Measuring CFM?

[cheesewonton]

cheesewonton,

Blackheart is correct...now onto other matters.

This will be my last response in this thread. You literally have no idea what you're talking about because you obviously have never been in a lab, written college grade reports and been overseen/graded by PhD professors. I have (think graduate level). I have also taught Math, Physics and various computer science (think programming/networking/hardware) courses in High School and College. I actually make great efforts to obtain the most accurate, repeatable laboratory grade measurements as a rule on my channel. That's why I started it back in May of 2017.

I have two vane type anemometers, a GM8901 and a HP-846A. The HP-846A has a built in calculation (CFM) function, the GM8901 does not, so you use the ratio I stated before. You will see these in my videos on my YouTube channel.

From cheesewonton: "If you are using a propeller anemometer your measurements are not accurate."

Completely false statement made by someone who isn't familiar with the equipment. Stop repeating it!

At this point I can guarantee that you don't know how to use your hotwire anemometer either. Have you calibrated it for your environment?
1) Elevation correction
2) Temperature/Humidity correction
And don't forget a standardized supply load voltage for your vacuums.

Through using a series of cone shaped adapters (easily made), ANY vacuum port can be fitted properly to ANY vane adapter. Basic Physics dude.

My test lab typical specs: loaded test voltage range (120-121 VAC), temp. 67-69 F, humidity 35%-45%, elevation 840 feet (close to USA populated avg. of 636 feet).

Here's an elevation versus pressure pdf
https://www.nwflowtech.com/media/0y0aizb3/nwft-barometric-pressure-vs-altitude-table-122120-v2.pdf

I've spent about 1000 hours in high-end labs (chemistry, physics, biology (yuck)) before I fully understood how to setup my own correctly.

Best of luck in your testing journey but you'd better learn how to use your equipment properly and refrain from posting false info which you have here.

Bill

Lol, I just retired from a career in one of the Navy's premier weapons labs. I made a career in R&D. I think I know my way around instruments and data.

 

[cheesewonton]

With the GM8901 to obtain an accurate airflow measurement you would multiply the speed in feet per minute by the area of the hose opening in square feet. Hoses have different diameters and thus different surface areas at the opening, so there is no one size fits all factor. If you are measuring a 1 1/4 inch diameter hose you would multiply the observed airspeed in ft/min times the surface area 0.0088 square feet. If you were measuring a 35mm hose on something like a Miele you would multiply the observed airspeed in ft/min by 0.0104. Ect. Each hose diameter will have a different square foot opening to use in the calculation.

Likewise with the HP-846A, directly from the operating manual, you have to manually enter the surface area of the hose opening of the vacuum being tested. If you are not entering the correct value the resulting CFM calculation will be incorrect. As before for accuracy there is no one size fits all factor to multiply airspeed by.

A general shortcoming with rotating vane anemometers are bearing friction and the amount of obstruction to airflow inherent in their design. Hot wire anemometers, like you find in automobile Mass Airflow Sensors do not create as much of an obstruction to the airflow so there are less losses and greater accuracy. HVAC pros will use capture hoods with differential pressure sensors or a thermal ( hot wire ) sensor.

 

[vaclab]

cheesewonton,

I simply had to respond to such a grossly ignorant comment. While I have GREAT respect for our armed forces, if what you claim is true, you couldn't pass an 8th grade Algebra or 9th grade Geometry test. Geez, what a disappointment. I posted these calculations many years ago on Vacuumland, but here they are again.

For the GM8901 anemometer:

Diameter of GM8901 Anemometer Detector = 2.1875 inches
Radius = 1.09375 inches = .0911458 feet
Detector Area = 3.1415926 x .0911458 x .0911458 = 0.0260990 (rounded)

Soooo, if I obtain a reading of say 5747 ft/min, that converts to about 150 CFM.
5747 (ft/min) x 0.026099 (area) = 149.9 CFM

I also noticed you refused to provide ANY of your lab specs after I stated mine (as expected). No pics, no vids, just false claims. Par for the course I suppose.

Lastly, you did mention a 9.5 on the Baird meter, which equates to 109 CFM. And you somehow can't manage to clean (dust) with 109 hose CFM? What world do you live in anyway? The typical hose CFM is around 80 CFM, so your Kirby has plenty of above the floor cleaning power.

Bill

 

[vaclab]

Here we go again. If you had bothered to read/understand my previous posts and/or view some of my extensive YouTube videos, you would clearly see the cone adapters I use. These type of adapters have been used in the industry for decades. They adapt (without interference) diameter "A" to diameter "B" very easily. Try and make one rather than whining so much. How on Earth do you think that airflow measurements were made say, 50 years ago?

Example #1: if a hose is 1" diameter and you want to measure its flow, you can with any measuring tool that is 1" or larger. Yup, you can create a 1" to 2" cone adapter and proceed to mate it to a 2" vane.

Example #2: if you have a large 12" tube/square (say an A/C vent), you can use the same 2" vane detector to measure part of the area (say 10%), then multiply by 10.

 

[cheesewonton]

You are multiplying airspeed in ft/min times 0.26099. That is the diameter of the fan. You are using the instrument incorrectly. You need to multiply airspeed by the diameter of the hose opening. The operators manuals for both anemometers ( I looked at them ) tell you to multiply airspeed by the surface area of the duct. In this case the duct is a vacuum hose. This explains your overly high airflow readings. That is also how my anemometer explains the airflow calc.