Popcorn Machine

My goal for this project was to end up swimming in a pool of popcorn. I didn't quite make it, but I'm not giving up on the task. To help me out, leave a message down below with your ideas.

Popcorn Science

To figure out what temperature popcorn would pop at, I slowly raised the temperature inside a toaster oven. The water inside of the kernels started to turn from a liquid to a vapor. The vapor takes up much more room than the liquid (much less dense), so the pressure inside the kernel goes up until the shell, called the hull, cannot take the stress any longer. The hull then rips and the popcorn expands until the compressed vapor inside and spread throughout the popcorn kernel expands enough to reach approximately atmospheric pressure. And Kablamo, popped popcorn!

Once I figured out the popping temperature in my extremely precise experimental conditions, ~340 F for my popcorn I can now find the pressure that the popcorn was containing. I'm assuming that the water in the kernel was in saturation, which means partially liquid and partially vapor (a point where the pressure changes dramatically with little increase in temperature). What is cool is that there is a one to one mapping of temperature to pressure when in saturation, so 340F corresponds to exactly one pressure. I got my data from a book, but you can get the same data from this website: NIST Chemistry Webbook: Thermophysical Properties of Fluid Systems. Be sure to pick "Saturation properties � temperature increments". Here is a curve for water with PSIA vs Temp.

Design

The idea that shaped my design was that I could separate the popped kernels from the unpopped through air drag. The popped kernels will lift at a velocity lower than what will lift the unpopped kernels. This makes sense when you look at the Drag Equation - For the same air velocity and popcorn mass, a larger area into the wind combined with a larger coefficient of drag due to the newfound roughness of the popped popcorn kernel surface can combine to make a dramatic increase in drag force.

Construction

The construction of this design seemed simple, but there were several things that got me hung up. I got the steel ducting from Home Depot. The smaller diameter ducting was 8 inch diameter, the larger was 10 inch. My home Depot didn't sell any 10 inch, so I used two 5 inch ducts connected together to form a nice 10 inch duct. When you but the ducts they come rolled but with the seam down the length of the duct unsealed. Getting the duct sealed was a major pain - I can't believe that HVAC specialists have to go through all of that trouble when they put in A/C systems, so perhaps there's a trick that I'm missing. To make it easier I used sheet metal screws instead of the built-in seam sheet-metal "latch". Aside from that, putting things together was rather straightforward. In order to make one section of duct fit into another, it may be necessary to use crimpers to scrunch up the edge of the pipe to allow it to fit inside of the next section.

Popcorn Popping Technology

After making this machine I found this book: Snack Foods Processing (Purchase on Amazon). It has an extensive section on industrial popcorn popping, which would have been very helpful to see for ideas before designing my own!