The picture is a change of phase.

If you own a fridge, an air conditioner, or a heat pump, you already own a working copy of the picture above. You've just never seen it drawn as a career before.

The diagram is a change of phase, the same physics that keeps your food cold and your home comfortable. For a few years, designing those systems was my job, and I drew my career the same way on purpose. This is the explanation that wouldn't fit on the homepage.

What the picture is doing

Every fridge and air conditioner runs the same quiet trick, over and over. It uses a single substance called a refrigerant. The refrigerant travels around a closed loop and never leaves. Nothing is added. Nothing is thrown away. The only thing that changes is its state. That change is the whole point. The picture zooms in on the one stretch of the loop where it happens.

Follow it from left to right.

On the left, the refrigerant is a liquid under high pressure. Picture it packed tight. It holds a lot of energy, and it has nowhere to go. Engineers call this stretch the liquid line. In the drawing, it's the dense copper cluster on the left. That's the foundation, where the molecules sit close together.

Then comes the narrow part. Between the two sides sits a long, thin restriction. In a lot of fridges it's a capillary tube, an inner bore barely wider than a pencil lead that the refrigerant has to work through for a stretch. It goes by a few names. A metering device, an expansion valve, a capillary. The job is always the same. You force all of that high-pressure liquid through one long, narrow passage. In the picture, it's the thin neck in the middle, where everything has to funnel through at once.

On the far side, something quietly dramatic happens. The moment the refrigerant clears the restriction, the pressure collapses. Part of it flashes from liquid into a cold, spreading vapor. It happens in an instant. This is the change of phase. It's also the moment the system finally does its job. That cold vapor is what pulls the heat out of your room. In the drawing, it's the wide blue field on the right. The molecules are suddenly free to spread out and travel.

The restriction is the design. Without that narrow passage, the pressure never drops. The liquid never changes phase. Nothing ever gets cold. The squeeze is the mechanism. It's the reason the whole cycle does anything useful at all.

Why I drew my career this way

I spent twelve years as a mechanical engineer before I moved into data science, and for part of that time I designed heating and cooling equipment. So I've stood in front of the real hardware this diagram describes. I've held the very kind of capillary tube I'm now using as a metaphor. The analogy is my own resume, read through a thermodynamics textbook.

Those twelve years were my liquid line. I had a feel for how real systems fail, how they get built, what they cost, and where they break under load. Somewhere in there came the realization that I could do more with all of it than my job had a way to use. I'd make the case for training models on years of our test data and sketch what they could do, then hit the same wall every time: I could see the work, but I didn't yet have the tools to build it myself. That is what a high-pressure liquid is. A lot of stored energy and no outlet wide enough for it.

So I made my own outlet. I started by studying on the side. Then came two employer-sponsored AI and machine-learning programs at UT Austin, while I kept working. Then the bigger step: a full-time, in-person masters. I could have done it online, around my job. I chose not to, because I wanted no back door and no turning back. Each step was narrower than the last, like the long capillary run a fridge forces its refrigerant through. That narrow passage is the mechanism. Forcing everything I knew through it is what let it change state.

And then came the expansion. On the other side of that opening, the same material changed phase. The engineering became the working fluid. Knowing how a compressor fails turned into features. A feel for tradeoffs turned into models. Twelve years of standing next to physical systems turned into the judgment behind them. And the work keeps spreading into industries I've never set foot in.

That's the one thing I most want you to take from the picture. It's the same refrigerant from start to finish. I didn't swap myself out for someone who happened to know Python. The missing tools felt like a wall. Going and getting them turned out to be the capillary tube, the one part that let everything I already carried change state and go do a different kind of work.

So the diagram is about one substance that finally found the pressure drop it needed.

Read it twice

This whole site is built on a single idea. You can read the same thing twice. Once as physics, and once as data. The skills picture is the cleanest example I have. Read it one way and it's a change of phase. Read it the other way and it's my own career. Twelve years in engineering, the crossing into data, and an expansion that hasn't stopped. They happen to be the same drawing.