Calculator Inputs
Single column page layout with a responsive input grid: three columns large, two smaller, and one on mobile.
Example Data Table
These sample values are generated from the default generalized settings for ammonia. They help you compare typical saturation pressure behavior across temperature.
| Temperature (°C) | Temperature (K) | Vapor Pressure (bar) | Vapor Pressure (kPa) | Vapor Pressure (atm) |
|---|---|---|---|---|
| -40.00 | 233.15 | 0.69637 | 69.637 | 0.68726 |
| -33.34 | 239.81 | 0.99263 | 99.263 | 0.97965 |
| -20.00 | 253.15 | 1.89185 | 189.185 | 1.86711 |
| 0.00 | 273.15 | 4.33932 | 433.932 | 4.28257 |
| 20.00 | 293.15 | 8.73061 | 873.061 | 8.61644 |
| 40.00 | 313.15 | 15.85814 | 1,585.814 | 15.65076 |
Formula Used
1) Lee-Kesler Generalized Vapor Pressure Model
This method estimates the reduced vapor pressure using reduced temperature and the acentric factor.
Reduced temperature: Tr = T / Tc
ln(Pr) = f0(Tr) + ω·f1(Tr)
f0(Tr) = 5.92714 − 6.09648/Tr − 1.28862 ln(Tr) + 0.169347 Tr6
f1(Tr) = 15.2518 − 15.6875/Tr − 13.4721 ln(Tr) + 0.43577 Tr6
Final pressure: P = Pr × Pc
2) Clausius-Clapeyron Estimate
This option is useful when you know one reference saturation point and want a quick thermodynamic estimate.
ln(P) = ln(Pref) − (ΔHvap/R) × (1/T − 1/Tref)
The calculator converts all outputs into multiple pressure units so you can compare bar, kPa, MPa, atm, mmHg, psi, and Pa instantly.
How to Use This Calculator
- Enter the ammonia temperature and choose its unit.
- Select the output pressure unit you want to see first.
- Choose the generalized model for broad engineering work, or the Clausius option for a quick estimate.
- Adjust the advanced thermodynamic inputs only when you need custom property assumptions.
- Press the calculation button to show the result above the form.
- Review the converted units, engineering note, and pressure trend graph.
- Use the CSV or PDF buttons to save the result summary.
FAQs
1) What does ammonia vapor pressure mean?
It is the equilibrium pressure exerted by ammonia vapor above liquid ammonia at a specific temperature. Higher temperature usually gives higher vapor pressure, which matters for storage, refrigeration, process design, and safety checks.
2) Which method should I choose?
Use the generalized Lee-Kesler option for wider engineering temperature studies below the critical point. Use Clausius-Clapeyron when you have a trusted reference state and want a fast thermodynamic estimate.
3) Why does pressure rise so quickly with temperature?
As temperature increases, more ammonia molecules gain enough energy to escape the liquid phase. That raises the vapor concentration above the liquid and increases equilibrium pressure rapidly.
4) Can I use this near the critical point?
Yes, but interpret results carefully. Near the critical region, small temperature changes can strongly shift predicted pressure, and real-fluid behavior becomes more sensitive to property assumptions and correlation choice.
5) Why are several pressure units shown?
Different industries report saturation pressure in different units. Process teams may prefer bar or kPa, laboratory users may want mmHg, and equipment documentation may show psi or atm.
6) What is the acentric factor doing here?
The acentric factor helps the generalized model account for how a real fluid departs from simple spherical behavior. It improves vapor-pressure estimation beyond an idealized corresponding-states approach.
7) When is the Clausius-Clapeyron method less reliable?
It becomes less reliable when enthalpy of vaporization changes strongly across the temperature range, or when you move too far from the reference state used to anchor the estimate.
8) Can I export the results for reports?
Yes. The calculator provides CSV and PDF exports so you can keep a calculation record, attach it to lab notes, or share a clean summary with colleagues.