A process simulator that runs in your browser: steady-state, pressure-driven and dynamic flowsheets, rigorous thermodynamics, and an AI copilot that builds and explains them. There is nothing to install.

Does the AI calculate the results?

No. The copilot proposes a flowsheet or a change and explains it; the deterministic solver computes every temperature, duty and composition you see. A flowsheet from the copilot that does not validate is not applied.

Will it feel familiar if I have used Aspen Plus or HYSYS?

That is the intent. The workbench has a ribbon, an All Items tree, a form for each block and the three run modes — steady state, pressure driven and dynamics — so the habits carry over.

Can it open my Aspen or HYSYS cases?

Aspen Plus .bkp and .apw, HYSYS .hsc and DWSIM files import with deterministic parsing and a report of what was recovered. A HYSYS .hsc import is partial — unit names and types, not connectivity — and the report says so.

Which thermodynamic models are included?

Peng-Robinson and SRK (including Gᴱ mixing rules), NRTL, UNIQUAC, UNIFAC, PC-SAFT, CPA, GERG-2008, electrolyte NRTL, Pitzer and the IAPWS steam tables — more than 30 property packages in all.

Yes. The Python SDK (pip install flowsim-sdk) creates, runs and reads simulations, and its results are the same objects the canvas shows.

How much does it cost?

It is free to start, with no credit card. Paid plans add higher limits and team features; the pricing page has the details.

A process simulator that runs in your browser: steady-state, pressure-driven and dynamic flowsheets, rigorous thermodynamics, and an AI copilot that builds and explains them. There is nothing to install.

Does the AI calculate the results?

No. The copilot proposes a flowsheet or a change and explains it; the deterministic solver computes every temperature, duty and composition you see. A flowsheet from the copilot that does not validate is not applied.

Will it feel familiar if I have used Aspen Plus or HYSYS?

That is the intent. The workbench has a ribbon, an All Items tree, a form for each block and the three run modes — steady state, pressure driven and dynamics — so the habits carry over.

Can it open my Aspen or HYSYS cases?

Aspen Plus .bkp and .apw, HYSYS .hsc and DWSIM files import with deterministic parsing and a report of what was recovered. A HYSYS .hsc import is partial — unit names and types, not connectivity — and the report says so.

Which thermodynamic models are included?

Peng-Robinson and SRK (including Gᴱ mixing rules), NRTL, UNIQUAC, UNIFAC, PC-SAFT, CPA, GERG-2008, electrolyte NRTL, Pitzer and the IAPWS steam tables — more than 30 property packages in all.

Yes. The Python SDK (pip install flowsim-sdk) creates, runs and reads simulations, and its results are the same objects the canvas shows.

How much does it cost?

It is free to start, with no credit card. Paid plans add higher limits and team features; the pricing page has the details.

Thermodynamics — Equations of State

Cubic EoS (Peng-Robinson, SRK) for hydrocarbons/light gases and activity-coefficient models (NRTL, UNIQUAC, electrolyte-NRTL) for polar/non-ideal liquid mixtures — selected per `thermo_package` on the flowsheet schema.

thermodynamicseosnrtlpeng-robinson

Concept

Two families, picked per-flowsheet via thermo_package. Cubic EoS (Peng-Robinson, SRK) model the whole fluid — vapor and liquid — from one equation, good for hydrocarbons/light gases across pressure. Activity-coefficient models (NRTL, UNIQUAC) instead correct an ideal-vapor assumption with a liquid non-ideality factor γᵢ, tuned to real VLE data — the right tool for polar/hydrogen-bonding mixtures like ethanol-water.

The math

Show the governing equations

P = \frac{RT}{V-b} - \frac{a\,\alpha(T)}{V(V+b)+b(V-b)} \quad \text{(Peng-Robinson)}

\ln\gamma_i = \frac{\sum_j \tau_{ji}G_{ji}x_j}{\sum_k G_{ki}x_k} + \sum_j\frac{x_jG_{ij}}{\sum_k G_{kj}x_k}\left(\tau_{ij}-\frac{\sum_m x_m\tau_{mj}G_{mj}}{\sum_k G_{kj}x_k}\right)\ \text{(NRTL)}

K_i = \frac{\gamma_i P_i^{sat}}{P} \quad \text{(activity-coefficient K-value)}

Execution

Failure codes

SPEC_THERMODYNAMICALLY_IMPOSSIBLENRTL/UNIQUAC selected for a component pair with no pinned binary interaction parameters (only ethanol-water is pinned) — the server auto-coerces to Peng-Robinson and attaches a warning rather than crashing.

FLASH_NO_SOLUTIONRachford-Rice found no physically valid vapor fraction in [0,1] at the given T/P/composition.

The ethanol water distillation flowsheet in the MaximaLabs workbench

The example as it opens in the workbench. Click to enlarge.

Launch in MaximaLabs Workspace

Try it live

NRTL VLE curve

Live T-xy diagram — ethanol/water, NRTL, 1 atm

Computed on load by the same NRTL gamma-phi flash the solver runs — including the minimum-boiling ethanol-water azeotrope at ~x_ethanol ≈ 0.89.