Learning Forum

[sj21]

In the mixture multiphase model, the temperature that is specified during the initialization and the temperature obtained after solving the energy equation, do these temperature belong to the primary phase or secondary phase?.

[Rob]

Yes. You may want to read the Theory Guide. 

[DrAmine]

Please get the ropes of the model by lookiong into the Theory Guide. That is the mixture / bulk temperature as we are solving only one Energy Equation.

[sj21]

I read about the governing equations in the guide. I have another doubt,can you please help.

In the energy equation it is given, sensible enthalpy () is used in .

So , is the standard state enthalpy not used in this equation ? is it not necessary to mention in material properties?

 

 

[Rob]

 

We only need formation enthalpy etc when looking at chemical reactions (so we know how hot it’s going to get) and phase change (but we only need the latent heat). Otherwise, we’re just solving the Q=m cp dT to see how much energy is needed to make it hotter. 

To add, if you're checking heat flux in/out of the domain we use the above to account for hot/cold material flowing in/out of the model: it's often non-zero on the inlet and outlet because of the hard coded reference temperature. 

 

[sj21]

I am following this paper: https://www.researchgate.net/publication/274921586_Multiphase_CFD_Simulation_of_Solid_Propellant_Combustion_in_a_Small_Gun_Chamber.

The solid phase is a combustible material which burns and turns to gas and also releases energy.

I included the energy released as a source term in energy equation and the mass transfer from solid to gas using DEFINE_MASS_TRANSFER.

For this case, is it necessary to mention the enthalpy of formation for the materials? I took the enthalpy of formation as 0 for gas and solid and performed the simulation.

The pressure is not rising as rapidly as in the paper and the solid is also burning slower than in the paper.

In that paper nothing is given about the enthalpy of formation in material properties.Can you please help.I am not getting what I did wrong.

[Rob]

If you're manually adding energy into the system then you need to see if you're accounting for the phase change: I don't know what you're doing. The other consideration is if you're using compressible gas, and what's holding the gas in place: in a gun (of whatever size) the bullet/ball/shell holds the gas back as it's shot out of the barrel.