Help with the Wagner Equation

  • Thread starter CrazyDiamond
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In summary: The Wagner Equation is an equation used in physics to calculate the vapour pressure of a liquid at a given temperature. It is named after the German physicist Gustav Wagner.
  • #1
CrazyDiamond
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I'm using the Wagner Equation for Vapour Pressure at work.This equation is :

lnp=((-7.7069(1-T)) + (2.4932(1-T)^1.5158) -(2.9212(1-T)^1.9907) -(3.8684(1-T)^4.3798) + (0.46898(1-T)^1.7461) - (0.00008336))/x

[I haven't been able to find an online version of this equation]

Here, T and p are variables. Its obviously easy to find p if I know T, but now I need to find T given that p is known. This is getting very complicated, and I don't have access to MatLAB either.Could someone who has MatLAB please help me out - I simply need an equation for T in terms of p.

Online Equation solvers give me an answer for T if I feed in the equation, but they do not give me an equation for T, which is what I need so I can put it into an Excel Spreadsheet.

Thanks.
 
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  • #2
It is not possible to get equation of the form T(p), since p(T) is a complicated enough rational polynomial. Wherever you need to use T(p), you will have to have a numerical solver for it in the background (what those online solvers do). Perphaps Excel has a function for that too?

If not, you may try another thing to patch up for the moment. In the range of T that you expect, plot in Excel the graph of p(T); if it doesn't look to non-linear, make a regression fit to it, using one of the expressions that can be easily inverted to obtain an approximate T(p).

--
Chusslove Illich (Часлав Илић)
 
  • #3
caslav.ilic said:
In the range of T that you expect, plot in Excel the graph of p(T); if it doesn't look to non-linear, make a regression fit to it, using one of the expressions that can be easily inverted to obtain an approximate T(p).

And that worked perfectly.Thanks !:smile:
 
  • #4
I just happened to browse this forum and this post piqued my curiosity.

What is the Wagner Equation? Can you refer me to any online references where I can read more about it?
 

1. What is the Wagner Equation?

The Wagner Equation is a mathematical model used to predict the vapor pressure of a pure substance at a given temperature. It is commonly used in thermodynamics and is named after the German physicist, Johannes Diderik van der Waals.

2. How is the Wagner Equation derived?

The Wagner Equation is derived from the van der Waals equation of state, which is an equation that describes the behavior of real gases. It takes into account the size of gas molecules and the attractive and repulsive forces between them.

3. What is the significance of the Wagner Equation?

The Wagner Equation is significant because it allows scientists and engineers to accurately predict the vapor pressure of a pure substance, which is important for various industrial and scientific applications. It also provides insight into the behavior of real gases and helps improve our understanding of thermodynamics.

4. How is the Wagner Equation used in practice?

The Wagner Equation is used in various industries, such as the chemical, pharmaceutical, and energy sectors. It is commonly used in the design and operation of distillation processes, as well as in the development of refrigeration and air conditioning systems.

5. Are there any limitations to the Wagner Equation?

Yes, the Wagner Equation has limitations and may not accurately predict the vapor pressure of substances that deviate significantly from ideal gas behavior. It also does not take into account factors such as impurities and temperature variations, which can affect the accuracy of its predictions.

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