LN2 Evaporator Design and Reference Links

[Gautam]

I'd prefer you removed that pic. There aren't any photos on the net of the slow base, but your rendering is pretty damn close to one.

 

[m0r7if3r]

is that the speed base or the slow base? Also, just worth noting that based on the surface area and that drawing, it would be relatively easy to derive the size...just as long as you're aware (it's just a sum of parts problem)

EDIT: ninja'd

 

[I.M.O.G.]

Gotta run, for now I removed the pic. Let's not post stuff that isn't really readily available.

 

[nzaneb]

I'd prefer you removed that pic. There aren't any photos on the net of the slow base, but your rendering is pretty damn close to one.

Can do.

Edit: someone already got it Cleaned up my post as well, as to not draw attention.

 

[nzaneb]

This is using your your initial measurements a few posts ago. It is going to be VERY heavy, although centering the holes over the core may provide a bit of pouring response, there is still alot of mass that will increase the pull down time. The stored cooling potential in this pot (once it's down to temp) would be phenomenal. Might take more than a propane torch to heat it back up though

 

[ChanceCoats123]

Very nice Nzaneb. Can you do square steps as well? I'm wondering personally. Also, which software are you using, and have you seen this post? If you have a common format, I can save my square stepped pot and email you the file.

 

[m0r7if3r]

This is using your your initial measurements a few posts ago. It is going to be VERY heavy, although centering the holes over the core may provide a bit of pouring response, there is still alot of mass that will increase the pull down time. The stored cooling potential in this pot (once it's down to temp) would be phenomenal. Might take more than a propane torch to heat it back up though

having seen vince's slow base (on the forum at the right time and I saw the model) and looked at the fast base and some other stuff, I think it needs more surface area down low, so that the lower copper gets cooled and the response time is decent with good hold...I think 6 holes, 5 in a pentagon and one in the middle, that almost connect would be a pretty good design...though you might have to widen the overall design to make it work

 

[I.M.O.G.]

That looks great, thank you. I really don't care about the steps - could be a slope even, I don't know if that makes much difference in the surface area for pull downs really.

Why do you say its going to be really heavy? Thicker walls? Base seems pretty comparable, albeit with less surface area, maybe that adds to the mass more than I'm thinking it does also. Heavy isn't a bad thing tho necessarily, other than the pull down maybe.

Can always do more holes, and I agree that having a layout with a center hole probly better utilizes the space above the center of the die (since we're kinda hoping that will help compensate for some responsiveness, or at least I am).

Why isn't anyone using graphite for this stuff? Haven't looked much, and read something about its conductivity depending on the flow of heat in relation to the crystal structure. I suppose its generally not a good idea for heatsinks and stuff because its electrically conductive, but then we're already insulating and worrying about ln2, ice, and moisture.... Whats a little graphite gonna hurt if thrown in the mix? Costs seem similar to copper for 75mm diameter rods, didn't find bar stock but only glanced... I'll look more but there's probably a good reason not to use it I'd imagine.

 

[m0r7if3r]

Are you getting graphite and graphene mixed up? I'm not sure if they're different, but I know that graphene is the super-conductive one. I think it would be really soft and rather difficult to work with.

 

[Bobnova]

Graphene is a single layer of graphite.

I don't think a graphite pot has ever occurred to anybody, you'd have to look up it's basic conductive properties (heat wise) as well as it's specific heating value (whatever it's supposed to be called) compared to copper.

 

[I.M.O.G.]

Sucks, found one source implying it may be good by presenting a thermal conductivity number a few times higher than copper along with a bunch of other accurate numbers (that number must have been in some specific circumstance, there were 2 numbers for diff types of graphite), but other sources don't support that from what I'm seeing around in past testing with heatsinks. Not a good idea.

 

[Bobnova]

The difficulty with graphite as i understand it is that the crystal structure is largely 2d, with very very small connections between each layer. Along the axis of the crystals it conducts like diamond (surprise surprise), along the axis of the tiny interconnects.... not so much.

 

[I.M.O.G.]

Thats pretty much what I gathered... And a lot of work was done with it in the first half of this decade regarding heatsinks, using graphite composites to compromise between conductivity and weight, where its performance was between aluminum and copper.

 

[nzaneb]

You could probably still use it, you just wouldn't have a traditional looking pot. Copper and Graphite could not be interchanged freely. If I'm understanding correctly, you'd simply need a thinner base. It's reaction to LN2 would be nice to know, before designing/ building a pot around the idea. Probably a bit too much research to tackle with a first pot attempt Although... you don't seem to be one to shy away from a challenge Matt, lol.
What if you stepped in a downward direction? A bit lower mass, with the same surface area. You would just be lowering the ratio. The reason I said it would be heavy, is due to the fact that the base is primarily 2" thick, except at the 4 hole configuration (they bore down 1" to 1" depth). So it's essentially a 2.5" x 2.5" x 2" block of copper, with 4 holes drilled in it, and an extension on the top. Yes the stepping will add surface area. Steeping inward(current) will funnel LN2 to the holes, only allowing contact with the stepping when the LN2 pour volume exceeds that of the hole volume. If we invert the stepping (a stepped hump in the middle) you could filled the perimeter of the pot and have the LN2 stay where you pour it. If you need some sensitivity, pour in the holes centered over the proc; pulling temps down, utilize the increased surface area of the perimeter stepping (and the holes if need be)

@chance: Yes square steps would be created the same. This is done in AutoCad Full Version (which has 3d capabilities). It's a little cumbersome compared to Inventor/ Solidworks, but this is a fairly straightforward simple design. So complexity is not needed.

 

[ChanceCoats123]

So if you would like, I can email the file in one of the mentioned formats.

Other than that, are you suggesting we keep the four holes in the middle, and then from that level,step down the outsides? I kind of like the originality of that idea.

 

[splat]

i'm not entirely familiar with graphite heatsinks, but just from general materials knowledge i'd say the number one limiting factor is probably the workability of the material. It's very easy to put aluminum or copper on a lathe or a mill but i don't think graphite would be quite the same. and it probably wouldn't be pure graphite, it would be a composite which would drop the conductivity but make it stronger. graphite is very brittle iirc.

 

[splat]

made a real quick model in solidworks finally. I did some thermal analysis but it didn't give me exactly what i wanted so I need to play a little more

 

[m0r7if3r]

made a real quick model in solidworks finally. I did some thermal analysis but it didn't give me exactly what i wanted so I need to play a little more

Just out of curiosity, were the stepped sides left out for a reason?

 

[splat]

to make it quicker. i haven't working in solidworks in a while and i just wanted to hope in to it and play with the analysis. i was also going to see if the steps had any effect at all too.

 

[m0r7if3r]

to make it quicker. i haven't working in solidworks in a while and i just wanted to hope in to it and play with the analysis. i was also going to see if the steps had any effect at all too.

curiosity satiated...I'm interested to see whether they help or not.