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#2500 by Rodal on 23 Oct, 2014 18:14
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...only that there was prima facie evidence that not all that much is happening....
Went back and fix'd that. Much more (orders of magnitude more) is happening with Shawyer's demo experiment and the Chinese experiments but unfortunately they are not as well documented as NASA's experiments hence the discussion centers on NASA's.
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#2501 by JohnFornaro on 23 Oct, 2014 18:17
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There are microneutons of force moving lbs of mass against an unknown damped spring constant to equilibrate after an unknown distance in an unknown time.
Which implies what, that the illustrated scenario here is just around the corner?
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#2502 by JohnFornaro on 23 Oct, 2014 18:21
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Time to create theory, not attempt to understand that which is being kept under wraps.
Well, there are still those of us here whose only purpose being in this thread was and still is to objectively understand the reason for EMDrives's measured thrust.
Sorry, sorta, that I expressed my frustration at the death of information from those who would know.
Edit: Dearth. Death. Whatever. -
#2503 by Rodal on 23 Oct, 2014 18:22
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....
Thanks for calculating that. I continue to be impressed with the useful amount of information you get from the reports. I had not noticed "Shawyer's cooled test stand"
For the Brady cases (first 3) the moving air volume and velocity would be overlooked if they were not watching for it.
Shawyer tested his experimental device within an enclosure to avoid artifacts from external air currents. Ionic wind would have been internal to his enclosure.
Shawyer tested his demonstrator on a cooled test stand. That would probably mask any ionic wind.
I don't know anything about the test setup for the flight model or about the Chinese test setup, as regards to detecting ionic wind.
I will be posting the force/PowerInput from an ionic wind calculation: it comes pretty close to the measured values. -
#2504 by aero on 23 Oct, 2014 18:34
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....
Thanks for calculating that. I continue to be impressed with the useful amount of information you get from the reports. I had not noticed "Shawyer's cooled test stand and his enclosure"
For the Brady cases (first 3) the moving air volume and velocity would be overlooked if they were not watching for it.
Shawyer tested his experimental device within an enclosure to avoid artifacts from external air currents. Ionic wind would have been internal to his enclosure.
Shawyer tested his demonstrator on a cooled test stand. That would probably mask any ionic wind.
I don't know anything about the test setup for the flight model or about the Chinese test setup, as regards to detecting ionic wind.
I will be posting the force/PowerInput from an ionic wind calculation: it comes pretty close to the measured values.
Wait a minute - Of course it comes close. I picked an mdot number rather arbitrarily, but then used the measured force value to calculate Ve. They should match exactly. There is no deep analysis here, just choosing some numbers that satisfy the measured force. This to show order of magnitude of the air mass and velocity of the ionic wind that would create the measured force, nothing more. -
#2505 by zen-in on 23 Oct, 2014 18:49
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Not to forget the energy stored in the spring. (the plots record displacement)
The two plots I attached are marked with units of thrust; micronewtons on graph from the Bray, White, et al paper and gram in Shawyer's 2008 paper. This thrust is derived from the torsion spring angular displacement. For the thrust to continue after the RF has been switched off, which is the case in both plots, there must be stored energy. The torsion spring is part of the measuring system and works in opposition to any thrust generated by the em drive so it is not the source of the stored energy. Thermal energy, if it was the source of the measured thrust, would continue to radiate from the cone section after the RF was switched off. The heated air would create a thrust in the same direction as is claimed for RF effects inside the device.
quoting Aero:
Shawyer tested his demonstrator on a cooled test stand. That would probably mask any ionic wind.
end quote
So with Shawyer's much higher RF power level (dissipating more power into the device's copper walls) and with the test stand and surrounding air cooled, the thermally generated thrust would be much greater.
Until they are able to show there is thrust in a vacuum chamber I will be convinced the force measured is a thermal anomaly. -
#2506 by Rodal on 23 Oct, 2014 18:52
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... This to show order of magnitude of the air mass and velocity of the ionic wind that would create the measured force, nothing more.
I am reviewing papers on ionic wind (electrohydrodynamics) that place constraints on the wind generated under AC fields. We also know the magnitude of the Electric Field, the frequency, the TE modes, etc. -
#2507 by Rodal on 23 Oct, 2014 18:58
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I recall that Paul March wrote that the EMDrives tested at NASA Eagleworks had a temperature that never rose more than 1 deg (F ? or C?) above room temperature.
Anybody recall that statement? Is the temperature measurement in the NASA Eagleworks report? Using search I cannot find it in the text. Is it in the pictures?
I also recall AcesHigh reporting on information elsewhere reporting March's statement he made on this thread regarding temperature. Was that at nextbigfuture? Does anybody still have a link for that? -
#2508 by aero on 23 Oct, 2014 19:18
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I recall that Paul March wrote that the EMDrives tested at NASA Eagleworks had a temperature that never rose more than 1 deg (F ? or C?) above room temperature.
Anybody recall that statement? Is the temperature measurement in the NASA Eagleworks report? Using search I cannot find it in the text. Is it in the pictures?
I also recall AcesHigh reporting on information elsewhere reporting March's statement he made on this thread regarding temperature. Was that at nextbigfuture? Does anybody still have a link for that?
Quoting a post by Paul March on Talk-Polywell, (Sept 9, 2014 ?)QuoteBTW, the copper frustum's temperature never rose more than 1.0 degree F. when using the above average power levels and test articles.
Best,
_________________
Paul March
Friendswood, TX
Here is the link http://www.talk-polywell.org/bb/viewtopic.php?f=10&t=2949&hilit=paul&start=210#p115832 -
#2509 by Rodal on 23 Oct, 2014 19:47
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Quote
BTW, the copper frustum's temperature never rose more than 1.0 degree F. when using the above average power levels and test articles.
Best,
_________________
Paul March
Friendswood, TX
No way that the measured forces can be due to thermal expansion of the copper frustum or due to thermal drafts produced by the copper frustum itself if its temperature never rose more than 1.0 degree F. -
#2510 by Rodal on 23 Oct, 2014 19:55
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Also Paul March wrote:Quote
We found that this slope change after the test article and RF amplifer were turned on for 10-to-20 seconds was apprently due to IR radiation from the amplifier's heatsink that is mounted on the back side of the torque penlulum on an 8" square platform was affecting the top C-flex bearing more than the lower one. We tried aluminum shielding the top bearing assembly from the heatsink IR source and managed to reverse the metioned thermal slope in the thrust plots, but after shielding the bottom one we could reduce it but still coundn't completely get rid of this thremal drift artifact. Currently we are just living with it.
and from the report:QuoteThe null force testing indicated that there was an average null force of 9.6 micronewtons present in the as tested configuration. The presence of this null force was a result of the DC power current of 5.6 amps running in the power cable to the RF amplifier from the liquid metal contacts. This current causes the power cable to generate a magnetic field that interacts with the torsion pendulum magnetic damper system.
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#2511 by aero on 23 Oct, 2014 19:56
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Don't want to forget that thrust has been measured in the same axial direction relative to the thruster whether the thruster was pointed up, down, left or right. This speaks strongly against outside thermal drafts.
It does not speak to thermal expansion of course. -
#2512 by Notsosureofit on 23 Oct, 2014 20:02
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Just noticing in "White_thrust.jpg", that the "Pulse 1" at the left hand side of the picture shows an underdamped response of the 300V Calibration pulse. The vibration period would seem to be of the order of 4 to 5 sec. Really too bad they did not put the displacement scale there as well as the force.
Can you fit that w/ Mathamatica ? -
#2513 by Rodal on 23 Oct, 2014 20:15
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I presume notsosureofit is referring to this picture:
NotSoSureOfIt:
That's the kind of excellent, scholarly observation that makes it possible to extract information even where the researchers have not explicitly provided.
I had been asking for the magnetic damping constant from Paul March, but he went mute in this forum.
You are 100% right. I had not noticed that picture. It seems that it makes it possible to figure out the magnetic damping constant, as it gives the response and I can scale it by the 60.1 microNewton level.
It certainly looks below critical damping.
Great observation!
Thanks!
Thanks also to zen-in that provided the picture that motivated the discussion that motivated this insight. Great discussion. -
#2514 by Rodal on 23 Oct, 2014 20:29
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I also notice that this picture refers to:Quote
Prior to the TM211 evaluations, COMSOLŽ analysis indicated that the TE012 was an effective thrust generation mode for the tapered cavity thruster being evaluated, so this mode was explored early in the evaluation process. Figure 22 shows a test run at the TE012 mode with an operating frequency of 1880.4 MHz. The measured quality factor was ~22,000, with a COMSOL prediction of 21,817. The measured power applied to the test article was measured to be 2.6 watts, and the (net) measured thrust was 55.4 micronewtons. With an input power of 2.6 watts, correcting for the quality factor, the predicted thrust is 50 micronewtons. However, since the TE012 mode had numerous other RF modes in very close proximity, it was impractical to repeatedly operate the system in this mode, so the decision was made to evaluate the TM211 modes instead.
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#2515 by Rodal on 23 Oct, 2014 21:27
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The previous plot was with a magnetic damping of 6 N s/m = 6 kg /s
(the value of a magnetic dampening system that was investigated for a LIGO pendulum).
Here is a plot of the response using a magnetic damping constant of 1.75 N s/m = 1.75 kg /s instead.
The horizontal scale is in seconds.
As one can see, this is pretty close to the [300V Pulse 1] calibration time response at NASA Eagleworks. This is very close taking into account that industrial magnetic dampers can exceed 210 000 N s/m. It is pretty clear that the magnetic damping used for the NASA Eagleworks tests was around 1.75 N s/m.
It was an excellent idea from NotSoSureOfIt to think of this, as this is a much better way to obtain the magnetic damping constant than any value provided by the researchers, as they themselves would have to use a similar procedure (model the response and then obtain the magnetic damping from it) because the actual magnetic damping depends on the distance of the magnets from the metal being damped -see the last picture attached below as to how close are the magnets and how unsymmetrically they did this (two magnets to one side and one to other, and it is closer to one side than the other).
[I haven't scaled the response yet, just the magnetic damper constant. Then I will investigate the response for different inputs.]
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#2516 by zen-in on 23 Oct, 2014 21:43
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Don't want to forget that thrust has been measured in the same axial direction relative to the thruster whether the thruster was pointed up, down, left or right. This speaks strongly against outside thermal drafts.
It does not speak to thermal expansion of course.
My theory on thermally generated thrust claims the cone section transmits heat energy to the surrounding air by conduction. The two ends do not have exposed Copper so the heat flow from each end would be much less. FR4 (high density fiberglass as used in PCBs) is a better insulator than Copper. The fact that March saw < 1 degree change in temperature would be expected because of the good heat transfer from the Copper cone section to the surrounding air. There is no mention of the surrounding air temperature so I am assuming this < 1 degree change refers to just the Copper section of the device.
Earlier I posted a picture of a Crooke's radiometer. The paddle wheels of this device have high and low emmissivity coatings on opposite sides. The high emmissivity side radiates heat at a faster rate, imparting more momentum to the few air molecules on one side of the paddle than on the other. The tiny amount of thrust this gives to the paddle, and the very low bearing and air friction are enough to make it spin when light hits it.
The cone section of the JSC device transfers heat to the surrounding air. After all RF power is being dissipated inside it, being turned into thermal energy, so it has to go somewhere. This dissipated heat adds momentum to the surrounding air molecules, at right angles to the cone's surface. When all these momentum vectors are resolved in a cylindrical coordinate system with the Z axis going through the two end caps there are components that are normal to the Z axis and components that are collinear with it. These collinear components are all additive, resulting in a thrust that is in the same direction as the thrust that is said to be caused by an internal em effect.
Only by experimentation can this alternative theory be eliminated. For example if the large endcap was replaced with a solid Copper one would that reduce the measured thrust? What if the cone section was covered with an insulating layer; isolating it from the surrounding air? Would that reduce the measured thrust or would it not change because of it?
One counter experiment that was done by the JSC team was to use a dummy load. In that case no thrust was measured. However the power was not dissipated inside the device. What if the same amount of power was dissipated inside the device using a DC power source; ie: a heater pad? That would be a better baseline test because it would test for thermal effects.
Shawyer's device has some differences form the JSC device. Some pictures show the device with endcaps that appear to be solid Copper. This would result in a completely balanced thermally generated force. However as the attached picture shows (from the 2008 paper) a non metallic disk and Aluminum end plate are attached to the wide end before the whole assembly is fastened to the experimental test stand. So the same thermally generated thrust could be produced by Shawyer's device as well. Without more photos it is hard to tell.
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#2517 by aero on 23 Oct, 2014 21:52
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Ok. That's well thought out. Now can you explain the lack of thrust from the Brady device without dielectric? Remove the dielectric and there is no thrust. What happened to the heat dissipation?
The other problem that continues to arise is the total momentum .vs. the power dissipated -
#2518 by zen-in on 23 Oct, 2014 22:08
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Ok. That's well thought out. Now can you explain the lack of thrust from the Brady device without dielectric? Remove the dielectric and there is no thrust. What happened to the heat dissipation?
The other problem that continues to arise is the total momentum .vs. the power dissipated
It could be that without the dielectric there is less power being dissipated in the cone section. Maybe the RF field inside the device results in all the power being dissipated on the end caps. There are no network analyzer plots for the dielectric-less configuration. It could be that without the dielectric the reflection coefficient is much higher; ie: most of the applied RF power is being reflected at the feedpoint and is being dissipated in the RF amplifier or circulator external to the em-drive device. So with no power entering the device there is no thermal effect. -
#2519 by Rodal on 23 Oct, 2014 23:09
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You must have meant to write "transmits heat energy to the surrounding air byDon't want to forget that thrust has been measured in the same axial direction relative to the thruster whether the thruster was pointed up, down, left or right. This speaks strongly against outside thermal drafts.
It does not speak to thermal expansion of course.
My theory on thermally generated thrust claims the cone section transmits heat energy to the surrounding air by conduction. The two ends do not have exposed Copper so the heat flow from each end would be much less. FR4 (high density fiberglass as used in PCBs) is a better insulator than Copper. The fact that March saw < 1 degree change in temperature would be expected because of the good heat transfer from the Copper cone section to the surrounding air. There is no mention of the surrounding air temperature so I am assuming this < 1 degree change refers to just the Copper section of the device.
...conductionconvection" because heat transfer by convection in fluids like air occurs much faster than by conduction. Air has very low thermal conductivity and very low thermal diffusivity, so heat does not get transferred in air by conduction, but by convection.
Heat transfer by convection:
q/A = h dT
q/A = heat transfer per unit time per unit area
h = heat transfer coefficient
dT = temperature difference between the surface and the bulk fluid = Ts - Tf = 1 deg F = 0.56 deg C
Natural convection heat transfer coefficient = 2 to 20 Watt/((m^2)degC))
q/A = 0.56 deg C * 2 Watt/((m^2)degC)) = 1 Watt per square meter
q/A = 0.56 deg C * 20 Watt/((m^2)degC)) = 10 Watts per square meter
l = Sqrt [h^2 + (R - r)^2] = Sqrt [ 0.332^2 + (0.199 - 0.122)^2] = 0.341
Total surface area of truncated cone = Pi × ( r × (r+l) + R × (R+l)) = Pi × ( 0.122× (0.122+ 0.341 ) + 0.199 × (0.199+ 0.341)) = 0.515 m^2
Input Power was from 2.6 Watts to less than 16.9 Watts, so if 100% of the power would have gone into heat:
2.6/0.515 = 5 Watts per square meter
16.9/0.515 = 33 Watts per square meter
The lateral surface area is Pi×l×(R+r) = Pi×0.341×(0.199+0.122) =0.344 m^2
So that only increases the flux by 0.515/0.344 = 1.50, or 50% even if you consider both ends to be completely thermally insulated and that 100% of the heat escapes through the lateral surfaces (which would not be quite the case). It increases the flux so that it ranges from 7.5 W/m^2 to 49 W/m^2.
So, the delta T given by Paul March (1 deg F =0.56 deg C) makes sense, if a fraction of the input power went into heat that got transferred to the air.
The speed of an air convection current due to only 1 deg F temperature difference is so small, that any air convection naturally occurring within the chamber for other reasons could easily overwhelm it. (The vacuum chamber itself may have had a larger delta T within it for other reasons unrelated to the EM Drive).
Further bad news for explaining the measured forces as due to natural convection circulation is that this can only work with the warm part (the EMDrive) on the bottom of a natural convection circulation system such that the bottom part (the EM Drive) is warm and the top part of the chamber is cool and therefore the convection would be from the warmer EM Drive towards the cooler top of the chamber. (Natural convection taking place because of the extremely small amount difference in temperature: less than 1 deg F, producing extremely small differences in density of the air).
But at NASA Eagleworks the measured forces were in the horizontal direction. Furthermore, the direction of the force was always oriented towards the large diameter base, even when they flipped the EM Drive to point 180 degrees in the opposite direction. Furthermore, in the up and down test performed by Shawyer, the direction of the force should not have flipped (as reported by Shawyer) when Shawyer flipped the test article upside down, as natural convection always works such that the warmer part is on the bottom, and the air circulates from the warmer bottom part to the cooler top part of the chamber.
Further bad news for explaining the NASA Eagleworks response as natural convection from the warmer EM Drive is that the NASA Eagleworks test show a pulse response rapidly rising in 2 seconds which coincides with the inertial response of the inverted torsional pendulum, and is way too short a time compared with the Fourier dimensionless time based on the thermal diffusivity of the materials involved and the characteristic length. So the initial time-response cannot be explained in terms of thermal natural convection. The speed of heat transfer is restricted by the thermal diffusivity of the material.