Learning Forum

[Jeroen]

I have set up a model using a particle surface reaction with a UDF to include a custom reaction rate. However, I also want to specify the heat of reaction (used in equation 16-181 in the theory guide for version 19.3) but this parameter is not present in my material properties dialog box. I am using the combusting particle and the multiple surface reactions model and I can specify the all other relevant properties such as the combustible mass fraction (which I set to 100%) and the reaction heat fraction absorbed by the solid (30%).nHow can I include the heat of reaction when it is not shown in my dialog box?n

[subhamdas]

Can you share a screenshot of the species model that you are using(along with coal calculator)? It is a key parameter for combustion and shouldn't be missing. I have been using the species transport model and have been adjusting the parameter by selecting coal-particle from Materials->combustion. Sharing screenshots for a setup that I had used earlier.nnnnn

[Jeroen]

I am not using the coal particle, but I have defined a custom particle named iron-oxide.nAs you see in the last 2 screenshots, I do not have the heat of reaction input parameter. According to the fluent manual (version 19.3) it should however be there.n

[subhamdas]

Please share your case file, so that I may try to figure out the issue.n

[Jeroen]

Unfortunately, I am not able to share my case file.nI have however noticed when changing the combustion model from multiple-surface-reactions to any of the other types that the heat of reaction parameter returns to the dialog box. Why then is it not there for the multiple surface reactions model?n

[subhamdas]

I found an explanation for this on the User's Guide. Hope this helps!nn

[Jeroen]

Would it be possible to explain how the heat of reaction parameter is computed from the particle surface reactions defined in the reactions dialog box? My reactions dialog box is given below, and the stoichiometric ratio is given as an input here. However, the heat of reaction is not specified here.nn

[subhamdas]

Since the stoichiometric equation for your reaction is 3Fe + 4H2O ----> Fe3O4 + 4H2, the heat of reaction can be computed by the following equation(AFAIK from high school chemistry):nnHeat of reaction=(1*heat of formation of Fe3O4 + 4*heat of formation of H2) - (4*heat of formation of H2O + 3*heat of formation of Fe)nnYou can find the heat of formation of the above compounds on the internet easily. n

[Jeroen]

The thing is that I have added some of these components manually. So how does Fluent get the heat of reaction for each of the components. Do I need to specify this in the specie material properties as the Enthalpy value? Or does it take the heat of formation of the individual components from somewhere else?nn

[subhamdas]

Yes, you need to specify the standard state enthalpy for Fluent to compute the heat of reaction. You can also cross verify this by putting in different values of the standard state enthalpy and study its effect on the heat of reaction(obtained during post processing)n

[Jeroen]

Thank you for your help, my problem has been solved.n