Thermal Energy per Element in Transient Analysis

Albert

Hi,

I'm working on a transient analysis where it is important to know the thermal energy of each element in our model. We want to apply the following equation to each element:

Q = m*Cp*T

1) With m being mass
2) With Cp being the specific heat capacity
3) With T being the temperature of the element

These are the problems we face:
1) To calculate the mass of an element we can use the specified density and the volume. the density is user specified therefore we have it, however we do not know the volume of each element. The volume of an element can be found individually by selecting them and then using the Tools drop down, this does however not help as there are many cells and doing them manually would take forever, is there a way to output the volume of each element in the table of the solution?

2) The specific heat capacity and conductivity is temperature based in this model and it works well. Is there a way to also get the value that is used for each element regarding the specific heat capacity?

3) From the table output we only find temperatures for the nodes not for the elements themselves, is there a way to get a temperature output for the element not the nodes?

With regards to the final answer of the thermal energy is there a way to combine these values as specified in the equation in Mecway?

I have really been enjoying my experience with Mecway, thank you

Kind Regards
Albert

Victor

Hello Albert

1) You can write a script using the API function solution.mass(element_id)

2) I don't think so. You might have to re-implement that calculation yourself. Don't use the specific heat variable in the solution formula because it doesn't currently work for temperature dependent specific heat.

3) You can use the API functions solution.volume_integral(variable, element_id) and solution.volume(element_id) to calculate the average temperature over an element.

Attached is an example that generates a file containing each element's ID, mass and average temperature at time step 1. Delete the .txt extension that's just there to satisfy the forum software. Change the path in the first line before running it. To run it, first add it through Tools -> Scripts -> New then execute it through Tools -> thermal_energy. Units are in the m,kg,s,K system.

disla

¿Is ENER or ELSE the right variables to extract the Internal energy of a hot material?
¿Do I have to compute manually according to the instructions given in this post or has something change since August 2020.?

It doesn't seem to give any result to me.

Thermal transient with temp and Heat flow but ENER and ELSE All zero.

Thanks in advance.

Victor

From the manual, it looks like ENER and ELSE are just for mechanical energy in dynamics.

Q = m*Cp*T is really heat added for temperature change T when Cp is constant, not total energy at temperature T.

What do you mean by internal energy here? The energy that can be released as heat if the object is connected to a reservoir at absolute zero? I don't think that's really a useful quantity, but I guess you could integrate m Cp dT over the whole temperature range using temperature dependent specific heat.

disla

Hi ,

Energy variation or final temperature is the simplest check I can think about.
I have an adiabatic system that seems to lose energy through faces in which Heat Flux
has been set to 0.
I was looking to find some variation in the internal energy due to inlet or outlet energy.

I have to look into more detail, but it seems like some heat drill an adiabatic barrier through the corners or “overflow/jump from the sides” if there is another surface connected.

Attached the model.

Victor

A 0 heat flux load really means 0 heat flux in addition to whatever else is there - conduction, other heat fluxes, convection, etc. So it has no effect. It's not a constrain that forces heat flux to be zero.

disla

What a blunder.
I'm using contact thermal conductance =0 instead.

Thank you Victor.