Reverse engineering of roots blower selection software 1

[hirschaplin]

Hello,

I have an old roots blower selection software, issued some 20 years ago. The manufacturer no longer exists which means that the support of the software has stopped since some 15 years back.

The input values are:
Flow rate in m3/h or Nm3/h or kg/h or fixed rpm
Inlet pressure
Inlet temperature
Outlet pressure
Gas mw
Gas Cp
Gas K value (Cp/Cv)

It is also possible to input the ambient temperature and the atmospheric pressure but it seems like these values doesn't affect the calculated result.

The calculated output values given by the software for each blower model that has been setup in the software, are the following:
Blower rpm
Outlet temperature
Shaft power

I am looking for a way to reverse engineer the formula used to calculate the output values and setup my own selection calculator in excel.

For each blower model I have the original performance curve, displacement and the original selection software to validate results of the new formula.

Any pointers to how I can do this? Any people or companies that can assist? Or can we figure it out here on the forum?

Thank you.

 

[Tuckabag]

This might be a good starting point :

https://www.pdblowers.com/tech-talk/positive-displacement-blower-calculations/

However, you'll find slip figures are going to vary across manufacturer/models.

 

[hirschaplin]

Thanks for sharing that excellent article Tuckabag. Something like that is what I have been searching for without success.

In the slip calculation I need the SLIP[sub]APPLICATION[/sub] input to complete the equation. Do you know how I can obtain that data without the need to actual measure:

SLIP[sub]application[/sub] is determined by blanking off the discharge of a blower and rotating the blower at the speed that will generate a 1 psi at the discharge. This is also referred to as 1 psi slip.

 

[Tuckabag]

I would think that the slip data would be IP for most manufacturers.

If you can find data with the volume/rpm for the particular blower you are looking at, manufacturers will give a chart/table with actual flow capacity at various outlet pressures.
You can then work out the slip at these exact conditions.

 

[hirschaplin]

Thanks but I was actually able to find the slip rpm at 1 psi in an old catalogue from the 1980's.

Some other questions about the parameters in the SLIP[sub]corrected[/sub] equation:

Δ Pa
Differential Pressure in psi [hirschaplin] : I understand this one.

Δ Ps
Standard Pressure rise = 1 psi [hirschaplin] : What is this parameter for?

Ps
Standard Absolute Pressure in psia [hirschaplin] : What is this parameter for?

Pa
Actual absolute inlet pressure in psia [hirschaplin] : I understand this one.

Ta
Actual absolute inlet temperature in °R (°F+460) [hirschaplin] : I understand this one.

Ts
Standard absolute inlet temperature in °R, 528°R [hirschaplin] : What is this parameter for?

Gs
Standard Specific Gravity of air, 1.0 [hirschaplin] : I understand this one.

Ga
Actual Specific Gravity of gas [hirschaplin] : I understand this one.

I have already created my formula and it works well, when I compare my result to the original OEM calculation software all calculated key parameters are within 0,5% from each other but not exactly 1:1. Perhaps because of some decimal rounding. I guess that is good enough.

My next step is to try translate the formula to include metric UoM but I am afraid that might require some work since the constants may vary.

Highly appreciated if someone can help clarify the above parameters that I have commented.