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18 votes
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Why was Freon used in spray cans before it was declared a threat to ozone?

Spray cans work by containing a propellant which has a boiling point a small amount below room temperature. When the can is sealed the liquid and vapour reach equilibrium at a relatively modest ...
Chris Johns's user avatar
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10 votes

Why are train brakes so complicated?

This answer addresses the following sentence: So I'd expect to see the brakes applied by a spring that is capable of stopping the wheels of a fully loaded car, and a single-acting cylinder that works ...
NMech's user avatar
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10 votes

Why are train brakes so complicated?

You need to consider what happens if a hose bursts, and your spring-applied brake locks the wheels on one or more cars - how do you get that train back to the depot? There could be a manual brake ...
jayben's user avatar
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6 votes
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Why air compressing mechanism "Trompe" is not popular in usage?

Simply because it's so wasteful regarding energy. If you employ the flow and height difference of water for a hydroelectric generator to power a standard compressor (be it piston, centrifugal, or just ...
SF.'s user avatar
  • 6,105
5 votes

Is it safe to use a 125PSI rated auxiliary air tank with a 150PSI air compressor?

Don't do it!! Just buy a pressure regulator to put between the two tanks that will decrease the pressure to below 125. You can get these for \$17 at home depot (https://www.homedepot.com/p/Husky-1-4-...
Daniel K's user avatar
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4 votes
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How do you actually control the cooling level of AC?

The temperature of evaporated refrigerant gas is constant as a property of refrigerant material. And usually it is considerably below the thermostat setting in the controlled space. The design of the ...
kamran's user avatar
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4 votes

Why are train brakes so complicated?

With an "spring apply / air release" system the spring pressure may not be enough to apply adequate braking force. Using compressed air to apply the brake allows much higher braking forces. ...
Transistor's user avatar
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3 votes

What is the best method to generate heat from a compressed air canister?

One possibility would be to use the air to drive a turbine (probably a radial turbine as they are used in turbochargers). The turbine could be connected to a generator and the generator to a resistor. ...
rul30's user avatar
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3 votes
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volume comparison of compressed air and gas duster

According to to the SDS found here the product contains tetrafluoroethane as an ingredient. I looked around and found other similar products with the same ingredient. For sake of simplicity lets say ...
Drew_J's user avatar
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3 votes
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Tubing for explosive gas or hydrogen transfer

I would say that it is true and for that case there will be many relevant codes / regulations that need to be respected. Make sure you read them all before designing / altering the system.
Solar Mike's user avatar
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3 votes
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Can Compressed air be used as a thrust component in a spacecraft to propel the craft through space or to orient the craft?

In the case of aircraft carriers the compressed air is generally a working fluid for a mechanical catapult rather than providing direct thrust like a rocket (steam is also used for the same job on ...
Chris Johns's user avatar
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3 votes

Compressing gas with liquid

Yes indeed, air can be compressed by pressurized liquids directly as you suggest. However, there are problems that accompany this sort of scheme. First, if the gas is significantly soluble in the ...
niels nielsen's user avatar
3 votes

Regarding design of a compressed air delivery system based on a screw air compressor

That is on the high pressure end of normal pneumatic conveying blowers, but they are out there. See the notice at the bottom of the attached chart. http://www.hsiblowers.com/products/high-speed-turbo-...
Phil Sweet's user avatar
  • 4,755
3 votes

Why do high pressure multistage air compressor have different piston diameter sizes?

There is a simple reason and a useful added benefit. As you compress air of a fixed mass it occupies less volume. If you give it more space again, it will immediatly decompress and the multiple ...
totalynotanoob's user avatar
3 votes
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Slow Driving an Air Compressor

Google dugout aeration windmill system. There are various makers. Here's one: https://koenderswatersolutions.ca/ The compressor on them does one cycle per revolution of the windmill. While not as ...
Sherwood Botsford's user avatar
3 votes

Is using your mouth and lungs to blow away dust inside your computer somehow bad for the computer?

Another option would be to use a vacuum cleaner, that way any dirt is not pushed inside the computer but its pulled outside.
NMech's user avatar
  • 24.4k
3 votes

Why are train brakes so complicated?

Because the system has worked for a long time and railroads don't want to spend money on improving a technology is time tested. Most railroads run locomotives that is over 25-50 years old. (Most north ...
benjm's user avatar
  • 31
2 votes

Can Compressed air be used as a thrust component in a spacecraft to propel the craft through space or to orient the craft?

The SAFER, used by NASA for EVAs ("Space Walks"), uses compressed nitrogen for thrust. Air is mostly nitrogen, and the properties are fairly similar. So, essentially it not only could be done, but ...
Adam's user avatar
  • 257
2 votes
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Compression and check valves

No, because the pump is designed to limits and if you exceed its working or maximum pressure then, for example, its seals fail and it just does not pump any more.
Solar Mike's user avatar
  • 15.8k
2 votes

Is compressed air energy storage economically viable in the home?

The existing answers do a pretty good job of explaining the sizing and the economics, but surprisingly for an engineering site, skip over the equipment. And that's where this becomes totally ...
ericksonla's user avatar
2 votes

What is the best method to generate heat from a compressed air canister?

Any engine that can run on compressed air will do this. There are quite a few, but as an example imagine a cylinder that has a bit of compressed air in it. The pressure will push on the piston doing ...
Gunchars's user avatar
  • 151
2 votes

What is this "johnson controls" device on the wall in airport?

It might have been a old thermostat. In ancient times, thermostats sometimes worked pneumatically. When the temperature got too low, the thermostat would open a valve that released the pressure on ...
Olin Lathrop's user avatar
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2 votes

How to calculate added lift from ground effect

Assuming you mean a wing-in-ground-effect vehicle, which is in flight during its cruise phase, the ground effect is relatively easy to calculate, at least for potential flows. The boundary condition ...
AEhere supports Monica's user avatar
2 votes
Accepted

How do you read a blower/compressor curve with multi-curves for inlet guide vanes?

Old topic but... to be sure you have the correct info : The IGV positions are given by the seperate lines as indicated at the top (continious, dashed, dotted and dash-dot) At these IGV positoins, ...
Redmer's user avatar
  • 36
2 votes
Accepted

What's the difference between a vacuum regulator and pressure regulator?

The difference is the side on which pressure is regulated, and the reaction curve. Typical pressure regulator takes arbitrary input pressure (from compressor) and provides specified (lower) pressure ...
SF.'s user avatar
  • 6,105
2 votes
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What is the idea behind an expansion valve?

Have you ever held your hand in front of a spray of atomized liquid from a can of liquid sprayer such as an air freshener? It's cold! Because the molecules of liquid have consumed heat energy of ...
kamran's user avatar
  • 22.4k
2 votes

How to decrease Nitrogen gas consumption in Iron & Steel Plant?

I have been in 100 steel mills and never noticed a nitrogen system. However it seems they could use inert gas blasting somewhere. And nitrogen would be so cheap and convenient because steel mills will ...
blacksmith37's user avatar
  • 6,144
2 votes

Is it safe to use a 125PSI rated auxiliary air tank with a 150PSI air compressor?

A 10 or 25 psig overpressure of a tank is well into a potential failure for the tank. The 140 psig safety valve is used because that accounts for the true pressure capability of the tank plus the ...
J. Ari's user avatar
  • 478
2 votes
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Specific heat at constant volume used in non constant volume processes

Start with the first law. $$dU = \delta q + \delta w$$ Isentropic sets $dS = \delta q /T = 0$, giving $dU = \delta w$. For an ideal gas with a constant specific heat, $dU = C_v dT$. This gives the ...
Jeffrey J Weimer's user avatar
2 votes

Can Vortex tubes be used in cooling rooms?

Can it? Yes, but it's only practical if you have a cheap supply of compressed gas. This is a niche application, and is nowhere close to the amount of heat you can move with traditional refrigeration ...
Tiger Guy's user avatar
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