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Time dependent analysis - Time to reach steady state

Posted Apr 18, 2012, 3:22 a.m. EDT Heat Transfer & Phase Change, Studies & Solvers Version 4.2 6 Replies

Benjamin
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Hello everyone,

I am trying to model transient radiative heat transfer in a cryo vacuum chamber.

I want to know how much time it takes to reach steady state temperature in my chamber.

For the moment I do a time-dependent analysis on a huge time period but I think that there are simpler way to do that.

Do you have any idea ?

6 Replies Last Post Apr 19, 2012, 2:47 a.m. EDT
Ramamoorthy Venkataramanan
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Posted: 1 decade ago Apr 18, 2012, 4:27 a.m. EDT

Hello everyone,

I am trying to model transient radiative heat transfer in a cryo vacuum chamber.

I want to know how much time it takes to reach steady state temperature in my chamber.

For the moment I do a time-dependent analysis on a huge time period but I think that there are simpler way to do that.

Do you have any idea ?




Hi,

a. Pl start with the steady state analysis and give number of iteration as a high value as the problem is highly non-linear.
b. Then try for the transient state with the less output interval, so that computational time will get reduced.

Thanks,
Ramamoorthy V
[QUOTE] Hello everyone, I am trying to model transient radiative heat transfer in a cryo vacuum chamber. I want to know how much time it takes to reach steady state temperature in my chamber. For the moment I do a time-dependent analysis on a huge time period but I think that there are simpler way to do that. Do you have any idea ? [/QUOTE] Hi, a. Pl start with the steady state analysis and give number of iteration as a high value as the problem is highly non-linear. b. Then try for the transient state with the less output interval, so that computational time will get reduced. Thanks, Ramamoorthy V
Benjamin
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Posted: 1 decade ago Apr 18, 2012, 5:30 a.m. EDT
Thank you for your answer.

I don't understand correctly what you explained.

I have initial conditions (different from the steady-state solution), then I should do a steady-state analysis with enough iterations in order to capture it. This I understand

However I don't understand the part on the time-dependent analysis what do you mean by "less output interval"?
Thank you for your answer. I don't understand correctly what you explained. I have initial conditions (different from the steady-state solution), then I should do a steady-state analysis with enough iterations in order to capture it. This I understand However I don't understand the part on the time-dependent analysis what do you mean by "less output interval"?
Ramamoorthy Venkataramanan
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Posted: 1 decade ago Apr 18, 2012, 12:01 p.m. EDT

Thank you for your answer.

I don't understand correctly what you explained.

I have initial conditions (different from the steady-state solution), then I should do a steady-state analysis with enough iterations in order to capture it. This I understand

However I don't understand the part on the time-dependent analysis what do you mean by "less output interval"?


Hi,

a. Why are you performing a transient state analysis, and why not steady state analysis.
b. Generally transient radiation problem wil take huge time.
c. If you could solve using steady state analysis, that results holds good.


--

Thanks,
Ramamoorthy V
[QUOTE] Thank you for your answer. I don't understand correctly what you explained. I have initial conditions (different from the steady-state solution), then I should do a steady-state analysis with enough iterations in order to capture it. This I understand However I don't understand the part on the time-dependent analysis what do you mean by "less output interval"? [/QUOTE] Hi, a. Why are you performing a transient state analysis, and why not steady state analysis. b. Generally transient radiation problem wil take huge time. c. If you could solve using steady state analysis, that results holds good. -- Thanks, Ramamoorthy V
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago Apr 18, 2012, 5:52 p.m. EDT
Allow COMSOL to take larger time steps in its transient analysis. These large time step will usually kick in when the solution is closer to steady state. It is common for COMSOL to take time steps at that point that are several orders of magnitude larger than the small steps required initially.

The output interval described in a previous post is the info you put in the “Times” input in the Time Dependent solver node.

Nagi Elabbasi
Veryst Engineering
Allow COMSOL to take larger time steps in its transient analysis. These large time step will usually kick in when the solution is closer to steady state. It is common for COMSOL to take time steps at that point that are several orders of magnitude larger than the small steps required initially. The output interval described in a previous post is the info you put in the “Times” input in the Time Dependent solver node. Nagi Elabbasi Veryst Engineering
Santhosh Kumar CT
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Posted: 1 decade ago Apr 19, 2012, 1:09 a.m. EDT
hi ...
i guess the HUGE TIME PERIOD that you are talking about .. should be in terms of few days ...
but that should not matter.
Start with steady state analysis for having an idea of your final values.
Then compute transience for a very short period ( time interval being your own choice)
and finally complete the full computation for the required time period based on the result that you obtained for limited time interval evaluation. This is how i did my problem which is a surface to sruface radiation module based thermal calculations inside a furnace !
hi ... i guess the HUGE TIME PERIOD that you are talking about .. should be in terms of few days ... but that should not matter. Start with steady state analysis for having an idea of your final values. Then compute transience for a very short period ( time interval being your own choice) and finally complete the full computation for the required time period based on the result that you obtained for limited time interval evaluation. This is how i did my problem which is a surface to sruface radiation module based thermal calculations inside a furnace !
Benjamin
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Posted: 1 decade ago Apr 19, 2012, 2:47 a.m. EDT
Thank you for all your answer.

I am aware that the cooling time by radiation is quiet high, and I did firstly a steady-state analysis.

I deduce from your answer that there is no way to impose to a transient analysis to stop when it reaches steady-state, am I correct?

Thank you again!
Thank you for all your answer. I am aware that the cooling time by radiation is quiet high, and I did firstly a steady-state analysis. I deduce from your answer that there is no way to impose to a transient analysis to stop when it reaches steady-state, am I correct? Thank you again!

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