How can I calculate the R value for a solid in OpenFOAM CFD modeling?

In summary, during CFD modeling of a gas-solid flow, the flow of solid is modeled as a perfect fluid using OpenFOAM. The density of the perfect fluid is calculated using an equation provided in the documentation, which includes parameters such as pressure, temperature, and a constant R. However, there is no mention of how to calculate R for a solid or fluid. Some attempts have been made to plot the density for water and mercury, but there is still no clear solution. The only suggestion is to look for density data in databases and approximate R from there.
  • #1
rasikaj
2
0
During CFD modeling of a gas-solid flow, flow of solid was modeled 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 + ρo , where ρo 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 ρo = 1027 kg m-3.

Also for mercury
R = 6818 with ρo = 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.
 
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  • #2
I'm still tryng to figure out how you are applying the ideal gas law to solids and liquids.
 
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Likes rasikaj
  • #3
Actually this is the equation, OpenFOAM has mentioned in their user guide. Not my idea. I thought this is some physics that I cannot understand.

You can see the equation in page U-203 of their user guide. Here is the link.
http://foam.sourceforge.net/docs/Guides-a4/OpenFOAMUserGuide-A4.pdf

I have seen the same problem asked in cfd-online.com, but with no answers

https://www.cfd-online.com/Forums/o...velopment/195068-r-constant-perfet-fluid.html

Thanks for your comment anyway. I would be grateful if you could give me a solution.
 
  • #4
I have no idea too, but the only thing that you can do -i think- is to look in some database for ##\rho_0## and ##\rho## for the solid you are interested in and then calculate an approximation of R.
 

What is the definition of density for a perfect fluid?

The density of a perfect fluid is defined as the mass per unit volume of the fluid. It is a measure of how much matter is present in a given volume of the fluid.

How is the density of a perfect fluid different from the density of a solid or gas?

The density of a fluid is different from that of a solid or gas because the particles in a fluid are able to move freely and are not held together in a fixed position like in a solid. This allows for a more uniform distribution of mass throughout the volume of the fluid, resulting in a constant density.

What factors can affect the density of a perfect fluid?

The density of a perfect fluid can be affected by changes in temperature and pressure. An increase in temperature can cause the fluid to expand, resulting in a decrease in density. Similarly, an increase in pressure can cause the fluid to compress, resulting in an increase in density.

How is the density of a perfect fluid measured?

The density of a perfect fluid can be measured using various methods, such as hydrometers, density meters, and density gradient columns. These methods involve measuring the mass and volume of a given amount of the fluid and using the formula density = mass/volume to calculate the density.

What is the significance of the density of a perfect fluid in fluid mechanics?

The density of a perfect fluid is an important parameter in fluid mechanics as it is used to calculate other properties of the fluid, such as pressure and viscosity. It also plays a crucial role in determining the behavior and movement of fluids in different situations, such as in pipes, pumps, and aerodynamics.

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