DIY Ecavuated Tubes
DoItTomrrow
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
they're free.
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?
Thanks
azuredu
> 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.
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.
Robert Scott
>That's not so easy.
>
>You need 10^-4 torr vacuum, which is not what you can get with a usual
>vacuum pump.
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?
Robert Scott
Ypsilanti, Michigan
azuredu
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.
Robert Scott
>reaches, say, 10^-2 torr...
Thanks for the info. Good to know.
Robert Scott
Ypsilanti, Michigan
GEOD998
just an off the top of my head suggestion/question .Why couldnt one
fill the space with CO2 or someother "greenhouse gas" while it may not
offer max. insulation,should it not increase insolation? making the
inner tube get warmer because of the lensing effect of a greenhouse
gas? .Would there be any insulating quality with these gasses because
of the heat trapping effect they have? not by R value but possibly E
value. i've been wondering about useing CO2 or even methane[kaboom] in
other projects.Hell even bill nye the science guy does experiments
showing higher temp increases when shining light thru methane
vs.normal atmo.,lol. any advantage to be had??
Father Haskell
> 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
> they're free.
>
> Has anyone tried to make their own evacuated tubes from these?
>
> Maybe coating the inside bottom half of the tube with some reflective
> matrial,
I've done that to boost the output of fluorescent grow lamps by
running foil duct tape along one side of each tube. Not sure
how well the tape would hold up inside a hot solar panel.
> centering a black coated copper pipe inside, a short tube to
> evacuated it with, and sealing the ends with fiberglass resin.
Evacuated tubes I've seen were sealed with a torch. If
you're set on gluing the ends, RTV silicone will seal
best and last longest.