Step 7: Solution with Varying Heat Capacity

  The strong temperature and composition dependence of the specific heat has a significant impact on the predicted flame temperature. In this step you will use the temperature-varying property information in the ANSYS FLUENT database to recompute the solution.

1.   Enable composition dependence of the specific heat.

Materials Mixture Create/Edit...

(a)   Select mixing-law from the Cp drop-down list in the Properties group box.

  Scroll up the list to find mixing-law.

(b)   Click Change/Create.

  The specific heat of the mixture will now be based on a local mass-fraction-weighted average of all the species.

(c)   Close the Create/Edit Materials dialog box.

2.   Enable temperature dependence of the specific heat for CO $_2$.

Materials carbon-dioxide Create/Edit...

(a)   Ensure that piecewise-polynomial is selected from the Cp drop-down list in the Properties group box.

(b)   Click the Edit... button to open the Piecewise-Polynomial Profile dialog box.

i.   Retain the default values in the Coefficients group box.

  The default coefficients describe the polynomial $C_p(T)$ and are extracted from the ANSYS FLUENT property database.

ii.   Click OK to close the Piecewise-Polynomial Profile dialog box.

(c)    Close the Create/Edit Materials dialog box.

3.   Similarly, ensure that temperature dependence of specific heat is enabled for the remaining species (CH $_4$, N $_2$, O $_2$, and H $_2$O).

4.   Request 500 more iterations.

Run Calculation

  The residuals will jump significantly as the solution adjusts to the new specific heat representation. The solution will converge after approximately 235 additional iterations.

5.   Save the new case and data files ( gascomb2.cas.gz and gascomb2.dat.gz).

File $\rightarrow$ Write $\rightarrow$ Case & Data...