LPG Vaporization and Entropy Calculator

How Do We Calculate the Vaporization Rate of Your LPG Mixture?

Our calculator uses advanced thermodynamic principles to predict whether your propane and butane mixture will undergo flash vaporization when passing through a restriction. Here's how to explain the process in simple language:

1. We Determine the Pure Vapor Pressures

​

For each component (propane and butane), we calculate the pressure exerted by their vapors at the temperature you specify. We use proven scientific equations (Antoine's Equation) that mathematically relate temperature to vapor pressure.

2. We calculate the vapor pressure of your mixture

​

Depending on the model you choose:

Ideal Model (Raoult): We simply average the pressures based on the percentage of each gas

Real Model (Margules): We adjust the calculation considering how different molecules interact with each other

3. We compare it to your downstream pressure

​

The moment of truth: if the pressure after the restriction (P₂) is lower than the vapor pressure we calculated, vaporization will occur! This is because the liquid cannot remain stable at that pressure.

4. We show you what percentage vaporizes

​

We don't just say "yes" or "no," but we calculate exactly what part of your mixture will change to vapor and what part will remain liquid, representing this in an easy-to-understand graph.

5. We calculate the energy involved

We determine the entropy of vaporization, which tells you how much energy is required for this phase change—valuable information for designing efficient systems.

 

Model Limitations

 

1. Range of Validity
-Temperature: -50°C to 100°C (outside this range, results may lose accuracy).
-Pressure: Up to 20 bar (not applicable for cryogenic or ultra-high-pressure conditions).
-Composition: Only valid for binary mixtures of propane/butane. Does not consider:

• Impurities (methane, ethane, pentane).

• Additives (odorizers, corrosion inhibitors).

2. Calculation Assumptions

• Raoult's Law: Assumes ideal behavior (no molecular interactions).

• Margules Model: Considers interactions, but with fixed coefficients (A₁₂ = 0.143, A₂₁ = 0.128).

• Antoine Equation: Reduced accuracy near the critical point (T > Tc).

3. Factors Not Considered
-Kinetic effects: Does not evaluate expansion rate or residence time.
-Heat losses: Assumes an adiabatic process (no heat exchange with the environment).
-Restriction geometry: Does not take into account the type of plate/valve (orifice, globe, etc.).

​

Uncertainty in Results

 

Vapor pressure (Pv) ±2-5% Antoine equation (experimental setup)

Composition ±1% Rounding in % propane/butane

Temperature ±0.5°C Thermocouple accuracy (if actual measurement is used)

Margules model ±3-8% Approximate interaction coefficients

*Reference values for standard conditions (25°C, 70/30 mixture).

​

Recommendations for Professional Use

✔ Validate with specialized software for critical designs. ✔ Consider a safety factor of 10-15% in industrial applications.
✔ Do not use for:

Pressure vessel design (ASME/API standards require more rigorous methods).

Blends with >5% other hydrocarbons.

Interpretation:

• If P₂ is within the uncertainty range of Pv, further analysis is recommended.

​

 

Final Note
This tool is useful for preliminary estimates, but technical decisions should be based on international standards (API, ISO) and experimental measurements.