Posted by DoItTomrrow on December 17, 2008, 12:02 am
One day while dumpster diving, I noticed some large neon bulbs. They
were regular neon tubes, but there were larger tubes around the neon
bulbs. I guess they keep dust off the neon tubes. I doubt these tubes
are borosilicate glass, but they should be usefull for something, and
Has anyone tried to make their own evacuated tubes from these?
Maybe coating the inside bottom half of the tube with some reflective
matrial, centering a black coated copper pipe inside, a short tube to
evacuated it with, and sealing the ends with fiberglass resin.
Any info on how to make your own tubes from trash?
Posted by azuredu on December 17, 2008, 5:46 am
That's not so easy.
You need 10^-4 torr vacuum, which is not what you can get with a usual
vacuum pump. So you'll have to evaporate getters in the half-evacuated
tube. That's with special equipments.
Then resin (or anything organic) is not a good vacuum sealant: air
will permeate thru it. So your vacuum level with grow to 10^-2 torr
after a few days, and the tube becomes useless. That's why people
always use copper-to-glass seals.
A more hopeful method is in my paper: http://wims.unice.fr/xiao/collector.pdf .
But that's for the new collectors to come.
Posted by Robert Scott on December 17, 2008, 12:15 pm
I would have guessed that the heat loss of a partially-evacuated tube was
approximately proportional to the air density inside the tube. Wouldn't a tube
at half-atmosphere be twice as good is resisting heat flow as one with
full-atmosphere? Where can I find info on exactly how the heat loss of a tube
like this depends on the air density?
Posted by azuredu on December 17, 2008, 6:48 pm
On Dec 17, 1:15 pm, n...@dont-mail-me.com (Robert Scott) wrote:
Unfortunately, absolutely not.
If you evacuate the tube to, say, 1/5 of atmosphere, the heat loss by
convection becomes negligeable. However, the heat loss by molecular
conductivity remains more or less constant untill the vacuum level
reaches, say, 10^-2 torr.
You need huge industrial vacuum pumps to pump to below, say, 1 torr.
That's the difficulty.
Posted by Robert Scott on December 18, 2008, 3:08 pm
Thanks for the info. Good to know.