# Air Pressure and flow to power calculations?

• infamous_Q
In summary, the energy stored in a fluid is determined by its total entalphy, which is h_t=e+v^2/2+P/\rho. However, in order to determine the total content of energy of a gas you need a mechanic variable such as 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.
infamous_Q
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.

use Bernoulis Equation.
$$PE = P_{atm} + \rho gh + \frac{1}{2} \rho v^2$$

Regards,

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)

## 1. What is air pressure and how is it measured?

Air pressure is the force exerted by the weight of air molecules in a given area. It is typically measured in units of pressure such as pounds per square inch (psi) or pascals (Pa), using instruments such as barometers or manometers.

## 2. How does air pressure affect the flow of air?

Air pressure plays a critical role in determining the direction and speed of air flow. Air will naturally move from areas of high pressure to areas of low pressure, creating a pressure gradient that drives air flow. The greater the pressure difference, the faster the air will flow.

## 3. How is air pressure used in power calculations?

Air pressure is a key factor in calculating the power generated by air flow. The power generated is directly proportional to the pressure difference and the flow rate of air. This relationship is described by the equation P = Q x ∆P, where P is power, Q is flow rate, and ∆P is pressure difference.

## 4. What factors can affect air pressure and flow in power calculations?

Several factors can impact air pressure and flow in power calculations, including temperature, humidity, altitude, and the physical properties of the air itself. Changes in any of these variables can alter the pressure gradient and affect the resulting power calculations.

## 5. How is air pressure and flow used in practical applications?

Air pressure and flow are used in a wide range of practical applications, including HVAC systems, industrial processes, and transportation systems. In these applications, air pressure and flow calculations are crucial for understanding and optimizing the performance of equipment and systems.

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