Calculator Inputs
Pressure Trend Graph
The chart shows absolute pressure versus temperature for the current density and compressibility settings.
Example Data Table
| Basis | Temperature (°C) | Input Value | Z | Pressure (kPa) | Pressure (bar) | Pressure (psi) |
|---|---|---|---|---|---|---|
| Specific volume | 180 | 0.85 m³/kg | 0.98 | 241.113 | 2.411 | 34.971 |
| Specific volume | 220 | 0.62 m³/kg | 1.00 | 367.079 | 3.671 | 53.240 |
| Density | 260 | 2.4 kg/m³ | 0.99 | 584.612 | 5.846 | 84.791 |
| Mass and vessel volume | 300 | 12 kg / 4.5 m³ | 1.00 | 705.357 | 7.054 | 102.303 |
| Density | 350 | 4.1 kg/m³ | 1.02 | 1,202.675 | 12.027 | 174.433 |
Formula Used
Compressibility-corrected gas relation:
P = Z × R × T ÷ v
P = Z × ρ × R × T
- P = absolute pressure in kPa
- Z = compressibility factor
- R = steam gas constant = 0.4615 kPa·m³/(kg·K)
- T = absolute temperature in K
- v = specific volume in m³/kg
- ρ = density in kg/m³
This method works best for superheated vapor away from the saturation region. For strict design work, verify results against steam tables or a validated equation of state.
How to Use This Calculator
- Select a calculation basis that matches your known data.
- Enter steam temperature in degrees Celsius.
- Enter a realistic compressibility factor for your condition.
- Provide specific volume, density, or mass and vessel volume.
- Set atmospheric pressure if you need gauge pressure.
- Choose decimal places and press the calculate button.
- Review the result card, graph, and export options.
- Check steam-table accuracy when working near saturation.
FAQs
1. What does this calculator estimate?
It estimates superheated steam pressure from temperature and one density-related input. It also converts the result into bar, MPa, psi, and gauge pressure for quick engineering review.
2. Which input basis should I choose?
Choose specific volume when steam tables give m³/kg. Choose density when you already know kg/m³. Choose mass and vessel volume when you know the steam mass inside a known space.
3. Why is a compressibility factor included?
Real steam does not always follow an ideal gas model. The compressibility factor adjusts the estimate so the pressure better reflects nonideal vapor behavior.
4. Is this as accurate as steam tables?
No. This page gives a fast engineering estimate. Steam tables or IAPWS-based software should be used for final sizing, code compliance, safety calculations, and near-saturation conditions.
5. What is gauge pressure here?
Gauge pressure is absolute pressure minus local atmospheric pressure. If the result is negative, the absolute pressure is below the atmospheric value you entered.
6. Can I use this for boilers and steam lines?
Yes, for quick screening and education. It helps compare scenarios, estimate trend direction, and prepare initial calculations before checking final values with detailed property references.
7. Why does the graph change with temperature?
The plotted line keeps density and compressibility fixed. As temperature rises, the formula predicts higher absolute pressure, so the graph climbs almost linearly under the same assumptions.
8. What units are used inside the formula?
Temperature is converted to Kelvin. Pressure is calculated in kPa. Density uses kg/m³, and specific volume uses m³/kg so the gas constant stays dimensionally consistent.