Vacuum chamber heat transfer
Vacuum chamber heat transfer
(OP)
I have a heat transfer problem. I use an electron beam vacuum deposition system to coat lithium on a nickel foil substrate in a continous web operation. Yes this is for making batteries!
The problem:
The foil collects heat by radiation from the e-beam guns,sufficient to melt the lithium back off the substrate.
I have a cooling drum cooled by a chiller at 20deg C , the foil is wrapped around approx. half the drum , drum is 20" in dia. 10" wide. contact with the drum is by tension.
Drum is 6061 aluminum with a polished surface.
I need a way to get maximum heat transfer from the foil to the drum. Remember this is a high vacuum operation.
Any kind of coating?? surface prep?? different material??
All ideas accepted.
Thanks
The problem:
The foil collects heat by radiation from the e-beam guns,sufficient to melt the lithium back off the substrate.
I have a cooling drum cooled by a chiller at 20deg C , the foil is wrapped around approx. half the drum , drum is 20" in dia. 10" wide. contact with the drum is by tension.
Drum is 6061 aluminum with a polished surface.
I need a way to get maximum heat transfer from the foil to the drum. Remember this is a high vacuum operation.
Any kind of coating?? surface prep?? different material??
All ideas accepted.
Thanks





RE: Vacuum chamber heat transfer
Andreas
RE: Vacuum chamber heat transfer
TTFN
RE: Vacuum chamber heat transfer
As suggested by IRstuff, can't you provide radiant screens on the e-beam gun to shade the area around the melting zone?
prex
motori@xcalcsREMOVE.com
http://www.xcalcs.com
Online tools for structural design
RE: Vacuum chamber heat transfer
The foil I am using is very thin .0007 and at least a 32 finish as it comes from the supplier. Contact is probably at it's max right now.I was hoping that someone had a new type of coating that could be put on the drum that would improve conduction of the heat.Unfortunatly that doesn't exist yet.
Positioning of the guns IS helpfull, a slight off-set from direct line of sight did help, (tried that) I believe I am going to try some additional cold-plates near the drum to block more of the radiant heat.
This is best described as a thick film process as I am putting about .0005 thick deposit on the foil.
I guess I'll have to be satisfied with what I have.
Woody Ebersold
Consulting Engineer
"AN EXPERT IS ALWAYS SOMEONE FROM OUT OF TOWN"
RE: Vacuum chamber heat transfer
Andreas
RE: Vacuum chamber heat transfer
Due to the properties of the material I am using, I am limited in choice of metals.
Thanks
Woody Ebersold
Consulting Engineer
"AN EXPERT IS ALWAYS SOMEONE FROM OUT OF TOWN"
RE: Vacuum chamber heat transfer
aluminium = 234
copper = 398
argentum = 429
That shows that the coefficient of "Hütte" for Al is wrong or the computer indutry uses an Al-alloy. Perhaps there it is possible to cover an copper drum with argentum getting rid of the reaction between copper and lithium.
Andreas
RE: Vacuum chamber heat transfer
http://www.matweb.com/search/SpecificMaterial.asp?bassnum=BA2C
TTFN
RE: Vacuum chamber heat transfer
RE: Vacuum chamber heat transfer
Another angle to look at is whether the problem may be because the heat is not removed from the drum, then it will be a pumping or chiller capacity issue.
RE: Vacuum chamber heat transfer
RE: Vacuum chamber heat transfer
The heat xfer by conduction to the drum should overwhelm the xfer by radiation unless the guns are really hot, 1300F and very close to the foil, say, 5 inches. What are your parameters? Without air your contact with the drum should be quite good with a thin flexible foil. In general it sounds like what you have should work quite well. What are you experiencing?
RE: Vacuum chamber heat transfer
The heat problem.
e-beam crucible temp is 550deg C and distance is 8" from foil. Deposition thickness must be .0004 to .0007,yes REAL thick film. Foil transport speed is 9 to 15 ipm and only sees the heat for about 40 seconds. need that long for deposition build-up.
Problem is trying to increase yield by raising crucible temp to 600deg C but foil gets hot enough to remelt the deposition coating at about 180deg C creating blisters and generally making a mess.
After all things considered, I may be at the wall with 550C
System works well but more is better.
I saw a trick a few years ago that I think I will try.
Nickel is magnetic so I will have some (about 40) rare earth magnets machined into the drum surface to get a good mechanical bond with the drum. Expensive way to go but!!!
Woody Ebersold
Consulting Engineer
"AN EXPERT IS ALWAYS SOMEONE FROM OUT OF TOWN"
RE: Vacuum chamber heat transfer
RE: Vacuum chamber heat transfer
don´t look at the drum - the really problem is the nickel foil. Let´s have a look to the energy content of Lithium layer - at 600°C it is 2.03 J/mm foil when Li has specific heat of 3.58 kJ/(kg*K) and a density of 530 kg/m^3.
The heat transfer coefficient of Ni is 89.99 W/(m*K), the Ni layer is 1.7*10^-5 m thick. Putting in the temperature difference of 580°C, the contact time of 1 mm length of the foil is 126.67 s (speed of = 381 mm/s, contact length to drum = 781 mm). We get the energy transport of the Ni-foil with 1.23 J but the energy content of the Lithium layer is 2.03 J/mm (38.5% remain in the Lithium-layer).
The simple calculation shows that the Ni-foil is unable to transport the energy content of Li-layer with that temperature difference (even suggesting that we neglected the energy content of Ni-foil itself in this ratio).
The conclusion is that you have only two parameters to play with - contact time to the drum and temperature difference between the drum and the Ni-foil.
Andreas