Re: Measurement Of Fan Air Volume
dear mall,
Assuming VP means velocity pressure.
Under 2) you measure the VP, SP (static pressure) before and after the fan.
Then you state that you assume VP(in) equals VP(out)
Why measure first and the assume the values are equal?
The only assumption you can make is the the mass flow in equals the massflow out.
If there are no leakages, you can build your calculations on that truth
The measurement itself has to be carried out accurately and with knowledge.
F.i
measure the VP and the SP at exactly the same location
Measure a velocity profile and average the measurements, weighed for the appropriate area.
success
teus ■
Teus
Re: Measurement Of Fan Air Volume
teus
normally we assume VP in equal to VP out but in actual condition this doesnt happen.
as i measured VP in before fan and VP out after fan, i found out Q, air flow outlet fan is higher than Q in of fan inlet.
i just want to know why this phenomenahappen?
regards
mall ■
Measurement Of Fan Air Volume
Mall,
Measurement error. Try to choose a location well away from flow disturbances, bends, the fan discharge and inlet etc.
Michael Reid. ■
Re: Measurement Of Fan Air Volume
michael
i wish to if i have the other location. but due to system design is like that, the disturbance eg elbow, damper is close to each other.
i have to use this location to measure inlet and outlet of fan.
your advice tq ■
Measurement Of Fan Air Volume
Mall,
Airflow in = airflow out. If there is a difference, it is due to error or leakage. Measurement close to the fan discharge is problematical, due to poor velocity distribution. Best place to measure after the fan is in the vertical stack (if there is one).
Airflow close to the fan inlet is already rotating so the alignment of your pitot will not be accurate.
It is sometimes possible to measure in two or more smaller ducts to get the aggregate inlet flow.
Michael Reid. ■
Re: Measurement Of Fan Air Volume
tq michael for good reply........
it's true Q in =Qout.
because i just measure before and after fan. of coz high turbulance.
what do mean by measure in two or more smaller duct ....see below? pls elaborate more pls
Mike wrote "It is sometimes possible to measure in two or more smaller ducts to get the aggregate inlet flow."
tq ■
Re: Measurement Of Fan Air Volume
Mall,
Depends how complex is your duct system, one duct or several branches.
Michael Reid. ■
Re: Measurement Of Fan Air Volume
mike
single duct inlet to fan and two duct 1 for stack and another duct return pipe ■
Measurement Of Fan Air Volume
Mall,
Post a sketch of the ducting and stack. I will try to make more suggestions.
Michael Reid. ■
Fan Performance
hi my friend
i have a project about air condenser fan and i must find out the fan air flows with the highest accuracy
i have seperated the fans surface to 4 part and measure each part velocity and at last gain the air flow volume but it wasnt really accepteble do u have anu other method or numerical method to use ■
Measurement of fan air volume
hi there
just want to check with you, why after fan Q with spec Q=124000Nm3/hr is always higher if compare to the fan Q inlet.
the method of measurement as follow;
1) using pitot tube and digital manometer and temperature
2)measure the VP,SP before and after fan. then convert the VP to velocity by taking the air temperature Tair =85-100 deg C for correction. plus area of cross section of duct.
we always make assumption for fan VPin =VPout but this doesnt happen in actual condition.
i find out the VP out is higher than VPin. in other word Air volume out is higher than air volume in. Why???
is it due to compressible factor that i ignore? pls advice how to calculate compressible factor for fan.
need your prompt reply pls.......
thanks ■