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In this video I'll examine the "Autocascade" refrigeration cycle. The Autocascade cycle is a vapor-compression cycle that achieves multiple stages of refrigeration with a single compression. This is done by compressing a high-boiling and low-boiling refrigerant together. In this video, the high-boiling refrigerant is Propane or R290 (-42C at 1 atm) and the low-boiling refrigerant is Ethylene or R1150 (-104C at 1 atm).
When the refrigerants are compressed and cooled back to ambient temperature, the high-boiling refrigerant will be liquefied, while the low-boiling refrigerant will still be gaseous. A phase separator uses gravity to separate the liquid from the gas. The liquefied refrigerant falls into a sump at the bottom of the phase separator, which then flows through the expansion valve or capillary tube into an evaporator, then returns to the compressor inlet.
When the high-pressure, low-boiling gaseous refrigerant leaves the phase separator, it travels across the cold evaporator, causing it to condense into liquid. The low-boiling liquid refrigerant then travels to its own expansion valve or capillary tube where its pressure drops, causing it to boil and deliver the system's cooling to the load in a second evaporator.
The catch is that the compressor has to be able to deliver a very high pressure in order to both condense the high-boiling refrigerant AND pressurize the low-boiling refrigerant enough that it will condense at the low-boiling refrigerant's evaporation temperature. This results in significant compressor heating, and in the case of my system, it had to be run at less than 100% duty cycle to avoid overheating.
Here's a few performance figures from the device in this video:
Average Power Consumption: 750W
High Side pressure: 450 psi (32 BarA)
Low Side pressure: 50 psi (4.5 BarA)
Ultimate Temperature: -81C
Refrigerant: Approximately 110g Propane and 70g Ethylene
The main use of this system is to serve as a cold trap in applications that normally require expendable dry ice, such as freeze-drying or condensing certain gases at atmospheric pressure. The example I used here was condensing Ammonia gas to make Anhydrous Ammonia, which is extremely useful for making a variety of compounds.
Control Board Schematic:
https://drive.google.com/file/d/1NGpC69HgCdLxXWXaIiD8q-F3X98ENsUe/view?usp=sharing
Music Used:
Kevin MacLeod - George Street Shuffle