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May 19, 2019, 18:16 
how fluent calculate energy equation?

#1 
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Weiqiang Liu
Join Date: Feb 2018
Posts: 278
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Hi all,
I am doing a porous media combustion with fluent. In the literature, I found the energy equation is solved with enthalpy change. I also know that energy equation sometimes can be represented with specific heat. The author mentioned that both enthalpy and specific heat is temperature dependent. I defined temperature function of specific heat. However, I cann't see any reason I should defined temperature function of enthalpy. I wonder does the author mean enthalpy is a function of temperature because specific heat is temperature dependent and enthalpy is a function of specific heat. Therefore, enthalpy is temperature dependent indirectly? I put the energy equation in the paper below: It's more a question of thermodynamics than CFD. Can anybody help me? Best regards. 

May 20, 2019, 00:36 

#2 
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Alexander
Join Date: Apr 2013
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is you assume, that specific heat is constant, than enthalpy is not a function of temperature
best regards 

May 20, 2019, 09:14 

#3 
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Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
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What are you even discussing... Enthalpy depends on temperature or we'd violate at least one law of thermodynamics....
Enthalpy is heat (or heat potential) and temperature (from kinetic theory) is the average kinetic energy of the molecules in the volume. More temperature = more kinetic energy = more enthalpy. 

May 20, 2019, 10:35 

#4 
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Weiqiang Liu
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May 20, 2019, 10:57 

#5  
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Weiqiang Liu
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Quote:


May 20, 2019, 12:05 

#6 
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Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
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You should state specifically your setup because it varies.
For combustion modeling for example, you normally use the nasa 7polynomials which specifies the specific heat + a reference enthalpy and you are done. 

May 20, 2019, 12:17 

#7 
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Weiqiang Liu
Join Date: Feb 2018
Posts: 278
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is it because anthalpy is an integration of specific heat plus standard state enthalpy. if I know temperature dependent specific heat, then I know enthalpy under different temperatures. By mass fraction weighted calculation, I know enthalpy of the whole system?


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enthalpy, specific heat, temperature dependent 
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