# Calcuating energy from Air Tank

1. Mar 31, 2013

### Kayne

Hi,

I was working with my Air compressor today and was wondering if there is a way to calculate the amount of work or energy that is stored within a air tank? The air compressor is a 2.5hp, 112L/m 120Psi and volumes is 40L.

From these details can the work be calculated or is more information required.

Any guidance would be great

Thanks

2. Mar 31, 2013

### CFDFEAGURU

Yes, it can be calculated.

First you need to determine the mass of the air stored in the tank at the final temperature and pressure of the air in the tank.

Second use the gas constant for air at standard conditions. R = 287 J/(kg-K) (be careful with standard conditions as they are not always standard)

Next calculate the Specific Heat at Constant Volume using the above values. Gamma for air is 1.4

Next the energy in joules per kilogram can be calculate by multiplying the Specific Heat at Constant Volume by the temperature of the air.

Lastly, the total energy is the above energy times the mass of air. The ending units will be Joules.

3. Mar 31, 2013

### Kayne

This sounds easier then it looks, so please bare with me on this explanation

So I have taken real measurements off the compressor which were
Temperature = 33°C
Pressure = 120Psi

Can you please explain in a little more detail how to calculate the Mass, and what variables are required?

The air tank volume = 40 litres
Temperature = 33°C
Pressure = 120Psi
Gamma = 1.4
gas constant = R = 287 J/(kg-K)

$Specific heat = Mass \times Gas Constant \times Pressure \times Temperature \times Volume^{gamma}$

Am I on the correct path with the equation

Do you mean the temperature of the air inside the tank or ambient temperature which was 29°C

$Energy (J/kg) = Specific Heat \times Air temp$

$Joules = Energy \times Mass$