Is There an Optimal Size for Magrid Casings?

Discuss the technical details of an "open source" community-driven design of a polywell reactor.

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Postby KitemanSA » Sun Mar 15, 2009 3:17 pm

Last edited by KitemanSA on Sun Mar 15, 2009 9:32 pm, edited 1 time in total.

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Postby tombo » Sun Mar 15, 2009 9:33 pm

-Tom Boydston-
"If we knew what we were doing, it wouldn’t be called research, would it?" ~Albert Einstein

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Postby KitemanSA » Mon Mar 16, 2009 1:13 am


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Postby tombo » Mon Mar 16, 2009 5:25 am

-Tom Boydston-

"If we knew what we were doing, it wouldn’t be called research, would it?" ~Albert Einstein

tombo
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Postby tombo » Mon Mar 16, 2009 5:52 am

Square loop & triangle loop fields.
From:

Square loop B at the center of a square 1 turn coil B=(sqrt(2)*u0*I)/(pi*(side_of_square/2))
Similarly:
Triangle loop for 1 leg B=I*(u0/(4pi*(distance_to_center))*2*sin(60)=I*(u0/(4pi* distance_to_center))*2*SIN(Pi/3)=I*1e-7*2*SIN(Pi/3)/ distance_to_center
Triangle loop total B=3*2*I*1e-7*SIN(Pi/3)/(distance_to_center)=I*6*1e-7*SIN(Pi/3)/((side_length)/2)
Where “distance_to_center” is the perpendicular distance from center of the equilateral triangle to the middle of a side.
Putting these into a spreadsheet I get:

[Well, mostly I get garbage because the forum’s editor eats any spreadsheets, tables, tabs or spaces I use to line up the data columns. I’m afraid you will just have to count the 2 columns of Labels and the 3 columns of data]

Current I 2,721,655 13,608,276 27,216,553
Polywell "Radius" Rpw 2 2 2
Polywell CubeSide Sc 4 4 4
CoilSide (diamond shaped) Ss 2.828 2.828 2.828
permitivity of vacuum u0 1.257E-06 1.257E-06 1.257E-06
B at center of square coil Bsquare 1.09 5.44 10.89
B at center of Triangular coil Btriangle 1.00 5.00 10.00

The center of the (virtual) Triangular coil is the lower B field for a given current, so it is the controlling point that determines the coil current.

Blackbody Temperature
Find black body temperature of an uncooled part at the Magrid location.
Assuming 100MW 2m radius, outer wall at 648K = critical point of steam (boiler outer wall) Power Flux=emissivity*Stephan Boltzman constant*Area*T^4, reactor power flux is on ½ of the surface area, radiant heat from the wall and to the wall is from the whole surface area.

[Again Well, mostly I get garbage because the forum’s editor eats any spreadsheets, tables, tabs or spaces I use to line up the data columns. I’m afraid you will just have to count the 1 column of Labels and the 6 columns of data]

emissivity 0.05 0.2 0.5 0.7 1 0.9
Temp K 4,328 3,062 2,437 2,241 2,052 2,502
Temp C 4,055 2,789 2,164 1,968 1,779 2,229

The last column does not reduce thermal input but uses the full surface area for both absorption and radiation.
It models a graphite (3500C) surface facing toward the heat source. And it works. It needs no conduction across the part to work.

If we can get the emissivity up then the temperatures are not too obscene.
But, Yes, they are very tough.
It would help a lot to orient any structural ties edge-on to the heat source.
I can get down to quite reasonable temperatures depending on the assumptions.
The radiation comes from an extended source, so this strategy has a limit.
Another help is the fact that a large part of the surface faces partly or wholly the nearby actively cooled Magrid itself which is at a cooler temperature.

But, this assumes the part conducts heat away from the surface facing the center to the re-radiating surfaces (not really a good assumption). Although it could have graphite (3500C) coating on the surface to shield the strength portion from the worst of the heat.

I’m not saying it is a done deal I’m saying it might be possible to use a few strategically placed, well designed, non cooled parts.
This analysis also suggests that coating the main Magrid with a layer of graphite might be a viable strategy to reduce heat load on the outer water jacket.

It might be especially viable for solving the problem of the superheated skin of the first wall layer.
A pyrolytic graphite coating should be deposit-able in situ after assembly.
Perhaps just a thin layer to protect the Boron (mp=2300C) layer on the outside of the Magrid.
-Tom Boydston-

"If we knew what we were doing, it wouldn’t be called research, would it?" ~Albert Einstein

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Postby blaisepascal » Mon Mar 16, 2009 12:49 pm


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Postby KitemanSA » Mon Mar 16, 2009 3:08 pm


tombo
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Postby tombo » Mon Mar 16, 2009 6:53 pm

Oh, You mean arrayed 4 times around the Z axis.

Image

Image

Image

Image

This looks just about like what I did before except for the extra copies of the feed lines.
This is inscribed in a 4m cube with 20" thick coils.
These parameters should be easy to change. (unless the model crashes again.)
Also what is your minimum bend radius? Notice that the square (90 deg bend) and triangle (60 deg bend) have different bend radii. I needed that flexibility because in the first version I wanted to make the metal to metal distance the same on the 2 different kinds of kissings. I did not optimize this version for that.

Looks like there will be voids inside the crossovers.
That might give much needed elbowroom for connecting to feed lines etc.
Although the feedlines would need to be repositioned to feed into the areas with voids. (That is easier said than done because of the way the model was put together.)
-Tom Boydston-

"If we knew what we were doing, it wouldn’t be called research, would it?" ~Albert Einstein


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