# Example for Vapour Pressure Data fitting

Navigation: User Guide ➔ Species Table ➔ Vapour Properties ➔ Vapour Pressure Data Fitting

## Data Fitting

We will use Ammonia to demonstrate how to convert data into useable SysCAD formats. Reference: Perry's Chemical Engineers Handbook, 6th Edition Page 3-46.

Data: Equation Fitting
Vapour Pressure (atm) Temperature (C) Temperature (K)
1 -33.6 239.55
2 -18.7 254.45
5 4.7 277.85
10 25.7 298.85
20 50.1 323.25
30 66.1 339.25
40 78.9 352.05
50 89.3 362.45
60 98.3 371.45

We have to fit the data into this equation format:

• $\displaystyle{ \log(Vp) = a/T + b*\log(T) + cT + d }$
Where pressure is in Atmospheres and Temperature is in Kelvin.

Using Data fitting and SysCAD vapour pressure format VpAtm(a,b,c,d), this becomes

• VpAtm(-939.0199537, 3.908218312, -0.002862661, -4.673321372)

## Entering Vapour Pressure Equation

• To enter the vapour pressure equation into the SysCAD species database, Edit the User Species Database
• Add in physical properties for Species NH3(g) and NH3(l). For instructions on how to do this, refer to Enter or Change Species data.
• Type in the Fitted equation for Ammonia Vapour pressure as per image below:

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