Hyperspace Pirate - 2023-02-17
This is the 4th part in my video series on designing/building/testing a pulse-tube cryocooler in an attempt to create low enough temperatures to liquify nitrogen (-196C or 77K). In this video, i'll be investigating an entirely different type of pulse tube that uses two valves - one connected to a compressor and another vented to the atmosphere - to create the pressure oscillations in the pulse tube. This is known as a "Gifford-McMahon" (GM)cycle, and is more commonly used in a refrigeration cycle with a moving displacer, but can also be found in use with pulse tubes. The GM cycle is less efficient than using a piston (stirling-type) to generate pressure oscillations, but has the advantage that it's cheaper and easier to build, since it can be coupled with a variety of different compressors and matching acoustic impedance is not neccesary. GM-type cycles typically operate at a COP of under 5% of Carnot, whereas advanced stirling-type coolers can approach 30% of Carnot. Despite this, GM cycles are the primary type used in terrestrial applications, such as cryocoolers in labs and production facilities where modest quantities (under 10L per day) of LN2 are required. Despite the increased energy consumption, this configuration is typically cheaper to install/maintain than stirling cycle coolers, which are usually reserved for aerospace applications, like being mounted onboard sattelites or missiles to cool optics. For the valve assembly, i used a pair of solenoid valves activated by MOSFETs which could have their timing controlled by an arduino with a front panel display, allowing me to know the exact timing I dialed in, which was very convenient for repeatability. Real GM cycle coolers use a rotary valve connected to a motor inside the pressurized assembly, which is more reliable than solenoid valves. The entire assembly runs at around 0.5 hz. Typical commercial units range between 1-2 hz, in contrast to stirling cycle units, which can operate anywhere from 20 hz to 100 hz. However, pressure ratios are typically much higher on a GM unit, ranging from 2-3 with a baseline pressure typically from 10-30 atmospheres, whereas pressure ratios on stirling units are usually in the neighborhood of 1.1-1.3. Most GM units will have a high pressure side around 200-400 psi and a low pressure side from 50-200 psi, depending on the cold head and compressor being used. The lowest temperature i achieved running on compressed air was -83C, but I didn't consider this a valid result, because I wasn't able to repeat it. The lowest repeatable temperatures were in the low 70's, basically matching the performance of my previous stirling-type pulse tube. Considering that the power input required was close to 1 kW, compared to the previous design's power of ~120W max., it's clear that this setup is far less efficient. One of the major sources of inefficiency is the fact that my low-pressure side is simply connecting to the atmosphere, rather than being connected back to the compressor in a closed loop. This is because my current compressor isn't hermetically sealed, and not meant to operate with input pressures over 1 atm. With my high side pressure at 100 psi, theoretically, the most efficient low side pressure would be somewhere between 40-60 psi. In the next part of this series, I'll be generating hydrogen and using it as a working fluid instead of air, with a closed-loop system running off a hermetically sealed fridge compressor. This will dramatically increase internal heat transfer, making the whole system more powerful and efficient, and should bring me much closer to my goal of -196C. Part I: https://www.youtube.com/watch?v=GjRoThMyNGA Part II: https://www.youtube.com/watch?v=WOmjJFk8rl0 Part III: https://www.youtube.com/watch?v=cy8aGMH8Tz4 Music Used: Kevin MacLeod - Lobby Time Kevin MacLeod - George Street Shuffle
This is awesome! There are only two channels that make me enjoy looking at graphs and diagrams - this one and Huygens Optics :-)
consider checking out suckerpinch! pretty funny visualizations, even if i don’t remember any traditional graphs rn
agree
Agree! 😉
Agree
yeah, graphs are awesome :)
Instead of using acid for H2 production, you may want to try Lye (NaOH) and Al foil; it generates copious amounts of H2 and there is no corrosive acid mist or vapors generated, and the sodium aluminate byproduct is much less corrosive than the lewis acid aluminium salts produced as byproducts from most readily available acids. If you want to dry the hydrogen produced then you can pass it through a drying tube packed with just more fresh NaOH, which you can then feed forward as more reactant for future cycles. If you use HCl for example, you're stuck with having to also neutralize the acid vapors and mists, which requires additional consummation of reagents without the potential for feeding forward the reagents as reactants.
i second this
How hard can electrolysis be? I'm sure he has water in a tap and electricity in an outlet, just put them together and voila, Hydrogen, right?
@@MrRolnicek Separating the oxygen from the hydrogen is the issue
@@nedshead5906 But if you just separate the electrodes and make sure the liquid connects them BELOW the height of the electrodes then you get O2 bubbles on one side and H2 bubbles on the other, right?
Yep.. not hard to separate the two right from the initial process,.. i think though there are some other hydrocarbons that are produced making the gasses not totally pure.. really depending on purity of everything in the electrolyte..
When Applied Science, AND Nighthawk in light are following along, you know this is good stuff.
Excellent.
Calm down, mr. Burns.
Wood gas powered air compressor next? :D
Yup nice video
I wonder what comes first:
100k subscribers
-100K temperature
🥶🥳
100k subs, -100K isn't possible. Even with -100c i think the subs will come first
I presume they meant 100k subs or 100K temp (no minus)
@@V8Power5300 :ø)
Isn't -100K 'just' a drop in temperature, from whatever ambient starting point?
But absolutely - yes, -100K is like going faster than light. It is currently not possible - but who knows if it will be (or was possible) ;ø)
Anyways, so much respect for doing such amazing projects - you really deserve it, and much more!
@@V8Power5300 Wow.. I just got smarter..
Negative temperatures can only exist in a system where there are a limited number of energy states (see below). As the temperature is increased on such a system, particles move into higher and higher energy states, and as the temperature increases, the number of particles in the lower energy states and in the higher energy states approaches equality. (This is a consequence of the definition of temperature in statistical mechanics for systems with limited states.) By injecting energy into these systems in the right fashion, it is possible to create a system in which there are more particles in the higher energy states than in the lower ones. The system can then be characterised as having a negative temperature.
A substance with a negative temperature is not colder than absolute zero, but rather it is hotter than infinite temperature. As Kittel and Kroemer (p. 462) put it,
The temperature scale from cold to hot runs:
:+0 K (−273.15 °C), …, +100 K (−173.15 °C), …, +300 K (+26.85 °C), …, +1000 K (+726.85 °C), …, +∞ K (+∞ °C), −∞ K (−∞ °C), …, −1000 K (−1273.15 °C), …, −300 K (−573.15 °C), …, −100 K (−373.15 °C), …, −0 K (−273.15 °C).
The corresponding inverse temperature scale, for the quantity β = 1/kT (where k is the Boltzmann constant), runs continuously from low energy to high as +∞, …, 0, …, −∞. Because it avoids the abrupt jump from +∞ to −∞, β is considered more natural than T. Although a system can have multiple negative temperature regions and thus have −∞ to +∞ discontinuities.
In many familiar physical systems, temperature is associated to the kinetic energy of atoms. Since there is no upper bound on the momentum of an atom, there is no upper bound to the number of energy states available when more energy is added, and therefore no way to get to a negative temperature. However, in statistical mechanics, temperature can correspond to other degrees of freedom than just kinetic energy (see below).
It is on the Wikipedia page on Negative temperature
274k subs and physics breaks!
hidden gem youtube channel.
this is inspiring stuff, "pulse tube cryo cooler in the basement" is now on my list of things I didn't know I needed
6% density is probably plenty. You should do it as a ratio of mass of the air you are regenerating vs mass of regenerator. Even at elevated pressure, you only have maybe 1 or 2 grams of air moving through that thing. I guess it depends on how many liters of air are passing through each cycle. 115 g of steel wool to 2 grams of air being regenerated... you might even go less to see if the reduced flow restriction is hurting more than a few extra grams is helping. Checking the pressure drop across regenerator vs mass through it per cycle could be enlightening.
This is brilliant, I was not expecting to see a 4 part series on this. I love the process you use to explain the design process, its a lot more transferable
-100C is impressive. Could you be running in to issues with CO2 freezing and clogging your heat exchanger? I can't imagine it takes much to reduce it's efficiency. Would be interesting to try this on nitrogen instead of raw air.
I have a quick video on a dental drill turboexpander which may be of interest. I managed 15C drop at 4 bar with no heat exchanger.
I'm curious to see your results if you go forward with that project. I tried to do a brayton cryo cycle with a 3d printed turbine, but got frustrated trying to make my the turbines efficient enough to produce a reasonable amount of cooling. I'd like to see what happens if you connect that thing to a regenerator (or recupterator, or whatever they call it in the case of continuous flow)
@@HyperspacePirate Yes turbine design seemed way beyond my level so I tried to find something already available in the right power range.
I've been having issues loading the turbine output as those small motors I've been using as a generator don't seem to last long at dental drill speeds (and produce more heat than electricity). I'll definitely try a counter-flow heat exchanger once I can run the expander for any significant length of time.
I'm currently experimenting with 2 of these turbines on the same shaft to form the usual compressor-expander set up but haven't had much luck yet, I'll do a video if I get anywhere with it.
@@matthewbeardmore For loading the turbine, how about a diametrically polarized cylindrical magnet running in a hole inside an aluminum or copper block? At those speeds, the eddy currents should be pretty significant, so might be able to provide a decent amount of load. K&J Magnetics and Applied Magnets both sell these, and K&J also has elongated ring magnets (cylinders with central holes) that might make mounting easier. Only trick would be to support and mount them precisely enough for them to spin that fast without the whole assembly flying apart.
Pure science, with all the numbers. Its a voyage of discovery. Taking energy out of a thing is so much harder than putting energy in, and that's what makes it so interesting. 15 and 6% mesh fill, thats supprising. Nice winding the aly tube , I would be scared of kinking. Exceptionally well presented.
pro tip for small diam tubing bending, tape 1 end shut fill with sand/sugar/salt/fine granular material cap the other end and bend carefully. the interior filling keeps the kinks from happening,
I’m impressed that you managed a 100C delta-T with just air and a low side pressure of 1 bar. Mega-props, can’t wait to see more in this series!
Definitely some of the best project and video quality out here! Vastly underrated Chanel!
Thanks for so the ruff drawings of the puzzled guy that so adequately represents me! 😅
Very cool, pun intended. :). I want to get one when they become commercialized.
thanks alot for not giving up and continuing the project! cant wait to see it working, looking to make iron nitride magnets so this is definitely a project that will help a ton
Knowledge is like having superpowers.
Pulse Tube Cryocooler (Part 5) - Staring at even more graphs!
This is like the most awesome project ever, turned into a crappy power point by that one guy at work.
Calm your horses 😅
I’m really looking forward to the next video. Ads a teenager i used to build single and two stage compressor coolers for CPUs. Using propane in stage one and ethene in stage two i got to -108C at 200W+ loads. That was using reciprocating (Danfoss) compressors but I think rotary or screw will be better for you in higher pressure applications.
I also have a 2 stage cascade using R22 and ethylene.
What was your power draw for get 200W at -108
Best video series!
Really loving these videos, great to watch along with your progress.
Absolutely love this series, excited to see what you come up with next!
All that for a chunk of ice; Doc Brown would be proud :)
Always excited to see an update on this project. Keep it up!!
This project has evolved so far. Keep at it!
Such a cool project ! Can't wait for more.
Absolutly love this series and looking forward to Part 5!
I never klicked so fast after seeing the thumbnail.
This experiment is so dang cool! Excellent work both with the experiment and the video!
love your tenacity!
Man i really love this series! Great stuff!!!
What a great day! Waking up to part 4. Time to learn.
Thanks for creating the best Darth Vader soundeffect since sliced bread. Good job, I love these scientific tinkering videos.
Can’t wait till part 5. Excellent video. 👍👍
Dude you are awesome, explaining all math involved, love it
very interesting. thank you for the details, and for explaining the inefficiencies
You deserve way more credit great work
Looks very promising, can’t wait to see more
Great video, it must be hard keeping track of results and having so many variables you can tweak.
Love your work. Please keep it up!
Really nice project, and so impressive taking into account that you're building it from scratch. About using hydrogen as a cooling gas - you have to remember that it will be leaking out of the system quite substantially because of its super small molecular size, and also might be hazardous when combined with electrical valves. Helium, despite limitations caused by price, might be a better choice when taking into account your safety. Also, after longer usage, hydrogen might intercalate metal parts of the system reducing their lifespan.
My plan is to use hydrogen for prototyping since i expect to lose a lot to leakage, but it would be very easy for me to replenish with electrolysis / chemical generation. If i get a cryocooler working close to LN2 temperatures with that, i'll switch to helium.
This is by far the most interesting youtube series I'm following atm.
If i just had the space i would build and experiment along with the series, but at least i will be entertained while waiting. :)
Now that you mention that it looks like something from a Dr. Soose book, ya it really does. Thanks for the perspective that you did not want
Honestly I am thoroughly enjoying the consistency of your uploads, and how you thoroughly explain your fault finding process and how you go about problem solving.
I can't say I ever even knew about Stirling coolers before your videos but I am hooked, keep it up brother. 👌
Thank you for understanding and explaining
I'm in awe at how much time you must have put into this project. Its all very interesting... thx
Excellent videos as always
Great project. You grabbed me from the start. I have always wanted to make my own liquid Nitrogen. Eagerly watching to see if you crack this.
Very nice content! Tank you from France
@gkdresden - 2023-04-28
I was one of the guys responsible for the 4-valve pulse tube cryocooler at the University of Jena. For GM-type pulse tube cryocoolers you have to avoid a too high pressure ratio. It is not wise to go over 3 to 3.5 because otherwise you get a superheating somewhere in the middle of the pulse tube length, because you cannot exchange about more than 30 to 40 per cent of the gas contained in the pulse tube across the cold and hot heat exchangers.
The heat exchangers are very crucial for the performance of such coolers. So for the heat exchange with the environment (aftercooler, cold hx, hot hx) we have used slittet copper parts manufactured by electro-erosion. For the regenerator we have used stainless steel mesh screens which were slidely over sized in diameter (0.2 mm) to get a dense package with no void passes at the rim of the regenerator tube.
The double-inlet version may be more powerful than the orifice or inertance tube version. But the adjustment of the hot end bypass valve is very tricky. In general it is almost impossible to avoid dc flow in the system which lead to enthalpy flow losses. So the 4-valve version is the most powerful one even in the case that it has comparable dc flow losses.
From the viewpoint of efficiency the stirling-type pulse tube cryocooler is better. The best design is the active reservoir system, which I invented in 2010. In this design you can regain a lot of the expansion work with a second piston / cylinder system at the pulse tube hot end and you can exactly set the phase shift between pressure wave and mass flow, like in the case of a comparable alpha-Stirling cryocooler.
@HyperspacePirate - 2023-05-03
That's really interesting. I read several papers about the benefits of active buffers, but i felt it was too complex and I didn't understand them well enough to attempt to build one and make a video about it.
@gkdresden - 2023-05-03
@@HyperspacePirate It is more or less like in the case of an alpha-Stirling cryocooler. I think, active reservoir is very easy to understand. I use SAGE from Gedeon Associates to calculate my designs.
Active reservoir also runs as an engine. In this case the heater sits between the regenerator pulse tube and the after cooler between pulse tube and active reservoir.