Compressed air Definition and 145 Threads

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. C

    Valve lift & variable air flowrate in compressed air

    How we can incorporate valve lift and variable flow rate in compressed air engine Mechanical power = air power torque * angular velocity = pressure * flow rate
  2. S

    Gas confusion -- cooling air in a pipe using venturis and mixing

    Hello everyone! I am new here. I have used this forum on and off through google searches in the past and learned a fair bit from the posts. This is the first time asking anything. The question is probably extremely simple but has been overrun in my head for a week! It is in regards to...
  3. Evanish

    Some help on Compressed Air Energy Storage

    I was reading this article about different types of energy storage, and it gave this formula for compressed air. Joules = P0V0ln(P/P0) Where P0 = Atmospheric pressure 105 Pa V0 = Volume of air to be compressed in m3. P = Pressure in tank when compressed in Pa. Note: This formula is for...
  4. A

    Designing a compressed air vehicle

    I am doing a school project, building a compressed air powered vehicle to reach desired destination. What I am thinking is: I will use a paintball compressed air tank. Four nozzles. And an controller board to control valve opening. Valve will only open for certain time like (50ms). After each...
  5. Scott Davies

    Easy way to find the potential energy in compressed air

    I have a .81 Cu. Ft. cylinder which is at a static pressure of 80 Psi. What is the easiest way to calculate the Potential Energy of the compressed air?
  6. J

    Need suggestions on transfering compressed air to rotating object

    If you had a rotating object like a tire or barrel that you wanted to distribute compressed air to while it's rotating, what would some ways to do it? One way I'm thinking is just a tight seal at the axis, but then there would be a lot of friction. Any other ideas??
  7. K

    Air machine and compressed air

    Homework Statement Air at pressure 20[atm] enters an air machine and leaves at 1[atm]. what must be the temperature of the air at the entrance so that when it leaves it is 00C. Assume adiabatic process. Homework Equations PV=nRT Adiabatic: ##P_1V_1^\gamma=P_2V_2^\gamma## The Attempt at a...
  8. stephenranger

    Using Compressed Air Tools Outdoors: Can it be Done?

    Homework Statement Car mechanics use compressed air tools to open bolts. Instead of using an air compressor one can also use a tank of pressurized air. There is an air tank with a volume of 50 L to work with. The pressure of the tank is 50 bars when it is stored indoors at 20 °C. The bolt...
  9. C

    Calculating time required to pressurize compressed air tank

    Hello, I searched as best I could but could not find a direct answer to my question; I've seen similar questions but without the required data to be able to make the calculation. I thought this would be a simple calculation to find but apparently not. Compressed air source is 4.46cfm @ 93psi -...
  10. S

    What factors determine the energy storage capacity of compressed gases?

    What defines how much energy we could store in some gas by compressing it to a certain volume by applying a certain pressure? The compessability coefficient? Is there some gases which allow to store more energy than air? Which gas has the largest compressibility coefficient?
  11. B

    Help with compressed air thrust

    I'm working on a kinda-sorta confidential device. I would like to know how much psi is required to lift approx. 400 pounds 120m (about 393ft and 8 13/32 inches) into the air. The thing I'm working on is still in the designing stage, so don't worry about the specifics of individual thrusters and...
  12. C

    Cooling compressed air from pump

    I have a fairly large (for household use) 7.5HP electric motor driven two-stage air compressor, which charges the receiving 80 gallon tank to a limit of 175PSI. There is a short 3/4" diameter copper pipe that connects the pump to the tank. I have not measured, but guesstimate that the...
  13. M

    Simulation of Compressed Air Driven Piston

    I am writing a MATLAB script that generates a dynamic simulation of a piston being driven by compressed air. My starting values for pressure and volume are as follows: P0 = 14000000; %nm-2 or 140 Bar V0 = 0.005; %m3 or 500cc The simulation needs to be quite detailed and must take into account...
  14. J

    Compressed air flow rate from pipe to container

    Hello All,I was given a problem today that I could use some guidance on. I have a compressed air pipe flowing into a container. This container has a pressure of 5 psi while the pipe has a pressure of 90 psi. There is a valve that controls when the air is released into the vessel and only...
  15. I

    Calculating the effect of humidity volume and temp of compressed air

    This isn't homework, I'm a hobbyist, not a student. Posting here because questions I've previously posted were moved to this section. My intent is to better understand humidity and it's role in compressed air for an automotive application. All help and direction is greatly appreciated. Thank...
  16. C

    Pressure to volume relationship in compressed air

    Hi guys need help. We've been encountering compressed dry-air related problems here in our plant. Most machines pressures were fluctuating when their equipments are running. As I've checked, the problem is not regarding the pressure since the line pressure is 10psi higher than machine...
  17. M

    Calculating compressed air expansion when heated

    Can anyone help me with this calculation? I'm trying to figure out how much compressed air (generated from screw compressor) will expand by a ratio of what when fed into a wood furnace. 1) Wood Furnace Fuel Input: 30kg dry wood fuel/hr 2) Compressed Air Pressure: 8 bar 3) Compressed Air Flow...
  18. H

    Compressed Air Tank: Temp & Condensation

    If I allow a tank that's pressurized(3000 psi) and initial temp (121) to cool to room temperature (25 C), will that increase the rate of condensation or is there a fixed amount of condensation that occurs while at that pressure? Having a tough time understanding that phenomenon. If no change in...
  19. J

    Compressed Air Car: Is My Thermodynamics Calculation Correct?

    Background: This is my first post here on physics forums. I have perused for quite a while. I am a Chem Eng. student at University of Houston and this question is from my Thermodynamics class. I have enjoyed working on this problem (for hours) but am certain i have made a mistake...
  20. G

    Does Mass Occupying Volume in a Compressed Air System Transfer Energy

    In a compressed air space there is a suspended mass with 10 cubic meters volume. The pressure vessel is 20 atm. The suspended mass is suspended 100 meters over water that is kept at bay by the air pressure inside the vessel. The moment the mass is released its potential energy converts to...
  21. Y

    Adding pipes for compressed air delivery

    Hi all! I have a problem here, anyone here knows what will be the effect on pressure and flow rate of compressed air by adding additional pipes leading out from my compressor? For eg. if i were to increase the number of delivery pipes from 1 to 2, will the flow be slpit evenly between the two...
  22. T

    Friction of a pipe and the effects on compressed air?

    Let's say a receiving device that requires compressed air is 1.5 miles away from the source and demands 600 cubic feet per minute. Let's say the pipes have a diameter of four inches and already contain air at 90psi. If friction in the pipes would be ignored, it would require the same amount...
  23. C

    Force / Thrust from Compressed Air Container 90ci/4500psi

    Hello All, I was wondering that what is the force/thrust we can get from 90ci/4500psi compressed air container, which are available in market for Air guns. Also how long that force will last continuously (2 min or 5 min or more) ? For more info about the container ...
  24. N

    How Can I Control Syringe Pressure with Compressed Air and Vacuum Pump?

    I would like to try and set up a pressure control system in my lab using house vacuum and compressed air. Or otherwise using a compressed air source and vacuum pump. I want to be able to control the pressure in a reservoir (a syringe) within the range of -15 to +15psi. I was thinking...
  25. I

    Temperature drop when expanding heated compressed air

    Homework Statement I need to know how much the temperature drops after an inline heater which heats an airflow of 5 lbs/min up to 88 °C with an pressure of 54 PSI. When the air exits the heater it is released into the free air where it is 20 °C. I know that the air will expand to a...
  26. H

    Compressed air lift question (thermodynamics)

    Homework Statement A platform is supported on a piston by compressed air in a cylinder. The mass of the platform and equipment being lifted is 1100kg. The pressure needed to support this mass is 800kPa, and it rests initially at a height of 0.5m. The pressure supply is closed so that no gas...
  27. Vorde

    Dispose of Compressed Air Can Safely on Hot Day

    For starters, I have no idea where to post this question but I think this is a good place. Earlier today I bought a compressed can of moisture-less duster to clean my computer fans with. That is all good, but when I was done I wasn't sure where to dispose of the can. Normally it would be...
  28. S

    Reusing lost energy from Compressed air

    Why is Heat not normally trapped when compressing Air, and reused again in the expansion process of the same air?
  29. R

    How do you calculate BTU of expanding compressed air

    I would like to know if there is a measure, in BTU's, of the cooling effect from the release of compressed air through a nozzle and how it relates to PSI
  30. H

    Automotive How can heat management be optimized in compressed air powered bikes?

    hey mechies, i know "compressed air powered bike" is one of the oldest concept of our engineers but still in their developing stage.. i am in my final year of mechanical engineering undergraduate course. And i am about to do final project by end of this year.. when searching for real time...
  31. B

    How Does Heat Transfer Affect Compressed Air Energy Storage in Salt Caverns?

    Hi all, I am trying to model temperature variation with time of compressed air energy storage in a salt cavern. For now I have considered a spherical (hollow) cavern in which air is injected. I have to solve [U]{T}+[M]{T_dot}={Q} (here, Q is the first term and all other entries are zero)...
  32. P

    Model airplanes powered by compressed air ? Anyone ?

    Model airplanes powered by compressed air ...?? Anyone ?? Hello, Has anybody explored idea of powering aeroplane models by compressed air? Does this seem to be viable idea? Prima-facie: Let's say a rubber tire tube (old days of car tires - now its all tube less) inflated to say 60...
  33. D

    Compressed air discharge calculation for CFM and volume

    Ok here is my problem. We have a static value that we use for determining the cost of air based on the pipe size and the CFM used. What I have is the size of the pipe openings and what my constant static pressure is. The air is being blown into a vacuum. System details: Lead pipes is 4...
  34. B

    Dart Energy from Compressed Air

    Hi Everyone, I am trying to calculate the exit velocity of a dart which is propelled by compressed air. Please see the attached jpeg for diagram and my work so far. My final formula appears to be incorrect. I'd appreciate any help figuring out what is wrong. A pressure tank of Volume...
  35. R

    Find time to evacuate compressed air tank (conceptual verification)

    Homework Statement This is a first-order differential equation problem involving a changing fluid density and changing tank pressure. Tank contents: Nitrogen Tank pressure: 390 psig Temperature of compressed nitrogen: 0 CAtmospheric volume = infinity Atmospheric pressure = 14.7 psi...
  36. S

    Power generation using buoyancy, gravity and compressed air

    Hi all, this is my first post. I was wondering if it would be possible to use a deflatable/inflatable bladder inside a housing with an air valve at the top and bottom of said bladder secured through the housing. The housing material would be heavy, placticised metal or stainless steel. This...
  37. C

    Using compressed air to displace water

    Not really sure how to word the title better! Anyway, I'm looking at how I could design and do some basic flow calculations regarding compressed air. The idea is to have a tank of highly compressed air piped to a tank of water. When the valve between them is opened, the compressed air rushes...
  38. F

    Compressed Air - Bernoulli Equation

    I'm trying to ascertain the dynamics of a compressed air system in terms of flow rate, air consumption, pressure drop etc. To keep it simple my system consists of a 5.5 bar supply (550000Pa) supply on 12mm OD Nylon Tubing and is reduced to 6mm OD Nylon through a valve (pressure drop assumed...
  39. F

    Compressed Air System Dynamics: Calculating Pressure Drop & Cv

    I want to work out the dynamics of a compressed air system consisting of a filter/regulator unit some spool valves and a rotary actuator with all the associated fittings. Essentially I have a 2" nominal bore compressed air line at roughly 7.5 bar, I have a system which feeds off this air main...
  40. C

    Does Nozzle Orientation Affect Speed in Compressed Air Powered Boats?

    I saw on myth busters where they took compressed air tanks an attached them to a boat and then opened the valve and then the boat started to move. They did 2 trials, one where the exhaust nozzle was pointed above the water and one where it was pointed in the water. Then one that was pointed...
  41. I

    Under Pressure Finding the height of compressed air

    Homework Statement A 1.0--tall cylinder contains air at a pressure of 1 . A very thin, frictionless piston of negligible mass is placed at the top of the cylinder, to prevent any air from escaping, then mercury is slowly poured into the cylinder until no more can be added without the cylinder...
  42. B

    In replacing a compressed air motor with a nozzle where does the energy go?

    Assume a compressed air motor, whose input power 1 cubic metre/minute at 200 psi. The motor exhaust is say, 20 psi at the appropriate volume say 10 - 11 cubic metre/minute. The motor produces 1KW due to its inefficiencies. Suppose the motor is replaced with a nozzle whose flow rate is the...
  43. F

    Volume of compressed air question.

    Hi, Can anyone help me with a personal project I am working on? I wish to compress air in a container up to 100psi. I'm making a small single cylinder compressor to achieve that. The container is small, approx 0.05 cubic feet. I'm trying to work out how many strokes of the compressor...
  44. T

    Compressed Air Engine for a cycle

    A friend and I are working on this idea which is fairly common, but I'm having trouble starting out. The idea is that of a compressed air engine. Where we take a normal, small capacity engine and modify it such that only compressed air, stored in tanks is sufficient to move the piston. Now...
  45. M

    Using Shipping containers as compressed air 'Batteries

    Using Shipping containers as compressed air 'Batteries" Just joined the site, you have a much more practical captcha system, I am surprised its not more widely implemented. Anyway! Obviously if you have seen a peak energy demand graph you will notice that the peak energy requirement is from...
  46. S

    Compressed air help (adiabatic processes)

    Homework Statement i'm trying to work out how much energy can be extracted from a compressed air system using an adiabatic process. given how small scale the system is(an most likely unrealistic), the values for the energy that can be extracted seem very high from my calculations. Homework...
  47. B

    Calculating Air Velocity in a Duct with a Consistent Cross-Sectional Area

    Suppose I have a straight, frictionless duct, with consistent cross-sectional area, and air is flowing straight through and exiting into a free stream. A fan at the beginning of the duct draws stagnant air at atmospheric pressure, and then the air exits the end of the duct into another room also...
  48. R

    Calculating Compressed air leaks within a system

    Hi all, new to the forum, but I was wondering if anyone could help me as I'm going round in circles. After completeing an air leak survey and noting the hole diameter, dB reading of the leak and knowing the pressure of the system (bar) how can I calculate the leak rate CFM and the Energy wasted...
  49. A

    Compressed air cylinder temperature during rapid depressurisation

    Hi guys, Here's an interesting problem for you. I'm trying to understand what happens to the temperature of air cylinders as the compressed air within is rapidly expanded to see if the surface in contact with the expanding air gets so cold it passes through the ductile to brittle transition...
  50. B

    Buoyancy in Compressed Air: Can Objects Float or Will They Fall Due to Gravity?

    If air would be compressed to have equal pressure to that of water would objects which are buoyant in water be buoyant in such compressed air too or would they still fall down due to Earth gravity? Or asking differently, what would have to be the pressure of air (lower, equal or higher than...
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