pressure measurement in air duct system with U-tube manometer 2

[CARF]

Dear all,

I want to measure the air pressure in an air duct system both on the head and suction side of a big air ventilator. The channel is square 1.5 x 1.5 meter, air velocity is around 10 meter/sec. The motor is 100 kiloWatt.

Now I want to apply a good old U-tube manometer to measure the air pressure. Does anybody have experience with this method? How to avoid pressure readings induced by speed (p = 0.5 rho x V^2) and carburetter-like sucction effects?

What pressure readings I can expect (approx), I mean what pressures are typical for this size of ventilators?

Please let me know,
MVD

 

[DougMSOE]

I hve done this a few times but only needed relitive nos. Suggest that you contact ASHRAE and maybe they could help.

 

[BRT549]

Find a Dwyer catalog and buy a static pressure tip. The A-303 model even has a magnet on it so you don't have to hold it while getting your measurement. These tips are made to cancel any venturi effects, etc. I suppose they have a website too.

The catalog also has good technical sections on how to take various velocity and pressure measurements. As for guessing what you'll get for pressure measurements, not enough info.

 

[BRT549]

I'm not trying to sell you anything, but here is a link to what I was talking about:

http://www.dwyer-inst.com/htdocs/airvelocity/qsprestipsandfit.cfm

 

[pharoofthermo]

MVD,

I agree with BRT549. You only need a static pressure gauge for the application. At the velocity/area values provided I would only expect pressures in the range of 0-10 inches of water.

Pharo of Thermo

 

[hacksaw]

static pressure measurements can be made with a connection that is flush with the plenum wall.

There are also special insert fixtures that accomplish the same.

You can also take a pitot reading and subtract out the velocity term.

Manometers are fine but have been replaced by electronic types.

If you are in a hurry a plastic tube filled with water works great. In practice the velocity effects are not that great unless to direct the tube suarely into the flow.

 

[CARF]

Dear All,

You are great!

Thanks for all the information. I'm going for the web-link you gave me. Thanks for all the tips.

: )
MVD

 

[CARF]

For anybody curious; the air pressures I measured where:

Pressure head: +9 cm water
Pressure suction -3 cm water

Cheers,

 

[BRT549]

Those numbers sound reasonable. What are you going to do with the data?

 

[CARF]

Hi,

I'm checking the air mass balance of a sausage drying tower. Mass In = Mass OUT and the air mass flow [kg/sec] is dependend on pressure , temperature and the volume flow [m3/sec].

Here's some equations I used:

http://home.hccnet.nl/m.dijk/pressure_drop_calculator/calcs/calcs.html

(=Physical Properties of Water and Air.)

Greetings from Holland,
MVD

 

[BRT549]

Sounds very interesting. I enjoy doing air balances in the fertilizer plant I work in. The web link looks useful, and I'm adding it to my "toolbox".

Greetings from Wyoming, USA.

BRT-549

 

[CARF]

The website is now:

http://www.carf-engineering.com/

Cheers,
C.