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Author Topic: The Covid-19 Steampunk Hat Thread  (Read 1079 times)
J. Wilhelm
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« Reply #50 on: September 14, 2020, 11:58:39 pm »

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

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


I'm cracking up while watching this video. But here's a practical solution for the specific problem I have of reducing pressure.

In this 1920s inspired video  Roll Eyes Cheesy, Aneer explains the nature of a two stage pressure regulator. This is exactly what I need to "decant gas" from O[2 kpsi] to O[0.1 kpsi]  Grin

Working Principle - Two Stage Pressure Regulator


These things are really expensive, typically on the order of $500. I found a beer keg CO2 two stage regulator (daisy chained) for $136.49.  It reduces from 3000 to 60 psi (actually stops at 55 psi before the release valve is activated). Let's say I can safely get 50 psi out of it, that is 344 kPa, or the back pressure ratio is 29%,which is below the maximum of 53 when choked flow is no longer possible (assuming the pressure of the basketball pin outlet matches ambient pressure - I don't even know if that is true, but I can check.

https://www.webstaurantstore.com/micro-matic-642-battery-premium-series-double-gauge-dual-primary-co2-low-pressure-regulator-battery-with-2-shut-offs/379642BATTRY.html



Since the mass flow rate is linearly proportional to the stagnation pressure, and I defined a 10-fold human respiration rate at Po=78 psi, then it follows that you'd get a ratio of V/Vmin=10(50/78)=6.4 times the minimum respiration rate of a human being. Just enough to allow a person to run while wearing the mask... Assuming I can sustain choked flow. This is nearly ideal for what I need to do...

Maybe I can pull this off, if I can get a cheap enough tank and two stage regulator for the right price. I worry about the cost and weight of the system, though.. I'm not in the best of financial circumstances,especially after a self audit I made on my expenses. Came to the conclusion I'm barely making enough money to pay for all of my bills, minus food. So I'm literally eating my savings right now. *sigh*

I'll be exploring the "compress as you go" paradigm as well. It might turn out to cheaper.

Either way, I'll Charleston my way into making one of these systems...

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« Reply #51 on: September 15, 2020, 10:54:45 am »

Greetings J

quick note, I am literally running to try to compress some sleep, then go get tires, car battery, oil, food, Rx
blahg bala, chase Quigong Healing DVD's and then get winter preperations started.... oooh more concrete... and windows,
and flushing water heaters...

look into the used Medical Oxygen tank regulators. I got a couple at thrift stores for ~ $5 each.
they fit on all standard O2 tanks and are designed to regulate oxy flow from ~ 2k psi at in the tank down the the "trickle" needed at the canula or mask.
at full blast I can hear them hiss and the oxy flow feels cold, but not too high a pressure like from my 125psi  nailgun compressor.

hope this helps
prf mumbles
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J. Wilhelm
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« Reply #52 on: September 19, 2020, 02:01:33 am »

Given that compression of tanks in the order of 3 kpsi will be difficult anyway (need a special compressor.), I'm concurrently looking at other options.

A liquid air generation device is not out of the question, for the simple fact that air becomes very compact at a density of about 0.8kg /m3. The main issue with liquid air is insulation, and also the fact that the nitrogen content of air will boil off before oxygen starts to boil, so it'd be very difficult to insure that you can get a stream of gas that is not all nitrogen or all oxygen. It seems freezing air is good for separating the gases..

Making Liquid Nitrogen From Scratch!


The other option is to go back to the idea of compression on a continuous basis. Most compressors, however are noisy, vibrate a lot and don't last very long due to the heat and wear of their components. So I've been looking at the principle of compression in rotary devices, to see if I can find a viable quiet compression device. Turbine style compressors are really not that efficient,compared to piston type compressors. But there is one device that we know of that has the same efficiency as a piston: the Wankel engine.

There's are a couple of technical papers on the use of Wankel engines as compression devices, and I'm going to be looking at miniature wankel models as a possible compression device.

https://iopscience.iop.org/article/10.1088/1757-899X/232/1/012065

https://www.google.com/url?q=https://docs.lib.purdue.edu/cgi/viewcontent.cgi%3Farticle%3D3303%26context%3Dicec&sa=U&ved=2ahUKEwjD3vrwlPTrAhWFVc0KHbxeDDwQFjACegQIBBAB&usg=AOvVaw31rT9R-Gc_71mzfYkj67Mn


« Last Edit: September 19, 2020, 03:29:33 am by J. Wilhelm » Logged
J. Wilhelm
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« Reply #53 on: September 21, 2020, 05:22:03 am »

It looks like I'm out of luck with rotary compressors. The Wankel type compressor is at the moment just a concept on paper. It's not available commercially anywhere as far as I can tell, even though it's quite viable. The current Wankel compresor concept is being designed for aerospace applications such as compressors aboard satellites. A quick look at what is available reveals a variety for the reverse, that is, compressed air motors. So at first, I thought I could get a small air motor and run it in reverse:

Rotary Di Pietro compressed air motor used for automotive applications
https://www.engineair.com.au/


A more conventional compressed air motor for rotary tools and the like



Unfortunately the motors are not reversible, at least not efficiently. Thermodynamics' Second law prevents the reverse operation without gross inefficiencies. Besides, the large Di Pietro motor, as it's much smaller air tool cousins would both contaminate the air supply with oil.

So I continued searching, and found that a company in Scotland invented a "screw type compressor" that is very efficient and is rated up to 10 bar (1000 kpsi). Their design was also developed for the aerospace industry in satellite applications.

Vert Rotor's 10 bar rotary compressor
http://vertrotors.com

Looks like an ideal solution with no oil lubrication, until you realize that the Vert Rotor compressor requires water injection to work. Sadly, the result is a drink cooler size box around the compressor.

So it looks like I'm stuck with piston type compressors, or noisy diaphragm-bellows style compressors like my hand held unit, which is good at most for 15 minutes before it needs to shut down due to heat. If I want a quiet portable compressor, I might actually need a foot operated compressor! It sounds ridiculous, but I'm thinking of having a foot operated compressor attached to my shoe, so I can supply air while I walk!  Cheesy It would definitely be quiet... Though you would get tired quickly.  Undecided

What was that Mr. Bailey said about bellows?  Roll Eyes

A more realistic solution is a worm drive or rack and pinion driven by an electric motor to run a bicycle frame inflator. For about $15 at the wall in the mart it is rated to 120 psi and includes its own pressures gauge:

« Last Edit: Today at 09:16:06 am by J. Wilhelm » Logged
J. Wilhelm
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« Reply #54 on: Today at 08:22:07 am »

So I'm going to step back a bit from fancy math and do some practical experimentation here. I bought the bicycle frame pump above and ran some simple calculations. The basic air mass flow rate for a human being is 6 L/min in a state of rest and 36 as a maximum in an agitated state. Whatever the speed or pressure of the gas, in the end you have to supply 6 Liters of expanded (1 atmosphere) air. How does that feel on your face? How hard is it to push the pump ? Do you need an air tank at all? Are there simple tanks you can make/find for 100 psi or less?  Is that possible with a tiny pump like that?

I attempt to answer those questions today.



The frame pump is entirely made from plastic. It is made from a two-cylinder telescopic tube with two settings: low volume - high pressure, and high volume - low pressure. Air comes in through a small opening near the pressure gauge. In the high volume setting, by blocking the outlet of the pump with my thumb, it's actually hard to get much above 30 psi, because the area of the piston inside at that pressure provides a large reaction force. But using the low volume setting (locking the outer cylinder and using only the inner cylinder), I can easily get up to 50 psi momentarily (the piston leaks a little so pressure goes down immediately after the stroke - it's the job of the tyre valve to keep the air in the tyre, so it doesn't matter if the pump's piston leaks a little).

Most importantly, the piston is almost 100% quiet and the operation very smooth with no vibration. It gives me confidence that getting to 60 psi would probably be trivial. Getting to 80 psi looks entirely doable with a simple pulley and electric motor. The pump is rated 120 psi - and it's just a plastic and rubber piston!! The outer cylinder wall is transparent Lexan/Acrylic or similar and no more that 1.2mm thick!


It seems to me that a simple pulley-piston setup would be able to pull it off with a flywheel frequency of a few cycles per second. Let us assume that air enters the cylinder of the pump at ambient pressure and temperature. The travel of the inner cylinder is just 11.5 cm. The inner diameter of the inner cylinder is about 1.7 cm (estimated). This translates to a volume of ~2.61 X10-5 m3 of air at 1 atmosphere. Since we have 1000 liters in one cubic meter, then that corresponds to 0.0261 L/stroke. If we divide the minimum flow rate of 6 L/min by the volume of 0.0261 liters per stroke we get the number of strokes per minute to get 6 liters which is ~230 strokes/min, and if we divide again by 60, we get the number of strokes or cycles per second, which is 3.83 strokes per second to pump the 6 liters of air. This does not take into account pressure or temperature at all. The needle in the pressure gauge hardly moves when I pump air through the needle at this rate. These numbers are just for getting the required air supply of expanded air.

Given the physics of the problem, that seems to me to be an entirely achievable goal. Getting a rate 6 times that for the maximum minute respiration rate (36 L / min) seems to me will probably be a challenge, but at least I know I can get the minimum respiration rate with this pump. May no be good for jogging, but if you're riding the bus, shopping in the supermarket, or waiting in line it seems doable. As an experiment I tried pumping 4 cycles per second with my hand - it's not difficult, but your arm will get tired in about 20 seconds, and let me tell you, it's quite a stream of air on your face coming from that needle! The stream of air does come out noticeably cooler, but not much below ambient.

Again I'm not paying attention to cooling at all or pressure at the moment, its all near 1 atmosphere at ambient temperature, because I realize that we are in Fall, and Winter is upon us. It may not matter if by November I don't have a cooling system ready. But my idea is to pursue the development of the system WITH the Bell-Coleman refrigeration cycle, using with a flywheel and piston - its the quietest most efficient setup I can fathom, because other practical compressors are too noisy and rotary compressors are expensive/difficult/non existent yet. All in all it will be a very Victorian setup  Roll Eyes I would prefer to get my hands on a screw type compressor, but the water requirement is ridiculous. With more time, I may try to build a Wankel compressor if I can get my hands on a working small-scale die cast model.


I'm actually very disappointed that the engineering community has not given us a quiet, cheap, practical compressor for something as simple as 100 psi. It just sounds ridiculous to me in the 21st century. To give you a feel for the kind of pressures we're talking about, a 2 liter soda bottle packs about 40 psi of pressure at room temperature! That's more than a car tyre which is between 25 and 35 psi !! Actually most sources I researched agree on the 40 psi maximum for a plastic soda bottle when filled with soda, and about 100-150 psi for a maximum failure pressure.

Air Compressor vs 2 Liter Pop Bottle



I don't even need to buy a tyre or steel pressure tank! I can just make a pressure vessel out of a soda bottle, or make my own using PVC pipes. But I would much prefer to use PVC pipes as I can adjust the size to what I want, they're much thicker, less prone to puncturing, and one can use tyre valves like these, which I can find at my local Wall of Mart:


So this knowledge save me a lot of complications by allowing me to build stagnation tanks with simple PVC pipes and off the shelf fittings. I would use two valves, one for inflating the tank and another for bleeding the tank.

Do you even need the tank? Well, that depends on how hard the pump needs to work to keep the pressure up to 80 psi. I can tell you it will have to work a lot harder than 4 cycles per second. And for 80 psi the material will probably need to be good enough to deal with the heat generated during compression. The mass flow rate I calculated for a stagnation tank at 80 psi was 10 times that mass flow rate, and that's not paying attention to how much you need in excess to start building up pressure. At 4 cycles per second you will get the basic mass flow rate for respiration, but no cooling at all because the pressure will not increase much throughout the system - speed is close to zero. Likewise with little compression the tank will not heat up by much. If this is Winter and you don't care about choking the needle and expanding a stream of air at Mach 1 or above air to cool, one way to go is to just build a small tank with the sole purpose of stabilizing the air flow coming from the pump, to avoid getting a single puff of air for every cycle in the flywheel/stroke of the cylinder.

I think I will build a small PVC pressure tank and will engineer a pulley system with a DC motor and see what happens... I still need to estimate the electrical consumption and size of batteries, but I imagine one can buy large power tool batteries.
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