I spent the last eight years as a process engineer. Most of that time went into two things: drawing flowcharts in Visio, and doing mass balances in Excel.
Draw the flowchart, then open Excel and type the same numbers again. Change a parameter, update both. After a while, the diagram and the spreadsheet start to disagree. I'd spend an hour tracking down whether the drawing was wrong or the calculation was.
It's a dumb workflow, but almost everyone does it.
Why the existing tools don't fix this
I tried a lot of options.
Aspen and HYSYS can calculate, but they're rigorous thermodynamic simulators. Expensive, slow to learn, and designed for detailed chemical process design. I just wanted a mass balance. I didn't need a full property database, and I definitely didn't want to spend weeks learning a new interface.
Visio and Lucidchart can draw, but they're drawing tools. What you get is a picture. It doesn't calculate, and it's not meant to.
And doing recycle loops by hand in Excel? If you've done it, you know. One loop means dozens of manual iterations. Two coupled loops means you're basically guessing.
I couldn't find a tool that treats the flowchart itself as the calculation model. So I wrote one.
The idea is simple
A flowchart is not just a picture.
Every node is a unit operation. Every stream is a variable. Every connection is a constraint. If the flowsheet already describes the process structure, why rebuild the same thing in another tool?
IAutoDrawSim does one thing: the flowsheet on the canvas is the calculation model.
You drag a reactor onto the canvas, connect an outlet stream, write a conversion formula. The solver assembles all the nodes and streams into a system of equations and solves it. If there's a recycle loop, the steady-state solver converges it automatically. No manual trial-and-error.
Change a parameter, and the whole diagram recalculates. The drawing and the numbers stay in sync.
What it is not
I don't want to oversell it.
It is not an Aspen replacement. Aspen's property database and rigorous thermodynamic models are its moat. IAutoDrawSim doesn't try to compete there. If you need rigorous distillation calculations or vapor-liquid equilibrium data, Aspen is still the right tool.
It is not another Visio. Visio is far more mature for pure diagramming. If you only need to draw, there's no reason to switch.
It fits a narrower use case: you need to calculate, but not with rigorous thermodynamics. You need to draw, but you don't want to open Excel afterward.
Mass balances, capacity planning, inventory flow, approval workflows — these problems share one thing: their core is flow distribution and balance in a network, not thermodynamic properties of components.
A real example
Not long ago I had to do a material balance for a process with two recycle loops.
The old way: assume a recycle composition in Excel, calculate forward, compare with the assumption, adjust, repeat. Sometimes dozens of iterations. With two coupled loops, you also have to think about convergence order.
In IAutoDrawSim, I drew the flowsheet, filled in reaction conversions and separation efficiencies on the nodes, and hit run. The solver handled both loops simultaneously. It converged in seconds. The balance closed to 0.001%. I exported the stream table and sent it to the client.
The time saved isn't "a little." It's a day versus ten minutes.
About generality
When I designed the tool, I made one deliberate choice: don't limit node types to chemical equipment.
In chemicals, you have reactors, heat exchangers, separators. In manufacturing, you have workstations, buffers, rework loops. In logistics, you have warehouses, routes, sorting centers. In approval workflows, you have submissions, reviews, sign-offs, archives.
These look different on the surface, but mathematically they're the same thing: a directed network where material, information, or resources flow, transform, and accumulate between nodes.
So nodes are customizable. Formulas are customizable. Connection rules are customizable. Whatever domain you draw, it becomes a model in that domain.
Where it is now
IAutoDrawSim has a free trial. It supports up to 80 unit elements and 50 simulation nodes. The commercial version is a one-time perpetual license — no annual subscription, runs fully offline, data never leaves your machine.
There are builds for Windows, macOS, and Linux.
If you want to see whether it fits your workflow, you can download it from the website（[https://www.iautodraw.com/#/en]
）. If it doesn't fit, that's fine too. It's not a universal tool. It just fills a gap between "drawing" and "calculating" that I kept running into.
Top comments (1)
Perform custom calculations directly
on the flowchart.
try it: iautodraw.com/#/en