Learning Forum

[d.matthis]

Hi all 

i need to get the energy of a transient analysis and am now at 99% :

(1)  file heatTransfer.wbpz  
==> picture: AIM_small changes in curve bigg changes in result.png

(2) file EVAL_THERM1.wbpz ==> eval_therm1.png
the 212Ws is a typical result => howto get it?
   and nearby: zipped file contains 4mb of files which are unneeded?

🛈 This post originally contained file attachments which have been removed in compliance with the updated Ansys Learning Forum Terms & Conditions

[Naresh Patre]

Hello DM

I will check the models and get back to you.

[Naresh Patre]

Hello DM

(1)  file heatTransfer.wbpz  

In first case, the heat generation input value for last 20 sec (80 to 100 sec) is constant and has a value of 0W, whereas in the other case, it is linearly dropping from 35000W to 0. This clearly explains the reason behind heat flow value being higher on the second case as compared to the first case. If you check out the heat flow chart, you can understand how the values are dropping down.
 

 

(2) file EVAL_THERM1.wbpz

I am not able to understand the values 0.434 and 0.604 that you have used in calculating Q. What do they represent and how did you get them? I understood the last term in the equation which is deltaT (800-22=778C). 

[d.matthis]

Naresh Patre 
Thank you
please let us concentrate on  (2)
i have appended the data : 0,434 ist a mat-constant and
0,604kg is the mass (can i measure the mass inside AIM? or only in sc)

Do you agree that the energy should be 212Ws?
Can is get this energy inside AIM?

[Naresh Patre]

Hello DM

Thanks for the clarification. I now understand that you are using Q = m*Cp*deltaT for calculating the energy. Let me look into it and get back to you.

[Naresh Patre]

Hello DM

For this example, the mass (m) is 0.604 kg. It can also be calculated in AIM using result type as "Calculated value"

 

The Specific heat (Cp) from the Material properties is 434 [J kg^-1 C^-1] (and not 0.434 which you have used in your calculation. Since the unit of mass is in Kg, we need to use the value of Cp with similar units.

 

The initial and final temperatures are 22 deg C and 800 deg C respectively.

So using the equation Q = m*Cp*deltaT, we get the value of Q as 204011.3643 J. Or if we convert this value in Watts, it will be 204011.3643 W (J/s). So this much energy or heat is required for the cylinder to raise the temperature to 800degC in 1 second. 
Coming back to your problem where the time taken to raise the temperature is 4 sec, that means you need to specify 204011.3643/4 = 51002.8411W in the Heat Generation panel. See below snapshot. This value is closer to what you have already specified (50000W). So this value (Q) is the one which you are specifying as an input in simulation and it is not something which you want to see it as a result output.

 

Using above value, if you now solve the problem in AIM and check the temperature value, you can see the final temperature as 800 degC. This value matches with the value that was specified in the equation. This validates the results from simulation and the equation.
Regarding the heat flow result, it's value is 0 because there is no flow of heat within the body. And this value is not equivalent to the energy (Q) value. If you check the temperature contour, the temperature is uniform everywhere. 

[d.matthis]

Naresh Patre 

yes, now the calculation is clear, sorry: the rough  calculation was untested
But again: Can AIM-function calculate the (higher) energy in this system after 4seconds?
If not, please close this task.

[Naresh Patre]

DM I am not able to understand your question clearly. What do you mean by higher energy?

[d.matthis]

Hi Naresh
As you worte : So using the equation Q = m*Cp*deltaT, we get the value of Q as 204011.3643 J.
So the increase of energy in the system (after 4sec) is 204011kJ. 
This increase is important for planning the cooling.
=> but how to get this energy from AIM? (it is a sum over time)

Sorry, for the sum of heat flow (which AIM shows)
i cannot see a practical use => do you see a use?

[Naresh Patre]

Hello DM

Instead of specifying Heat Generation as input, specify Temperature thermal condition for the volume and specify the temperature in tabular format as shown below.

Now, solve the analysis and under Results section, add Heat Flow Reaction. This will give you the value of energy required per second to raise the temperature of this geometry to 800deg C.

I hope this is what you were looking for.