Heating up glass with Resistance wire
serg...@gmail.com
250x300x4mm about 10° Celsius above room temperature. I've made some
plans on how to do this, however I need some more guidance, especially
choosing and obtaining correct resistance wire.
Electricity will be supplied @ 12V DC @ 1A, or 5V DC @ 500mA if
possible.
See this diagram: http://img236.imageshack.us/img236/907/glass0zn.png
for proposed/designed layout.
As pictured in the diagram - 240mm of wire every 10mm for 290mm =
240x29 + 10x29 = ~7,300mm. That's 7.3m of resistance wire. Assuming
room temperature is 20°, the wire will temperature will need to be
~35°, to keep the glass at just under 30°.
The wire will be attached to one side of the glass surface using
self-adhesive clear plastic wrapper (similar to those used to wrap
books).
1. Are these calculations/assumptions correct?
2. What kind of wire (thickness) should I be looking for?
3. What will my power consumption be (will 12V @ 1A be enough)?
I'll be very thankful for any advice on this matter.
Rich Grise
Go to the department store and get a hotplate or toaster-oven.
Good Luck!
Rich
GMV
I think it is a nickle chrome alloy
It is used to ignite rocket motors.
Anything else probably too expensive.
<serg...@gmail.com> wrote in message news:1122663301....@g14g2000cwa.googlegroups.com...
Moonraker
wrap around water pipes to keep them from freezing? Or a waterbed heater?
<serg...@gmail.com> wrote in message
news:1122663301....@g14g2000cwa.googlegroups.com...
Al
"Moonraker" <moon...@NOSPAMbellsouth.net> wrote:
Use nichrome wire ripped from an old toaster. If you want 1 amp at 12
volts, cut a piece that will give you 12 ohms. The hard part is
connecting to it. You will have to weld it it. If you try to solder, it
may get hot enough to melt the solder under normal operation. You might
get away with crimping to it. Good luck!
Al
CWatters
> 250x300x4mm about 10° Celsius above room temperature.
The main problem will be knowing how much power you need to keep the glass
at the right temperature. To predict this by calculation you need to know a
lot more details most of which you probably won't know.
Two questions:
1) How well insulated is the set up? eg What is the thermal resistance
between the glass and where you measure "room temperature"? If you knew
this the sums would be simple but my guess it you won't know this. If you
build it and find it doesn't get hot enough then measure how hot it does get
and the power and you can work it out.
2) How fast do you want the temperature to rise? Does it matter how long it
takes to go from room temp to room temp +10C ? If you know the specific heat
of glass and the mass of the glass etc you could estimate how much power you
need to achieve the warm up time you need.
The only easy answer is to build something, test it and then have another go
if it doesn't perform quite right.
My gut feeling is that 12 W might be the right order of magnitude but could
be on the low side.
I'm away from my PC for the next week.
Dave
250x300x4mm about 10° Celsius above room temperature. I've made some
....
As pictured in the diagram - 240mm of wire every 10mm for 290mm =
240x29 + 10x29 = ~7,300mm. That's 7.3m of resistance wire. Assuming
room temperature is 20°, the wire will temperature will need to be
~35°, to keep the glass at just under 30°.
The wire will be attached to one side of the glass surface using
self-adhesive clear plastic wrapper (similar to those used to wrap
books).
1. Are these calculations/assumptions correct?
2. What kind of wire (thickness) should I be looking for?
3. What will my power consumption be (will 12V @ 1A be enough)?
The general idea seems ok, but I wonder about heat losses and acceptable
temperature variation. If the losses are significant, than the wire spacing
of 10mm for 4mm thick glass sounds a bit high - glass is not a good
conductor of heat. One approach might be to use a piece of printed circuit
board (unetched), and place a continuous copper plane next to the glass,
with heating elements attached to the other side (nichrome wire is good).
The thin copper sheet will spread the heat to give a more uniform
temperature. Based on experience with heaters for telescopes, 12W will not
be enough unless the losses are absolutely minimal.
Dave
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Ron Jones
Your main problem will be control. If the wire gets to 35C, and you have it
well insulated, then unless there is a fixed heat flow into the tube (are
the tube contents moving?), then the tube will also eventually get to 35C.
Why the need to only use 12V? I would have wrapped a lab heating tape round
the tube, with a K thermocouple underneath, and connected to a small PID
controller - just dial the temp you want - then if the tube is too hot or
too cold then change the tape temperature accordingly.
As an aside to another poster, nichrome wire can be successfully crimped. I
once made a 1 metre x 100mm gas phase reactor (in glass), with 8 x 250V
circuits of nichrome wire, running at 4 amps each, generating some 8000W.
Glass fibre tape was wrapped round the tube, and then the wire was laid,
with a glass fibre tape laid over the top. Centre of packing reached 350°C,
and you could feel the heat at least 10 feet back... Somehow I feel that
our current laws would not allow this anymore... [but it did work, and made
lots of product]
--
--
Ron Jones
Don't repeat history, see unreported near misses in chemical lab/plant
at http://www.crhf.org.uk
Only two things are certain: The universe and human stupidity; and I'm
not certain about the universe. ~ Albert Einstein
nJb
Crimping or clamping is the usual method. Used wire is often brittle and
new wire isn't really that expensive.
Here's a great source with much info to answer your heating questions.
--
Jack
Plonked by Native American
bobo1148atxmissiondotcom
Jim Yanik
news:1122738...@spool6-east.superfeed.net:
Why try to bond wire to glass?
Paint or silkscreen resistive paint in a grid or other pattern like a
auto's rear window defroster.
You get better thermal transfer,it's far simpler.
Bond connnecting wires with silver conductive epoxy.
--
Jim Yanik
jyanik
at
kua.net
Mike Firth
tray with a glass plate and foil heating on the back. The wire to do this
will have to be real thin.
--
Mike Firth
Hot Glass Bits Furnace Working Website
http://users.ticnet.com/mikefirth/hotbit47.htm Latest notes
"Rich Grise" <rich...@example.net> wrote in message
news:pan.2005.07.29....@example.net...
quietguy
car window demisting? Included the wire/tape etc and instructions
David
mike
That's a pretty big piece of glass for 12W. Will take forever to heat
up. You're gonna have a hard time keeping the temperature uniform
over that large area with only one control. Glass ain't terribly
thermally conductive. And convection and air
currents are gonna play havoc with it unless it's well insulated and you
don't care how long it takes to heat up.
You can run it open loop by balancing losses if EVERYTHING else is
invariant...which it never is.
Disclosure of your end objective would be useful in assessing the situation.
mike
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low.
#37 AWG enameled magnet wire has a resistance of 0.5 ohms/foot and it
has a handy insulating coat (NiCr is bare)to reduce shorting during
layout and it can be soldered!
24 feet @ 0.5 ohms/foot = 12 ohms which is the resistance you will need
to take advantage of the 12v @ 1A available for 12 watts heating.
Radiant loss from the glass surface (1 side) assuming you will insulate
the bottom is
5.67e-8*0.075m2*303.15K^4 = 36J/s
ambiant radiation absorbtion @ 20C =
5.67e-8*0.075m2*293.15k^4 = 31.5J/s
total radiation loss with these parimeters is 4.5 watts at 30 C
I am sure the 7.5 watts left over will be more than enough to
compensate
for convection loss, depending on what you are trying to heat of
course.
I would also recomend a coat of silicone rubber over the heating wires
to provide a thermal path as well as keep everything in place.
Also cover the bottom with foam insulation to reduce the thermal sink
to one surface.
A temp control can be implimented using a string of 4 or 5 1n914 diodes
in series located at intervals across the heating side of the glass.
Diodes have a nearly linear temp relationship of 1mv/K.Using 5 averages
the temperature deviations across the glass and gives 5 mv/C output.
This signal can be fed into an lm311 noninverting input with the
inverting input to a reference pot for temp setpoint. The output will
feed a power pass transistor through a 2k2 resistor as an example.
The high thermal mass and low power input should give reasonably stable
temperature control.
onehapp...@yahoo.com
wonder if the step-down transformer alone will generate more heat than
that. Insulated box, step-down transformer and glass enclosed,
extension cord (plus fuse) to the wall outlet (fuse in case of a leak
or short of some kind).
Hey, why not just use a small light bulb for the heat, if it's going to
be plugged in anyway.
onehapp...@yahoo.com
1. Get a Celeron 2.7 GHz computer
2. Overclock it to 3.2 GHz. You might need to swap out the
motherboard; I recommend an Asus P4S800-MX.
2b. Install an AGP video card
3. Install a cooling fan in the case ($10; most computers don't have a
cooling fan on the case, *ahem*, hp a305w, *ahem*)
4. Run a program that makes the computer sweat (Prime95, Unreal
Tournament 2004, RSA Factoring Challenge code)
5. You now have a nice source of heat. In fact, I did all of the
above (cooling fan installed last night), and the room (the ROOM!)
increased in temperature by about 5 degrees F above ambient (er, other
rooms in the house).