Conditional enthalpy properties Workbench 1

[AliceEng]

Could you please give a hint how to apply conditional enthalpy properties depending on thermal loads?
For example I have a material with different enthalpy properties for cooling and heating processes.
How can I specify that during cooling one values must be applied and during heating
the other ones.

Initially I apply the temperature dependent enthalpy values in Engineering Data in Workbench (ANSYS 15.0) and then time dependent heat flux. To specifiy values during cooling when heat flux is equal to zero I use a command line in my transient thermal model and I write like this

*IF,_load(4,1,1),EQ,'0',THEN
mptemp,1,0,26,27,28,29,100 ! for temperatures 26,27...30
mpdata, enth, matid, 1, 0, 100,150,200,250,500 ! enthalpy values 100,150..300
*ENDIF

Obviously it is not working. Looking forward to hear some suggestions! Thank you.

 

[Latexman]

AliceEng,

Could you explain in detail what is meant by "different enthalpy properties for cooling and heating processes" of this material. I was taught that enthalpy was a state function and path independent.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[chicopee]

The best thing for you to understand enthalpy is to go on line and check this particular topic under thermodynamics. You should not expect us to teach you enthalpy in few sentences when thermodynamics is covered in college during a quarter.

 

[AliceEng]

Dear Latexman, thank you for you reply. I have attached the data sheet of the material that I use. If you look at the partial Enthalpy Distribution you may find red and blue indicators for heat and cool. This material is able to store heat, moreover for some of the materials from this series the melting and congealing temperature range can also differ. I hope I have answered on your question.

Dear chicopee, I do not expext from you to teach me. If you see that someone´s question is wrong why do you even spend your time answering on it at all...

 

[willard3]

I agree with Chicopee

 

[ione]

Great post Randy as usual

 

[Latexman]

AliceEng,

I do not use Workbench (ANSYS 15.0), so I cannot help with your approach and code you provided. My advice is to educate yourself thoroughly on the physical and thermodynamic behavior of these compounds. Research and buy the best book on the subject. Buy some pertinent cutting edge journal articles. Ask the supplier's technical expert (yes, call them up and ask to speak to their expert) how they model the fluid. The brochure says it is a pure PCM. I wonder if the fluid is a pure single component, or a mixture of components. The fluids behavior makes sense to me if it is a mixture of similar compounds, maybe isomers or just different molecular weights. One of the first questions you need to answer is, how sophistocated does your model have to be to be close enough. Can you model it as a pure component with a melting point of 35^oC? It'll only be off +/- 1-2^oC. In my opinion, that's pretty close. Maybe in your application, it's not. In that case, model it as a mixture of similar compounds that have a range of pure component melting points between 33 and 37^oC. Call Workbench and ask their technical support how to medel the fluid.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[AliceEng]

Thank you very much for the replies.