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| Electroboom: How Right IS Veritasium?! Don't Electrons Push Each Other?? |
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| PlainName:
--- Quote from: electrodacus on July 13, 2022, 04:55:00 pm --- --- Quote from: dunkemhigh on July 13, 2022, 04:36:46 pm --- That wasn't the question. You've effectively said that if a propeller is turning, it isn't having any interaction with the air. That's like saying air going through a turbine doesn't exert a force on the blades under any circumstances. Oh, but you allow that if the propeller knows it's powered by a particular source, it can interact with the air. How can your other stuff make sense if something this basic is misunderstood? --- End quote --- No that is not what I'm saying. Obviously propeller will have interaction with air is just not directly accelerating the vehicle. --- End quote --- Again, that wasn't the question. The question was: does the turning propeller produce thrust? Nothing about acceleration. --- Quote ---You get that wind (moving air particles) is the only energy input in this system. --- End quote --- Frankly, I seem to get that a lot more than you do! --- Quote ---The only ... --- End quote --- Sorry, had to cut all the obfuscation. Talk of this many W or that many W is irrelevant. That can come much later once we know what we are trying to apply them to. Currently, you seem to think that the propeller has no effect because, 100W. Forget throwing 1.2kg balls around - either it has an effect (even if that is just air moving 0.000001m/s into a headwind of 20000mph), or it doesn't. Once we're clear on that we can come up with some formula for figuring out just what effect it will be, where the power comes from and goes, etc. |
| Naej:
--- Quote from: electrodacus on July 13, 2022, 05:47:41 pm --- --- Quote from: Naej on July 13, 2022, 05:27:34 pm --- --- Quote from: electrodacus on July 13, 2022, 04:36:42 pm ---You are getting very close to understanding pressure differential energy storage. --- End quote --- Yeah I understand dams and pneumatic systems. But here there is no fluid, so you can't make up some nonsense about fluid energy storage. There's only kinetic energy storage. --- End quote --- You may have seen the graph below. Air is a compressible fluid (gas). Link to source https://en.wikipedia.org/wiki/Axial_fan_design Do you think that below graph is wrong / incorrect ? The red line is the propeller as seen from the side and this is how the air(compressible fluid) will look around the blackbird if motion was from right to left. If you agree with the fact that there is a pressure difference between the two sides of the propeller swept area (a disk) then you will also agree that will require energy to create and also this pressure differential pulls and pushes the propeller witch is attached to the vehicle so it pulls and pushes the vehicle. That swept area of the propeller on blackbird is about 20m2 and if you take just 1m on each side and the that volume will be 20m3 on each side of the propeller and for just a 2.5% above and below ambient pressure so ambient is about 100kPa then say 102.5kPa for P2 and 98.5kPa for P1 the total energy stored there is about 28Wh and that is about 4x more than needed to accelerate the 300kg blackbird to 13m/s (their speed record). --- End quote --- I'm glad you agree that my mechanical example shows that you can accelerate beyond the speed of matter around you. Now, you say that there is 4 kPa difference on an area of 20m². This means a force of 80000N on the propeller. Neglecting friction, this would imply 27 G's on the 300kg car. I'd say you're a bit off, by a factor of around 200. Of course the 1m you invented is probably as valid as the 4kPa… More importantly the whole point you're trying to make is pretty silly: yes the propeller slows down the wind around the vehicle, yes there is stored energy in the propeller blades. Who cares? It means that not only the car can go at 3 times the speed of wind but also store energy. :-+ Perhaps you want to claim, without evidence, that the prop can be connected to an engine to accelerate the car even faster. Do you see the prop slowing down significantly while the car is accelerating? No. |
| electrodacus:
--- Quote from: dunkemhigh on July 13, 2022, 07:31:02 pm ---Again, that wasn't the question. The question was: does the turning propeller produce thrust? Nothing about acceleration. Frankly, I seem to get that a lot more than you do! Sorry, had to cut all the obfuscation. Talk of this many W or that many W is irrelevant. That can come much later once we know what we are trying to apply them to. Currently, you seem to think that the propeller has no effect because, 100W. Forget throwing 1.2kg balls around - either it has an effect (even if that is just air moving 0.000001m/s into a headwind of 20000mph), or it doesn't. Once we're clear on that we can come up with some formula for figuring out just what effect it will be, where the power comes from and goes, etc. --- End quote --- It is like discussing about the energy conservation for a DC-DC converter and you asking "is there not an output current on the DC-DC converter?" Or you may say that current output is higher than input current instead of looking at input and output power or even better energy. Do you understand the analogy that I made above and why talking about input/output voltage and current is irrelevant. Unless you want to dimension the wires / fuses or in mechanical equivalent the strength of different mechanical components you do not care about current/voltage (speed/forces). To go even further with the DC-DC converter analogy is like you having two DC-DC converters. One connected with input to a power supply say that 200W, 20V, 10A CC-CV and the other DC-DC converter connected with input to the output of the first DC-DC and the output to the input of that first DC-DC. If you seen that you will think that is incredibly silly to have two DC-DC converters connected this way. But that is how blackbird is designed. Now you are asking if the second DC-DC converter contributes to the output of the first DC-DC converter. Will that not seem a silly question to ask ? |
| PlainName:
--- Quote from: electrodacus ---two DC-DC converters --- End quote --- And off you go again. Well, you are very skilled. Pity that particular skill is only useful to the likes of politicians rather than engineers. OK, I give up. |
| electrodacus:
--- Quote from: Naej on July 13, 2022, 08:09:52 pm ---I'm glad you agree that my mechanical example shows that you can accelerate beyond the speed of matter around you. Now, you say that there is 4 kPa difference on an area of 20m². This means a force of 80000N on the propeller. Neglecting friction, this would imply 27 G's on the 300kg car. I'd say you're a bit off, by a factor of around 200. Of course the 1m you invented is probably as valid as the 4kPa… More importantly the whole point you're trying to make is pretty silly: yes the propeller slows down the wind around the vehicle, yes there is stored energy in the propeller blades. Who cares? It means that not only the car can go at 3 times the speed of wind but also store energy. :-+ Perhaps you want to claim, without evidence, that the prop can be connected to an engine to accelerate the car even faster. Do you see the prop slowing down significantly while the car is accelerating? No. --- End quote --- It was an example to show that energy is stored there thus there is an energy storage device. When I made the calculations I used energy stored there and not pressure and volume. The shape of the volume as you seen in that graph is quite complex and a lot larger than just 20m3 I was using. And of course you will be right to say that forces will be to high if the volume was that small at that pressure delta. I'm not talking about the kinetic energy stored in the propeller (flywheel effect). I'm talking in pressure differential energy storage. Are you just ignoring that there is a pressure differential as seen in that graph P2-P1 ? I used some random average pressure values and a super small volume to show how much energy can be stored (way more than needed) The pressure as seen in the graph is not constant in that volume it drops gradually to atmospheric pressure as you get away from the propeller. Also that pressure is not pushing only against the propeller but also against the air at atmospheric pressure surrounding that volume. I'm not claiming to be an expert in fluid dynamics (in fact I barely got a passing grade at university in fluid mechanics) all I claim is that energy is stored there and that stored energy is both valid for sails as well as for rotating propellers. Is just that for a sail that pressure differential drops to zero as it gets to wind speed while a propeller connected to wheels maintains most of that pressure differential by using the wind energy while vehicle is below wind speed. That pressure differential will start to drop for the propeller version also even before getting to wind speed and will continue to drop as the vehicle speed exceeds wind speed as that energy covers the vehicle friction losses. What you think accelerates the treadmill model as there is zero wind speed in that much more controlled experiment? |
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