localisation of these conditions. There again you would neeed Matalb , I believe

--
Good luck
Ivar
Hi I'm afraid that in 3.5 you need to go through matlab to have full control on the results. In v4 you can easier use "filters" to limit the amount of data to i.e. a range of the bolean expression (T>LowerLimitOfT)*(T

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