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Rollin Karg 08-03-2010 10:16 AM

Moly cooling
 
5 Attachment(s)
A friend sent me a schematic of a European built Moly furnace. At that time we were changing a pot and doing some upgrades on one of our furnaces. I noticed that the cooling tubes on the schematic seemed to be metal and quite a lot larger than what we do here. It made for a nice uncluttered look.

It made me start thinking about this area and I decided to build a plenum with some 2" flexible tailpipe attached to it. This would allow us to aim the air flow at the element tops. I gathered up some parts and formulated a plan.Then I had to leave town.

When I got back my plans had been modified and my guys had come with a new and I think better approach. We installed one of these a few months ago and it seems to be working well. We did the second one last week and that's what these photos are about. Still a work in progress but I like how it's going.
The blower is from Grainger and costs I think $112. It puts out 463 CFM. If you stand at the edge of the furnace and look at the elements you can feel a nice little breeze on your face.

Steve Stadelman 08-03-2010 10:33 AM

That is a really nice way to do that Rollin.

Rollin Karg 08-03-2010 11:14 AM

Thanks boss !!

Larry Cazes 08-03-2010 11:48 AM

Nice manifold, Rollin. Very clean design.

Charles Friedman 08-03-2010 01:10 PM

Paint it all gray. It will help it disappear.
That seams like a bit too large of a blower.
But, if it works? it works.

Rollin Karg 08-03-2010 01:48 PM

Quote:

Originally Posted by Charles Friedman (Post 89940)
That seams like a bit too large of a blower.

Yeah ,probably. I just took a guess at the size to start and at $112 I can't see I would saving much to downsize. I do think some reflective paint would be a good idea.

Eben Horton 08-03-2010 03:23 PM

looks really nice, but is that actually cooling the top of your furnace along with the elements?

Kenny Pieper 08-03-2010 04:35 PM

Rollin I am curious. Have you found that Steve's way with the two washers welded to a tube that blows the air just on the top shaft of the element to be inadequate?

Rollin Karg 08-03-2010 05:15 PM

Eben, the way it's setup, all the air is directed at the top of the elements and I can't see it having much impact on the overall temp of the furnace. The European unit had the airflow coming down from the top and I think that might have a small impact.

Kenny, I'm getting more air where I want it and I don't have hoses to deal with, so this what I like about it. The other way works, but I think this is a little better. We're using four furnaces right now and that's a lot of hoses. Plus with this system the top of the element is a little less cluttered. I don't see this an earth shaking improvment, but I think it's a little better.

Scott Garrelts 08-03-2010 09:16 PM

looks like it should be a lot easier to change out a broken element. :crossing fingers:

plastic hoses melt, sheet metal usually doesnt.

i like it

Steve Stadelman 08-03-2010 11:00 PM

I think that this is a really good way to do this, i started using hoses because I got it out of the kanthal super handbook. There are lots of ways to skin a cat and keeping the transition from the strap to the heater is what is important.

Pete VanderLaan 08-04-2010 05:17 AM

It does look good. I would again stress that cooling the leads at your transformer is a place where you can prevent a lot of serious damage. I have a blower running there whenever I go to High Fire.

Jon Myers 08-04-2010 01:37 PM

That looks good Rollin, how much insulation do you run on the top of your furnace?

Lawrence Ruskin 08-04-2010 02:33 PM

How much insulation do you run on the sides?

In my opinion, as a guy who used to insulate his SiC furnace with 18 '' of fiber all 'round, the Stadelmelter is under insulated.

I think a combination of Steve's ideas and the Electroglass furnace, is where the furture of the electric furnace is going.

An ovel crucible is easier to gather from and the glass sits closer to the elements.

The door mounted from below as in Electroglass leaves more room to insulate the sides.

A thermal engineer I know told me that heat flows like water going down a stream. If it hits a rock, it flows around it.If heat hits a barrier, (insulation) it will flow to and through the area of lesser insulation.

So if you have 10'' on top and 2'' on the sides, guess where the heat is going to go...

Eben Horton 08-04-2010 02:44 PM

if you have 18 inches of fiber, your actually paying to heat up the last 9 to 8 inches of insulation when you turn your furnace up due to conduction. :)

Scott Novota 08-04-2010 03:41 PM

Eben,


Are you saying that anything out more than 9 inches of fiber? IE> after 9 inches of fiber it does you no good.


Am I reading this right?


Scott.
.

Eben Horton 08-04-2010 03:55 PM

Quote:

Originally Posted by Scott Novota (Post 89965)
Eben,


Are you saying that anything out more than 9 inches of fiber? IE> after 9 inches of fiber it does you no good.


Am I reading this right?


Scott.
.

I believe so. especially when you turn up to charge. the outer layers will draw heat out from the core due to conduction.

This is why most furnaces have 8 inches of fiber and not 15

Jeff Thompson 08-04-2010 04:53 PM

If you increase the insulation from from 8" to 15", you've increased the surface area of the exterior of the furnace so much that like Eben says, it's conducting the heat away from the furnace. Under or over insulated in no good, it's the Goldie-locks syndrome.

Larry Cazes 08-04-2010 05:22 PM

Quote:

Originally Posted by Eben Horton (Post 89964)
if you have 18 inches of fiber, your actually paying to heat up the last 9 to 8 inches of insulation when you turn your furnace up due to conduction. :)

Eben, I agree in concept. How have you determined that 8" is optimum? Theoretical data or just by experience?

Paul Hayworth 08-04-2010 05:22 PM

steel flex piping for cold air
 
http://www.gsl.cz/en/products/pot-furnaces.html

Eben Horton 08-04-2010 05:42 PM

Quote:

Originally Posted by Larry Cazes (Post 89969)
Eben, I agree in concept. How have you determined that 8" is optimum? Theoretical data or just by experience?

I am not sure- its sort of the industry standard in glass furnaces- Hub, wetdog, etc....

Pete VanderLaan 08-04-2010 06:11 PM

I recommend 8 inches as well and I documented the diminishing returns on insulating about ten years ago. I set a furnace at a floating temp with fixed settings. I kept adding insulation and the temps kept going up with the fuel input constant. After eight inches, it stopped changing. It didn't drop after 12 inches, it just didn't change at all.

Enough?

Eben Horton 08-04-2010 07:05 PM

Quote:

Originally Posted by Pete VanderLaan (Post 89972)
I recommend 8 inches as well and I documented the diminishing returns on insulating about ten years ago. I set a furnace at a floating temp with fixed settings. I kept adding insulation and the temps kept going up with the fuel input constant. After eight inches, it stopped changing. It didn't drop after 12 inches, it just didn't change at all.

Enough?

And.. if you stuck a thermocouple in the insulation at 8 inches, you would see that the tempature of the insulation would in increase dramaticly as you added more and more. So, when you are idling at 2000 and turn the furnace up to charge, you would have to heat up all of that hot insulation..

Edward Skeels 08-04-2010 07:18 PM

Quote:

Originally Posted by Eben Horton (Post 89973)
And.. if you stuck a thermocouple in the insulation at 8 inches, you would see that the tempature of the insulation would in increase dramaticly as you added more and more. So, when you are idling at 2000 and turn the furnace up to charge, you would have to heat up all of that hot insulation..

No. Wrong.

Eben Horton 08-04-2010 07:32 PM

no. right.

Pete VanderLaan 08-04-2010 07:46 PM

I think it's the case that if you see no change in the temps after eight inches keeping the fuel constant, that should work both ways Eben and it becomes a zero gain or loss. After eight inches, you're just wasting insulation and getting no change in your performance. You could certainly prove it if you have enough insulation and you want to take the time to do the experiment. I spent quite a number of days on it.

And Ed, it's always good to see you out there.

Peter Bowles 08-04-2010 09:26 PM

so it would be perfectly appropriate to wrap copper pipes around the furnace at 8 inches of insulation but no more...

Jon Myers 08-05-2010 01:08 AM

Quote:

Originally Posted by Larry Cazes (Post 89969)
Eben, I agree in concept. How have you determined that 8" is optimum? Theoretical data or just by experience?

There is a program from RHI called Heat Flow.... pretty interesting

Rollin Karg 08-05-2010 04:17 AM

Quote:

Originally Posted by Jon Myers (Post 89962)
how much insulation do you run on the top of your furnace?

Six layers of one inch. On this one, it looks like it has become compressed and we probably should add some more.

Pete VanderLaan 08-05-2010 05:45 AM

Quote:

Originally Posted by Peter Bowles (Post 89977)
so it would be perfectly appropriate to wrap copper pipes around the furnace at 8 inches of insulation but no more...

*******************
The ghost of David Williams is rattling its chains.

Lawrence Ruskin 08-05-2010 08:23 AM

Actually the guy I was talking about was the guy that designed my last furnace.

He was the head designer for Inproheat, a company that makes equipment for heavy industry.

He said three bats of insulation of different density,the heaviest on the inside; it worked like a charm, you could give that furnace a little kiss on it's steel shell which I sure can't do to my Stadelmelter...

David Russell 08-05-2010 10:05 AM

dangerous temps
 
hello to all. i have a question for steve, rollin, pete and any of you other knowledgable "molly men", that has been in my mind for a while and this topic seems the place to ask.

All this cooling on the top of the elements is too keep from reaching what temperature range?

i have documented the temps( with a heat gun) on my unit in all various stages of operation, staying between 175f - 220f.

Where does the danger zone start temperature wise?

thanks everybody

Larry Cazes 08-05-2010 10:31 AM

Quote:

Originally Posted by Jon Myers (Post 89979)
There is a program from RHI called Heat Flow.... pretty interesting

I have built theoretical models similar to this in past lives. The devil is in the details. The experimental data from the members here is very interesting, though.

Pete VanderLaan 08-05-2010 10:40 AM

Cooling the element tops keeps the fiber from melting into nothing, it keeps the passage brick from melting into nothing, It keeps the 0000 wire insulation from vanishing and the porcelain clamp from turning to powder. Anything that hits those parts at 2300F or higher is going to eventually dine on it. The element makes it to 2800F.

Cooling the buss block in the transformer keeps the aluminum buss bar from melting and going down in to the coils where if it goes through the enamel coating on the copper windings, you will need a new transformer.

These furnaces require vigilant maintenance and they can be wonderful.

And yes the small Stadelman furnace is underinsulated. It also cost 1/4 of the larger units. It was not designed as a production furnace but rather for the weekend glassblower. Steve always made that clear.

Pete VanderLaan 08-05-2010 10:42 AM

Quote:

Originally Posted by Peter Bowles (Post 89977)
so it would be perfectly appropriate to wrap copper pipes around the furnace at 8 inches of insulation but no more...

**************
It would be interesting to try this if you put constant fuel input into the furnace and then stabilized it. Then add the pipes. See if the temp goes down. If it does then the laws of thermodynamics are speaking. If it stays the same, we have a new ballgame.

It would take days to do this by the way.

Steve Stadelman 08-05-2010 11:04 AM

400f is a bad point for the junction between the aluminum straps and the heater shanks.

Yes, the 75lb unit was designed for the hobbyist, smaller, lighter, easier to ship and with a smaller profile to fit into a tiny workspace.

Edward Skeels 08-05-2010 12:03 PM

back to what Eben posted.

You are not paying to heat the addtional insulation. The furnace is not working harder. The additional insulation is simply containing the heat that would have been lost to the atmosphere after the eighth inch.

Jeff. How does insulation switch properties and go from retarding heat loss to promoting it? or were you just kidding around?

I agree with Jon, the Heatransfer program at HWR is very helpful.

Jeff Thompson 08-05-2010 12:20 PM

The cheapest part of this whole scenario is buying extra boxes of fiber blanket and buying sheet metal. Electricity, on the other hand, is very expensive, and it's a recurring cost. Don't you think that if it was possible to save money on electricity (or fuel) by simply adding a bunch more fiber and sheet metal that all our furnaces would be triple the circumference they currently are? I sure would.

David Patchen 08-05-2010 01:18 PM

Isn't the question about which absorbs heat more readily after 8 inches--the air or more blanket?

Edward Skeels 08-05-2010 04:56 PM

Quote:

Originally Posted by David Patchen (Post 89993)
Isn't the question about which absorbs heat more readily after 8 inches--the air or more blanket?

the question is whatever you want it to be.

Thermal Conductivity
at 80F,
air is approx .174 BTU/Hr ft2 (F)/in
8# 2600f fiber blanket is listed at .29 BTU/Hr ft2 (F)/in

at 500F,

air is approx .275 BTU/Hr ft2 (F)/in
8# 2600f fiber blanket is listed at .51 BTU/Hr ft2 (F)/in

so it would appear that air is a better insulator

but,

with added thickness, additional fiber retains more heat than free air

assuming a hot face temperature of 2000f on a vertical wall:

with a material thickness of 3 inches kastolite 30 backed by 6 inches of 8# density 1" blanket,

307 BTU/Hr ft2 heat pass through

add 6 more inches of fiber and

162 BTU/Hr ft2 heat pass through

ceramic fiber is simply a low mass material that contains a lot of air. Lower mass is lower conductivity. Mizzou is above 150#/cu.ft and not much of an insulator. 8# blanket is, well, 8#/cu.ft. Fluffy material provides more air pockets. It's the air pockets that slow down the energy transfer. Sawdust or shredded newspaper insulates well, but kind of flammable.

resources:
Heatransfer application at hwr.com
http://www.matweb.com/tools/unitconverter.aspx
http://users.wpi.edu/~ierardi/PDF/air_k_plot.PDF


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