Building a snow-making machine
At an engineering consultancy firm, I was tasked with the full design process of a low-cost, efficient, user-friendly machine to produce natural-imitating snow. After multiple prototypes and a lot of cut-up styrofoam, this is what I built.
I used my knowledge of thermodynamics to make water mist freeze into snowflakes during a short drop of about 2 meters. The basic idea was to cool down a styrofoam box to about 210 K, and then shoot mist from 10 spray nozzles at the top of the box, perpendicular to the ground. During the droplets' parabolic drop, they have time to freeze into snowflakes before landing in the cooler.
I optimized cooling system by spraying the liquid nitrogen out of a copper wire that reached both the lower and upper halves of the box. Also, any snow accumulation on the wire was easy to knock off into the cooler.
To save on liquid nitrogen and allow for multiple batches to run smoothly, I cut the box's front panel in two, such that I would only need to open a smaller door to empty the cooler. The box stayed much colder that way, and was also safer to operate.
After building and testing it, I developed a user manual, a specs sheet with snow-rate specifications for different settings (mist temperature, mist power, box temperature), and safety guidelines.