Rossi Lugano/early demo's revisited. (technical)

Zeus46

Newtons law of cooling is likely too over-simplified to give an accurate result, especially over a wide variation in temperatures. It assumes that each unit area transfers the same amount of heat (And also that h isn't affected by T).

The thermal exchange coefficient h is affected by T, but in an indirect way.

First of all the Rayleigh number is calculated with :

The volumetric thermal expansion coefficient

The kinemathic viscosity

The thermal diffusity

All three are dependent on the temperature.

Then using the Raleigh number to calculate h, we also multiply by k, the thermal conductivity of air, also temperature dependent. Thus the calculated value of h is largely depent on temperature.

But I agree that we work with an average temperature and that h over the area is constant.

That is indeed a simplified approach, which however gives for situations which have been researched many times in literature, such as horizental tubes, adequate results.

An other approach would be to use CFD (Computional Fluid Dynamics) software to calculate the convective heat transfer of a part of the rod for a given temperature. Additional we can then also calculate h.

I have CFD software, but have still to learn how to use it beyond the basics. But I have seen in literature several quite complex simulations with CFD software which give errors of 1% to 2 % compared to the real measured data. This because CFD is not using approximations in calculating the convective heat transfer coefficient, but is instead solving the differential equations governing the heat transfer. So maybe this is the way to go.

Instead of using h = Q/(A(Ts-Ta)), the more accurate method is to calculate an average h (taking the shape of the object into account) - done by first working out the Prandtl, Raleigh & Nusselt numbers for the system.

Using h = Q/(A(Ts-Ta)) is using the forumula as used by the Lugano team in a reverse way using their data. As such that should give the exact value of h they used.

Can't paste the formula's for those easily, but this should give you what's needed:

I had the link myself, but must concede that I did not look at the contents lately.

The formula showed in the link is somewhat different from the one the Lugano team and I used.

If time allows it migh be an idea to use the formula in the link and see how much the data differs.

But there are many formula's for calculating the convective heat transfer coefficient of a horizental tube (or round heated wires).

The formula used by the Lugano testers is normally used for much larger Rayleigh numbers then those valid for the Lugano case.

As such it might be worth the effort to find a better (more accurate) formula for the lower Rayleigh numbers.

AlainCo

I understand now why the manufacturer of the IR cam advise to calibrate, and not to trust any emissivity number...

Alain,

While radiated heat transfer is part of the calculated power and emissivity can then be important, the above posts are about convective heat transfer.

As far as calculating radiated heat transfer, then indeed if you measure the temperature with the Optris, then for a correct temperature measurement you need to use the correct in band emissivity.

Hoevever for the in band emissivity often a fixed value of .95 is quoted, but in reality the in band emissivity is also somewhat dependent on temperature.

In an earlier post I showed that you can also calculate the power using the Optris without calibration. see

Revisiting the power calculation in the Lugano report

We cannot replicate the active rod, but maybe can Dewey Weaver obtain a dummy from the stock? or Maybe is the dogbone of MFMP not far enough from the shape (maybe it can be painted with the ZrO2 paint cited by Dewey Weaver ) to give interesting approximation of emmissivity over temperature?

The ZrO2 paint from Aremco is a special paint which is as Armeco says specially fitted for fixing heater coils. So they could have fixed the heater coil with it before casting the ECAT with Alumina.

That would fit both Dewey's story and also fit the analysis of the Lugano report that the outher casting was almost pure Alumina.

IH built the Lugano reactors, three of them, and were surprised by the paint, so your theory doesn't work.

The argument goes also otherwise. The outside of the ECAT was by analyses almost 100% Alumina.

So in the same way we can argue that the theory that it was painted with Zr paint doesn't work.

So the question is who is right and who is wrong.

On that question I don't know the answer.

Paradigmnoia

For your info

Paradigmnoia

Although the error % seems large for the coolest end of the rods, the final W difference, in terms of the total power budget, should still be rather minor. I believe that I had a similar result when I did it, and it did seem to be rounding that made the difference.

I agree, except for the dummy run where convected and radiated power are of the same order.

The calculations for working out the Rod segment temperatures and Rod temperature gradient, and therefore power, during the active period is much more complex. There're is very little in the report to go on, since just the final total power is reported for each run.

Agreed. And that also means that I have currently no plans to do any calculations for estimating the COP of the active runs.

You should be close enough, however, with your model that it should be possible to test if the 2/3 factor was in fact applied, or not, to the active period Rod power in the report, since a total 33% overestimate error should be obvious. (It is my opinion that the 2/3 adjustment was not made to the active period Rod power in the report, and therefore the Rod power reported is too high for all active runs. (Easily fixed, since they lump those results into two periods anyways, an indication of how concerned the Professors were about the Rods contribution)).

First of all can you explain what you mean by my model ?

Any ideas how to test with my model if the 2/3 factor was applied ?

If the Lugano testers made the error as per your opinion then indeed the COP value would be less.

But in a previous posts we showed that they made an other error, being that they did not calculate with the fin area combined with the view factor to the background and also did not correct the emissivity for the reflection between the fins. And that total correction has about the same value as when the 2/3 factor was not applied, but with the opposite polarity.

So we end up with about the same power budget

Don't forget the minor Joule heating in the rods added in the report from the cables,

Thanks for the warning . I was already aware of it

and consider carefully the contribution of the heater coil extensions entering the Rods for 4 to 5 cm, which affect calculations for both the temperature of the initial Rod segments (Cap end) and the power budget of the Main Tube since these wire extensions, six in all, reduce the amount of input Joule heat available to the Main Tube and Caps, possibly explaining a portion of the previously calculated excess (COP 1.2 or similar)

Good point !

Once, here in the Forum, I calculated exactly the parameters of the twisted 15 ga Kanthal resistance wire for the three parallel coils, from which the 6 X 4 cm (estimated) could be subtracted so that the end lead power % of the entire heater windings could be correctly attributed. Off the top of my head, each of the 3 coils have about 1.5 m of wire, which is twisted to make a pre-coiled length of slightly less than half of that. Probably better for me to look it up again. I believe that the Caps and wire extensions combined contain about 30% of the total calibrated resistance heater wire, and therefore the wire extensions could net about 15% of the Total input power.

I am still wondering about the heater wire seize of AWG15 they supposedly used.

AWG15 wire has a diameter of 1.45 mm. But they seem to have been braided with two wires.

Twisting two wires will double the diameter, thus 2.9 mm

For about 70 windings total, without inter winding spacing, the length of the heater coil would have been 70 x 2.9 mm = 203 mm. But the photographs of the heated Ecat gives me the impression that a reasonable spacing was used between the windings.

Proper engineering practice for heater coils uses strech factors between 2.5 to 4 for the inter spacing between the coil windings to prevent shortages due to the coil windings moving when heated.

Using a stretch factor of 2.5 (the minumum) gives a minimum length of the coil of 2.5 x 203 = 507 mm. That is much longer then the total Ecat length of 280 mm.

Or is my calculation wrong ?

Quote from LDM

IH built the Lugano reactors, three of them, and were surprised by the paint, so your theory doesn't work.

The argument goes also otherwise. The outside of the ECAT was by analyses almost 100% Alumina.

So in the same way we can argue that the theory that it was painted with Zr paint doesn't work.

So the question is who is right and who is wrong.

On that question I don't know the answer.

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Not I think inconsistent

The Lugano report says that the alumina sample was taken from one of the rods, not the reactor body.

THH

Quote from THHuxleynew

Not I think inconsistent

The Lugano report says that the alumina sample was taken from one of the rods, not the reactor body.

THH

The following quote is from appendix 2 of the report

In order to determine the nature of the material covering the reactor, a sample from one of the ridges was analyzed.

As far as I know the rods had no ridges, but the reactor body had

Quote from LDM

The following quote is from appendix 2 of the report

In order to determine the nature of the material covering the reactor, a sample from one of the ridges was analyzed.

As far as I know the rods had no ridges, but the reactor body had

I must have misremembered!

I think I did so because it is still inconclusive. The "fragments" analysed would not be all paint, and might in fact contain no paint at all. So, given the reactor was painted, we don't have much info, unless as P says above we are sure that the ridges were not case from something that bakes to 99% alumina.

Should this analysis be incorrect it is another example of the Rossi effect. Not only do small ceramic tubes miraculously deliver a X3 power gain when used as radiant heaters, but also lab analyses deliver (completely) incorrect results! For example the 62Ni.

Axil will have the answer, it is probably all about muonic BE condensates (and yes, since muons are leptons I know that does not make much sense, but then it is par for the course. It would be muons bound in pairs and then forming the BEC).

Paradigmnoia

However, the reactor (including ridges) was cast from Durapot 810, which is not made of 100% alumina, nor is it 99.9 % alumina with no detectable other elements in concentrations to make up the 0.1% , although it is alumina based.

So we now have three possible materials with their respective emissivities to choose from

1. Durapot 810 (stated by Dewey ?).

2. Zirconiumoxide coating over the potting (also by Dewey ?)

3. Analysis of the material of the ridges by x ray crystallography, giving as a result that it was almost 100 % pure Alumina.

Note that the x ray christallography analysis did not detect any signals on positions 28 and 32 which are the main peaks for zirconiumoxide.

So in the samples analyzed there was indeed no zirconiumoxide present .

The German safety sheet of Durapot 810 says that it is made up of only two components, Alumina and the solvent.

That would make Durapot 810 after casting also a 100% alumina cast.

However how did they increase the thermal conductivity compared to Durapot 801 ? Is the casted Durapot 810 denser ?

In that case the specific weight of Durapot 810 should be higher.

Did they do that by adding synthetic corundum particles?

In that case it explains that also Al2O3 with the corundum crystal structure was found by the x-ray chrystallography in the Lugano report.

In my opinion it is not likely that the x ray christallography equipment is giving incorrect results but that al least contradicts point 2.

So what information are we missing , is incompete or wrong ?

THHuxleynew

I think I did so because it is still inconclusive.

Agree that it is inconclusive

The "fragments" analysed would not be all paint, and might in fact contain no paint at all.

Seems very unlikely to me that the samples would not contain some coating material if it had been coated.

So, given the reactor was painted, we don't have much info, unless as P says above we are sure that the ridges were not case from something that bakes to 99% alumina.

The x ray christallography equipment has no interest in this story.

It will tell the composition without trying to cheet on us and it told us it was more then 99% alumina.

I have no doubt about that, but as mentioned above, maybe Durapot 810 is also 100% alumina.

Para has Durapot 810 ?

Would it then be possible for someone with acces to x ray chrystallography equipment to test a casted sample for it's contents ?

Many universities seem to have x ray chrystallography equipment.

The most likely version is that the reactor was painted with Aremco 634-Al, rather than 634-Zr.

If it was painted on the outside I agree.

That simplifies things a lot.

It does not make things simpler (except that we in that case possibly can use alumina emissivities in calculating radiated power, but that is possibly also dependent on the layer thickness of the paint)

Even if the outside was painted with Armenco 634-Al, the samples analysed of the Lugano ridges would then also contain some of the underlying material and the contents of that material would have shown up in the results.

If that underlying material would have been Durapot 810 as per Dewey then the contents of Durapot 810 would have shown up. In that case we arive, based on the analysis in the Lugano report, to the conclusion that Durapot 810 does not contain any additives in adition to alumina / corundum.

So it is still interesting to know the contents of Durapot 810.

If it contains other materials then those which showed up in the Lugano report, then we know for sure that Durapot 810 was not used for the casting of the ridges.

If it only contains alumina and corundum in about the same relations as in the report , then we know that Durapot 810 was probably the casting material used.

Concerning your suspicion that the ingredients include manganese because of the pyrolusite-like stain, note that also corundum powders comes also in about the same colors as pyrolusite (At least that is what I make up after searching for some pictures), so corundum as a part of Durapot 810 is still an option.

I am curious to know how your Durapot 810 casts compare in color to the Lugano Ecat.