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## Main Question or Discussion Point

During CFD modeling of a gas-solid flow, flow of solid was modelled as a perfect fluid using OpenFOAM.

The density of the perfect fluid is calculated using the following equation as given in the documentation.

ρ = P/RT + ρ

My struggle is to calculate the R (J kg

Also for mercury

R = 6818 with ρ

I tried to plot the ρ with P/T for water and the linear equation was

ρ = 0.4321 (P/T) + 848.78, where R = 2.314

So could anyone please tell me how to calculate R for a certain fluid or solid. I have searched the internet for days and still didn't find any reference to this equation.

The density of the perfect fluid is calculated using the following equation as given in the documentation.

ρ = P/RT + ρ

_{o}, where ρ_{o}is the density at T = 0 kelvin, ρ is the density of the perfect fluid at pressure P (Pa) and temperature T (K). There is no other mention about this in the documentation of OpenFOAM.My struggle is to calculate the R (J kg

^{ -1}K^{-1}) for the solid. In the OpenFOAM tutorials for the normal conditions of water R = 3000 with ρ_{o}= 1027 kg m^{-3}.Also for mercury

R = 6818 with ρ

_{o}= 13529 kg m^{-3}.I tried to plot the ρ with P/T for water and the linear equation was

ρ = 0.4321 (P/T) + 848.78, where R = 2.314

So could anyone please tell me how to calculate R for a certain fluid or solid. I have searched the internet for days and still didn't find any reference to this equation.