How much power required to generate a particular pressure

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Discussion Overview

The discussion revolves around the power required to pressurize a cylinder to a specific pressure, exploring whether there are general guidelines or formulas applicable across different volumes and fluids, particularly air. Participants examine the relationship between power, pressure, and the method of compression, considering both theoretical and practical aspects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about general guidelines for calculating the power needed to pressurize a cylinder of a given volume to a specific pressure.
  • Another participant asserts that there is no meaningful general relation between power and pressure, nor between energy and pressure.
  • A participant discusses the safety differences between testing cylinders with water versus air, highlighting the energy implications of air compression.
  • There is a repeated question about whether an equation exists for calculating power when compressing air to a specific pressure, indicating a need for specificity regarding the compression process (isothermal vs. adiabatic).
  • One participant notes that the power required depends on the rate of air input and factors such as temperature and thermal mass of the container.
  • Examples are provided comparing different methods of inflating a tire, illustrating that while the end result is the same, the power required varies significantly based on the method and time taken.

Areas of Agreement / Disagreement

Participants express differing views on the existence of a general formula relating power and pressure, with some asserting that no simple rule exists while others seek specific equations for air compression. The discussion remains unresolved regarding the applicability of general guidelines.

Contextual Notes

Participants highlight the complexity of the relationship between power, pressure, and the method of compression, noting that factors such as temperature and the speed of compression significantly influence the calculations. There are also indications that practical examples may provide insights into the theoretical questions raised.

Who May Find This Useful

This discussion may be of interest to individuals involved in engineering, physics, or practical applications of pressure systems, particularly those exploring the dynamics of air compression and safety considerations in pressurization.

escape_velocity
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Are there any general guidelines or rule of thumb regarding how much power in watts would be required to pressurize a cylinder to a particular pressure and can I use this as a general rule,

For eg. I want to pressurize a vessel of volume 1 cu. m how much power would be required and can we generalize this so the this formula can be applied to a vessel of any volume?
 
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There is no meaningful general relation between power and pressure. Not even between energy and pressure.
 
Testing divers' compressed air cylinders is done by pressurising them with (nearly incompressible) water). If they 'fail' catastrophically, they just form a split and there is very little disturbance. There is very little energy stored.
OTOH, if a cylinder fails when being over-pressured with air, you have a BOMB on your hands. So much more energy involved. You can pressure test a cylinder with a few strokes of a manual water pump but an air compressor (a few h. p.) runs for minutes and everything gets too hot to touch.
No simple rule to connect the two. [emoji846]
 
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sophiecentaur said:
No simple rule to connect the two. [emoji846]
What if I say that the fluid is "air" now would there be an equation for power to pressurize a cylinder with air to a particular pressure?
 
escape_velocity said:
What if I say that the fluid is "air" now would there be an equation for power to pressurize a cylinder with air to a particular pressure?
OK But that is still not specific enough. Are we doing this quickly or very slowly? (Isothermal or Adiabatic) Diving cylinders are kept cool (in a water bath) during compression or their 'final' pressure will go down as their temperature drops.
Actually, if you Google Divers' Air compression, you may find some actual examples. That could answer your question if it is practical rather than theoretical.
 
The pressure (and other info such as temperature) give you the energy stored in the tank.

Power = ΔEnergy/ΔTime so to calculate the power you need (at least) some info on how fast you are putting the air in.

Even then it's not that simple because (as Sophiecentaur says) the temperature may also depend on how fast you put the air in and factors such as the thermal mass of the container, how well insulated it is etc.

How accurate an answer do you need?
 
sophiecentaur said:
OK But that is still not specific enough...
Actually, if you Google Divers' Air compression, you may find some actual examples. That could answer your question if it is practical rather than theoretical.
Let me provide some examples in hopes they may help:

Say, you are pressurizing a car tire to 200 kpa. You can:
1. Use a base mounted compressor with a tank, which can provide compressed air at thousands or tens of thousands of Watts.

2. You can stomp on a foot-pedal pump for a peak power of perhaps a thousand Watts.

3. You can use a hand-held bike pump with a peak power of perhaps 50 Wattts.

As you can see, all of these give the same result (an inflated tire) but require/use vastly different power to do it. The main difference is how long it takes. So you see, there is more to finding the power required than just the final pressure.
 
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