# how do fluent calculate energy equation?

Member

Hi all,

I have a question : how fluent calculate energy equation? I put the energy equation in enthalpy change formulate below:

the author mentioned both enthalpy and specific heat are temperature dependent. I have defined temperature function of specific heat. However, I cann't see why enthalpy should be defined with UDF. Does the author mean enthalpy is a function of specific heat and specific heat is function of temperature. Then enthalpy is function of temperature indirectly. Therefore, I just need to define temperature dependent function of specific heat in fluent?

Best.

Weiqiang.

• GermanyForum Coordinator
edited May 2019
Enthalpy is always temperature dependent. You can define temperature dependent specific heat.
• Member
edited May 2019

Do you mean I have to define temperature-dependent enthalpy of species by myself or fluent can calculate the temperature-dependent enthalpy automatically?

Best.

Weiqiang

• GermanyForum Coordinator
edited May 2019
Fluent does it automatically. Enthalpy is integral of Cp wrt dT plus ss enthalpy all is mass fraction weighted so the sum goes over all species.
• Member
edited May 2019

thanks very much!

Best regards.

Weiqiang