Learning Forum

[accounting]

I am trying to assign specific heat for a custom material as a function of temperature in my transient simulation. It works if I am running a steady state simulation but throws an error about using 'Temperature' in a expression when I switch to transient simulation. I am attaching some pictures for reference and any help would be appreciated. If there is a better way to assign specific heat as a function of temperature using expressions instead of tables, I would like to learn how to. I understand that specific heat as a material property might not play a role in steady state simulation but I am trying to a transient case for my setup, so I tried to see if I will get same error if I switch to steady state.

[Gaurav Sharma]

Hi Rahul Mulinti ,

As far as the Static Thermal analysis is concerned, conductivity is the only required property. The presence of Density and Specific heat is both redundant in the first place as the simulation results are not going to affected by the density or Specific heat inputs. Since these inputs are altogether ignored, program doesn't care if the value is specified as a single value or in a table format, and doesn't produce a warning/error.

Whereas in Transient Thermal analysis, the governing equation has an additional Heat storage term which is derived from specific heat and density values. But, it is important to understand that typically these values are found to be temperature dependent for phase change problems. As the phase change capability is not exposed in AIM, it is not allowed to define Specific heat and Density as a function of temperature. Hence, you are getting an error when you are attempting to input Specific Heat as a table.

Please let me know if you seek any further clarification.

Thanks & Regards,

Gaurav

[accounting]

Hi Gaurav_ANSYS ,

 

Thanks for your reply, I have been traveling and saw your prompt response today.  I realized that it might be intentionally hidden as well. I was trying to find a way to run a phase change model using AIM, so I tried to use Cp_transition based on latent heat value for the material. I am sure using expressions is also going to throw the same error because temperature will be a variable again. 

From your experience, do you think there are other ways to model phase change in AIM? I am not really looking to study phase change dynamics but to model thermal behavior of an assembly with phase change material acting as a sink at its melting temperature. 

 

Thanks again,

Rahul

[Gaurav Sharma]

Rahul Mulinti 

Sorry for the delay in my response, I was on leave for a couple of days. 

I understand your requirement about incorporating the effects of latent heat on thermal behavior through a varying specific heat input. However, I cannot think about any possible workaround that may help you, though ANSYS legacy products are capable of doing this.

Though a possible workaround seems unlikely but I am still checking with the team here to see if there is something available beyond my knowledge, that can help you. Will get back to you soon.

Thanks & Regards,

Gaurav

[accounting]

Thanks for your reply Gaurav_ANSYS , I really appreciate it. I will keep an eye out for your response. 

[Gaurav Sharma]

Rahul Mulinti I am glad to tell you that one of my colleagues shared an example (attached herewith) wherein APDL commands are used to define enthalpy as a function of temperature. This is how effect of Latent heat can be taken care of. Please follow the 3 step process as specified below: 1. Define a "Selection Set" which is a named selection of your geometry and name it "Selection Set 1" (Default name). This nomenclature has to be consistent with the one mentioned in commands you will use. 2. Go to solver options and add "User Commands". 3.Go to PREP7 tab and copy paste the command (please make sure to change the MPTEMP and MPDATA) as per your inputs FYI, The example shared above inputs the following enthalpy vs time chart: Kindly refer the attached sample AIM model for further help. Thanks & Regards, Gaurav

[rahulm]

Gaurav_ANSYS I had to switch my Ansys email account to access this forum but it is still me, Rahul Mulinti. I will definitely give this a shot and I really appreciate you going beyond what I was hoping for in terms of support. Kudos to you and your team!