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Pulse Tube Cryocooler - Part 2 (-75C)

Part 1:    • Pulse Tube Cryocooler - Part 1   This is the second part of my video series on attempting to build a Pulse Tube cryocooler. I managed to make significant progress by removing the linear motor and using a conventional rotary motor with a large gear reduction ratio and a flywheel to produce the larger forces needed for higher compression ratios. For pistons, I used pneumatic actuators. I evaluated a 25mm bore and a 40mm bore piston, both with a 50mm stroke. Pneumatic actuators have more friction than conventional pistons due to their rubber lip seals, but theoretically have zero blowby, so they hold pressure, which makes them more effective for low frequency applications. Here are some specifications for the cooler: Pipe diameter: 18mm Regenerator Length: 30mm Regenerator Material: Fine steel wool Pulse Tube Length: 100mm Flow resistance source: 1/8 NPT needle valve Inertance Tube Length: 10' (~3m) Inertance Tube Diameter: 4.4mm Buffer Tank Volume: 2L Piston Swept volume (25mm): 23CC Piston Swept volume (40mm): 57CC Compression Ratio (25mm): 1.4 Compression Ratio (40mm): 2.0 Maximum Frequency: 15 Hz Motor KV: 750 Motor Voltage: 16V Motor reduction ratio: 5:1 Flywheel moment of Inertia: 0.012 kgm^2 Maximum recorded temperature drop below ambient: -91C Lowest recorded temperature: -75C I think with some more optimization, this system can probably reach -100C, although without helium or hydrogen as a working fluid, I think it's unlikely that I'll reach cold enough temperatures to liquefy oxygen/nitrogen. In part 3 of this video, I'll do more investigation into hot-end heat exchanger design, regenerator design, and the effect of increasing the power density of the system by pressurizing it. I'll also be comparing the pulse tube performance to a similar spec alpha stirling cooler. Links for parts: Motor: https://www.amazon.com/dp/B084QCLTM1?... 25: and 40mm pistons: https://www.amazon.com/gp/product/B08... https://www.amazon.com/dp/B08YYQZ5CQ?... Music Used: Kevin MacLeod - Lobby Time Kevin MacLeod - Groove Groove