The world contains some pretty nasty stuff. Venomous spiders. The black plague. The neoliberal ideology. And then there is nastier stuff. Like every animal roaming the continent of Australia. Quantum mechanics. The colonial past of France. But the worst of them all is fluid dynamics.
It comes to no surprise that this word appears often on suicide notes of engineers. Because we’ll eventually understand how gravity relates to the other fundamental forces and other stupid little puzzles the universe keeps offering us. But how water behaves in a pressurized system? Forget it! You can either accept it or go mad. You’ll neither be the first nor the last one, that’s for sure.
Once we’ve accepted our fate, we can observe the horrors of non-linear math under real-life conditions. After thinking too much about it I started confusing left with right, good with bad, my brain with the coffee puck; you get the idea. Nothing is as it seems. Nothing is real. Time is an illusion.
What happened?
Glad you’re asking. My wonderful friend (the one who caused all this madness) came all the way from Vienna to France to visit me. While he’s trying to untie his shoes, I already drag him in my kitchen. I want to show off with my coffee machine. Since he’s also on the crazier side of things we start pulling shots immediately. They are good. But not perfect.
We’re using a lever machine profile for our tests. After some tinkering, my friend notices that the flow restriction on the 9 bar phase is getting in our way. We decide to lift it. So now the machine is free to pump as much water as it wants until it hits 9 bar. Then, it lowers the pressure second by second until the shot is done. The flow is unrestricted.
Little guessing game: Lifting a flow restriction causes:
a. more flow
b. less flow
Wrong, it’s b. The flow spikes up, sure. But after 2s it goes FURTHER DOWN and stays there. And I’m talking about 2ml/s vs 3ml/s before. That’s a lot. Same pressure as before. WTF.
With flow restriction
Without flow restriction
The coffee is nicer though. Rounder, if that makes sense. If it doesn’t, worry not. Nothing makes sense after all.