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Author Topic: The Covid-19 Steampunk Hat Thread  (Read 1071 times)
SeVeNeVeS
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« Reply #25 on: August 02, 2020, 12:06:56 pm »

Latest suggestions by Dr. Fauci in the United States are now extending protection for the eyes as well.


I said that back in April, Good to know the people in the know are keeping up with us plebs, lambs due for the slaughter.  Roll Eyes

Everyone is banging on about masks, what about eye protection? Tear ducts lead to the nose and therefore the throat, therefore the respiratory tract. Just saying.......What do I know?, I hit stuff with hammers for a living Undecided

But in all fairness it didn't take a genius to figure it out.
Sort of my point! Wink
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« Reply #26 on: August 04, 2020, 12:45:24 am »

Latest suggestions by Dr. Fauci in the United States are now extending protection for the eyes as well.


I said that back in April, Good to know the people in the know are keeping up with us plebs, lambs due for the slaughter.  Roll Eyes

Everyone is banging on about masks, what about eye protection? Tear ducts lead to the nose and therefore the throat, therefore the respiratory tract. Just saying.......What do I know?, I hit stuff with hammers for a living Undecided

But in all fairness it didn't take a genius to figure it out.
Sort of my point! Wink

What is surprising is not how many people couldn't see that, but how many still argue against any measures.

Anyhow, I sort of took a break this weekend. I have to get a battery operated tyre pump, which I think might be a the right size. One thing about pumps is that it's preferable to not operate them 24/7. A stagnation chamber (tank) will serve as air storage and provide energyffor ventilation and cooling, but obviously can't be as large as a scuba diving tank. The idea is to get a traction for how large the system will be.

Another thought is that I'm not bound to subsonic flows. I can expand a stream of air as much as I want by accelerating it to supersonic flow (since I know how to do it). That might help in the efficiency department. The only problem is that as soon as airflow goes supersonic it will become very noisy due to turbulence in the flow, and worse, shock waves. I could in theory accelerate the flow through converging diverging nozzle making the flow very cold and use that to make a radiator, for a secondary system, then re-compresss the flow though a diffuser, slowing the air down for ventilation. If I chose to recycle the compresses air, then I'd need a separate ventilation system.

A diagram showing the pressure to stagnation pressure ratio in a converging-diverging nozzle
As you increase the pressure differential (i, ii, iii..) between the pressure tank (stagnation chamber) and the ambient,
the airflow accelerates more and more and pressure decreases with a minimum at the "throat" of the nozzle.
At some point the pressure difference is large enough that at the throat the flow becomes trans-sonic (Mt=1)
Beyond that pressure difference, (iv, v...) the speed of the flow at the throat becomes stuck at Mach 1, and the
speed of the flow anywhere else is determined by the shape of the nozzle; a given speed has a
one-to-one relationship to the relative diameter of the nozzle. If the supersonic flow undergoes a shock
due to sudden repressurization, that's shown in "squiggly" lines.




I can make the air cold, the question is *how much air * I need to remove the heat rate I'm producing with my body and the incoming solar radiation plus conduction from the outside heat. I may have to do an energy estimate of the heat radiated from a human head and try to do a very simplified heat transfer analysis.
« Last Edit: August 04, 2020, 02:29:13 am by J. Wilhelm » Logged

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« Reply #27 on: August 05, 2020, 03:56:39 pm »

Dr. Fauci: "Wear goggles"

Can't argue with that advice on here, for sure.

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« Reply #28 on: August 07, 2020, 03:59:18 am »

Dr. Fauci: "Wear goggles"

Can't argue with that advice on here, for sure.

HP

Yep. But he and his family are now receiving death threats. Why are people so stupid? Makes me think that we NEEDED this virus, just to give humanity another chance to live. And no, looking at the world in the last decade, I don't think I'm exaggerating. It's like moronic behaviour just cropped out of nowhere, fed by an increasingly pampered population. A sedentary lifestyle stopped evolution and we need to restart natural selection somehow.

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Anyhow, I need to survive. It's time to get the toys out to play.


Here I just acquired a battery operated tyre inflator. It is rated 100psi and has a built-in pressure gauge to inflate tyres to a preset pressure (no manual inflation is possible). It runs from a USB charged battery or a 12V car outlet. Has a display capable of rating pressure in psi, bar and kPa, not that it matters. It also comes with a short extension tube which is useful as I can use for both pressurising a tank or letting the air out of the tank. I'm going to see if I can find another similar extension.

Since I can go up to 100psi or about 3 times the pressure range of a normal car tyre, then I have a range of potential pressure vessels I can pair to it. The only thing is that the compressor can only operate continuously for about 15 minutes or so before taking a half hour break, because it will get hot.

This is where you actually begin the refrigeration cycle. In the Bell-Coleman cycle, no one said that the radiation of heat from the control volume had to take place at the same time as the cooling. You can start the cycle by pumping heat into the atmosphere hours, days, even months or years or however long a tank can hold pressure before you actually go to the cooling phase! The heat released by the compressor is equal to the work done by the compressor plus any associated inefficiency, plus the heat that you will remove from your body in the future, plus the special tax due to entropy that mother nature will charge you for doing something she doesn't like, like taking heat from a cold reservoir (your body) and pumping it to a hot reservoir (Texas in summer).

I'm thinking that the pressure vessel will need to be the most portable part of the system more than the compressor. It still remains to be seen how big it needs to be. At this point we have the means to do something, we just don't know how much air we need to store, hence how much potential energy you're storing in the air. If I can get at least half an hour of continuous cooling an ventilation from a pressure vessel, then the system would be useful. If I can get one hour, then that would completely fill my needs (bus ride plus walking home). The compresor is light and rechargeable with a USB adapter. It can't be better than this, and better still, I can carry the compressor separately in my backpack. I kind of like the idea of an entirely pneumatic device with no fan or electrical parts, because it'd be very simple and 100% weatherproof.

I'm thinking that a small tractor tyre (about the size of a dinner plate) might be a good starting point to see what I can do with this toy. The procedure would be something like this: use extension line with screw connector to hook up to the tyre. Inflate tyre to maximum rating. Let the compressor and extension line cool down (or use second extension line). Connect extension line from tyre to pipe leading to face shield / mask /helmet.

To be calculated:

1. Amount of heat that needs to be removed and translate that to volume of air needed for circulation
2. Volume of air needed for respiration.
3. Based on 1 and 2,compare to the volume of appropriate vessels (eg tank or tyre)

To be designed:

1. Pipe system and vent nozzle for mask. Existing vinyl tubes for air pressure systems look nice. Need to hunt for adapters
2. Size and nature of tank.

More thermodynamic analysis as well as fluid mechanics will ensue to see if the system is feasible. I will also be making corrections accounting for the effects of viscosity in thin pipes (boundary layer effects). I will try to ignore turbulence... But will see. It's doubtful I'll go into supersonic flow, but I'm not ruling anything out if it makes the system portable. The noise and complexity of strong expansion is not something I'm looking forward to, so I'll try to keep it simple unless the physics force my hand. The only thing nice about expanding flows is that it's isentropic flow. Mother nature likes expanding flows, so that makes calculations easy.
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« Reply #29 on: August 07, 2020, 10:33:06 am »

A little more progress on the faceshield. I added two aluminium flat bars to provide stiffness. They are meant to be deformable to adapt to your face, though I suspect it'll be a bit hard to adapt to the shape of the chin. Might as well, because I'm thinking that the lower portion of the mask would be appropriate to hold outgoing air filters. So I'm not going to start cutting off excess plastic just yet. It might turn out that I need every bit of it.

Unfortunately, it's so chunky now that it's really starting to look like a firefighter respirator mask. It's also perceptible more heavy with the aluminium bars, even though the bars are very light.



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« Reply #30 on: August 07, 2020, 11:04:29 am »

I'm thinking that a small tractor tyre (about the size of a dinner plate) might be a good starting point to see what I can do with this toy.
You are aware that a rubber tyre imparts a certain… "olfactory character" to the air it contains.
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« Reply #31 on: August 07, 2020, 11:28:31 am »

I'm thinking that a small tractor tyre (about the size of a dinner plate) might be a good starting point to see what I can do with this toy.
You are aware that a rubber tyre imparts a certain… "olfactory character" to the air it contains.

Unfortunately you are 100% correct. But today the same boss who tested positive 12 days ago and which caused my former boss and myself to get tested, made a surprise visit to the shop. He says he's OK now after symptoms subsided. While some medical websites agree, I'm sure he violated the 2 week requirement for confinement after testing *negative * not positive! Technically I can put him in jail, and I'm ruminating about it. I'm so angry.

I can't tell you how much that drove in me the urgency to finish this mask. Not just for summer, but for winter. Assuming I'm not infected now and while I decide whether to spend another $135 on another test in less than a month, I don't care about the tyre smell, as long as I don't get cancer, or something (which unfortunately is possible as well). I can explore other options, but I want to see if the system is feasible at all. Off the top of my head I can't tell if that is a certainty.

If this works, I'll call it the Anti-Covidiot Mask, because that's what it's really for, to not breathe the same air as sub-Neanderthal humanoids.
« Last Edit: August 07, 2020, 11:30:09 am by J. Wilhelm » Logged
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« Reply #32 on: August 08, 2020, 06:13:26 am »

A bit more work today. I had some issues with the adhesion of the glue. Apparently the latex glue was not holding on well to the aluminium bars. That got solved with 4 rivets. I gave it a mediocre paint job with acrylic paint, since I don't think this will be the last prototype.




It's looking more medieval+Sci-fi now. "My lord, I will find those heathens and quickly dispatch them with my de-moleculator."

To be honest, it's looking too big for me. I still have to add more padding for the chin, because I was not able to m as make the lower part of the mask any tighter, in spite of the added aluminum bars. So this begs the question whether this approach is the correct one.

The other alternative is to make a strictly rigid frame,custom made for my face. If you can make a stencil to curve some sort of material with a square cross section, then it's possible to make a relatively thin frame (albeit with some sort of gasket as well, and then attach a much thinner piece of plastic on top, so there is no need for great mechanical strength to hold the shape of the plastic.

I wonder if I could mold sculpey around a rod or wire mesh,to make a thinner frame more like the masks I showed above. Finding the right material is key. A thermoplastic? Will Worbla /Thibra be too thin? Thermoplastic pellets?
« Last Edit: August 08, 2020, 06:25:32 am by J. Wilhelm » Logged
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« Reply #33 on: August 08, 2020, 07:23:08 am »

Oooh! This is interesting. I wonder if I can make rectangular cross section bars using this method, and then reheating and bending them according to a stencil? The idea is to make a thin rigid frame.


Polly Plastics Moldable Plastics Instructional Demo


Otherwise if I want to go full Steampunk, I can always go this route...  Roll Eyes


« Last Edit: August 08, 2020, 09:40:14 am by J. Wilhelm » Logged
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« Reply #34 on: August 11, 2020, 09:20:47 am »

While the visor mask I've made is not bad per se, it's really not what I'm looking for. I'm not interested in looking like Sir Galahad in the 24th ½ century. I'd like to approach something that looks more like this:



This is a student's design study for a scuba mask that never came to fruition. The design is far too impractical for diving, including poor seal, no measure to prevent fogging, no way to touch your nose to equalize pressure in Eustachian tubes, etc. But I'm thinking that a poor seal for diving does not equate to a poor seal for a COVID mask, especially if you are blowing air into the mask and keep positive pressure. By placing the nozzles near the eyes, the stream of air doubles as an anti fogging device.

The only thing was finding the material to do it, and also noting that the mask frame can't be so thin, on account that I can't easily make a plastic bubble that bends in two planes. I can practically, at most bend in one plane. But then I realized that would imply a "brow cap" and a "chin bib" were needed to couple the plastic shield to the face. And that basically means a flat piece of material. I then though that a plain plank of craft wood could do the job. The sides of the mask are straight anyway. Why not make the frame out of wood? Since I've earned my chops cutting near perfect circles in craft pine for the speaker project, I can do the same for the mask!

I took the wire template I made of my face and measured against the plastic shield above, then drew the required "brow cap" and "chin bib" pieces I'd need to have a near perfect match to the contours of my face. The only thing I did was leave a 5mm gap for a foam strip. The gap between the ears and the visor will be wider, but I can use the same rubber insulation I used for Sir Galahad's mask.


Hopefully this takes me a bit closer to my goal. Certainly the mask will be smaller and lighter now. I can see some advantage to using wood, and those "cap" and "bib" parts can be drilled to accommodate any number of pipes, devices, filters, etc. So after today's brainstorm I'll be studying the best way to adapt this wood frame...







As for the finish, the sky is the limit, but I'm one of those people who thinks that wood looks best when decorated like wood. I'm not a fan of painting of you can never hide the grain texture. If I wanted to, however, I could buy a primer so I can lay a thick layer and sand it smooth. If I had my choice of colors for a "modern" mask, I'd choose that metallic green above. But I'm not going to rush into it unless I know I can do it right. And as far as Steampunk, well wood is more Steampunk followed by copper, brass, etc. But I loathe faux metal finishes.

Any suggestions?
« Last Edit: August 11, 2020, 10:05:26 am by J. Wilhelm » Logged
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« Reply #35 on: August 15, 2020, 07:02:32 am »

The new direction of the mask looks promising. I ended up destroying the previous one, because there's very little transparent sheet plastic in my city at the moment, and I needed to continue building. I will replace the shield you see for a new one later. I had to order a new face shield replacement from a tool supply chain, and I'll be picking it up on Monday. The polycarbonate plastic is surprisingly pleasant to work with. It's 100% shatterproof to the point you can cut it with snips, it deforms instead of cracking. It's better to use a very fine scroll saw to cut the plastic, and it's surprisingly fast to cut.





Very little other than the interior surface of the "brow cap" and "chin bib" will be visible, other than the "sideburns." really the new mask looks more like an oversize skier's goggles. A black bead of silicone sealer will be used to attach the plastic shield to the wood frame, but I imagine I could add a pair of screws. Because the black sealer is opaque, I'll use the sealer to make the entire edge of the lens black, like a frame, so the edge of the wood frame behind is not visible. One can imagine how'd it look with a polarized lens. My goal is to make it as light and attractive to wear as possible. I know that by November there will be a great need for people to go out tothe  street, as there will be elections in our country. I may capture people's attention before they venture out en mass, in cold weather, at the height of the flu season   Smiley


So I'm a little ambivalent about the finish I want to give the wooden frame.i wanted something modern and appealing to the crowd, otherwise I'm wasting my time, and short of using metallic auto paints, I had to stop myself from buying copper color paint at the shop today. I have this concept of what I want it to look like, but I also have visions of the wood drinking all the paint and having to lay multiple layers, only to end up with a piece that looks like, well, painted wood.

What I'm going to do instead is just treat it the same way I would any other piece of wood I've made. Golden Oak stain and several layers of polyurethane to make it look nice, before I even drill, screw or glue anything else. I would like to have some cool features, such as LED lighting on front for illumination and perhaps something else. There should be filtered air passages in case one needs to wear the mask without the air hose, and also as the normal exhaust of the respirator. Any pipes coming into the mask would come from the bottom, like a beard of sorts...
« Last Edit: August 15, 2020, 07:12:27 am by J. Wilhelm » Logged
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« Reply #36 on: August 16, 2020, 03:46:12 am »

Looking at the available tyre inflation hardware, I looked at the different options and did a quick test with a ball inflation needle. It puts out a decent jet of air, which definitely feels cooler than ambient air, at whichever initial pressure the pump can muster. The real test is to do the same with a pressure vessel. As long as the nozzle is not choked, the flow will be subsonic and the speed dependent on pressure in the vessel, which is a variable in time. Me thinks that an expression describing the deflation of the vessel and hence the speed and pressure at the outlet as a function of time will probably require solving a differential equation, but I have to write it out on paper first (it'd be awesome if it's just an integration).

What I know is that this ball inflation needle is probably the smallest nozzle I can make with off the shelf materials, unless I get creative and make my own nozzles (not a bad idea, though), so as a first approach, my calculations should use that diameter as a realistic nozzle diameter. The fight now is to get as much time of operation as possible. Sadly,  I only got a few minutes of pump operation, on account that the battery died out  Roll Eyes. Oh well. Considering the source (The Wall of Mart) I shouldn't be surprised. The good news is that now I know that the hardware has a decent shot of doing what I want as long as the hardware is of sufficient quality. The only unknown is the pressure vessel, ventilation and cooling needs for a human. That's going to involve some math and research.

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« Reply #37 on: August 18, 2020, 06:52:14 am »

I got the replacement lens. In the meantime I used wood stain and a couple of layers of polyurethane over the wooden frame. Not as polished as I wanted, but really brought out the color. I should have picked a piece of wood with more grain to showcase, but I'm being practical about this.





It's looking more Steampunk than I had planned, and might as well. I just doubt it would look good just as painted wood. At least the wood looks the way it should, and I can use this prototype for the Steampunk version of the mask. It blends well with all my Steampunk paraphernalia, and can accommodate my Luftschiffengel hat  Cheesy

It looks like I have several choices. Initially I though of using black silicone caulking, but I realize that the nicest part of the frame is the edge where the grain took an almost black tone as if the wood had been burnt with an iron...


The only way to showcase that is to use a crystal clear caulking I saw at the hardware shop the other day. So I'll try to get it. On the other hand, rather than making a permanent installation, I have foam strip (window insulation) which I am using as interface between my skin and the wood edges. But if I used it on the exterior edge, that could make a seal for the plastic lens and allow the lens to be removable for replacement, etc.





I'm ambivalent about what to do. Transparent caulking, black caulking or foam strips.

I'll probably just cut the new lens to size and move on to the next step so I can decide later. The last thing I want is to scratch the new lens when working on the frame to drill, attach pipes, etc.

I also replaced the faulty pump, and realize that if I really need to, I could use a bicycle frame pump to be included with the mask as a kit. What I need to do next is the necessary math and perhaps buy the small tractor tyre and start experiments right away. Doing experiments allows me to get a feel for the physical reality, while the math will tell me how big or small the system will need to be. So you end up spending a bit of money and time just trying to size the system, before you actually build a working prototype.
« Last Edit: August 18, 2020, 09:34:06 am by J. Wilhelm » Logged
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« Reply #38 on: August 25, 2020, 04:44:06 am »

Sorry to be tardy to the party-

you are progressing incredibly well!
If the wood turns out to be too heavy, you might try lightweight "basswood" or balsa wood, then
coating with 2 part epoxy for strength...

or emulate the modern surfboard, use rigid foam coated with fiberglass! light and strong...

with a tyre as a pressure tank, you might end up looking like The Michelin Man.

yhs
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« Reply #39 on: August 25, 2020, 05:11:05 am »

Sorry to be tardy to the party-

you are progressing incredibly well!
If the wood turns out to be too heavy, you might try lightweight "basswood" or balsa wood, then
coating with 2 part epoxy for strength...

or emulate the modern surfboard, use rigid foam coated with fiberglass! light and strong...

with a tyre as a pressure tank, you might end up looking like The Michelin Man.

yhs
prof marvel

The mask is very light, actually. It has an excellent fit. I will start experiments with a small tyre first. By the way the small tyre is made from vinyl, so that addresses Von Corax ' issue with the smell from rubber.

The great unknown is how much air I need. Hopefully the calculations are not too involved, to find the time it takes to empty the tyre. It will be an implicit function, even with Euler equations (adiabatic, inviscid flow). And because its the Euler equations, I still need to find the viscous effect of the boundary layer on the needle, which is the nozzle. One trick is to aim for a choked flow, and assume Mach 1 at the needle, if the pressure is high enough. Thenvcorrect for the viscosity (boundary layer). If I go full Navier Stokes equations, then I'd need a computer program. It's a good review on my rusty brain  Grin
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« Reply #40 on: August 25, 2020, 07:54:56 am »


The great unknown is how much air I need. Hopefully the calculations are not too involved, to find the time it takes to empty the tyre. It will be an implicit function, even with Euler equations (adiabatic, inviscid flow). And because its the Euler equations, I still need to find the viscous effect of the boundary layer on the needle, which is the nozzle. One trick is to aim for a choked flow, and assume Mach 1 at the needle, if the pressure is high enough. Thenvcorrect for the viscosity (boundary layer). If I go full Navier Stokes equations, then I'd need a computer program. It's a good review on my rusty brain  Grin

Damn The equations! Full Speed Ahead!

I mean, you have the pump, the tire and time.
Even without the mask completed, Just try it and time it.

Experimental Empiracle measurements will give you a great ROM (Rough Order of Magnitude)

prf mrvl
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« Reply #41 on: September 02, 2020, 12:07:27 pm »

*sigh*

Indeed. So I'm stuck at the moment trying to find the right hardware for the hose.

The idea is to have the connection between the mask and the hose be under the "chin" of the mask, which is really the only place where you can drill and make attachments. The issue at hand is that the tire inflation needle - which is an ideal size to fit in the mask, uses the standard Shcrader stem-compatible (0.305’’×32TPI) thread. Originally I was thinking of just sinking the needle into the wood, with the thread exposed on the exterior if the mask.But that may be mechanically weak if I use heavy hoses and adapters.


But most air hose extensions will use 1/4" or 1/2" FNPT (tapered) thread (USA), and are fairly beefy (240 psi). So I need to buy a length of male to male 1/4" FNPT hose and use adapters like brass tire inflation chucks to connect to the needle. Torque and weight will be an issue on the mask, though. I would have preferred to have as thin a hose as possible, and I may have to use a tire chuck extension hose, whcih had a thinner more flexible hose and a locking (bicycle type) tire chuck. Otherwise the weight and torque on the mask will be excessive (the mask is very light). I'm debating using screw-on type adapters as well, but thinking that a quick disconnect would be useful.

I really like the lightness of the hose extension and screw-on chuck provided with the cordless tire inflator, but getting more than a foot, or foot and a half extensions is proving difficult (see last link, that'd be the closest). Most chucks are not screw on, but rather lock or unlocked quick- disconnect types

Some links I'm perusing:

1/4" FNPT to standard Tyre Chuck
https://www.amazon.com/CZC-AUTO-Straight-Compressor-Accessories/dp/B07QMPVYK9/ref=asc_df_B07QMPVYK9/

GODESON Tire Air Chuck Heavy Duty Screw on Tire Air Chuck for Tire Inflator Gauge Compressor Accessories, Twist-on Chucks(Pack 2pcs
https://www.amazon.com/Godeson-Inflator-Compressor-Accessories-Twist/dp/B07JMNGBRG/ref=rtpb_6/130-9192710-6833415

18-inch Short Air Compressor Hose: 1/4" Male NPT to 1/4" Male NPT Connections (Lead-Free Brass)
https://www.amazon.com/18-inch-Short-Air-Compressor-Hose/dp/B07NDMPSVT/ref=asc_df_B07NDMPSVT/

1/4" x 3 ft EPDM Coupled Multipurpose Air Hose 250 psi BL
https://www.zoro.com/zoro-air-hose-14-3-ft-14-mxm-blue-g7370925/i/G7370925/

NORSMIC Auto-Locking Tire Chuck with Rubber Hose, standard US tire stem (0.305’’×32TPI) male to standard Schrader valve inflator chuck.
https://www.amazon.com/NORSMIC-Auto-Locking-Standard-Inflator-Adapter/dp/B0873BRGJB/ref=asc_df_B0873BRGJB/

or

Air Chuck, Straight type hose extension
https://masterflowair.com/products/air-chuck-clip-on-type

In relation to what the physics of the flow are within the hose, I realize that if the needle's diameter is small enough, the speed of air within the rubber hose will be very low, so the larger the diameter of the hose and the slower the flow, the only length of pipe were I need to worry about the boundary layer will be the needle itself. In other words, the hose is acting as an extension of the stagnation chamber (ie the pressure vessel). The needle is basically the only component of the system that comprises the nozzle (shown in diagram a few posts above), at least until the flow reaches Mach 1. We say in engineering that the flow inside a pipe follows a "no-slip" condition at the wall, that is. any flow (gas, liquid. etc.) basically sticks to the walls shearing and slowing adjacent layers of the flow. That region where air is shearing and slowing down is the boundary layer, and it's the only part of the flow where viscosity manifests itself.

Flow in a pipe with boundary layer effect

Because the speed in the rubber tube will be relatively small, I can assume there will be no turbulence in the pipe or the needle (that's good!). Turbulence has the net effect of increasing the "apparent" viscosity of the flow.

It's not like I have any control over this, but the flow will be faster at the center of the nozzle, because of the restricting effect of the boundary layer. That's important when fine adjusting the design for "choking the flow." And I say that because I think my first approach is to have that maximum velocity reach the speed of sound, because it's easy to calculate that way!! Mach 1 at the needle is useful to both simplify my calculations and design a nozzle extension if I need one (I can predict pressure distribution and hence temperature of the flow at every point of the nozzle as a function of the diameter of the nozzle.Then I can back-calculate how much pressure I need in my pressure vessel/tyre/tank (simple equations if the outlet is at least at Mach 1), so I can choose the size of the tank and estimate how long the air supply will last. This is by far the easiest mathematical approach, so I don't have to mess with differential equations and all that jazz.

Oddly. supersonic flow is simple, guys! But if the pressure ratio needed to make the Mach 1 flow is too high (greater than 120 psi or much above 30 psi for a rubber tyre) then I might have to rethink about using complex equations again.
 
What happens after that, well, it depends. If the flow is cool enough, then I can leave it as a Mach 1 flow, and accept whatever temperature drop I can get. Otherwise I can make the diverging part of the nozzle and attach to the needle somehow (again, the "flaring open" part in the diagram a few posts above is where the flow becomes supersonic) to speed the flow past Mach 1 and cool the flow further. I can probably expect to start making the flow noisy, because it'll become turbulent.


« Last Edit: September 02, 2020, 01:09:30 pm by J. Wilhelm » Logged
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« Reply #42 on: September 03, 2020, 01:34:18 am »

I believe you are on the right track....

First,what is the highest pressure that the tire will stand?
Logically, I would think you want the largest diameter hose and fittings you can get from the tire to the mask.

before one spends too much on parts, why not cobble together a prototype test bed of
- tire
- whatever hose you have on hand,
- ending in the nozzle
- inflate and time how long it takes to deflate.

If I must hazard a guess, it would be minutes.

This is based on my experience with SCUBA, Scott AirPacks, and Oxygen bottles.
Scuba and Scott Airpacks ( virtually the same thing) ... an 80 cu ft tank at ~ 3000 psi  will last about 60 minutes or less

This little .02 cu ft tank ( .5 liter) lasts about 5-10 minutes at ~ 3000psi but it is pricy!
https://www.amazon.com/dp/B086MV43LZ

and here is something in the middle -
https://www.ebay.com/itm/1-Oxygen-Tank-M6-Empty-Medical-Gas-Aluminum-Cylinder-Health-Care-Supply/264844645921

for about $31 shipped one gets a decent portable M6 oxy tank.

or this place, tested & refurbished -
https://www.noinsurancemedicalsupplies.com/responsive-respiratory-m6-b-oxygen-cylinder-tank/
about $40 plus ~ $6-8 shipping.

snip---------------------------------------
Lightweight medical cylinders offer exceptional weight savings over traditional steel tanks providing increased portability and extended gas delivery with exceptional strength properties. 164 Liter capacity 3.21" Diameter X 11.6" Tall.

The Responsive Respiratory M6 Oxygen Cylinder comes in brushed aluminum finish with clear coat-protective finish, which is lighter than steel cylinder. This cylinder designed with 5 year hydrostatic test capacity and its filling pressure is 2200 psi. These oxygen cylinders are shipped empty.

Each M6 Cylinder holds 165 Liters, with a . 5-8 LPM continuous flow regulator @ 2 LPM you get 1.3 Hours.
end snip---------------------------------------

You MAY even find them very cheap at local thrift stores, or thru "used medical supply" houses.

so if you fill with air at ~ 2000 psi I guarentee you will get more than 30 minutes of airflow

you will still need a valve and or regulator, and a high pressure pump,
AND you need to make sure the air from the pump (any pump) is "oil-free"
but common cannula hoses work from there to your needle.

hope this helps
prf marvel
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« Reply #43 on: September 03, 2020, 02:36:17 am »

I believe you are on the right track....

First,what is the highest pressure that the tire will stand?
Logically, I would think you want the largest diameter hose and fittings you can get from the tire to the mask.

before one spends too much on parts, why not cobble together a prototype test bed of
- tire
- whatever hose you have on hand,
- ending in the nozzle
- inflate and time how long it takes to deflate.

If I must hazard a guess, it would be minutes.

This is based on my experience with SCUBA, Scott AirPacks, and Oxygen bottles.
Scuba and Scott Airpacks ( virtually the same thing) ... an 80 cu ft tank at ~ 3000 psi  will last about 60 minutes or less

This little .02 cu ft tank ( .5 liter) lasts about 5-10 minutes at ~ 3000psi but it is pricy!
https://www.amazon.com/dp/B086MV43LZ

and here is something in the middle -
https://www.ebay.com/itm/1-Oxygen-Tank-M6-Empty-Medical-Gas-Aluminum-Cylinder-Health-Care-Supply/264844645921

for about $31 shipped one gets a decent portable M6 oxy tank.

or this place, tested & refurbished -
https://www.noinsurancemedicalsupplies.com/responsive-respiratory-m6-b-oxygen-cylinder-tank/
about $40 plus ~ $6-8 shipping.

snip---------------------------------------
Lightweight medical cylinders offer exceptional weight savings over traditional steel tanks providing increased portability and extended gas delivery with exceptional strength properties. 164 Liter capacity 3.21" Diameter X 11.6" Tall.

The Responsive Respiratory M6 Oxygen Cylinder comes in brushed aluminum finish with clear coat-protective finish, which is lighter than steel cylinder. This cylinder designed with 5 year hydrostatic test capacity and its filling pressure is 2200 psi. These oxygen cylinders are shipped empty.

Each M6 Cylinder holds 165 Liters, with a . 5-8 LPM continuous flow regulator @ 2 LPM you get 1.3 Hours.
end snip---------------------------------------

You MAY even find them very cheap at local thrift stores, or thru "used medical supply" houses.

so if you fill with air at ~ 2000 psi I guarentee you will get more than 30 minutes of airflow

you will still need a valve and or regulator, and a high pressure pump,
AND you need to make sure the air from the pump (any pump) is "oil-free"
but common cannula hoses work from there to your needle.

hope this helps
prf marvel

Thank you! Useful information, professor!

The pressure in most tyres is a full two orders of magnitude lower than the oxygen tanks. Most car tyres have a pressure rating of 25—35 psi, and the tiny vinyl tractor tyre I was looking at is rated 25 psi. The battery powered pump is rated 100 psi, and a bicycle frame hand/foot operated pump is typically rated at 120-180 psi. The battery powered pump is most likely oil free if it uses a bellows like the one I showed in the aquarium pump (hence the relatively low 100 psi, but that's still above 35 psi).

Then again it all hinges on the airflow rate through the needle. Even at a Mach 1, I'm guessing the airflow rate will be lower than that of a regulated flow from scuba gear, but off the cuff, I have no instinct for how much that'll be (I didn't crank numbers today; I slacked off and did absolutely nothing useful in my day off).  Grin

The needle really doesn't care how high the pressure behind it is, but it's a question of safety. I instinctively think that the required pressure to drive the needle will be higher than say 25 psi. It could be 3000 psi, and it wouldn't make any difference since the flow would be choked anyway. But even 25 psi needs a certain amount of safeguards to prevent injury. The tube leading to the needle really should be rated as high as one can find without the tube becoming a cumbersome hose. If we treat the tube as an extension of the stagnation chamber, then it should be rated as high as the pressure vessel itself. That is true for tire inflation hardware. The thread on the needle and the needle itself also need to be rated for the pressure you intend to push through. That holds true for most inflation equipment, even basketball needles.

As for the scuba gear, the hydrostatic pressure around you and your scuba equipment affects the ratings of the equipment. Generally speaking, water is 1000 times more dense than air. Hydrostatic pressure would force the pressure inside a balloon (similar to your lungs in your body) to be the same under water. So from the outlet of the regulator through to your lungs, the static pressure of the flow must match the ambient hydrostatic pressure. The pressure inside the tank, by necessity must be higher than whichever pressure is being pumped by the regulator, and it's insulated from the hydrostatic pressure by way of the pressure vessel's own structure. The pressure range, per your data is in the 1-3 kpsi range.

It may happen that a two stage decompression is necessary with a high pressure tank (oxygen tank) in the 1000 psi range, decanting by way of rigid tubes and a modified pressure regulator to a second pressure vessel in the 100 psi range , to reach the necessary pressure for choked flow, but not go over the rating of tire inflation gear - the tube leading to the  mask would become too heavy and cumbersome that way.

But the pressure regulator would play an interesting role either way. I may not need a two-tank system if I can rig a regulator to give me 100 psi.
« Last Edit: September 03, 2020, 03:46:15 am by J. Wilhelm » Logged
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« Reply #44 on: September 03, 2020, 03:19:28 am »

That M6 tank is looking promising.

The other thought I'm having is how to deal with cool weather. It may not even matter, provided that the tank is kept around body temperature, since all you get is a temperature drop from the decompression., so the final temperature is entirely dependent on the tank stagnation temperature.
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« Reply #45 on: September 03, 2020, 07:19:26 am »

That M6 tank is looking promising.

The other thought I'm having is how to deal with cool weather. It may not even matter, provided that the tank is kept around body temperature, since all you get is a temperature drop from the decompression., so the final temperature is entirely dependent on the tank stagnation temperature.

I have several of the 3 foot long oxy tanks, and a regulator. The things are dirt cheap on fleabay.  The trick is to get them filled somehow.
I am still looking for a reasonably priced commercial vendor....   or a dirt cheap "home oxygen concentrator/tank filler"  ... yupo they make those things!

Mine came from an estate sale, still filled. nobody would touch them for legal/medical reason so I got them cheap. I use them as the
Oxy tanks on my Bernzomatic Oxy/Propane torch. They last MUCH longer than the disposable Oxy cylinders ( ~ $14 ) and the hardware store.

the commercial oxygen regulators can be had for under $20, they handle "air" fine and are rated , like the tanks, to over 2200 psi.
 - again thrift stores & estate sales are your friend!
https://www.ebay.com/itm/Brass-Sleeved-50-PSI-Oxygen-Regulator/324275192296

https://www.ebay.com/itm/American-Bantex-Oxygen-02-Regulator-Brass-Sleeved-3500R-CGA-870-50PSI-0-8L-Min/233548667063

https://www.ebay.com/itm/Reliant-TMD-Brass-CORE-50-PSI-Oxygen-Regulator-8-99-use-no-oil/363091656370

but the big problem will be clean untainted air pumped at greater than ~ 200psi.
going from 125 psi to 2000psi means a huge difference in volume of air  and thus the time your system is good for.

search fleabay and amazon for "high pressure" pcp "air pump"

better yet, use this
https://www.google.com/search?q=+%22high+pressure%22+pcp+%22air+pump%22

you will find a plethora of devices, from $50 hand pumps ( omg getting form 2000 psi to 3000 psi can kill ya!)
to low end electric to high end commercial tank fillers.

here;s another thought - see if the U has a scuba club, they probably have access to some high pressure pumps!
hope this helps

prof marvel
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« Reply #46 on: September 04, 2020, 06:31:26 am »

Those hand pumps look useful, but let me work on one thing at a time. Let me define the problem first by finding the minimum pressure to generate Mach 1 at the nozzle. 50 psi out of the regulator may not be enough and I have to figure how much cooling power will be lost of if was to use a secondary pressure vessel or a pass valve to reduce the pressure. .
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« Reply #47 on: September 10, 2020, 12:13:55 am »

OK folks. I've disappeared from this thread for a while now. I was busy reviewing material I have not used for twenty years, and making sure I understood the physics of it. The good news is that I was forced to re-read my scanned notes and pdf copy of the textbook I used on college, so I'll be reading the whole text for the remainder of the year, and re-acquaint myself with the science.

As far as this project is concerned, my instincts were right. It doesn't look like I need to go to thousands of psi of pressure to drive this system. And it looks like the nozzle, in this case a 1mm diameter needle, even at a moderate stagnation pressure of about 80 psi can drive a flow of air about 10 times the slowest "tidal" respiration rate of a human being... Which is fine since the respiration rate will accelerate to not much more than about 6 times the slowest rate in situations of exercise or emergency.

The only caveat is that the temperature at the needles tip will be about - 29 C or - 20 F, very cold. If nothing else, I've invented the world's first bicycle pump driven wart remover!  Grin. Of course the flow will very rapidly warm up as it recompresses and slows down. If it goes back to Mach 0.333 (which is what I was talking about before deciding to take the needle to supersonic flow) then the temperature will rise to 13 C, 55 F.  Which means that I probably need to design a specially shaped little diffuser without accelerating the flow beyond Mach 1. I can't just attach a little cone to the needle, because at Mach 1 that constitutes a nozzle, not a diffuser, and that might accelerate the flow beyond Mach 1 and cool down it even further, making noise along the way with a little shock wave or such if I don't design the nozzle properly (I would say like a very loud hissing noise, or even whistle, depending on the physics)

The idea of driving the flow to Mach 1 was to simplify the calculations, and  maximize the mass flow rate of the flow relative to the diameter of the nozzle, in this case the tubes from the pressure tank and the needle. For a back pressure ratio (stagnation tank to ambient pressure ratio) above a certain minimum, the pressure at the tip of the nozzle (the needle) becomes only a function of the pressure of the tank, while the pressure anywhere in the pipe is dependent on the local pipe diameter and stagnation pressure. The Mach number (hence the speed) anywhere in the pipe or duct is just a function of the area ratio between the the local area and the throat of the nozzle, that is needle. These are short simple equations with simple algebra in 1 dimension. Thus at that point calculating how long it takes to empty the tank is totally dissociated from "pipe aerodynamics" involved in that calculation. You just assume you have a tank with a hole, and try to find how long it takes to empty while the flow is still choked (which means the tank will always have some pressure inside).

I could simply reduce the stagnation pressure and allow the flow to be subsonic, and that works too for the needle, but the mass flow rate will be lower relative to the needle and calculating properties of the airflow is more difficult. The choked flow scenario is an upper limit we can use as a baseline for performance. I still haven't tackled the problem of "tank duration" but like the good doctor said, this can be experimented upon. I'll call that the "sub choked regime" as the tank falls below that special stagnation to exit ratio and the flow becomes subsonic which no doubt will happen as you wait in a line of people. A strategy needs to be developed for that situation.

Let me gather my notes, and my next post will have the relevant equations with actual numbers crunched. But basically I gave you my results above.
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« Reply #48 on: September 10, 2020, 09:09:11 am »

I believe you are on the right track....

First,what is the highest pressure that the tire will stand?
Logically, I would think you want the largest diameter hose and fittings you can get from the tire to the mask.

before one spends too much on parts, why not cobble together a prototype test bed of
- tire
- whatever hose you have on hand,
- ending in the nozzle
- inflate and time how long it takes to deflate.

If I must hazard a guess, it would be minutes.

This is based on my experience with SCUBA, Scott AirPacks, and Oxygen bottles.
Scuba and Scott Airpacks ( virtually the same thing) ... an 80 cu ft tank at ~ 3000 psi  will last about 60 minutes or less

SNIP


So I was looking at my old textbook and formulary from my college days, over 24 years ago (!), and I realized that there is a very simple way to tackle the problem of flow in a pipe. There is no need to go into a differential equation or even go solving for implicit equations, because under some conditions it's really easy to treat flow in a pipe as quasi-1 dimensional, meaning that you don't even need to use radial geometry in property distributions, such as pressure, temperature and such, because flow properties for high speed flows can be very simple.

My original idea was to use compressed air to generate a cooling jet of air and give a person enough oxygen, but not necessarily to carry a large tank of air in the back. Not knowing how much a human breathes prevented me from knowing if my idea of using a tyre as a tank was even feasible. So I'm going to go back to the start and define the main problem: create a cooling jet that a human can breathe.

Since I don't have much choice on the materials that I can get (I don't have a metal working shop and a 3D printer or such), I had the idea of using commercial equipment for compressed air tools and tyre inflation equipment such as used in you car. My observation was that if a can of compressed "air" can produce a supersonic jet of gas from a pin-hole, it shouldn't be to hard to use equipment from you hardware store at a pressure about 100 psi or less to generate a similar flow of air. Along the way, the expansion creates the cooling effect which thermodynamically you already paid for by compressing air and radiating that heat to the environment, even before you place the mask on your face - the so called Bell-Coleman Cycle.

The good Prof Marvel pointed out the fact that respiration rates of human beings require more air than a small tyre could handle. Moreover, practical air tanks for scuba diving and medical oxygen tanks operate in a range of pressures between 2000 and 3000 psi and deliver volume rates of air in the order of 5 litres per minute (expanded gas out of the regulator - I assume rated at ambient pressure, 101 kPa). Much higher pressures and volumes of air than what I envisioned. The reason is that if you carry all your air with you, then storage becomes a problem. Humans consume a lot of air to stay alive.

There may no be a way out of carrying a large tank of air, but one thing I know is that I don't want the system to be too heavy or expensive. People will not wear the mask that way. Also, instinctively I knew that any system of O[1 kpsi] (read, "of order of 1000 psi") is between 1 or two orders of magnitude larger than what you needed to create a little jet. But I didn't know how to prove it unless I made calculations. And also I needed to convince myself of the actual requirement for a human being. Would the 2-5 LPM (Litres per minute) of an oxygen tank be enough? And what about Air, not Oxygen? Would my supersonic nozzle needle be able to provide enough? Those are answers I have on paper now.

~ ~ ~ ~

So let's start with human respiration. An average human breathes at a rate of 12 breaths a minute in a state of rest. In a state of distress or exercise, that rate will multiply by a factor of 6. For each breath you have a "Minute Volume" inhaled and then exhaled from the lungs. The average capacity of a human id 0.5 litres. Hence the average consumption rate of air is 6 litres per minute. The reason oxygen tanks give less than that is because that is supplemental oxygen only and you need less volume of air if you are inhaling an oxygen stream. So this answers the question whether a typical oxygen tank is enough. The answer is that it's good for supplemental oxygen only. That leaves scuba equipment as the only equipment rated to provide enough air.  But would my needle nozzle be able to do that?

Well I prefer to think in terms of kg of oxygen per second, because that is compatible with thermodynamics and fluid mechanics formulas. The net volume flow rate of air for a human V (I'm using a strike-through dash instead of a dot on top to indicate rate per second due to format limitations)

V = 6 L/min = 0.1 L/s

and if there are 1000 litres per cubic metre then

V = 1 x10-4 m3/s

The density of air at sea level in the Standard Atmosphere is 1.225 kg/m3, which means that the mass flow rate m is

m = 1.225 x 10-4 kg /s

So basically a human breathes only  a little over 1 tenth of a thousandth of a kilogram of air per second on average. 7 if very distressed. Air is very light, but very bulky.

~ ~ ~

Now I stumbled on a very useful equation which I'll use right now: The mass flow rate for expanding flows. The equation is a product of the zeroth (continuity) law of thermodynamics, the first law of thermodynamics (energy), the definition of speed of sound, and the equation of state for an ideal gas.

For basic supersonic flows and compressible flows where the temperature is not changing a lot (no combustion) you may treat air to be a calorically perfect gas, meaning that a rise in temperature correspond to a linear change in energy and enthalpy of the air by way of constants known as "specific heat".

Also we are assuming that the system we're studying is adiabatic - meaning there is no heat transfer going into or out of the system - which for fast flows is a reasonable assumption. Also we will be assuming that diffusion of mass (viscosity, friction) diffusion of heat (conduction) are negligible and all work done on the system is reversible. The above conditions imply we are assuming isentropic flow, which takes care of the 2nd law of thermodynamics.

The mass flow rate for expanding compressible flows in a duct starting from a stagnation chamber



A DeLaval converging diverging nozzle (flow is to the right). M = 1 at the throat. The nozzle I propose (needle) ends at the throat.
Note how pressure and temperature decrease as the flow expands. The far left of the nozzle is connected to the stagnation chamber (tank).
You need the pressure at the throat to be less than 53% of the pressure at the tank (Po) to "choke" the flow and reach M=1




The flow starts at a pressure chamber called the stagnation chamber at a pressure Po and temperature To. Then the flow accelerates continuously through a deLaval nozzle (shown) with the flow becoming supersonic at the narrowest part of the nozzle. If the flow is adiabatic To becomes a property of the gas at any pint of the flow - like a measure of thermal energy content, if you will, and if the flow is friction free dissipation free (isentropic) then Po is also a measure of constant "pressure energy" as well.

Gamma, γ, is the ratio of specific heats, at constant pressure Cp and at constant volume, Cv

γ = Cp/Cv ~ 1.4

which is about 1.4 for temperatures close to ambient temperature (say 20 C). I will assume this is constant, but in practice γ will be a bit higher for cooling temperatures. Generally we don't care unless we have temperatures in the thousands of Celsius (combustion) when it goes down to about 1.3. Kinda gives you an idea how stable that is.

R is the specific gas constant for air , 287 J/(KgK)

In the equation above, assuming γ = 1.4,  the Mach number-dependent term, α approaches the value 1.728 as M approaches 1 at the throat. So the mass flow rate equation becomes

m = √(1.4) Po A / [1.728 √(R To ]

where A* is the area at the throat, which for the basketball needle is ¼πD2, where D = 1 mm diameter. Plugging everything in, and assuming that the stagnation chamber (tank) has had a long time to cool down after being filled with air, so To = 293 K = 20 C = 68 F ( a cool day), then

m = 1.8545 x 10-9 Po

So now I can calculate how much mass of air will flow for a given stagnation chamber pressure. You have many choices here. I could start with asking what pressure I need to pass the 6 litres per minute through the needle, m = 1.225 x 10-4 kg /s. And if I plug the numbers in, Po turns out to be a very low value of 53921 Pa (53.9 kPa) about 7.81 psi, which is lower than ambient pressure (1 atmosphere) at 101 kPa.

Now what?

So this is not a physical answer, because the back pressure is higher than the stagnation chamber's pressure. The reason this is happening is that the mass flow rate formula is using "absolute pressure" and it's dumb enough not to know when the nozzle is choked. However if the nozzle was in orbit around earth in a near perfect vacuum, the 7.81 psi pressure would be enough to drive a Mach 1 flow through the needle. The way to fix this is to simply raise the stagnation pressure so the flow can take place through the nozzle. It turns out that theory predicts that at the throat with area A*, the pressure P* needs to be less than 53 % less that the stagnation pressure Po to drive the flow. We could tackle the problem by increasing the stagnation pressure so much, that you insure the pressure ratio will be less than 53% at the exit of the needle.

Why not just increase the mass flow rate by a factor of 10? In choked flow the Mach number at the throat will always be M*=1. And we know that maximum respiration rate of a human is six times higher than the 6 L/ min. So if I just multiply m by 10, then Po = 539 kPa, which corresponds to 78.2 psi. The ratio of exit to stagnation pressure should be less than 19%, I'll make calculations to see if this holds, but for the moment, seems reasonable.

So at near 80 psi, a 1 mm basketball needle, should (barring any errors) produce a M=1 flow of air equaling 10 times the respiration rate of a human at rest. Enough air to run around the block.

~ ~ ~


It all sounds very nice, but is there a caveat?  Yes there is: the flow is very cold.

Following an adiabatic path in a duct the stagnation temperature to local (ie static) pressure relation is given by

The stagnation temperature To to local static temperature relation
for an adiabatic expanding/compressing flow


When I plug the numbers in, the flow cools down from To= 293 K to T*= 244 K = -29 C or -20 F. This is a bit of an issue, but one must remember that cooling is a function of expansion and compression. That is the temperature just at the tip of the needle. If the flow slows down to M = 0.33 (which happens very fast) the temperature will increase to 286 K = 12 C or 55C, which is not so bad. What this means is that I have to design a special diffuser - which can't be just a tiny cone, because I don't want to "extend" the DeLaval nozzle such that the flow continues to expand and cool down. If the flow was too warm at the nozzle , then I would have done that, building a tiny rocket nozzle "bell" from the throat Aexit > A*with a bigger area, and the mass flow rate would have increased with the area (decreasing the pressure of the tank faster) but giving me more cooling.


~ ~ ~ ~

So this is what I have so far folks. The needle will give 10 times the slowest respiration rate, or 66% more than the maximum respiration rate of a human with a tiny stream of air at -29 C for a tank with a pressure of near 80 psi. The tyre will not really cut it for this experiment, I'm afraid (I haven't bought the tyre yet anyhow), unless I do the experiment for a non-choked case at M = 0.33 (the mass flow rate may not be enough though). The good news is that I can use readily available hardware. The bad news is that I must adapt hardware to reduce the pressure from O[1000 psi] to O[100 psi] and carry a large heavy tank on my back.

To be honest, there is no real need to carry all the oxygen with you, if you can have a battery pack do the job of compression for you. It might be noisy, but 80 psi is something even the battery operated compressor can handle. A hand bicycle pump can do 120 psi.  A self contained, all pneumatic device is an attractive idea, but one that may complicate the system more than it needs to. My original idea was to filter the air. So I think that I will revise that situation and see if a filtered system, such as an oxygen concentrator could fit the bill. If I could compress on the fly, that would preclude dealing with very large pressures and heavy tanks, no to mention pressure regulators. It may come down to carrying several battery packs on a bandolier  Grin

I welcome any further suggestions, though. And if someone can figure out a convenient way to carry a self contained tank I'll hear it, just note that having high pressure equipment near your head is never a good idea, so one must "decant" from a high pressure tank, to a low pressure tank, to serve as stagnation chamber!

~~~

Cheers, and thank you for your attention! I'm having a lot of fun stomping my old academic grounds mentally. At least I got to re-read my text books during the pandemic!  Grin

J. Wilhelm
« Last Edit: September 10, 2020, 12:50:46 pm by J. Wilhelm » Logged
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« Reply #49 on: September 12, 2020, 06:12:49 pm »

At this point everything's on the table. I'm stumbling on some interesting videos

Getting liquid oxygen by pouring liquid nitrogen and letting oxygen sink to the bottom!

How To Make Liquid OXYGEN! TKOR Experiments With Homemade Liquid Oxygen & How Oxygen Is Made


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