Converting Density to Standard Density

In summary, the conversation discusses the need to find the density of a substance at standard conditions from the density at recorded conditions for two different applications: natural gas and crude oil. The speaker mentions the availability of standard functions, but expresses a desire for a more fundamental thermodynamic description. They also mention the complexities of using ideal gas theory for this application and request an explanation for both ideal gases and real gases. The expert suggests starting with the equations of state for these gases and finding tables or equations that have already been developed for the substances. They also clarify that these results are not found through the ideal gas law, but rather through measured properties. Lastly, they question the accuracy of the posed problem and suggest using the ideal gas law for natural gas and
  • #1
fonz
151
5
I have an application where I need to find the density of a substance at standard conditions (101.325kPA, 15°C) from the density at recorded conditions (varies).

The first application is for natural gas at approximately 11Barg (160 psi, 1100kPA), 80°C (176°F).

The second application is for crude oil at approximately 11Barg (160psi, 1100kPA), 80°C (176°F).

There are standard functions available published by API/AGA to do this but I need a more fundamental thermodynamic description of how to do this.

If somebody can provide a brief explanation I can go away and study in more detail. A description for ideal gases and real gases would be appreciated as well. Obviously in this application the ideal gas theory will be inaccurate.

Thanks
Dan
 
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  • #3
UltrafastPED said:
You would start with the equations of state for these gasses. That will give you the temperature-pressure-volume relationships.

The other equations are here: http://en.wikipedia.org/wiki/Equation_of_state

It's not clear that 'crude oil' is a gas, especially at such conditions as described in the OP. In any event, 'crude oil' is a rather complex mixture of various hydrocarbons.
 
  • #4
UltrafastPED said:
You would start with the equations of state for these gasses. That will give you the temperature-pressure-volume relationships.

The other equations are here: http://en.wikipedia.org/wiki/Equation_of_state

This is where I get stuck because the there are several equations of state each with their own advantages/disadvantages. The question is for natural gas under these conditions which equation should be used?

Also, crude oil is a liquid and obviously will obey a different law. The question is how to find the corrected density for crude oil?
 
  • #5
You need to start with tables/equations that have already been developed for your substances.

A complete table will show all of the phases: solid, liquid, gas.
It will show this for all temperatures and pressures which have been studied.

For example, start by looking at water:
"Wagner and Pruss, The IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use, 1995"
http://www.teos-10.org/pubs/Wagner_and_Pruss_2002.pdf

These results are _not_ found via the "Ideal Gas Law" or any other law - they are measured properties of the materials. Hunting up the data is your job.
 
  • #6
Are you sure you have posed the problem correctly? "find the density of a substance at standard conditions (101.325kPA, 15°C) from the density at recorded conditions (varies)," or is it the other way around. If it is only to find the density at standard conditions, then you can certainly use the ideal gas law for natural gas (methane). And the density of typical crude oil should be readily available at standard conditions.

Chet
 

FAQ: Converting Density to Standard Density

What is density and why is it important?

Density is a measure of how much mass is contained in a given volume of a substance. It is important because it helps us identify and compare different substances, and can also give us clues about their physical properties and behavior.

What is the standard density and how is it calculated?

The standard density is the density of a substance at a specific temperature and pressure, usually at standard conditions of 1 atmosphere pressure and 25 degrees Celsius. It is calculated by dividing the mass of the substance by its volume.

Why do we need to convert density to standard density?

Converting density to standard density allows us to compare the densities of different substances at the same conditions. This is important for accurate measurements and scientific experiments.

How do we convert density to standard density?

To convert density to standard density, we need to use the ideal gas law, which relates the pressure, temperature, volume, and number of molecules of a gas. By rearranging the equation, we can solve for the standard density by plugging in the given density and standard conditions.

Can density be converted to standard density for any substance?

No, density can only be converted to standard density for gases using the ideal gas law. For liquids and solids, the standard density is typically calculated using other methods, such as using the substance's melting or boiling point.

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