Mass flow measurement-hot air

Mr Satish

This type of measurement can be done through Dantec Instruments ( Hotwire Anemometer ). For more details please contact Dantec people.

MOHD. SAEED KHAN

Hi Satish,

Hot-wire anemometry is good for dust-laden environments, but will only give you a velocity at the point where it is measured. To sufficiently obtain an accurate average velocity, many such measurements would be needed to be taken simultaneously with an array of hot-wire sensors on the plane of the cross-section of the duct. This average velocity is then used (along with sensed temperature and pressure) to obtain the mass flow rate.

Are you sure that the temp in the duct is 725ºC and not 725ºF? Being this hot would raise some problems even with hot-wire anemometry.

Is there another, cooler section where the measurement could be taken?

Your best bet would probably be an orifice plate. The pressure drop in the duct caused by the orifice plate is used to obtain an average velocity. If you also measure temperature and duct pressure, these can be combined to obtain the mass-flow rate. There will also be some calibration involved. This would be the best method considering the temperature and particulate content in the duct. What I can't tell you is what the accuracy would be. It is quite likely that, with proper calibration and accurate duct temperature and pressure measurements, you would be within the ±2%.

I have done work on coal-fired energy plant ducts using patented pitot devices (http://www.easterninstruments.com) but the temp was only 500ºF max.

Hope this helps.

Mike

hi mike...thnx. the hot air generator is a coal fired fbc. and the dust laden hot air is at 725Deg C and not F. we tried anemometry..but the temp is a problem. with the orifice plate..the pressure drop creates a problem downstream where the air is supplied. we are now convinced ..almost...tht the pitot tube is the best way...will refer the site u mention...thnx a lot.

Dear Mr. Satish ,

You can use Orifice Plate for such Flow measurement , which we manufacture. The following data are required to see suitability & estimate price

Pipe/ Duct OD & ID , Pipe/Duct Material , Operating Temperature & Pressure ,

Flow Range.

Regards

can you measure at the inlet before the addition of heat and dust? if so differential pressure transmitter to ddc for variable calculation or differential pieto readings at magnahelic guage a simple math from there.

hi conwaymech..& guest,

thnx..input is from 3 diffeerent sources and one being not measurable as also the largest. so for now i think i am going ahead with the pitot tube arrangement..will get back with the results. Mr guest..can u give me ur email pl? i wud like to mail u the details.

thnx..Satish

CONWAYMECH@YAHOO.COM

hi all,

we tried the pitot tube with a digital manometer and its working just fine. thanx a lot for all the inputs!

satish

Hi Satish,

Thanks for letting us know how things went.

Mike