Rate of Air Flow vs Volume of Air Flow

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RFGuy
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Re: Rate of Air Flow vs Volume of Air Flow

Post by RFGuy »

dusty wrote: Wed Nov 30, 2022 6:58 am No apologies needed. I am stumbling my way through this and I appreciate all inputs.

I understand that a closed system is required to obtain an accurate evaluation and I am approaching that now. By wrapping the one end of a 2 1/2" hose coupler with foam I am able to create a soft pad that couples the meter to the DC. I saw the effects of that with my first preliminary test of this coupler. I achieved readings that were much closer to expectations than any test before.

However, I believe I will never get readings with the anemometer that I have simply because of meter limitations. Even with perfect coupling the meter is incapable of measuring airflow rates that translate to 200cfm. This anemometer is max'd at 5905 ft/minute. If my calculates are correct I need something like 7200 ft/min to measure 200cfm.

I have no way of judging the ability of the DC to produce that rate of air flow.
Dusty,

IF you are getting a max'ed out reading now with your modified dust fitting and your anemometer that is a good thing. That means you are getting at least 165 CFM, but most likely significantly higher. Can you try with more than 1 port open and see if your anemometer stays pegged out or if the reading drops? The original DC-3300 performance drops precipitously when more than 1 port is in use. It would be good to confirm if this is NOT the case with the DC-3300 upgrade.
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dusty
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Re: Rate of Air Flow vs Volume of Air Flow

Post by dusty »

RFGuy wrote: Wed Nov 30, 2022 8:21 am
dusty wrote: Wed Nov 30, 2022 6:58 am No apologies needed. I am stumbling my way through this and I appreciate all inputs.

I understand that a closed system is required to obtain an accurate evaluation and I am approaching that now. By wrapping the one end of a 2 1/2" hose coupler with foam I am able to create a soft pad that couples the meter to the DC. I saw the effects of that with my first preliminary test of this coupler. I achieved readings that were much closer to expectations than any test before.

However, I believe I will never get readings with the anemometer that I have simply because of meter limitations. Even with perfect coupling the meter is incapable of measuring airflow rates that translate to 200cfm. This anemometer is max'd at 5905 ft/minute. If my calculates are correct I need something like 7200 ft/min to measure 200cfm.

I have no way of judging the ability of the DC to produce that rate of air flow.
Dusty,

IF you are getting a max'ed out reading now with your modified dust fitting and your anemometer that is a good thing. That means you are getting at least 165 CFM, but most likely significantly higher. Can you try with more than 1 port open and see if your anemometer stays pegged out or if the reading drops? The original DC-3300 performance drops precipitously when more than 1 port is in use. It would be good to confirm if this is NOT the case with the DC-3300 upgrade.
Good thinking. Thanks. I'll give that a go but not for a couple days. Doctor appointments are in the way.
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Re: Rate of Air Flow vs Volume of Air Flow

Post by JPG »

When the small anemometer is placed in a large air stream(the HVAC case) it essentially 'sees' a small(inlet sized) portion of the air stream and will be measuring a sample very close to that of the large airstream.

When the opposite is true(2.25 hose/whatever) the airflow is expanded to the size of the larger inlet(2.5). That causes a decrease in the velocity the anemometer 'sees'.

i.e. the first case does not alter the velocity the anemometer 'sees'.



That's the way I 'see' it.
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RFGuy
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Re: Rate of Air Flow vs Volume of Air Flow

Post by RFGuy »

JPG wrote: Wed Nov 30, 2022 10:48 am When the small anemometer is placed in a large air stream(the HVAC case) it essentially 'sees' a small(inlet sized) portion of the air stream and will be measuring a sample very close to that of the large airstream.

When the opposite is true(2.25 hose/whatever) the airflow is expanded to the size of the larger inlet(2.5). That causes a decrease in the velocity the anemometer 'sees'.


i.e. the first case does not alter the velocity the anemometer 'sees'.



That's the way I 'see' it.
JPG,

Thanks and I appreciate the discussion. I guess the way that I see it, the anemometer is sampling the air velocity in either case. One way, the airstream aperture is much larger than the anemometer and in another it is just slightly smaller than the anemometer. I have seen a fair bit of confirmation bias on the forum related to the DC-3300, upgraded DC-3300 and DC-6000 where forum members have a number in mind for what they think the performance is and are just trying to get the math to justify it. All that I am searching for is the truth here. I went out and measured my DC-3300 years ago and reported my findings on this forum. My DC-3300 works "okay"...about as good as a good shop vacuum, but this isn't saying much in my opinion since I can procure a new shop vacuum for $50-100. I am not a fluid dynamics expert, so I don't know what the answer is to this question related to airflow scaling. I am just having a hard time seeing that there is an abrupt 23.5% change in air velocity right at the anemometer<->DC-3300 inlet interface. This isn't a closed system, but rather an open system with an anemometer right at the DC-3300 inlet. Sure there will be compression of the airstream going from a larger duct to a smaller duct, but I am just questioning that it really is 23.5% larger velocity at the interface. Keep in mind since this is an open system, we are going from an infinite aperture on one side of the anemometer to a 2.5" aperture inside the anemometer to a 2.25" inlet of the DC-3300. Without inserting the anemometer into a closed system, e.g. inside a 2.5" hose, the air velocity is likely artificially raised due to that compression from the infinite aperture to the 2.5" aperture, correct? So, the real velocity could actually be lower. We may never really know what the actual performance numbers are...and that is okay. Relative performance is all that is really needed here. If Dusty is seeing his anemometer peg at max scale, then that is a good thing. IF we can confirm that all 3 of his ports continue to peg that anemometer when all 3 are open, then that confirms what Jim reported to us and indicates that as a system, the DC-3300 upgrade/DC-6000 are superior to the original DC-3300. Case closed, in my opinion, if we can get to that point.
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Mark V 520 (Bought New '98) | 4" jointer | 6" beltsander | 12" planer | bandsaw | router table | speed reducer | univ. tool rest
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Re: Rate of Air Flow vs Volume of Air Flow

Post by Matanuska »

RFGuy - The simple answer is because a measurement made in the middle of a large duct is not made in a closed system (only a portion of the duct's airflow is going through the meter and the measured velocity is more or less the same as the overall velocity measured any where in the duct. If the large duct were sweged down to seal the flow so all the duct's flow was going through meter the meter would measure a much higher velocity than the actual duct velocity and a correction factor would be necessary to calculate the actual velocity in the duct from the velocity measured by the meter.

The reverse is true in Dusty's sealed case - the meter ID is larger than the inlet suction ID so the velocity measured by the meter is lower than the velocity going through the suction inlet.

There is also a cool answer using formulas, but I won't bother you with it here unless you'd really like to see it (I'm a math nerd!).
1985 Mark V upgraded to 520 PowerPro. Shopsmith cast iron table bandsaw, jointer, belt sander, and 60's vintage 610 jigsaw SPT's. Makita 2040 15" planer, JessEm Mast-R-Lift II router table.
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Re: Rate of Air Flow vs Volume of Air Flow

Post by Matanuska »

dusty wrote: Wed Nov 30, 2022 6:58 am
However, I believe I will never get readings with the anemometer that I have simply because of meter limitations. Even with perfect coupling the meter is incapable of measuring airflow rates that translate to 200cfm. This anemometer is max'd at 5905 ft/minute. If my calculates are correct I need something like 7200 ft/min to measure 200cfm.

I have no way of judging the ability of the DC to produce that rate of air flow.[/color][/b]
Dusty,

If your measurement system is sealed, you can reliably confirm a 7200 ft/min velocity at the 2.25" ID inlet using your 2.5" anemometer. 7200 ft/min at the 2.25" inlet corresponds to 5828 ft/min at the 2.5" anemometer (below the max limit of your meter).

All of this discussion about flow velocities has got me wondering what my DustRight 650 with a 4" hose is actually doing. I might have to buy an anemometer(!)

I've contributed much more than two cents worth to this discussion now - I'll try to keep my mouth closed for awhile.

Matanuska
1985 Mark V upgraded to 520 PowerPro. Shopsmith cast iron table bandsaw, jointer, belt sander, and 60's vintage 610 jigsaw SPT's. Makita 2040 15" planer, JessEm Mast-R-Lift II router table.
RFGuy
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Re: Rate of Air Flow vs Volume of Air Flow

Post by RFGuy »

Matanuska wrote: Wed Nov 30, 2022 12:55 pm RFGuy - The simple answer is because a measurement made in the middle of a large duct is not made in a closed system (only a portion of the duct's airflow is going through the meter and the measured velocity is more or less the same as the overall velocity measured any where in the duct. If the large duct were sweged down to seal the flow so all the duct's flow was going through meter the meter would measure a much higher velocity than the actual duct velocity and a correction factor would be necessary to calculate the actual velocity in the duct from the velocity measured by the meter.

The reverse is true in Dusty's sealed case - the meter ID is larger than the inlet suction ID so the velocity measured by the meter is lower than the velocity going through the suction inlet.

There is also a cool answer using formulas, but I won't bother you with it here unless you'd really like to see it (I'm a math nerd!).
Matanuska,

Thanks. Yes, but no one is sealing HVAC ductwork (to reduce it down) in order to measure with anemometers in HVAC work. The anemometer is held right in front of the supply register and a CFM reading is calculated based on the measured air velocity of the anemometer and an input area for the supply register. Let's assume for a moment that is all correct and that an entire industry isn't misusing this simple instrument. So what range is this valid over is what I want to know? Let's say the anemometer is the same as mine with a 2.5" diameter fan. Is it valid to assume that the air velocity measured by the anemometer is valid for values of 1x (0.034 ft² area) and above? You are indicating that when you go below 1x (0.034 ft² area), that you must now apply a correction factor because the inlet is smaller than the anemometer fan shroud. The perfect case would be for us to insert the anemometer into a closed system, e.g. in the middle of a duct/hose that has the same size diameter on each side of the anemometer. I don't see Dusty's example as a closed system. Yes, he has sealed on one side, but the other side has an infinite aperture and draws in air from the open environment on the other side. Won't there need to be a correction factor on that side (infinite->2.5") as well that compensates somewhat the reduction of the 2.5->2.25" side? I don't know the answer here and you may be right on all of this. Math and flow pictures would surely help, but I am not asking you to go through that effort unless you really want to. Just trying to better understand this because I find it interesting.
DC_3300_Airflow_Anemometer.jpg
DC_3300_Airflow_Anemometer.jpg (164.22 KiB) Viewed 1257 times
Last edited by RFGuy on Wed Nov 30, 2022 2:23 pm, edited 1 time in total.
📶RF Guy

Mark V 520 (Bought New '98) | 4" jointer | 6" beltsander | 12" planer | bandsaw | router table | speed reducer | univ. tool rest
Porter Cable 12" Compound Miter Saw | Rikon 8" Low Speed Bench Grinder w/CBN wheels | Jessem Clear-Cut TS™ Stock Guides
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dusty
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Re: Rate of Air Flow vs Volume of Air Flow

Post by dusty »

Almost ready for a new round of testing. Doctor's appointment today so maybe tomorrow we can put this to bed.

The plan will be:

1. Test each port with other two closed.

2. Test a single port and take a reading. Then open the other two, one at a time, while watching for decline in readings.
11..30 Doupler with Foam.jpg
11..30 Doupler with Foam.jpg (31.16 KiB) Viewed 1266 times
11.30  Foamed Coupler.jpg
11.30 Foamed Coupler.jpg (22.91 KiB) Viewed 1266 times
11.30 Meter with Coupler.jpg
11.30 Meter with Coupler.jpg (31.42 KiB) Viewed 1266 times
Please note the diameter of meter and the coupler are close to the same size. When the meter is introduced a slight pressure on the foam creates a fairly good seal.

PS

The aperture on the meter is 2 31/64". The pass way through the coupler is 2 11/32". The ID of the coupler where it meets the DC is 2 5/32".

I don't believe that the deltas here make a significant difference in test results -- not if I have a good seal at the meter face.
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Re: Rate of Air Flow vs Volume of Air Flow

Post by JPG »

IIUC the goal is to determine the velocity of the air passing through the 2.25" hose. That same air volume passing through a 2.5" anemometer diameter will have slightly lesser velocity. The volume must(ignoring slight/possible compression occurring) be equal.

Since cfm is a ratio of velocity and area, the adjustment must be made for the differing areas.
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Goldie(Bought New SN 377425)/4" jointer/6" beltsander/12" planer/stripsander/bandsaw/powerstation /Scroll saw/Jig saw /Craftsman 10" ras/Craftsman 6" thicknessplaner/ Dayton10"tablesaw(restoredfromneighborstrashpile)/ Mark VII restoration in 'progress'/ 10
E[/size](SN E3779) restoration in progress, a 510 on the back burner and a growing pile of items to be eventually returned to useful life. - aka Red Grange
RFGuy
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Re: Rate of Air Flow vs Volume of Air Flow

Post by RFGuy »

JPG wrote: Wed Nov 30, 2022 11:40 pm IIUC the goal is to determine the velocity of the air passing through the 2.25" hose. That same air volume passing through a 2.5" anemometer diameter will have slightly lesser velocity. The volume must(ignoring slight/possible compression occurring) be equal.

Since cfm is a ratio of velocity and area, the adjustment must be made for the differing areas.
JPG,

The adjustment is made with the equation: CFM = (fpm * area). So, at every junction, if CFM is constant through the system then air velocity is required to change as a function of area to maintain this equilibrium (assuming the CFM equation is valid for this system). The problem is this discussion turned into incorrectly claiming this is a closed system, which it is NOT. For it to be a closed system, the anemometer would have to be inside of a ductwork or hose in the dust collector system - fully captured on inlet and outlet. We do NOT have that. I brought up how these anemometers are used in the industry they were manufactured for, but was told that no you don't scale for them. Honestly this makes no sense to me, i.e. why scale for one case of measuring in an open system, but not in another case of it?

To unwind this thread a bit, and hopefully put this to bed...All we had to do was to apply the CFM equation and report CFM values. I may have messed this up when I pointed out to Dusty that the true area of the inlet is 0.028 ft². In reality, I should I have just told him to take his measured airspeed (fpm) and convert to CFM using the anemometer area of 0.034 ft² since this is the aperture it is measured in. This would have been, and still is, accurate IMHO. What concerned me was the discussion on this thread about scaling the airspeed (fpm) number directly. If this was done and then the CFM equation was applied with the wrong area then the measurement could have been scaled 2x which would have been double counting the area change.

IF Dusty is seeing his anemometer peg now at 5905 fpm, which is measured in a 2.5" inlet, then I would say his measured airflow is at least 201.3 CFM (1 port). Do you agree with this? Sorry, if I confused anyone by trying to be a stickler for where the scaling is applied. I'd rather see it scaled via the equation and not just whipping out a scaling correction factor.
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Mark V 520 (Bought New '98) | 4" jointer | 6" beltsander | 12" planer | bandsaw | router table | speed reducer | univ. tool rest
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