Pulse Tube Cryocooler - Part 2 (-75C)

I've read through the comments and thought I'd address a few of them: -The 40mm piston is probably not optimally matched to the pulse tube geometry, since i optimized it for higher frequencies on the 25mm piston -For part 3 or 4 i'll probably try using Hydrogen as a working gas. It has a lower specific heat ratio than helium, but the highest thermal conductivity of any gas, so I should see an increase in performance as long as all the components are sealed well enough to avoid leakage -For part 3 I'll be looking at heat exchangers with multiple heat pipes and water cooling, as well as single tubes packed with copper wool. -I do intend to evaluate a segmented regenerator with polymer "heat breaks" to slow down axial conduction losses by breaking the continuity of the metal mesh -For higher pressures and lower temperatures, I'll be replacing the PVC with stainless steel to avoid explosion hazards. -The ESC has flyback diodes across the H-bridge MOSFETs, so any back-current from the flywheel after motor shutoff should be dissipated through those. -Multiple stages might be neccesary to reach LN2 temperatures with a DIY setup. Pulse tubes can be staged by connecting a much smaller pulse tube to the output of the compressor's aftercooler and thermally anchoring the second heat exchanger to the cold end of the first stage. Pulse tubes used for liquefying helium/hydrogen typically have 3 or 4 of these stages and can reach single-digit kelvin temperatures

This is by far, the most interesting video project recommended by YouTube in a long time. Great explanation and accurate presentation. Amazing work, keep up the good work. Hope to see -200C in a while :)

This is fascinating. The first DIY cryocooler that works sufficiently This is the first DIY project reaching really low temperatures without complicated multistage refrigerant stages.

That's some seriously impressive data analysis and scientific method for a simple prototype! Great work - subscribed!

When cleaning wire wool up wrap the magnet in a rag so you can separate the captured steel wool from the magnet to dispose. Great to see an explanation of why gas-gas heat exchangers are hard to design!

The clarity & detail in your explanations is absolutely amazing, the collected data and visualizations really help to make this more intuitive. You're a great teacher!

This is the best thing that YouTube has sent my way in a LONG time. Thank you so much for the amazingly well made video, and I can't wait for the next part!

I love how far diy projects have come since the early days of YouTube a decade ago which were 90% LED projects keep up the good work

this is incredible you are the only youtuber that shows how to make a cryocooler keep this up

The use of the scaling exponents to predict the behaviour, along with the brute force empirical parameter sweep was beautiful ❤️ I wanted to click like so many times in this video but sadly I am limited to just one. This is so beautiful.

I just want to say that in terms of video produciton, you've done an excellent job in the treatment of the calculations and design considerations. You've somehow kept your explanations concise without glossing over anything big, and made it accessible without dumbing it down. Your channel is the best one Youtube has recommended me in a long time.

You could try to improve regenerator performance by using several "sub-regenerators" to prevent heat conduction axially. In practice, instead of making one blob of steel wool, make several and stack them inside the tube.

Love this series, seriously. I feel like I understand now how “real” engineering is done. Keep the videos coming!

I more or less stumbled by accident over your videos, but the subject is very fascinating and they are one of the best youtube videos I ever saw up to now that combine practical use with scientific background. Wish my scool lessons in physics or thermodynamic would have been so interesting! As already said by others, you would be a very good teacher! Many greetings from Germany and all the best for upcoming 2023! 😃

Awesome video. I have been intrigued by pulse tube coolers since I heard about it on JWST, so to see a functional DIY build is astounding. Great work, looking forward to part 3!

This is super cool, I went down a rabbit hole of research into cryocoolers about 6 months ago but never found anyone else doing it DIY. I'm glad you took it to the next step and built it!

Fantastic progress!!! I admire your bravery to take on such a challenging problem. Can't wait for part 3. Thank you so much! 😘

So, I don't comment often, but you are fantastic. This is such a great example of scientific and data driven innovation. Finding ways to isolate, measure and iterate individual components is the name of the game, and you have done it wonderfully.

What a magnificent video. I love how well you are keeping track of all the variables and then plotting them on a graph, it's a very nice tool to have when trying to optimize such a system. Well done.

The explanations, calculations, and even concept presentation in this video is top notch. I’m learning and enjoying it