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Air Flow Validation in Large Size Ducts

12/03/2014 10:30 PM

We are having secondary ducts of size 4000X 5000 mm size with aerofoil and primary air duct of 2000X3000 mm size with ventury for air flow measurement. Pl help me in validation of these flow measurements using pitot tube or any other means.

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#1

Re: Air flow validation in large size ducts.

12/03/2014 11:15 PM

OK. Let's see what you've got so far.

Primary Air Commissioning - Dadanco

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#2

Re: Air flow validation in large size ducts.

12/04/2014 1:27 AM

I would measure more to the middle. The general assumption could be flow over area is constant which will neglect slip at the walls and corners. Do you need units in mass or volume?

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#4
In reply to #2

Re: Air flow validation in large size ducts.

12/04/2014 8:32 AM

To determine slip near walls and corners, if anything you need to emphasize measurements there rather than near the middle.

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#5
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Re: Air flow validation in large size ducts.

12/04/2014 8:04 PM

Thats would be the other way around!

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#7
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Re: Air flow validation in large size ducts.

12/04/2014 11:29 PM

Well, no; sorry.

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#9
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Re: Air flow validation in large size ducts.

12/05/2014 2:33 AM

Sure is!

If he wants to neglect the slip he can measure in the middle.

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#10
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Re: Air flow validation in large size ducts.

12/05/2014 3:48 AM

He doesn't want to neglect the velocity variations.

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#3

Re: Air Flow Validation in Large Size Ducts.

12/04/2014 8:27 AM

The word for today is "annubar". See also post 1.

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#6

Re: Air Flow Validation in Large Size Ducts

12/04/2014 10:57 PM

I have performed these airflow tests in Power Plants all over the United States and sometimes overseas. We use a Forward-Reverse/S-Type Velocity Probe. This is a routine tests for a power plant trying to tune a combustion process.

A traverse a plane of the duct is setup using an equal area test grid. We measure velocity head, temperature and static pressure. And validate any installed measurement device over the expected range of measurement. The data is then used to calculate mass flow. Primary air should use temperature (density) compensation due to the large differences in operating temperature.

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#8

Re: Air Flow Validation in Large Size Ducts

12/05/2014 12:36 AM

I am surprised that you come to a forum like this with such a broad question. You are obviously dealing with some serious equipment, or are a student (??), and you appear to know little - how about a little study on your part, then as required, a question on some point of confusion to this forum - that would be reasonable.

For me, I see problems in driving a large cross section uniformly (as needed for aerofoil work I'd think) with a relatively small feed cross section as you propose, in the absence of a large transition section that you've not mentioned - for the reason of avoiding turbulence.

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#13
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Re: Air Flow Validation in Large Size Ducts

12/05/2014 1:28 PM

These are two separate ducts.

Not one supplying the other.

Secondary Air is the term to describe the combustion air for a boiler and accounts for about 70-80% of air required for combustion. Primary air is the term used to describe the air used to transport pulverized coal through a pulverizer and fuel conduit. It accounts for the balance of the air need for combustion.

Primary air is usually tempered with ambient air to maintain a constant pulverizer outlet(140-180°F) temperature and can vary from 200-700°F. It has to be hot to dry the coal to aid in pulverization.

Secondary Air doesn't fluctuate as much, usually 600°F.

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#11

Re: Air Flow Validation in Large Size Ducts

12/05/2014 1:14 PM

I understood his question perfectly.

If turbulence is a consideration or increased accuracy is desired, a 2D or 3D velocity probe could be used.

I always insist on performing field calibrations on Venturi and Airfoils. Annubars or Pitot Arrays have a tendency to plug and/or erode if not properly maintained and should be calibrated with a traverse more frequently.

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#12

Re: Air Flow Validation in Large Size Ducts

12/05/2014 1:18 PM

Your PA duct size indicates a large coal pulverizer, I would guess..... about 120,000 lbs per hour capacity.

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