Air Pressure and flow to power calculations?

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SUMMARY

This discussion centers on calculating the power stored in compressed air, specifically at 30 psi and 100 cfm, using Bernoulli's Equation and principles from fluid dynamics. Key equations mentioned include the potential energy equation PE = P_{atm} + \rho gh + \frac{1}{2} \rho v^2 and the hydraulic power formula Power = p * Q, where p is pressure and Q is volumetric flow rate. The conversation highlights the challenges of applying these equations to air due to its compressibility compared to hydraulic fluids, emphasizing the need for accurate variables such as atmospheric pressure, density, gravity, height, and velocity.

PREREQUISITES
  • Understanding of Bernoulli's Equation and its applications
  • Knowledge of fluid dynamics principles
  • Familiarity with thermodynamic variables (pressure and temperature)
  • Basic concepts of compressible vs. incompressible fluids
NEXT STEPS
  • Research the application of Bernoulli's Equation in compressible flow scenarios
  • Learn about the calculation of power in pneumatic systems using the formula Power = p * Q
  • Explore the concept of total enthalpy for ideal gases
  • Investigate the effects of compressibility on energy calculations in gases
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Engineers, physicists, and students in fluid dynamics or thermodynamics who are interested in the calculations related to power and energy in pneumatic systems.

infamous_Q
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is there any easy way, or relatively easy way, to calculate how much power is stored in a certain amount of air with a certain amount of pressure and flow? i know that's VERY vague, so let's say (random number's being chosen...) 30 psi at 100 cfm.
 
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use Bernoulis Equation.
PE = P_{atm} + \rho gh + \frac{1}{2} \rho v^2

Regards,

Nenad
 
hmm...call me an idiot if you wish. but i guess I am going to have to guess at these variables:

Patm...no idea

p = density
g = no idea
h = no idea
v = velocity

thats bad i know..but could you maybe help me fill in the blanks?
 
Patm is Atomspheric Pressure
g is gravity of course
h is height
 
What exactly are you trying to get to using this? I have a sneaky suspicion I know, but I'd rather know for sure.

In hydraulic systems, one simply uses

Power = p * Q
Where:

p = pressure
Q = Volumetric flow rate

You can do that here, but you'll have some pretty decent errors due to the high compressibility of air vs. hydraulic fluid and availability to do work.
 
infamous_Q said:
is there any easy way, or relatively easy way, to calculate how much power is stored in a certain amount of air with a certain amount of pressure and flow? i know that's VERY vague, so let's say (random number's being chosen...) 30 psi at 100 cfm.

The amount of energy stored by a fluid is its total entalphy:

h_t=e+v^2/2+P/\rho=c_pT+v^2/2(J/Kg) in the case of an ideal gas.

In order to determine the total content of energy of a gas you need a mechanic variable such us velocity and two thermodynamic variables (P,T). If the flow is at low Mach numbers, it is only needed one thermodynamic variable and one mechanic variable because thermal and mechanical states become discoupled.
 
thanks guys. hey Fred...what's this sneaky suspicion you have? lol. also..how big would that margin of error be? and I'm assuming pressure is kpa and flow rate is m^3/s...(although i really think I'm wrong with the Q unit)
 

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