# What is Compressed: Definition and 319 Discussions

Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes, and is used for power tools such as air hammers, drills, wrenches and others, as well as to atomize paint, to operate air cylinders for automation, and can also be used to propel vehicles. Brakes applied by compressed air made large railway trains safer and more efficient to operate. Compressed air brakes are also found on large highway vehicles.
Compressed air is used as a breathing gas by underwater divers. It may be carried by the diver in a high pressure diving cylinder, or supplied from the surface at lower pressure through an air line or diver's umbilical. Similar arrangements are used in breathing apparatus used by firefighters, mine rescue workers and industrial workers in hazardous atmospheres.
In Europe, 10 percent of all industrial electricity consumption is to produce compressed air—amounting to 80 terawatt hours consumption per year.

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1. ### I Mass, Energy and a compressed spring

If I take a spring with clamps and I weight that system accurately. Then I compress the spring and clamp it thus giving it potential energy. If I now weigh the clamped spring I should see an increase in mass because of the added energy. Is this the case and something that could be proved in the...
2. ### Predicting Remaining Pressure in Compressed Gas Cylinder

Well, it's been nearly 10 years since my last post, and it's been about that long since I've thought about ideal gases, so here we go :smile:. Description of Setup I have a system that uses compressed gas cylinders as a source to slowly purge an optical payload. The source is 12x compressed...
3. ### Work done on a gas when it is compressed quasi-statically

For this derivation, I am not sure why the bit highlighted in orange is not positive since the displacement of the piston is downwards in the same direction as the force applied. Many thanks!
4. ### Two carts are forced apart by a compressed spring

It's an explosion problem. When two carts are pulled apart, the bigger one takes longer than the smaller one. So the velocity of the bigger one is small, and the velocity of the smaller one is large, and they are opposite each other. So the momentum before the explosion must be equal to the...
5. ### B Compressed R134A refrigerant as a store of energy?

How much energy is used to compress e.g. 0.8 Kg (typical mass in a typical fridge freezer; edit: I've just seen that 0.8 kg is not normal at all; it's more like 150 g - this means my idea should be quite cheap and compete well with rechareable batteries) R134A refrigerant and could it be...
6. ### Find elastic energy in the compressed spring.

a) Elastic potential energy stored in the compressed spring is written by, where k =400N/m, compressed spring distance x = 0.5m $$U_g = \frac {1}{2}kx^2$$ $$U_g = 50J$$ b) When block C is compressed, it has stored spring PE and when it is released, the block accelerates to the right, where it...
7. ### Using compressed air through a venturi pump to suck oil?

Hello, was wondering if I could pass compressed air through a venturi pump to pull floating oil from a tank? If yes, how do I control the eventual mixing of oil with the air from the outlet end? The requirement is given to me by one of my clients who wants an easy, and low-cost solution to...
8. ### I Filling a rigid tire from a pressure regulated compressed air line

This thought came to me while I was trying to fill my MTB bike tire a while ago as an exercise in laziness to not "check" the tire pressure with a separate gauge! Mostly, my mind just wanders... If I have some very large tank filled with compressed air at gauge pressure Ptank. The hose runs...
9. ### I Compressed gas energy storage formula

Hi, I’m looking for formula to find the energy stored in a compressed gas for non ideal gases, for example, argon. The formula should also include the thermal energy caused by compression. Thank you in advance.
10. ### Compressed Sensing - Questions from Forum Member

Hello, Anyone on the forum using or familiar with the topic of compressed sensing? I have some related questions. Thank you!
11. ### Pick the Best Compressed Air Inlet for Loop Pipeline

Which compressed air inlet to a ring (loop) pipeline would likely be best in terms of least turbulance and best flow (avoiding dead head)? Given: 1) The inlet has to be in the corner of the rectangular loop. 2) Air consumption will be constant and evenly distributed throughout the loop. 3)...
12. ### B Object falling through highly compressed air question

If you had a tube a couple of miles long filled with very compressed air, say 6,000 PSI, would an object you dropped in it fall very slowly? Even a heavy object like an anvil, how long would it take to drop?
13. ### Submarines that don't use compressed air to sink and rise?

I have been wondering about submarines for a while, and especially their ability to sink and rise on command. I understand that they do this through ballast tanks and replacing water with compressed air, which increases the buoyancy force and helps them rise. (I understand that my knowledge is...
14. ### Why does air have to be compressed first in gas turbines?

In all gas turbines air is first compressed using a compressor and then head added in a combustor and finally the hot pressurized air is expanded in nozzles to convert air contained energy to kinetic energy which can be harvested and transferred in the form of thrust or shaft rotation. My...
15. ### 2 Carts on a Track Compressed by a Spring -- What are their Velocities?

a)What is the total energy in the system? Only energy acting on the system assuming the track is level and there is no potential energy of the carts, is the potential energy of the spring. Comes out to 7.8125 using the potential energy of a spring equation. b) What are their velocities if the...
16. ### What speed v(t) enables constant power by release compressed spring?

We know linear spring force F = kx(t), k = spring constant, during any moment t of energy release. displacement x(t) = ʃv(t)dt the power p = F*V = kx(t)v(t)= kv(t)* ʃv(t)dt My question: Is there a mathematical function of special v(t) to make power p constant?
17. ### Design a compressed air energy storage for a PV plant

Summary:: Design compressed air energy storage for PV plant [Mentor Note -- Thread moved from a technical forum, so no Homework Template is shown] Hi All For a PV project of 5 kW, we will use a CAES. The preliminary design will consist of a compressor - 2 heat exchanger - Air receiver - air...
18. ### A spring being compressed between two masses

i attempted this problem by using conservation of energy, mgh=1/2kx^2 mgD=1/2kD^2 2mg=kD k=2mg/D why is it wrong ? btw the correct answer used mg = kx which is mg/D
19. ### Cylinder in a heat bath @ 0C contains water and ice & is compressed

You can use the change in volume to find how much ice turned into water, and then find the energy required to melt that ice - that I have no problems with. But then work done by piston = change in internal energy of ice/water combination (which we found) + heat released to the bath. And we...
20. ### Gas in a syringe being compressed - thermodynamic processes

1. Adiabatic compression (When compressed quickly, there is no heat flow to the environment Q=0) Isochoric with heat loss (The syringe is still compressed, there should be no change in volume) Adiabatic expansion (When the syringe is released, there is work done only) Isochoric with heat gain...
21. ### Compressed air pressure vs hydrostatic pressure

Hi all, I'm new on here and will start off with what I think is a simple clarification. I'm questioning my workings due to previous work being completed by another engineer and thought this was the best place to ask. Essentially we have compressed air being supplied through a hose, the hose...
22. ### Thermodynamic properties of compressed liquids

Hi All, I have review my thermodynamic notes (~35 year ago..), and I could not able to restore how to get thermodynamic properties (u,h,s,v ..) for compressed liquids. I have found properties tables for compressed liquids ( for water..) but unfortunately the data starts at 5MPa. What if I look...
23. ### B Is Any Material Truly Incompressible Under Special Relativity?

I thought that if something is incompressible, then when we push on this thing, the other end of it will move instantly, which is a kind of FTL information transport and is impossible. So does that mean literally everything, including atom nucleus or even some elementary particles(if they can be...
24. ### Physics: How much is this person's femur compressed?

Thats how far I got with my equation. Help me please.
25. ### Plumbing Compressed air powered water pressure

Hi there, I have a few interesting problems that I have been exploring for a while now, but i quickly get beyond my level of knowledge of physics, so wondered if members of this Forum may be able to assist. One of the projects that we have been trying to solve is how to maintain a decent quality...
26. ### Understanding energy losses in a compressed air system

When measuring pressure drop across a compressed air system shown in the included figure, I get different results depending on the system downstream of the actual component I am measuring pressure drop across. Btw this is a real experiment that has been ran. The numbers below are different but a...
27. ### Compressed air problem (pressure and flow rate calculations)

When dealing with a compressed air system I would like to know how to make some calculations to predict pressure and flow rate throughout a system. e.g. If I have a compressor that can supply 50 cfm @ 100 psi at the source, and the air flows through a system of pipes, filters, turns, etc. which...
28. ### How to advoid water condensation in compressed air piping

Hello all, I'm having problems with my compressed air system. In the factory have some clean rooms with temperature are maintained around 23°C. The outside of clean rooms are normal condition (around 32°C). When i checked some air supply points outside. There were no water in compressed air. But...
29. ### Relation between temprature and pressure of a gas bieng compressed

1. If a gas is kept at constant pressure of 1 atm & the temp. is raised upto the saturation temprature ( 99.97 C ) and just when Tsat is attained the heat transfer is stopped ( Hin & Hout both are 0 , adiabatic conditions ) . Now # If the adiabatic condition is maintained , then on...
30. ### Temperature of a compressed gas

How can I calculate the temperature changes of a pressurized gas as it is in a cylinder, then as it is when flowing into another vessel? my best guess was using the ideal gas law (with help from this forum), but I feel like I'm using it wrong. P = 300bar or 296.08 atm V = 112 L (is this...
31. ### 7.2 cubic metres of Nitrogen compressed, will last 30mins-1hr of usage

So I am currently looking to work on some projects with my brother. I have some questions regarding the usage of nitrogen. We are looking at a 7.2 cubic metre cylinder of Nitrogen Pure compressed and wondering at what rate of pressure will equal roughly 30-60mins of use? Nitrogen Bottle here...
32. ### Can I calculate the flow rate of a compressed gas from pressure?

I am using a compressed gas tank to fill an otherwise empty container, The gas tank is around 50bar and the container will be filled to 6bar. If I am using a pressure transducer to determine when the container has been filled to 6bar, can I use the information I gain from it to derive the flow...
33. ### I Liquid Air and Compressed Air Density

Densities of Normal Air is 1.225 kg/m3 at STP, whereas the density of Liquid Air is 870 kg/m3. That means liquid air is 710x denser that normal air. Then suppose, we compress normal air to more than 710 atmospheric pressure, then it could have a density more than that of liquid air. Is this...
34. ### Power spent to keep a spring compressed

I was wondering, I have an engine that should keep a spring compressed. How can I calculate the power necessary for this? The work is Force x Distance, as there is no distance, there is no work, so no power... But obviously to keep the spring compressed the engine will have to produce a...
35. ### A How to find the volume change of CO2 when compressed into liquid?

Hi, Can anyone guide me with an approach to find the liquid volume of CO2 when a gas of 4.14x10-6 m3 at -20°C and 1 bar is compressed to liquid at 25bar, without change in temperature?
36. ### Calculating Hydrogen Mass Storage in Compressed Vessels

Hello all; I am looking for an equation for calculating mass storage of Hydrogen in compressed vessels I have fount the following link (https://nanosun.co.uk/hydrogen-tools) which provides what i need but would like to create something similar for internal use Can you suggest an approach to...
37. ### How to measure the torque of a compressed air engine?

Summary: The main idea of my graduation project is to convert the motorcycle engine to work on compressed air that come from a 180 L tank (10 bar compressed air inside the tank ) I have some problems to how calculate the required torque to move the cart . The main idea of my graduation project...
38. ### Compressed Air Engine Calculations

Hi, I posted a question a while ago which I have managed to do some more calculations for. I need a bit of help to see if they are correct. I am trying to obtain power and torque values at different rotational speeds of a single cylinder compressed air engine. The inlet pressure into the engine...
39. ### Does pressure in a compressed air system increase....

does pressure in a compressed air system increase when going from a 2" air line to a 1" air line.
40. ### Compressed Air Engine Calculations

Hi,I am designing a compressed air engine for a project. A little stuck with calculations. I need to work out how long the engine will run at its top speed using a air pressure which is supplied from a compressed air tank.Compressed air pushed down a piston which is connected to a camshaft. As...
41. ### How Do You Calculate Work When Compressing Gas?

Homework Statement What is w when a gas is compressed from 42.1 L to 25.1 L using a constant external pressure of 739 Torr? Remember to include a "+" or "−" sign as appropriate. Homework Equations W = -P(dV) The Attempt at a Solution Pressure = (739 Torr / 760 Torr)*(101.325 kPa) W =...
42. ### Maximum Force of Compressed Air

What's the maximum force that air from a typical garage air compressor tank, the kind that's used to inflate tires assuming the pressure is around 150 psi.? Can the force be changed by nozzle design? Thanks.
43. ### Thermodynamics question: venting a tank of liquid oxygen

I am trying to figure out how you can subcool a dewar of liquid oxygen (vacuum insulated) just by releasing the pressure sitting on top of it. The liquid I am thinking of in this case is liquid oxygen, which boils at -297.33 F at 1 atm. Let's say I fill a dewar with LO2, then pressurize that...
44. ### Compressed air, heat and pressure?

Yes compressing air increase its temperature but does that necessarily increase pressure? In an pellet gun a spring driven piston compresses the air which increases the temperature but wouldn't any increasing pressure simply retard the piston's advance? Because the chamber volume is not fixed...
45. ### Kleppner - blocks and a compressed spring

Homework Statement A system is composed of two blocks of mass m1 and m2 connected by a massless spring with spring constant k. The blocks slide on a frictionless plane. The unstretched length of the spring is L. Initially m2 is held so that the spring is compressed to L/2 and m1 is forced...
46. ### How long will it take for compressed air to reach 29 psi?

A large tank filled with air is compressed to 49 PSI. A valve is open and air escapes through the hole (d = 0.04 ft) to the atmosphere. How long will it take for the compressed air to reach 29 PSI. Assume constant temperature. Not exactly sure how to approach this problem since the flow rate...
47. ### Compressed air flowrate calculation

Hi, I have a airbottle of 30bar pressure, 1000lit.From the airbottle I had made a line of 25 nb and fitted a pressure reducing valve in the line with set pressure 5bar.I am interested to know the flowrate in the line. Please help
48. ### Compressed Air Energy Storage System

Homework Statement I have a CAES system that takes air at a pressure of 102.2kPa and temp of 24 degrees C. It is compressed to 85 bar adiabatically at a rate of 168 kg/s. I know that Cp = 1.005 kJ/kgK and Cv = 0.718 kJ/kgK. The question is - determine the amount of work consumed by the...
49. ### I Compressed Nitrogen: Calculating Pipe Flow Time

Hello, first time on this site and wondered if anyone could help me on what the proper equation or equations would be to answer this question. I have a 300 cubic foot tank of nitrogen air that will provide nitrogen to a rectangular pipe at 5 psi with a flow rate of 10 CFM to atmosphere at the...
50. J

### I Gravity changes produced by a compressed and stretched spring

If I compress a spring beyond its most relaxed point it will have more energy and thus by General Relativity produce a stronger gravitational field than the uncompressed spring will. But suppose instead I pull in the opposite direction and stretch the spring beyond its most relaxed point it is...