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

Quote from LDM

Paradigmnoia

Para, do you have for me the natuaral time constant (0.632 of the step) for your rod when rising the temperature ?

You mentioned about 180 seconds, but I have no clue to what the reference value that was.

Reason is that that 180 seconds was much more then what I simulated (See post #10).

This was a reason for me to look again at the old simulation FEM data and must admit that for the density of Alumina I mistyped and used a value of 390 kg/m^3 instead of 3900 kg/m^3.

So I intend to redo this, but also with a better power distribution and the temperature dependency of material properties entered as piecewise linear curves instead of fixed values.

However a simulation run takes a lot of preparation time and every simulation run itself takes 4 to 6 hours on my computer.

As such it will take quite some time before I have gathered enough data to analyse.

If the results are interesting enough I will in the future publish them in this thread.

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I was only watching the minutes but not seconds counter just for a rough idea how long. I can do it better now that I have nailed down the input power levels required to hit the two different temperatures.

It was three minutes raising the temperature and dropping (zero input) it down between the 1295 and 1410 temperatures. Basically it means I was lucky on the way up that I didn’t turn it up too much. (I can easily give it enough power to burn it down). I can test it again today with proper time keeping. Problem is the TC temperature is not the IR temperature for that test. I think that the 1295 needs to be 1300 C also. The plots in the Lugano report are smoothed so the corners of the turns have lower lows and higher highs than the source numbers from Table 7. It is the turns I am matching...

Quote from THHuxleynew

Just in addition to P's excellent post. You need to look at the report really carefully, but it turns out that the dummy results did not suffer from emissivity issues AT ALL, in spite of the incorrect method used.

Why is this? Bceause for the dummy run they used TC's on the reactor to measure temperature. They actually state that they corrected the book emissivity values to make the IR measurements the same as the TC measurements during this test.

Rossi then persuaded them not to use TCs during the active test (or else they spontaneously decided to do this themselves) so we have no such check.

It interested me, because for a very long time I had no idea that those dummy temoperature measurements were not using the same methodology as the active ones. Of course, it does not help, because the band/total emissivity factor is small at low temperatures and gets very high at high temperatures. But worth nothing that they did not even do a fair control comparison of their methodology at low temperatures.

That report is about the most misleading scientific account I have ever read, and for reasons that are quite subtle.

Reference: bottom of page 9 of the Lugano report

We therefore took the same emissivity trend found in the literature as reference; but, by applying emissivity
reference dots along the rods, we were able to adapt that curve to this specific type of alumina, by directly
measuring local emissivity in places close to the reference dots (Figure 7).

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There are still several strange things about the Dummy. Not the least is that the manufactured Rods (weakly reflective) were used for calibration of the camera vs the quite different surface of the Device.

As you mentioned, they reported adapting the emissivity curve without showing the adapted version of the curve. Do they then use the adapted curve for calculating radiant power?

They also spend a whole page describing the recursive total emissivity (Plot1) matching exercise (using the Dummy as the example), which would ignore the results thermocouple-Kapton “dot” temperature matching.

Quote from LDM

I don't think it is important how the temperature is measured

Also it is not even important to get the exact same temperatures as in the report.

The time constant is not very much dependent on those.

I also have another question.

From a study on the mechanical properties of Alumina 98% castable (I should have it somewhere but can not find it quickly) I remember a density of the the cured castable of 3120 kg/m^3 instead of the 3900 kg/m^3 for high density Alumina.

Did you ever measure the density of the the casted Durapot after curing ?

If not, can you do so so that we have the right figure for the simulations ?

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I have been thinking a fair bit about extracting the thermal conductivity value out of the data here. Whether it could be done clean enough with my equipment.

On the the other hand, I can do a specific gravity test fairly easily... more or less. I’ll have to dig out my graduated cylinders box.

Looks like the SG is 2.52 , or a density of 2520 kg/m³

I'll test it a couple more times.

Quote from LDM

That is even less then the value I had.

Are you using vibration to make the cast more dense before curing ?

I think I will work on a prelimanary test first with the old FEM model to see what the general effect is of those differences before upgrading to a more accurate model.

Hope to find some time next week to do that test.

I did shake the cement, but this piece is not heat cured. Not sure how much that will make a difference. I will bake it out and see if anything changes. The SG does seem low.

Edit: Just tried a ceramic insulator from a J type light bulb. SG was 2.507.

Edit2: Got 2.84 SG for the same Durapot piece this time. I need to make a bit more reliable rig and give it a try again. Might have to coat the piece so it doesn't soak up any water.

Quote from LDM

One company uses the following firing process

heating rate: 22°C/min to 1000°C, 3.6°C/min from 1000 to 1670°C; Hold time: 1 hour at 1670°C; natural cooling.

And states that this increase the density then from 2.2 g/cm^3 to 3.4 gr/cm^3

So baking out will likely make a difference

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I'll have to wind a coil around the piece to heat it up enough. I have an assortment of unused coils so should be no problem.

I don't think that I have ever managed to get anything as hot as even 1400 C (real temperature) before, except when the coil burned out of Slab#1 and molten ceramic spewed out.

Quote from LDM

Whatever temperature you use, we should likely see a difference

Cooking now, wrapped in a orange hot coil.

Hmm. The heat treated (800 C for 1.5 hrs) Durapot chunk ended up 3.11 grams lighter than it began. (It was poured months ago, and just sat in garage since then)

The volume remained unchanged.

So now the SG is 2.3

Edit: The piece seems to have soaked up about 4 g of water when submerged, so I will dry it out, coat it with something to keep water out, weigh it, and try again.

Quote from LDM

Paradigmnoia

Using the total weight of the Lugano ECAT (452 gram) I did a calculation of the Durapot density in the following way

First the volumes of the Durapot casted volume and that of the internal rod with insert where both determined by measuring the volumes from the FEM model.

The results where :

Volume Durapot cast-----------------------1.611E-4 m^3

Volume internal rod with insert---------1.232E-5 m^3

Furthermore the total internal length of heater wire was determined to be about 120.36 cm.

Using for the AWG wire a weight of 12.5 g/m the weight of the internal heater wire is 15.045 gram

Using for the internal Alumina rod with insert a density of 3900 kg/m^3 the weight of the rod with insert is 48.048 gram

Thus the weight of the Durapot cast is 452 - 15.045 - 48.048 = 388.907 gram

Deviding this by the volume of the Durapot cast gives a density of the Durapot of 2.414 g/cm^3Indeed in the range you measured !

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That seems about right. I did a calculation like that once to work out the thermal resistances to see if the Dummy actually reached equilibrium.

I painted a layer on the piece last night after drying it out again (broiled in oven for two hours).

Durapot soaks up paint like a sponge.

The specific gravity of the Durapot 810 is a solid 2.3.

It is apparently strongly, if not aggressively, hygroscopic.

The piece managed to absorb 5.5 g of water even through the paint. This last time I recorded the weight drop of the water it was suspended in after each dunking, before resetting the tare, and the total water loss (absorbed into the piece) weight is almost exactly the same as the weight gain of the Durapot piece. (5.5 g of water was not sticking to the outside, it ran off the paint immediately after removal from the water.)

The "soaked" SG of the Durapot is 2.6. The water loss/gain stabilized at 5.5 g