In this video i'll show how to put together a single-stage vapor compression refrigeration system and explain the theory behind it. This machine uses propane (R290) as a refrigerant, because it has properties very similar to standard Hydrofluorocarbon (HFC) refrigerants, but is extremely cheap and readily available, and has almost no negative environmental effects. The obvious disadvantage is its flammability. If you're careful, though, propane or butane are perfect substances for a DIY vapor compression system.

This is still part of my long term project to build a DIY cryocooler to make my own liquid nitrogen, but I've pivoted away from gas-phase systems like stirling/GM and decided to focus more on phase change systems due to the greater availability and low cost of parts. In upcoming videos, i'll be staging multiple vapor compression loops together to get temperatures below -100C. After that, i'll use a joule-thompson cycle to make the final push down to liquid nitrogen temperatures, but will do so with a mixture of hydrocarbons rather than nitrogen.

Here's some performance specs of the device in this video:

Condenser Pressure: 10-15 bar
Condenser Temperature: 27-44 C
Evaporator Pressure: 1.2 bar
Evaporator Temperature: -37 C
Capillary tube ID: 1mm
Capillary tube length: 2m
Compressor nominal rating: 5,000 BTU
Compressor locked rotor amps: 27A
Compressor operating limit (estimated): 5.4A
Input power: 667W (529W from compressor, 138W from fans)
Refrigerant charge: ~50 grams of propane

Maximum recorded cooling power: 116W (COP 0.173)
*Note that this power was recorded by testing the temperature drop of water reservoir at room temperature with lots of heat leaks, which was a far from optimal condition.

Also, recording cooling power by multiplying the water flowrate of 13.5 grams/sec by water's heat capacity times the temperature differential across the coil of 3.3C yielded a higher cooling power of 186W.

In upcoming videos, this system will be used to cool the condensor of a second refrigeration circuit, which will then evaporate to a far colder temperature close to -100C. This requires ethylene as a refrigerant (R1150). It's pretty hard to find and expensive to buy commercially, so in the next video, i'll be showing how to make it.

Other useful tidbits:

Propane bottle NPT thread adapter:
https://www.amazon.com/Hooshing-Propa...

Condenser fan:
https://www.amazon.com/BLACKHORSE-RAC...

-Window AC unit that was stripped for condenser coil was rated at 5,000 BTU. The manufacturer/model number you use is not important as long as its sized right.


Music Used:

Kevin MacLeod - Lobby Time