Example data table
| Component | x | γ | A | B | C |
|---|---|---|---|---|---|
| Component A | 0.50 | 1.00 | 8.0000 | 1500.00 | 200.00 |
| Component B | 0.50 | 1.00 | 7.9500 | 1400.00 | 220.00 |
Formula used
For a liquid mixture at a specified temperature, the bubble point pressure can be estimated with:
- Pbubble = Σ (xi · γi · Pisat)
- yi = (xi · γi · Pisat) / Pbubble
If you provide Antoine constants, saturation pressure is computed by:
- log10(PsatmmHg) = A − B/(C + T°C)
This calculator treats γ as a direct activity correction. For rigorous VLE, use a validated activity model.
How to use this calculator
- Select the mode: compute bubble pressure from temperature, or solve temperature from pressure.
- Choose a saturation method: Antoine constants or direct saturation pressures.
- Enter mixture composition x for each included component.
- Set γ values to reflect non-ideality, or leave γ = 1.
- Press Calculate to show results above the form.
- Use Download CSV or Download PDF to save the summary.
Purpose
In vapor–liquid equilibrium work, the bubble point is where a liquid mixture first produces an infinitesimal vapor at a fixed temperature. Engineers use this point to set operating pressure targets, size condensers, and validate phase data before simulation. The calculator combines composition, saturation pressures, and optional activity coefficients to estimate the total bubble point pressure for non‑ideal mixtures.
Inputs
Accurate inputs drive reliable results. Enter liquid mole fractions x for each component and optionally normalize them to sum to one. If the mixture is close to ideal, set γ to 1. For non‑ideality, γ values from activity models or fitted data adjust each component’s effective volatility. Saturation pressure can be supplied directly or computed from Antoine constants matched to °C. Always confirm the constants’ valid temperature range.
Computation
The core computation applies a modified Raoult relation: P = Σ(x·γ·Psat). The tool also reports each component contribution x·γ·Psat and estimates vapor composition y = (x·γ·Psat)/P, then normalizes y for numerical stability. When solving for bubble temperature at a specified pressure, the calculator evaluates the pressure balance and uses bracketing plus bisection iterations until the residual is small, typically within 1e‑8 kPa. Target pressures like 101.325 kPa help reproduce atmospheric boiling points.
Interpretation
Interpret outputs in engineering context. A higher bubble pressure at the same temperature indicates more volatile overall behavior. If one term dominates, the mixture’s first vapor is enriched in that component, shown by larger y. Sensitivity is often strongest in high‑Psat components; a 5% change in γ or Psat can shift P noticeably. Compare calculated values against plant measurements or published VLE data; deviations often signal mismatched units, incorrect Antoine constants, or γ values inconsistent with composition.
Practice
Use the example table to sanity‑check workflows before entering real systems. Start with two components at x = 0.50 each and γ = 1, then adjust γ to see non‑ideality effects. For design screening, compute bubble pressure across a temperature sweep and map the curve for control limits. For safety reviews, convert results to bar or psi and export CSV/PDF for documentation and peer checks. Record assumptions, including basis temperature, component identity, and data sources, so audits remain fully traceable.
FAQs
It marks the pressure where the first bubble of vapor forms at a fixed temperature, supporting distillation pressure selection, flash calculations, and validation of volatility data.
Use γ=1 for ideal or near‑ideal systems. If your mixture shows non‑ideality, enter γ from an activity model (NRTL, Wilson, UNIQUAC) or fitted measurements to improve accuracy.
Enter A, B, C for log10(Psat_mmHg)=A−B/(C+T°C). Constants must match °C and mmHg. If your source uses other bases, convert or use direct Psat instead.
Most issues come from unit mismatch, invalid Antoine ranges, or mole fractions not representing the liquid phase. Check temperature units, ensure Psat is positive, and confirm Σx≈1 (or enable normalization).
Yes. Choose bubble point temperature mode, enter target pressure, and provide Antoine constants for all included components. The solver brackets a solution and uses bisection to reach a tight pressure balance.
Export CSV or PDF to capture inputs and component contributions. Record data sources for γ and Antoine constants, the basis temperature or pressure, and any normalization choice so reviewers can reproduce the calculation.