LDM ,
Using your model, do you have the ability to work out the time required to reach equilibrium temperatures relating to various data points in the Lugano report, based on nominal input power?
Such as reaching 450 C from 20 C, 1260 C to 1400 C, etc. ?
It is obvious that LT did those tests 
The finite element thermal simulation program I am using has the capability to do transient analyses. Never played with it and I don't know what it can step.
However the program. as other thermal simulations programs has shortcomings.
You can only set a fixed emissivity and thermal transfer coefficient to a surface. So what I did was dividing the dogbone in several sections, run the program, read out sections temperatures and based on those temperatures adjust the emissivity, the reflectivity and the thermal transfer coefficient. Then run the program again. I continued those iterations until the temperature differences of the sections between two runs was not more then one degree C. That is also one of the reasons why those simulations took so much of my time (I did it for the same heater powers as the MFMP)
Now if you do a transient, you will not be able to adjust the emissivity, thermal transfer coefficient and reflectivity in between and you will end up at the wrong temperature. But for fixed values we could adjust the starting heater power and final heater power such that the begin temperature and end temperature are about the ones you would like, do a transient ( if it indeed can be done) and measure the time to settle at the new value.
I don't know why you want to know those settling times, but as outlined in my posts I find currently no time to do new tests. And if I have time again I prefer to first simulate the Lugano dummy run with an extended heater and compare the results of such a test with the data in the Lugano report. It will show us if the reported Lugano temperatures for the dummy run where correct or not so that we can conclude if wrong emissivities where used on the Optris for the dummy test or not.
That said. I have worked in the past for a company (both in Europe and the USA) that designed and manufactured diffusion ovens for the semiconductor industry. Being part of the design team I have seen the FEM thermal simulations which our research lab did on new designs. While the simulated temperatures where in general not exact, they where close to the temperatures measured in practice. As such we could base our design decisions on it. Since the difference between the MFMP test and my FEM simulation are large I must conclude, based on my experience that the MFMP thermal dogbone test has been wrong. Thus in my opinion we can not use that report as a prove that in Lugano wrong emissivities on the Optris where used until the MFMP is redoing their test as they promised and their new results are known. And I realize that the results of a new MFMP test can show that my simulations where flawed instead of the earlier MFMP test, because we all can make errors. But there is nothing wrong with that, as long as they get corrected and we learn from it.
LDM ,
The heating rate for the object, combined with the thermal mass, if properly characterized, should clearly show that the range of input power that is most appropriate to reach one steady state temperature to another. If the steady state temperatures on are grossly exaggerated, the heating rate will probably be very different from that which was reported.
Purely for example, imagine a dummy unit that takes a very long time to reach steady state, but the input power and temperatures are reported as though they were at steady state. This could result in grossly underestimating the possible output power possible when steady state is actually achieved.
In case of Lugano, the "700 W" jump in output power with the 100 W increase of input power will still require a certain period of time to heat an object of a certain mass, etc. to the new temperature. If the "real" increase was only 100 W output matching the 100 W input increase, the difference in the heating time period will be very obvious, and only one of the two versions will closely reflect a real situation with a real object.
I understand these issues since I had to deal with them when developing control algorithms and PID constants for the diffusion ovens we worked on.
However I was wondering where you would compare these time constants with. So I looked again at the Lugano report and must admit that I never looked in detail to Plot 5 which gives the step response when the heater power was increased from about 800 Watt to about 915 Watt. Also I took a brief look at the options of the thermal simulation program and think that if I postpone an activity planned for the weekend, I might be able to do a transient analysis, stepping the power from 0 to 800 Watt and then after stabilizing to 915 Watt.
The emissivity and heat transfer settings will be those of for the latest simulated MFMP test (894.94 Watt). So the reported temperatures will not be correct, but at least you will see the time constants
So my question is if this will be useful for you ? If so I will give it a try, but can not guarantee that I will succeed.in doing the transient analysis since I have not yet experience with that option of the program.
LDM ,
I am merely curious (always). By all means, don't spend tons of your time if you are not interested in it yourself, or if it is very onerous. I was hoping that it was relatively easy, since you have a functioning model. Years have gone by already, so there is no rush...
Thanks for your concern about spending my time.
From a quick look at the program I came however to the conclusion that this would not take much time if I used the settings of the last test. Maybe the program does a wile to do all the steps, but I don't have to attend. And I am curious also, because looking at plot 5 of the Lugano report I think there are two major time constants in that plot. One shorter term an one long term.
If I had time I would digitize that plot and do a Fourier analyses to see what that gives but that takes too much time at the moment (anybody else who would like do this ? ) . But since from the outcome of the simulation we maybe can conclude if there was a secondary, non resistive heating effect it would be nice to know. So I am going forward anyway.
If I succeed I will post the results.
I had a discussion with Bob Greenyer on ECW about the FEM simulation.
He disagrees with the results and I then asked him about the promise to redo the MFMP dogbone thermal test. It turned out that this test was already done and he provided the links to the available data. See :
http://e-catworld.com/2017/11/…ition/#comment-3600322673
I was not aware that this test had already be done and his answer was :
" I was meant to widely publicise them but, you might understand, got a little sidetracked."
Taking a quick look at the results it turns out that the results of the MFMP measurements are about the same as for their first test. I still do not understand while there is such a large difference between my FEM analysis and also my radiated and convected energy calculations which did not match the heater power settings . However the data the MFMP now supplied is much more then for their earlier test and there are Optris ravi files available (the largest almost 600 MB). I am curious if their temperature profiles where more symmetric this time such that I have more confidence in doing recalculations.
After a few initial trials to find the optimum settings for presenting the results the transient analysis is now running. Hope to post the results in a few hours
Hereby the result of the transient analysis.
At time 0 the power of the heater was set to 800 Watt. At 100 seconds the power was increased to 915 Watt
First picture gives the overview, the second zooms in on the top.
Your plot estimates about 20 seconds to go from around 720 C to 760 C (?)
I get 22 seconds from the exported data
The Lugano report shows about 400 seconds to go from 1295 to 1400 C.
(The Lugano time period seems rather long).
Clarke estimated the Lugano temperatures to be 705 C rising to 775 C, rather than 1295 C. I thought those two temperatures to be slightly higher, but only by around 30 C, probably not enough to have a significant effect on the time period.
The exported simulation data goes from 720 C to 763 C, So the starting temperature from the simulation is higher, but the end temperature is lower. This makes the estimated delta from TC 70 degree C and the delta from the simulation 43 degree C.
But TC used for his emissivity correction the view factor of two endless plates under 90 degree. That is not the situation on the dogbone, where the angle is less end the view to the sides is less restricted because the fins are bending away due to their circular form. The smaller angle increases the view factor between the fins, the other decreases the view factor between the fins and the last one wins as the Monte Carlo ray tracing showed. As a result we can expect somewhat lower temperature then TC calculated.
Here is my estimate for one of the three Lugano device coil wires. (It can be fine tuned). The heat flux per coil can be worked out/adjusted, per input wattage, near the bottom (where the little coloured flame is).
The long time period for the Lugano coil seems consistent with the weak temperature output of the coil at low wattages relative to its wire size (less than 1000 W, here, each coil providing 1/3 of the total input). Inputting 35 mW/mm2 into the adjustable field makes for 297 W per coil in this example. (In comparison, my Durapot slabs are at the overheat range at around 120 mW/mm2, using a much smaller diameter 24 AWG wire. I should figure out what 35 mW/mm2 works out to for input W for the present slab and see what that heating rate looks like).
I still think that possibly two major time constants are involved in the Lugano plot.
I succeeded in digitizing that plot and will subtract the response of the simulation from that plot. Maybe the difference can tell us more. If that is the case then I will report back.
Where a complication is introduced into the Lugano figures is the use of the recursive emissivity method applied to the camera emissivity using the Plot 1 values, so that the original emissivity is not directly calculable by any method (if at all) and therefore the original temperature that was detected at some "original" emissivity setting, is in doubt. So we can calculate alternate temperatures based on alternate emissivities at some constant radiant power level, perhaps even perfectly, but the original temperature-emissivity measurement has been obfuscated by the manipulation through the recursive method, and therefore the actual measured temperature-radiant power level detected by the Optris is uncertain. Perhaps this is why you get lower temperatures from the model.
It is my understanding that the broadband temperature/emissivity curve in the Lugano report (are we talking about that curve , Plot 1 ) was from literature, not from using the recursive method.
For temperatures higher then a few hundred degrees that curve matches closely emissivity data supplied by NASA. In my model I am not using any other data from Lugano, except that curve, which was also used by the MFMP for their dogbone test. And to match my reporting with that of the MFMP I used the same curve.
All other material constants where from litterature.
For a static situation the power from the heating element must be dissipated to the outside, and that is determined by emissivity on the outside, thermal exchange coefficient, temperatures and area. Those are determining the temperature at the surface and that is what the FEM simulation program is using, not any Lugano data.
The FEM simulation program can also calculate back the radiated and convected power by selecting the surfaces and if I do that, that power is in agreement with the power assigned to the heater.
So I see not how Lugano can in any way have influence on the FEM thermal simulations. But maybe I did not understand the meaning of your statement above
It should also be remembered that the temperatures reported are composites of those of the respective measurement areas for the main tube and and the caps. This introduces yet more uncertainty. Interestingly, this means that some locations would be hotter than the reported 1410 C maximum, in turn meaning that the coil temperatures would be even hotter than some already very high temperature estimates, if the reported values were taken at face value. (Regardless of whether there was reaction heating or simple Joule heating, or some combination of the two).
I have stated earlier on ECW that based on calculations I did on the data of the Lugano report, that the reported temperatures in the second column of table 7 of the Lugano report might have been reported in error in that those temperatures are reported in Kelvin instead of Celcius. In that case the Kantal wire will withstand the temperatures and calulated radiated and convected power are in agreement with those reported.
After having completed further analyzing the transient plot I intend to calculate the radiated and convected power from an x axis temperature curve from ravi data supplied by the MFMP. It will tell us if that power matches their reported heater power.
What I also wonder about is if different types of casting materials where used for the MFMP and the Lugano device with different broad band emissivity curves. The MFMP said they used the same, but I don´t know how they knew what was used for the Lugano device. If you see the differences in gray-white levels between the two I wonder if it was the same material.
I tried to find a broadband emissivity curve for Durapot 810 to compare it with standard alumina, bit could not find it. I understand that you are using Durapot so wonder if you have such a curve from the supplier.
The recursive method (please review the Lugano report for details) is a feedback method that reiterates the temperature to get a new emissivity to get a new temperature several times in succession, using Plot 1. Try it with the Optris software if you have it. It shifts the final temperature reported from an original temperature reading based on the slope of the Plot 1 graph, (which is for total emissivity, not the Optris IR spectral sensitivity range).
I have studied the recursive method described in the Lugano report and agree that if we follow the letter of the text it will indeed give inflated temperatures.
But that's "IF"
There is another method to measure temperatures with the Optris which does not need calibration of emissivities or even using the correct emissivity but which will still lead to correct calculated powers. That method also closely follows (in part) what was written down in the Lugano report. Let me explain it in the following steps :
1. Set after completing the test the emissivity of the Optris back to 1
Setting back the emissivity on the Optris back to 1 gives you the equivalent in band black body temperature. Now if you had used a wrong emissivity when measuring the temperature, setting back the emissivity to 1 would give you the correct in band black body temperature, where it not for the term (1 – ε)·TambN. But for higher temperatures that term becomes small with respect to the term ε·TobjN. For example discarding this term for a temperature of 800 degree C gives a maximum error in the in band black body temperature of .1 % and at 1000 degree C the error is less then .05%.
So setting back the emissivity back to 1 will, even when you used the wrong emissivity, still give you the in band black body temperature with great accuracy.
2. Relationship between in band black body temperature and broad band black body temperature.
It is possible from data which can be found in literature to determine for Alumina the relationship between the in band black body temperature and the broad band black body temperature. I did those calculations. The result can be found in the graph below. (Note : I did not know a detail of the Optris spec, as such the graph might be slightly of)
3. Calculate the broad band black body temperature
Having found the relationship between in band black body temperature and broad band black body temperature we can use the in band black body temperature found under 1 to calculate the broad band black body temperature.
Having found the broad band black body temperature you will be able to calculate the power.
4. Determine the temperature and emissivity
If besides the power, you also want to know the temperature and emsissivity you can using the found black body temperature to iterate through a temperature versus emissivity graph to find the temperature and emissivity. Note that even is this graph is not without errors, the found combination of temperature and emissivity will always represent the correct power.
Unlucky for all of us who want to find out the truth we do not now if the Lugano team followed the text in the report and got inflated temperatures, followed the method which I presented above or did even use another method.
Display MoreI have studied the recursive method described in the Lugano report and agree that if we follow the letter of the text it will indeed give inflated temperatures.
But that's "IF"
There is another method to measure temperatures with the Optris which does not need calibration of emissivities or even using the correct emissivity but which will still lead to correct calculated powers. That method also closely follows (in part) what was written down in the Lugano report. Let me explain it in the following steps :
1. Set after completing the test the emissivity of the Optris back to 1
Setting back the emissivity on the Optris back to 1 gives you the equivalent in band black body temperature. Now if you had used a wrong emissivity when measuring the temperature, setting back the emissivity to 1 would give you the correct in band black body temperature, where it not for the term (1 – ε)·TambN. But for higher temperatures that term becomes small with respect to the term ε·TobjN. For example discarding this term for a temperature of 800 degree C gives a maximum error in the in band black body temperature of .1 % and at 1000 degree C the error is less then .05%.
So setting back the emissivity back to 1 will, even when you used the wrong emissivity, still give you the in band black body temperature with great accuracy.
2. Relationship between in band black body temperature and broad band black body temperature.
It is possible from data which can be found in literature to determine for Alumina the relationship between the in band black body temperature and the broad band black body temperature. I did those calculations. The result can be found in the graph below. (Note : I did not know a detail of the Optris spec, as such the graph might be slightly of)
3. Calculate the broad band black body temperature
Having found the relationship between in band black body temperature and broad band black body temperature we can use the in band black body temperature found under 1 to calculate the broad band black body temperature.
Having found the broad band black body temperature you will be able to calculate the power.
4. Determine the temperature and emissivity
If besides the power, you also want to know the temperature and emsissivity you can using the found black body temperature to iterate through a temperature versus emissivity graph to find the temperature and emissivity. Note that even is this graph is not without errors, the found combination of temperature and emissivity will always represent the correct power.
Unlucky for all of us who want to find out the truth we do not now if the Lugano team followed the text in the report and got inflated temperatures, followed the method which I presented above or did even use another method.
I don't find this much help.
(1) TC found that the COP disparity between the two high temp tests disappears when you correct the emissivity using the data from the paper and realistic IB emissivity. That is an independent check that the data from the paper is correct. It would be unlikely to happen by chance, and was got with no fudge factors, whereas this speculation on what error could rescue things is exactly trawling through fudge factors till you find one that vaguely fits.
(2) If the method in the paper for collecting data is not as described then even the experimental data from that test is useless. It is always possible to discount a negative test by supposing (on no evidence) that very carefully collected data was just wrong, or not a described. And except for the validation from (1) above I'd say the Lugano authors are so deficient in theoretical analysis that you cannot be sure there are no other errors.
(3) However, if you do argue their deficiency in this way you must similarly discount the apparently positive Ferrara test results.
Best wishes, THH
(3) However, if you do argue their deficiency in this way you must similarly discount the apparently positive Ferrara test results.
Best wishes, THH
I don't find this much help.
(1) TC found that the COP disparity between the two high temp tests disappears when you correct the emissivity using the data from the paper and realistic IB emissivity. That is an independent check that the data from the paper is correct. It would be unlikely to happen by chance, and was got with no fudge factors, whereas this speculation on what error could rescue things is exactly trawling through fudge factors till you find one that vaguely fits.
THH, I am really at this moment not interested if whether the COP was larger then one or just one in the Lugano test. For the moment I leave that to other people to decide.
(2) If the method in the paper for collecting data is not as described then even the experimental data from that test is useless. It is always possible to discount a negative test by supposing (on no evidence) that very carefully collected data was just wrong, or not a described. And except for the validation from (1) above I'd say the Lugano authors are so deficient in theoretical analysis that you cannot be sure there are no other errors.
I totally agree with you about that ! That's why I think that I cannot trust what was written in the report and have to be very critical about the contents. Analyzing the data gives many possible inconsistencies.
(2) If the method in the paper for collecting data is not as described then even the experimental data from that test is useless. It is always possible to discount a negative test by supposing (on no evidence) that very carefully collected data was just wrong, or not a described. And except for the validation from (1) above I'd say the Lugano authors are so deficient in theoretical analysis that you cannot be sure there are no other errors.
What' s bothering me most at the moment is that I see differences in my thermal simulations on the dogbone (Cop = 1) ,the results of the MFMP tests and the Lugano dummy test. However I have recently come up with some idea's which might explain those differences. To test those idea's I have to do some new FEM simulations, but that does take a lot of my spare time, so it will be a while before they are completed.
Why I do this ? Because if we can explain those differences we all will have gained additional knowledge about the issues involved. What to do with that knowledge may everybody decide for them self.
I myself am very interested in the technical aspects as a hobby.
(3) However, if you do argue their deficiency in this way you must similarly discount the apparently positive Ferrara test results.
As I said. Currently I am not interested in COP values greater then one. So Ferrara is for me not an option, also because making a model of the HOTCAT is much more difficult then the dogbone. That I sometimes give alternative explanations is to make people aware that there are sometimes other ways how things can be explained because many have fixed their opinions without considering alternatives. Does that make the ECAT work or not? Certainly not, because we don't in my opinion have currently the information to make the decision and as I stated above, I agree with you that we can not be sure about errors (But I would make a bet that there are !) .
Best wishes, THH
Best wishes to you also !
View factor and the influence on thermal radiation of finned areas
I have worked out the formula's having to be applied to calculate radiated heat from opposed surfaces (eg fins as on the dogbone). These formula's are already known, but it might be interesting to know how they can be derived.
We know that heat radiated by a heated surfaces has to be radiated to the background in order for that surface to get rid of it.
The amount of radiated heat of a fin directly radiated to the background is proportional to
e * Af * Fbg
e is the emissivity and Af is the area of the fin surface and Fbg the view factor, giving the amount of surface which directly sees the background in case there are opposing surfaces such as an opposing fin which can partly block radiation. If we apply this to the Lugano ECAT we have the following figures :
Area of the cenral part of the dogbone wihout fins .0125 M^2
Area of the central part of the dogbone with fins .0263 M^2
View factor Fbg (By Monte Carlo Ray tracing) .637
This gives that for a dogbone with fins we have to calculate with an equivalent area of
.637 * .0263 = .0167 M^2, this opposed to the .0125 M^2 without fins
Thus with fins we are able to dissipate a factor .0167/.0125 = 1.34 more thermal radiation then without fins, or a 34% increase.
In addition to this direct increase in apparent surface area we also have to take into account the effect of the reflected radiation between the fins.
The radiation directed towards the other fin is reflected, and this reflected energy by the other fin is with the factor Fbg directed to the background, thereby aiding in getting rid of the thermal radiation, and partly radiated back by the factor (1-Fbg) to the originating fin. Then we get again reflection and this process continues to infinity, albeit with every next reflection involving less radiated energy. For the first reflection we have :
Af x e (1-Fbg) arrives at next fin
at the next fin Af x e (1-Fbg)(1-e) is reflected
of which Af x e (1-Fbg)(1-e)Fbg is to back ground
and Af x e (1-Fbg)(1-e)(1-Fbg) is directed back to the other fin
Of the reflected back energy Af x e (1-Fbg)(1-e)(1-Fbg)(1-e) is reflected
of which Af x e (1-Fbg)(1-e)(1-Fbg)(1-e)Fbg to the background
and Af x e (1-Fbg)(1-e)(1-Fbg)(1-e)(1-Fbg) to the other fin
Summing all reflection to the background :
Af x e (1-Fbg)(1-e)Fbg
Af x e (1-Fbg)(1-e)(1-Fbg)(1-e)Fbg
.
.
etc
We can express the n th reflection as : Af x e x Fbg x ((1-Fbg)(1-e))^n
So in our case the sum of all reflected radiation to the background is :
Af x e x Fbg x Sum ((1-Fbg)(1-e))^n with n = 1 to infinity
If we combine direct radiation to the background with reflected radiation to the background this becomes :
Af x e x Fbg + Af x e x Fbg x Sum ((1-Fbg)(1-e))^n with n = 1 to infinity
which is equal to
Af x e x Fbg x Sum ((1-Fbg)(1-e))^n with n = 0 to infinity
Which represents all radiation directed to the background
Since the sum of a^n with n = 0 to infinity is 1/(1-a) ( a < 1 )
Then Sum ((1-Fbg)(1-e))^n - 1} with n = 0 to infinity equals 1/(1-(1-Fbg)(1-e))
Thus total energy radiated to the background is
Af x e x Fbg x { 1/(1 - (1-Fbg)(1-e))}
We can check the formula with the following two boundary conditions :
For e = 0 the total radiated energy will be zero
For e = 1 the total radiated energy will be proportional to Af x e x Fbg which is correct because there is no reflection.
We can rewrite the above formula as
Aeq x e^
With Aeq = Af x Fbg being the equivalent surface area and e^ = e x { 1/(1 - (1-Fbg)(1-e))} being the effective emissivity
Since both the view factor of radiated heat to the background Fbg and that directed towards the other fin ( Fff ) has to be equal to the total radiated heat, it follows that :
Fff + Fbg = 1
And thus since since 1 - Fbg = Fff we rewrite the effective emissivity as
e^ = e x { 1/(1 - Fff(1-e))} with Fff = 1 - .637 = .363 for the dogbone
This is the formula which also can be found in TC's paper since he used in his paper the view factor between the fins and not the view factor to the background.
The increase in emissivity van be expressed as
e^/e = 1/(1 - Fff(1-e))}
Taking the Lugano dummy run as an example with e = .690 it follows that the increase in apparent emissivity is a factor 1.127.
If we apply both the factor of 1.34 due to the larger apparent fin area and the factor 1.127 due to the increase in apparent emissivity the finned area of a dogbone will be able to dissipate a factor 1.34 x 1.127 = 1.51 more thermal radiation then if it did not have fins. (a 51 % procent increase).
