Calculating isentropic efficiency of a compressor

[MattH150197]

Homework Statement

We did an experiment which included having an electric motor provide power to drive the compressor and we had instrumentation available to measure the compressor shaft torque and shaft rotational speed and 6 water filled manometer tubes were used as measurements of the pressure. Using the manometer heights we was asked to calculate the isentropic efficiency.

Homework Equations

The equation we were given to used: isentropic efficiency = (air mass flow rate * Difference in stagnation pressure across the compressor)/ (air density * compressor shaft torque * shaft rotational speed)

The Attempt at a Solution

I calculated the air mass flow rate at 3.89 kg/s, the difference in stagnation pressure at 1900.92 pa, air density at 1.21 kg/m3, shaft torque at 213.86 N.m and rotational speed at 303.68 rad/s from those I got an answer of 0.094 I am new to this subject so not sure what kind of numbers I should be getting but that answer seems really low, is there any numbers you can see that seem unreasonable or could it be correct? Thanks

 

[Chestermiller]

Homework Statement

We did an experiment which included having an electric motor provide power to drive the compressor and we had instrumentation available to measure the compressor shaft torque and shaft rotational speed and 6 water filled manometer tubes were used as measurements of the pressure. Using the manometer heights we was asked to calculate the isentropic efficiency.

Homework Equations

The equation we were given to used: isentropic efficiency = (air mass flow rate * Difference in stagnation pressure across the compressor)/ (air density * compressor shaft torque * shaft rotational speed)

The Attempt at a Solution

I calculated the air mass flow rate at 3.89 kg/s, the difference in stagnation pressure at 1900.92 pa, air density at 1.21 kg/m3, shaft torque at 213.86 N.m and rotational speed at 303.68 rad/s from those I got an answer of 0.094 I am new to this subject so not sure what kind of numbers I should be getting but that answer seems really low, is there any numbers you can see that seem unreasonable or could it be correct? Thanks

Did you mean stagnation pressure or static pressure? Also, is this a tiny little compressor or a great big compressor?

 

[MattH150197]

Stagnation pressure and the compressor used was a Budworth two stage axial flow compressor

 

[Chestermiller]

Stagnation pressure and the compressor used was a Budworth two stage axial flow compressor

Please show us your calculations.

 

[MattH150197]

Im sorry it's really kind of hard to show you how I did the calculation because for example to get the air mass flow rate I had to do 3 separate calulations to get that value so I'd have to write lots of different calculations, I really appreciate you helping but would you say that the value I got for the isentropic efficiency is plausible or not? Thanks

 

[Chestermiller]

The mass flow rate seems OK. The pressure difference seems low (to me), for whatever that's worth.

 

[MattH150197]

Okay thanks very much