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a thermal conductor that does not conduct electricity?

i am looking to heat water to a boil in a pipe, using nichrome wire. the nichrome wire will be wrapped around the pipe. my problem is i don't want to short circuit the nichrome wire, so i need to insulate it, but i need it to still transfer as much heat as possible to the pipe.
 
any suggestion would be great, including other ways to, using electricity, bring water to a boil within a pipe.

*UPDATE: does anyone know of an affordable insulating paint or coating?
                    i found some (called Glyptal) but it cost $50, which is too much for me
                   rust-oleum is an enamel paint. will it insulate?

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YOu can get INSULATED nichrome, which I've used a lot over the years
Here's a link to a UK source I like
http://www.wires.co.uk/acatalog/ENAMELLED_NICKEL_CHROME.html

You could wrap that round a pipe.

What VOLTAGE are you thinking of applying ?

At a low voltage, I'd immerse the open coils directly in the water.

Steve

jrh0655 years ago
what about some sort of ceramic or something similar. Maybe plaster of paris, though I'm not sure how it will take the heat over time. You could set the wire in the plaster while wet to help it carry the heat to the pipe.
canucksgirl5 years ago
The first thing that comes to mind from your question is an "on-demand hot water system", where there is no storage tank. Instead the supply line runs into the on-demand unit and with a heat exchanger it rapidly heats the water and sends it to the tap that is "requesting" the hot water. When the tap is shut off, the unit stops creating hot water.

I'm not sure if that helps you at all (as I'm not sure what you are trying to make), but here is an image that helps to illustrate how the on-demand hot water system works. (They are also known as "tankless hot water systems").

tankless_water_heater_t8de.jpg
jg156 (author)  canucksgirl5 years ago
it is helpful to a degree, but the main thing i am trying to do is replace the " burner" element with an electrical (dc) powered heating element made of nichrome wire.

thank you
Fair enough. I tried to find you a good image/diagram of an electrical version of the on-demand water heater, but couldn't find one. They do exist, so instead of the gas they run on electricity.

This was the best image I could find. It's set up a little different, but may help you design your project.

electric_hotwater.jpg
Electric shower is perhaps the best example of a full flow instant water heater.

images lots on Google.
Here's a link for an "Immersion Heater". It uses a coated nichrome wire which is then hooked up to an electric power source and the coated wire (which is now the heating element) is exposed to water. This might work rather well for your plans, but instead of the wire being on the outside of the pipe, the wire goes on the inside. Anyways, have a look.
iceng5 years ago
Regulating electric current to heating a nichrome wire to heat water in a metal pipe Wow.....

Save all those steps...  Use copper tubing as the secondary of a transformer ( 8 or 14 turns ) to heat your water directly, easy stuff :-)

A
Hotpipe.png
DC.....
I also forgot to mention electric drip coffee makers. 
http://home.howstuffworks.com/coffee-maker1.htm
I don't know if you have ever seen the inside of an electric drip coffee maker.  Inside such a coffee maker, there is a short length of tubing which is both heating element and tube combined, and water is boiled inside of this tubular thingy, and that's what makes the coffee machine pump water and heat it too.
I forgot to mention aquarium heaters.  I don't know if you've ever seen one of these up close,
http://www.google.com/search?hl=en&tbm=isch&q=aquarium+heater
but it is basically just nichrome wire wrapped around a ceramic support, and placed inside a tube made of borosilicate glass (i.e. a "test tube").

For these gizmos, the heat is mostly being transferred just through the glass tube. 

I don't know if these work at boiling water temperatures, but it's not outlandish to suppose they might?  Although, I admit that boiling water would probably be too hot for fish, even the tropical ones.
;-)
One time I took apart an immersion heater,
http://www.google.com/search?hl=en&tbm=isch&q=immersion+heater
,like the kind intended for heating a cup of coffee, and I was amazed to discover that it was just a metal tube containing nichrome wire surrounded by fiberglass tubing for electrical insulation.   I wonder if I still have that thing around here somewhere?  I mean it was just so simple it sort of defied belief!  Looking at that thing, the only thermal conductors inside it were just fiberglass and air, which normally are not thought of as good thermal conductors.  However the heat only had to be transferred over a distance of a few milimeters, and since this was immersion heater, the colder side of it was assumed to be at the boiling point of water (100 C at 1 atm)

So for your application, fiberglass tubing might work.

If you need some material that actually is a decent conductor of heat, I think the stuff (thermal conductor, electical insulator) they use in those Calrod(r) type tubular heating elements is calcined magnesium oxide, and somehow, there is some process for packing the MgO into the volume around the nichrome wire, between it and the metal tube that surrounds it.  I have no idea how they actually manufacture those things, but here are some links that vaugely describe their construction.

http://www.wattco.com/calrodheater.html

http://en.wikipedia.org/wiki/Magnesium_oxide#Other

There is also stuff called "thermal grease"
http://en.wikipedia.org/wiki/Thermal_grease
,and I think it is silicone oil mixed with metal oxides like MgO, ZnO, Al2O3, but that stuff tends to be expensive, and maybe intended for just filling very small volumes, like the thin space between a microprocessor and its heat sink.