Blower Flow rate measurement

[ChemE2912]

Hi All!

Can anyone help us in finding out what would be the best possible location of a pitot tube for the flow measurement in a blower?

Currently, we are locating it at the discharge line, but we have seen some arrangements showing it at the suction of the blower. Is there any significant difference??

Thx,

ChemE2912

 

[CARF]

Hi,

Maybe it's better to ask this question on the measurement & control instrumentation group.

> There's no principal difference to measure in the suction or in the discharge.

1) Keep in mind to measure not to close to bends or other obstacles, because turbulence will spoil your measurement then.

2) Then what exactly do you want to measure? Volumeflow (m3/sec) or massflow (kg/sec). For massflow you need to measure pressure and temperature as well since the density of gasses change with pressure and temperature.

3) At what point are you going to measure? In the centre of the channel the flow will be higher then near the wall.

There are good Pitot systems around who take say 5 measurements across the whole channel and take the average.

See for example Endress + Hauser: Deltatop / Deltaset.

http://www.endress.com/

These are complete systems with flow computer, where all temperature and pressure caculations are done to covert to massflow.

Hope this helps,
MVD

 

[patrickraj]

You r measuring at the S/C r D/C, the flow will remain same,since you have to use correct density in the formula
V=sqrt(2GH),Where H is the FT of air column. H is obtained by multiplying the Press by density of manameter fluid and dividing Press by Density of air for the corresponding press where pitot is inserted.

 

[antisurge]

Suction flow measurement of an (atmospheric) air blower is the total flow of the blower. Discharge flow could be either the total or the net flow depending on the flow location relative to the location of the blow off line/valve. So, comparing total in suction to net in discharge would/could be significant. Do you want to measure net or total?

Averaging Pitot tubes are prefered to pitot tube (as MVD points out). Annubar is the name used by Rosemount.

Discharge lines typically have less diameter and often has the advantage of more choice in selecting the location. Another advantage is that pressure drop in discharge is less of a loss (operationally cheaper) than in the suction (dP/P). DPs in suction of blower, for pitot tube, are probably very small (draft range or less) which can be problematic.

dont forget to mount dp instrument above the taps with no utubes, condensed and trapped h2o will create alot of problems.

only observed pitot tubes in cheme lab, never in industry.

 

[CARF]

Hi ChemE2912,

drop your e-mail adress and I'll sent you two nice spreadsheets on air flow mass balance across an air blower.

Cheers,
MVD

 

[ChemE2912]

Thank you all.

MVD, My email address is abaumeister@member.aiche.org

Regards,

ChemE2912

 

[CARF]

done!

see further: thread378-47551

Good luck,
MVD