You have no reason to doubt that. Those same 7 points in your graph are indisputable proof that your flow rates are not uniform. If you measured only those 7, no one would argue that it was actually uniform and you happened to pick the only points in the whole circle that are off. That would be ridiculous. So, if you can prove that with only 7 points, why do you doubt that he proves the opposite? It makes no sense.
Fix the problem. Then measure those 7 points, or any other 7, or 77 if you like. They will all be the same.
IN SHORT, you need to replicate his results. You need to show those 7 points being the same. THEN maybe you can demonstrate that 7 points are not sufficient. I don't think you will succeed, but you cannot even start now, and you have no basis to judge. Make those points the same first, replicate his results with those 7 points first, and then find out if it is sufficient, by measuring other points.
I think we will be better served if someone else attaches a 65 of 66 mm ID 25 cm long (or 20 cm long or whatever it is) tube to the same type of fan as Mizuno's, does a bunch of traverses with an anemometer, and either agrees with my results or agrees with Mizuno's.
Then we will see where to go looking for answers.
You have that backwards. When the flow varies considerably, it is laminar. When it is turbulent the flow rate is uniform.
I get those two mixed up all the time!
There is no doubt your flow is laminar and Mizuno's is turbulent. I am sure you are both making the measurements correctly. Because after all, it isn't that hard to make them. Modern electronic instruments are hard to fool. Let us take these readings at face value. Your physical setup and equipment different for some reason. So what? Who cares? Make it the same and move on.
You cannot do calorimetry with the configuration you now have. If this thread is about "Airflow Calorimetry" then make it right and do air flow calorimetry. Don't fret about a trivial problem that you can fix easily, probably by smooshing the cardboard tube down to make it into a Venturi. After you see a uniform flow rate, carry on!
It is possible that Mizuno only showed the 7 points in the diagram because plotting many more traverse points would just make an ugly blob on the graph, but at this point I don't believe that the 7 points, (if those are the only ones), are sufficient to characterize the velocity profile in a tube that close to the fan, unless something was done intentionally to mix the uneven air flow profile. Sorry, but my data and the experience of many HVAC companies (which my data seems to agree with) seem to disagree with what is reported. It does not mean that the velocity numbers used by Mizuno are wrong. It just seems like some important detail is missing that would help it all make more sense.
Does Mizuno squash his tube into a venturi? Does he install some rings of some sort inside to keep the paper tube from getting too squashed?
I am certain that the temperature of the air in the outlet tube is well-mixed. The air basically goes through a blender before being ejected from the fan.
I can fix the velocity profile, but that is not the point at this moment. I will get the calorimeter working. However I am off for another trip for another 10 days or so, so it won't happen soon.
This is true,, but the traverses you have don't seem parabolic.
If you have hairy carpet on the walls you can laminarise the flow ..but you only have rough cardboard,
I think you mean well-mixed..rather than laminar .. perhaps there is better mixing at 60 cm.
I merely noted that the 60 cm tube is approaching laminar flow, in comparison to the 25 cm tube which is very asymmetrical.
Definitely even 60 cm is not enough to smooth things out using cardboard. I could stuff some nails or thick wire through the tube near the fan end and probably break up the asymetricity without drastically affecting the overall flow.
Paradigmnoia... you may be confused about what laminar flow means.
which traverses do you consider laminar? vertical,diagonalor horizontal?
I was considering the shape of the profile as a whole. Laminar flow in a full tube should have low(er) velocity along the edges and the peak flow rate in the center, with sort of a smooth parabola of flow rates with the peak in the center, no matter which traverse cross section angle is used. Perhaps that is wrong.
As you can see, even at a length 9.2x the tube diameter the velocity profile has not settled down. At 3.8 x D, the velocity profile is very messy, and clearly dependent on the fan projection characteristics of the fan outlet.
The very uniform velocity profile shown in the paper just seems weird to me. Obviously it is not what you get after allowing the flow to develop. However close to the blower you would not expect it either, the blower turbulence and asymmetry makes it unlikely - Paradigmnoia's uneven results, for what is notionally the same setup, seem more plausible.
So: a mystery.
That (I think) shows that with the turbulent flow not fully developed to its final state, and dominated by blower turbulence, we get higher (because more turbulent) measured average speed. Even though the actual average must be the same.You might expect the average from a short tube to be even higher. One thing though - are you sure you should be averaging points? Actually your points look as though they each hold roughly equal cross-sectional area - because the outer ones are closer together than the inner ones. Dis you calculate this?
But I don't understand how the Mizuno blower measured such a flat velocity profile. Maybe the anenometer used was very different from yours?
The readings bounce around a fair bit at each location, maybe +/- 0.2 m/s but generally a bit less. I didn't want to take the high number from each point, I just rotated the tip to ensure that it was reading as high as it would go (which looked like it was aimed straight into the flow), and let the probe sort it out after that. It is a lot harder to do a good traverse than it might seem. I have scratched measurement increments onto the probe end paint that continue those on the extension shaft (which zero at the hot wire center). Notably my first average of the many-point traverses for the 25 cm long tube was 5.12 m/s which compares favorably with 4.99 m/s the second time. I was aiming for equal areas but it won't be exact unless I build a rig to hold the anemometer in place for long periods.
No, it isn't. If you measure 7 point and they give the same answer, you know for sure that every point between those 7 is also the same. Anything between point 1 and 2 will be the same. Or 3 and 4. That's 1/4 of the surface. How likely is it that points to the left and points below are different? I would say zero to none. In any case, the method I just used, working backwards from calibration numbers, shows that the flow rate was 4.1 m/s, just as he said. That could not be a coincidence. It is not likely that it was 4.1 m/s at all 7 points, yet if he had measured 2 more they might have been 5.0 and 3.2 (averaging 4.1). That is implausible.
I have just measured the flow and it varies considerably. It is turbulent. (The 60 cm tube approaches laminar flow) That may mean well-mixed. That does not mean homogenous.
Here they are again: 25 cm tube (top), and 60 cm tube (bottom), same fan as Mizuno, 65 mm ID.
MORE TO THE POINT --
You can be sure 4.1 m/s is the right answer for the entire orifice. The data shows that, unless you think 3 power meters and 5 thermometers all got the wrong answer. The same wrong answer! -- which never happens. The only question is, could Mizuno have measured 4.1 m/s if there there were points outside those 7 with other values? Nope. If the unmeasured points varied as much as the ones you observed, they would not average out to 4.1. They would be some other value. Try averaging different groups of 7 from your measurement. They do not agree to the nearest 10th m/s. If the other points on the surface were different, the average would be some random value other than 4.1 m/s. It can only be 4.1 m/s if the flow is uniform, and we know for sure it was 4.1 m/s.
The 2019 CMNS paper claims the blower was run at 6.5 W (page 9 ) and yet the traverse plot (figure 9, page 6) shows a peak power evaluated of 5.5W at 5.0 m/s.
The rest of the argument above is pointless because the since only about 1/3 of the outlet area was tested. The other values could be anything that maybe average 4.1 m/s (if that is what the velocity is). Certainly 20 cm from the fan outlet the velocity profile will not be even. That would be a miracle.
Does Mizuno suggest scrunching up the outlet tube until the number one is looking for (one that gives COP=1) crops up at the outlet? I doubt it.
You don't need to do that. I did it above, just by looking the spreadsheet numbers. It is a lot easier to apply some basic physics than go to the trouble of doing a test.
After all, you are not trying to prove that top quality digital instruments work according to the manufacturer's specifications. Are you? That's pretty much a given. If an expensive hot wire anemometer says the flow rate is the same everywhere across the orifice, and another anemometer agrees, do you seriously doubt it? That's is 99.9999% a sure thing. It is a waste of time questioning that. The useful thing you can do is recreate it. If your method and configuration is a little different, who cares? What difference could it make?
The traverses shown by Mizuno only cover 1/2 of the diameter, on two 1/2 traverses. I have already shown that is sketchy. I am not going to spend a bunch of time fudging the outlet tube to match 1/2 done traverses. That is a waste of time.
The tube looks different to me. If it isn't exactly the same blower, you may need to adjust things and use a different method. I think some blowers are more laminar and some are more turbulent. Evidently, your's is laminar. So don't sweat it. Make the tube into a Venturi and Bob's Your Uncle. Probably. If that don't work, add a mixer.
The blower is the same model as Mizuno's. The tube has a thicker OD, because it is made of cardboard. It doesn't have insulation on it yet, so it will end up bigger around.The ID is 1 mm less than reported for the tube of Mizuno. If I squash the tube enough, it will not be round, and I could easily find another mm of "diameter". It is almost certain that I will have to squash it a lot to fit the fan to the calorimeter box, unless I build a riser.
Why the heck would I want to change a whole bunch of stuff for a replication? The calorimeter is part of the experiment, as you say.
If it can't be replicated (it is just a paper tube stuck on a fan) then the experiment cannot be replicated.
The tube seems a little short to me. The ratio of length to diameter seems smaller than Mizuno's. I suggest you make it considerably longer and then -- as I said -- crush it down at a point about one-third of the length from the blower. To form a Venturi. That should mix the air.
It may not be exactly what Mizuno has, but the point is to make the flow rate the same at every point in the orifice. Right? Pretty much the same. Who cares how that is done, as long as it works.
The point is to test Mizuno's calorimeter parameters with a replication of it.
So how long is his outlet tube?
I got mine as close as feasible by scaling the blower motor. It should be within 5 cm in length, (probably a bit longer than Mizuno's) and it is known to be 1 mm less in ID.
I rotated the probe end CW/CCW maybe 20 degrees each time to get the highest reading (oriented properly), then took the average from that point for each location sampled.
Edit: Averaging the points from the 25 cm long tube, the average velocity was 4.99 m/s, while for the 60 cm long tube it was 4.77 m/s average.
The axial fan was just a temporary thing while waiting for the correct fans. I don't intend to have anything else to do with it.
I do have a 24V, 8.6 W fan with the identical housing dimensions as the San Ace fan. That might be interesting a bit later on.
Here's a thought. Mizuno's tube runs from the blower which has a small square opening, expanding out to the 66-mm circular orifice. It may act as a Venturi. I suggest you take a section of the tube closer to the blower than the orifice and crush it in to form a Venturi.
There is no doubt that the tube will have to be squashed quite a bit, just to get the blower to rest flat on the calorimeter top, even with 5 mm of gaskets between the blower and the lid.
My tube is already compressed significantly to get the 65 mm ID tube to attach to the roughly 30 x 60 mm rectangular outlet of the fan. The arrangement is, as far as I can tell, nearly identical to what Mizuno has, with the possible exception that my outlet tube is stiffer.
Mailing tubes are a clever solution. I expect they are very regular (close to circular).
So, the flow rate is not uniform? That's interesting. Good observation. It shows that this sometimes does not work, and you have to check carefully.
For inspiration, read about the Wright brothers and their problems with the wind tunnel.
I hope I did not give the impression this always works and you don't need to check, or worry. Elsewhere, someone thinks I said the experiment overall is "easy." That's the last thing I would say! Mizuno has been working on it for years, often months with no heat. It appears to be relatively easy for people skilled in the art.
I made better notes, and here is a representative diagram of the results from another traverse.
The grey area represents the squirrel cage fan at the other end of the tube. Numbers are m/s.
The inlet side of the fan is on the left of this image.
(The missing number on the LH center is 5.29 m/s)
First pass with 8 points (as suggested in the report) resulted in 4.38 m/s (the anemometer software calculates the average once all the traverse points are taken).
Second pass using 21 anemometer points result was 5.12 m/s.
The overall traverse profile is far from flat, however. The tube edge corresponding to the blower forward fan blade section is as high as 6.28 m/s, while the tube edge corresponding to the blower fan retreating blade section is as low as 4.06 m/s.
Nearly ready for an air flow test using the correct fan.
I just wired up the fan power supply (regulated 12 V), and tested the tach signal. The tach signal is supplied by an internal Hall effect sensor and signal processing circuitry, integral to the blower fan, which reports two pulses per revolution. The yellow wire is a signal (ground), and the red (12v+ supply) is the positive terminal. It reports 128.4 Hz, or 3852 RPM at 12.08 V, free running (without outlet tube or attached to calorimeter).
I will begin taping on the outlet tube and will test with the anemometer shortly. The fan is much quieter than the axial fan I previously tried, and really doesn't seem to be blowing as hard as the axial fan. The anemometer will find out I guess. I have several lengths of cardboard mailing tubes with a 65 mm ID (but I will check that again).
Do you have a recent high-def photo of the front of the calorimeter box with the internal insulation installed? I am interested in the details of how the insulation is installed relative to the 5 cm hole and 10 x 20 cm reactor plumbing clearance notch when the calorimeter is operating.