Measuring CFM?

[cheesewonton]

Ideally I would move the anemometer probe around the circumference of the hose opening to see what the velocity reading is and take a reading at the center and average these but the length of the wire in the probe is nearly the diameter of many typical vacuum hoses so the best one can do is take a reading from the center. But I can see where I might get a high velocity reading from a given vacuum where someone using a vane anemometer 2 1/2 inches diameter with a hood would get an artificially low velocity reading. With hose openings as small as 28 mm I don't have a good work around unless there is an anemometer with a smaller sensor.

Japan has a method of rating vacuum performance they call Suction Work Rate that involves measuring total volume of air moved over a period of time. They don't use an instantaneous measurement of air velocity or airflow but instead measure volume in cubic meters over a period of time and this is accomplished at the end of the hose. They multiply this by, as best I can tell from the translation, a measurement of sealed suction at the hose end in Pascals and then by a factor to arrive at a value they express in watts. Some of the best Japanese bagged canister vacuums have pretty spectacular Suction Work Rate ratings.

 

[cheesewonton]

Sorry for my late reply. As I am not so familiar with these questions, I asked our expert Mr. Narisawa. Please see below his answer.

All the best for you!

Anton

From: n.narisawa <[email protected]>
Sent: Thursday, September 16, 2021 10:19 PM
To: 'Anton Jatsch' <[email protected]>
Cc: 厚木　奥津さん <[email protected]>
Subject: RE: Suction Work Rate

Dear Jatsch-san

The suction power is a unit (W) that expresses the suction strength of a vacuum cleaner unique to Japan. Thirty years ago, it was between 150W and 400W, but as consumers began to choose a vacuum cleaner with a strong suction, it became a meaningless competition for strength. It has a 680W home vacuum cleaner like no other in the world.

Calculation method of suction power

The method of measuring the suction power is defined by the standard "JEM 1454" set by the Japan Electrical Manufacturers' Association standard. The method is to attach the attached hose and extension pipe straight to the vacuum cleaner body with a new dust collection bag or filter, attach a measuring device to the tip of the extension pipe, and operate the air volume (per minute). The volume of the wind. The unit is cubic m / min) and the degree of vacuum (unit is Pa) is measured. Then, the suction power is calculated by multiplying the measured air volume and the degree of vacuum by the specified coefficient.

The formula is as shown below.

・ Suction work rate = 0.01666 x air volume (cubic m / min) x vacuum degree (Pa)

The suction power is the value required under the method specified in the standard. There is no doubt that the higher the number, the better the suction power.

However, as introduced earlier, when calculating the suction power, it is measured with only the hose and extension pipe attached. Also, at the time of measurement, it is not actually measuring while sucking dust, it is just sucking air. The value is calculated in a situation where the tip nozzle is not attached and the dust collection bag and filter are not clogged at all, so it is far from the actual usage situation.

In other words, the suction power is a value that measures only the suction force, not a value that directly indicates the ability when actually cleaning with the vacuum cleaner. For example, even with the same vacuum cleaner, the ability to suck in dust changes significantly between using a nozzle equipped with a power brush (a brush mounted on the head and rotating by a motor) and using a nozzle without a brush. increase.

The ability to suck in dust changes due to various factors. However, the suction power does not take that into consideration at all. This is the biggest drawback of suction power.


Kind regards,

Narisawa

 

[cheesewonton]

Now you know why all those old Japanese made Panasonic vacuums were called "Jet Flo 180" or Jet Flo 240". The numbers represented their Suction Work Rate.

Btw, I have one of those 680 watt ( Suction Work Rate ) vacuums from Hitachi and the power has to be experienced to be believed. One of my daily drivers is a 650 watt Hitachi CV-KP300J. These are available occasionally in the US through Amazon and even sometimes on eBay. I bought mine through a Japanese proxy buying service called Buyee. Great service!

For comparison sake using the Japanese rating system Tristars new and old sold in Japan manage 190 watts. My Vorwerk Tiger 260, sold in Japan as the Lux Sora, is likewise rated at 190 watts. Most Lux International vacuums sold in Japan earn 220-240 watt ratings. Modern Mieles sold in Japan earn the same. But in Japan even a low powered bagless vacuum has 300 watts and up and current production Panasonic bagged canister vacuums like the MC-PJ24G boast 580 watts. Then you have these over the top Hitachi vacuums that are teeny-tiny things with unbelievable power.

 

[Vacuum Facts]

So far, my involvement has just been to explain how the amateur measurements championed are not representative, and seemingly unknowingly, often in contrast to unsupported grandiose claims of capability. Solutions are possible but require a number of physical measurements. The Japanese standard (one of many, globally), referenced in the email, describes other methods, but they’re not really within the remit of amateur bedroom testers. Some of the statements in that email aren’t quite correct and can’t just be attributed to translation—won’t go into that here though, but it just goes to show that just because someone claims they’re an ‘expert’ or works for a vacuum cleaner manufacturer, doesn’t mean they are…

If I’d have spent more time developing that video before posting, I’d have proposed more methods which could be used to measure flow rate. You could, for example, machine a very precise orifice plate in a duct and measure the pressure drop across it and then use the Bernoulli equation and discharge coefficient across it to determine flow rate using Q=C_d . A. sqrt((2 deltaP)/Rho). I suspect this is a bit too complicated for many bedroom testers who would need skills in professional experimentalism (not least to accurately calibrate), basic circuit theory, fluid dynamics, and the ability to manufacture precise parts.

You could also measure the mass flow, if you had a mass flow controller (very expensive) and do the appropriate maths to determine flow rate. There’s also the method you used, which is to attempt to determine the radial velocity profile using your hotwire probe and apply a correction factor, but this is tricky at small physical scales, time consuming, and still rich with sources of error.

The easiest method that I’m surprised none of the alleged ‘experts’ commenting have thought of, or even the ‘experts’ from Vorwerk, since it’s obvious, is to use a simple sealed-bag displacement method, which measures how fast a known volume of air is displaced by the vacuum cleaner. Perhaps it’s the complete failure to understand what airflow is, even dimensionally, from what I’ve read in this very thread, that prevented such a simple test from being recognised. You start with a deformable bag of known volume, turn on the vacuum cleaner, and time how long it takes to suck that air out until the bag collapses fully (or partially). The rate of change of volume (V/t) is your volumetric flow rate.

I’m half tempted to remake that video and demonstrate this method with my bag, since I have one, and compare the numbers you get with those from a vane anemometer. Worth me doing (even though measuring airflow is literally irrelevant)? I do have a spare evening tonight, unusually.

 

[Vacuum Facts]

Based on feedback on my original video version and your comments, I've updated the video as discussed above. It now contains a demonstration of a simple and direct way to measure airflow. This is compared against a vane anemometer under the same conditions. In short, vane anemometers can overestimate the airflow measured through a hose or 'airflow box' because they assume a flow structure not always provided. Also worth remembering that measurements of airflow as often shown have no direct relevance to cleaning performance at all, as outlined in my lecture of the associated well-understood science, which I will also link below for convenience (click to watch on YT).

Updated airflow measurement science video:


Lecture covering the science of how vacuum cleaners really work:

 

[cheesewonton]

If, as you claim, airflow is not important for cleaning then explain why the normal measure of a vacuum's cleaning power, Airwatts, is the product of suction expressed in Pascals and airflow expressed in cubic meters per second? Looking at any vacuum motor performance chart you always see maximum air watts occurs where the lines for suction and airflow for a given orifice diameter intersect. It seems to me both airflow and suction are required and the more of both the better. Too much of one and not enough of the other doesn't get your home cleaned. Suction alone won't clean your home, even with good agitation.

In the fullness of time my plan is to build a device that allows me to measure airflow and suction simultaneously at the hose end. Not sealed suction but the suction measurable from an open hose end. Assuming the measurements are accurate ( not so easy ) one could calculate the airwatts being generated at the end of the hose. That would be more informative than sealed suction and raw airflow.

Also want to mention that the way the vane anemometer was used, the vane anemometer underestimates airspeed, not overestimates it. The overestimate of airflow is the result of using the diameter of the van rather than the diameter of the hose for the surface area of the orifice used to calculate airflow. You can see that the vane anemometer underestimates airspeed from my calculations of airspeed for Blackheart's Tristar. I took his claimed airflow numbers, divided these by the surface area factor he used and came up with airpseeds for each airflow value. For the Tristar his airspeeds are lower than those I measured using a thermal probe anemometer. This was compounded by using that duct because as the diameter of the duct opens airspeed will decline from the hose opening to the anemometer vanes.

 

[Vacuum Facts]

If, as you claim, airflow is not important for cleaning then explain why the normal measure of a vacuum's cleaning power, Airwatts, is the product of suction expressed in Pascals and airflow expressed in cubic meters per second? Looking at any vacuum motor performance chart you always see maximum air watts occurs where the lines for suction and airflow for a given orifice diameter intersect. It seems to me both airflow and suction are required and the more of both the better. Too much of one and not enough of the other doesn't get your home cleaned. Suction alone won't clean your home, even with good agitation.

In the fullness of time my plan is to build a device that allows me to measure airflow and suction simultaneously at the hose end. Not sealed suction but the suction measurable from an open hose end. Assuming the measurements are accurate ( not so easy ) one could calculate the airwatts being generated at the end of the hose. That would be more informative than sealed suction and raw airflow.

Also want to mention that the way the vane anemometer was used, the vane anemometer underestimates airspeed, not overestimates it. The overestimate of airflow is the result of using the diameter of the van rather than the diameter of the hose for the surface area of the orifice used to calculate airflow. You can see that the vane anemometer underestimates airspeed from my calculations of airspeed for Blackheart's Tristar. I took his claimed airflow numbers, divided these by the surface area factor he used and came up with airpseeds for each airflow value. For the Tristar his airspeeds are lower than those I measured using a thermal probe anemometer. This was compounded by using that duct because as the diameter of the duct opens airspeed will decline from the hose opening to the anemometer vanes.

Hi. I've given full treatment to what you ask in the lecture linked to in the previous comment, which fully explains the very question you ask, including a detailed explanation from first principles of the relationship between suction, air watts, and airflow.

As for your future box, the suction at the open hose is only relevant for above floor cleaning. There will be a huge drop due to the high leakage current and greater air power will be required to sustain it and the airspeed (which is what's important for cleaning). Again, you'd do well to learn the science from the lecture. It's all there for you.

There are a few mechanisms that cause minor underestimation of airflow, but the net result in this kind of system is overestimate. This is shown from the discussion of the well-understood fluid dynamics and also empirically in the above video. The method you used (area normalisation) is likely flawed for the reasons discussed in detail in the video, although without seeing sufficient detail of the experimental setup of the source you reference, it's hard to comment further on that data or be completely confident.

 

[huskyvacs]

I vote to bring back asylums to get rid of these narcissists that exist only to endlessly yap and try and 1UP each other's egos with minsinformation. Convinced its all one person parroting themselves across multiple accounts. All have the same manner of speaking - like an NPC.