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.
Blowers generally deliver air at higher pressure but lower velocity than axial fans.
When testing, if you restrict the output flow to increase backpressure, there will be some point where the blower delivers more air (CFM) than the axial fan.
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.
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When testing, if you restrict the output flow to increase backpressure, there will be some point where the blower delivers more air (CFM) than the axial fan.
Are you sure Robert? It seems counter intuitive that restricting the flow would increase the volume of blown air- increasing the pressure, of course, but overall it must be working less efficiently if restricted.
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.
Are you sure Robert? It seems counter intuitive that restricting the flow would increase the volume of blown air- increasing the pressure, of course, but overall it must be working less efficiently if restricted.
He means that when restricted the axial flow reduces more than the blower flow, compared with the low pressure difference case. At high enough back pressure the axial flow will be 0, and at that pressure the blower flow will still be positive.
Restricting the flow does not increase the volume of air. It decreases the volume from the blower less than it decreases the flow from the axial fan. You can see this when you look at pressure/velocity curves like this.
lenr-forum.com/attachment/9566/
From https://www.cibsejournal.com/cpd/modules/2011-12/
I am assuming lossy restriction, not just changing the diameter of the pipe which changes velocity but not total airflow.
P.
Re anenometer measurements, how do you know these are accurate? The idea being that all anenometers change airflow and HWAs can over-read in turbulent flow?
You could check this by traversing again 60cm from the fan where the flow should be more stable (but still turbulent). Or maybe by using lots of smaller tubes in parallel, with laminar flow, where the velocity profile can be calculated and the average worked out from central velocity. At very least all these different measurements could be compared to see if they give the same overall flow.
Good luck: fascinating investigation.
Here is a representative drawing of anemometer traverses with a 60 cm long tube attached (same ID as the last one - 65 mm).
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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 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.
By the way, you can confirm that Mizuno's flow is well mixed. You can confirm that his calorimeter read a single value everywhere across the orifice, and it continued at that value over time. You can do this by looking at the data for low power calibrations, and then running the equations backwards. That is to say:
Assume the average for input power, inlet and outlet temperatures are correct. Use the STP value for specific heat of air (it hardly changes anyway). Assume there is no heat lost from the walls, because very little is lost below ~50 W.
EXAMPLE:
For a 30 W calibration, the averages are: 29.69 W input power, 1.75 K Delta T, heat capacity 1.005 kJ/kg*K (close enough for government work: https://www.ohio.edu/mechanica…tables/air/air_Cp_Cv.html)
Energy kJ/s = Weight kg * specific heat kJ/kg*K * temp K
So, Weight kg = temp K (Energy kJ/s * Specific heat kJ/kg*K)
1.75 K / (0.02969 kJ/s * 1.005 kJ/kg*K) = 0.01688 kg/s of air
Based on the blower power, and assuming the flow rate is uniform, and calibrating blower power to the anemometer and cross checking . . . Mizuno computes the average weight of air per second is 0.01679 kg/s. Which is very close to 0.01688 kg/s.
It is a little lower because, in fact, there are losses from the calorimeter walls. Taking one thing and another, and adjusting specific heat to the actual temperature, Mizuno computes the output captured in air is 29.04 W, a little lower than 29.69 W input.
Anyway, we can work back from the weight of air 0.01688 kg/s to derive the blower flow rate in m/s. Assume the orifice really is 66 mm in diameter. THH will not accept that until we measure it to the nearest nanometer, but let's just assume it is 66 mm. Run the numbers and you get a flow rate of ~4.1, which, lo and behold, is what Mizuno recorded. Okay, let us add some meaningless digits of precision to satisfy THH: Mizuno's average is 4.12171222. (Actually, no matter how many digits I provide, he will say he needs more precision; 10,000 digits would not suffice.)
I did this for 10 W and 50 W as well. I have calibration data for 80 W, 100 W and so on, but it does not work as well, because losses from the walls become significant. We can account for these losses by deriving a function, as shown in Fig. 3. I have two functions: one to compute percent losses for input power, and another for the temperature of the reactor surface (which is what Fig. 3 shows). However, these functions depend on the flow rate being uniform and correctly measured, so you cannot confirm the flow rate with the function.
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.
The point is to test Mizuno's calorimeter parameters with a replication of 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?
So how long is his outlet tube?
I suggest you eyeball the photo and guess. But the shape of your tube is different, and I guess your blower is different, so the length alone may not make them the same. Your's may be laminar.
Here is a quote from an unpublished paper by Mizuno that may help:
"The Reynolds number required to judge the boundary between laminar flow and turbulent flow is expressed by the following equation:
Re = ρUL/μ --------------------------------------- (1)
ρ is the density of the fluid [kg/m3], U is the representative flow velocity [m/s] (cross section average flow velocity), L is the representative length [m] (pipe inner diameter), and μ is the viscosity coefficient [Pa·s].
. . .
Here is test data applied to this equation: ρ is 1.165 kg/m3 at 30°C, U is a representative value of 5 m/s, the inner diameter of the tube is 0.05 m, μ is 1.8 × 10−5 m2/s. Therefore, the Reynolds number is about 18,000, which is much larger than 2300, so the flow is obviously turbulent."
I got mine as close as feasible by scaling the blower motor. It should be within a cm in length, and it is known to be 1 mm less in ID.
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.
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.
test Mizuno's calorimeter parameters with a replication of it
Your traverse tube may not be as smooth as Mizuno's
or as springy
Smooth cardboard of something
like 600 gsm density (used for display posters)
might be closer
to what Mizuno used
The traverses shown by Mizuno only cover 1/2 of the diameter, on two 1/2 traverses. I have already shown that is sketchy.
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.
As a practical matter, the flow does not shift suddenly 1 cm away from a point. I think your data shows that. So those 7 cover more than 1/4. What I mean is:
Given that all these measure 4.1 m/s: The points between 1 and 2 have to be 4.1. It is extremely likely the points at the same radius as 3 and 6, falling in the top right quarter are also 4.1. Seriously, why wouldn't they be? A point 1 cm to left of 5 is going to be 4.1. It can't shift that much. Basically, the whole thing is covered.
If you manage to make the flow turbulent and well mixed, and you then measure 7 points in this configuration, I will bet you then find all the others agree. (Okay, there is some variation, as shown in 4.) That's the test you should be doing. Replicate the same level of turbulence first, then test it. Your orifice is obviously giving a different answer. To put it another way, if you take only the 7 points Mizuno measured, and read them off of your data, you see they are different. You have not replicated his conditions. Look at points he labels 1 and 2, in your figure. They are 4.8 and 5.1 m/s, which is a larger difference than he measured.
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.
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.
JedRothwell : Para likes troubles and experiments. You should (please!) post a picture (inside) of the airflow tube. This, may be, could help others that use an other type of fan than Mizuno did. This will also spare you a lot of time to answer THH's and Ascoli crude assumptions...
I'm pretty sure Para will at the end deliver a correct & fitting reproduction.
JedRothwell : Para likes troubles and experiments. You should (please!) post a picture (inside) of the airflow tube. This, may be, could help others that use an other type of fan than Mizuno did. This will also spare you a lot of time to answer THH's and Ascoli crude assumptions...
I'm pretty sure Para will at the end deliver a correct & fitting reproduction.
Could you tell me one crude assumption I am making about Mizuno's stuff? I was not aware I was making any assumptions - other than that Mizuno is honourable and therefore we should pay attention to what he writes whilst being aware of the deficiencies in his documentation and methodology. I'd guess ascoli makes even fewer assumptions...
Your traverse tube may not be as smooth as Mizuno's
or as springy
Smooth cardboard of something
I think it is most likely the numbers from both are correct. Those anemometers are reliable. The numbers are random in paradigmnia's data. It doesn't matter which points he measures. There will be a spread. Select 7 at random, average them. Take 7 others, and you will get a different average. The seven that correspond with Mizuno's 7 are quite different from one another. There is no doubt the air is not well mixed and the flow rate is not uniform. So, the conditions are not the same. That happens a lot in experiments. There is no point to trying to replicate the precise conditions of blower and paper tube in another country. (Or is this the very same brand of blower?) Blower motors, fans, and whatnot are bound to be different. For normal applications with a blower, there is no need to make the flow rate exactly uniform. That's not the purpose of a blower. It is intended to keep things cool. The manufacturer does not strive to make the flow rate uniform. It just has to move the same amount of air per watt of input. So, if this particular blower and this particular tube don't make the air uniform. So, rather than futz around trying to make them look like Mizuno's -- by guess and by golly -- just put in a Venturi or a mixer. Problem fixed. Go on to the next phase of the test, which I assume is air flow calorimetry. Who cares how Mizuno achieved uniformity? He has been working with blowers for many years. He probably knows various ways of doing it. So, you figure out one or two ways, and then go on to confirm your calibration numbers add up the way I showed above. If you don't see:
Energy kJ/s = Weight kg * specific heat kJ/kg*K * temp K
Something is wrong. It ain't working. If you do see that, it is working. Test a few more power levels to be sure, and you are on track.
This thread is titled "Mizuno Airflow Calorimetry." So do calorimetry. Calibrate! This is not a game of pin the tail on the donkey where you try to guess what the tube and configuration looks like in Sapporo. That is not documented. It is not the sort of thing that needs to be documented, because the data speaks for itself. Figure 4 and the calculations I just did give you the answer. There is no doubt your blower and tube give a different answer. There is some physical difference causing non-uniform flow rates. It is not an instrument artifact. You really do have different flow rates. So what? It is a trivial matter. Make them the same and get on with the next step. Don't sit there questioning whether Mizuno's anemometer is working. You can see it is! I can give you more numbers from the 10 W calibration, but what's the point?
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.
I was making any assumptions - other than that Mizuno is honourable
Who cares about that? Other people have measured the input power, temperatures and air flow rate with their own instruments. They get the same answer. We don't need to depend on Mizuno's personal integrity. Instruments do not lie.
You don't even need to measure the air flow rate. When I was in Sapporo I confirmed the temperatures and power levels are correct, with the previous configuration (water flow). As did several other people. As I showed above, when you confirm input power and temperatures, you can then work backward to derive the air flow rate. You get the same answer Mizuno's anemometer shows: 4.1 m/s. And you know that has to be uniform for the whole orifice, or it would not agree. That's first principle proof. It works with a calibration, of course -- not with excess heat. That's the beauty of calibrations.
