Heating a chamber using electrical resistance?

[iostream.h]

I would like to heat the air within a cylindrical chamber (diameter of 3/4", length of 1 1/2") to 400ºF. This chamber would most likely be made out of glass, although I am open to using other materials if recommended. To heat this, I'd like to have a heated element (perhaps a small screen, warmed through electrical resistance) at one end, and have the air drawn through this into the chamber. So my question is, how do I find out the area and temperature of the element to somewhat evenly (the lowest any one portion of the chamber could get is 390º or so) heat the air within the chamber? Thanks in advance! 8)

 

[Russlk]

Glass heating elements use tin oxide as the resistance element. You could coat the glass cylinder with tin oxide and heat the whole thing to 400 degrees F. You would need a transformer or variac to adjust the voltage.

 

[stevez]

Things to consider:

Heat transfer occurs by conduction (air passes by heating element and is warmed) and by radiation (IR goes right thru the air and heats whatever it sees). A red hot element "radiates" a lot of heat and will likely heat it's surroundings rather than the air you want to heat.

Air itself is somewhat of an insulator, especially if it is still. The molecules of air that touch the element get hot then conduct the heat to other air molecules. If the air flow is high enough so there is turbulence then mixing aids in the dispersion of the heat. If you heat the cylinder itself and there is no air flow then the temp is likely to settle at some uniform point in some amount of time. If air is flowing thru the cylinder then this won't be the case.

If your intent is to have some flow of air (or some other fluid) from one end to the other you might require a number of electric elements covering a cross section. Note that the air velocity may or may not be uniform and that might profoundly impact what you are doing.

This could get pretty involved depending on what you are doing.

 

[iostream.h]

Things to consider:

Heat transfer occurs by conduction (air passes by heating element and is warmed) and by radiation (IR goes right thru the air and heats whatever it sees). A red hot element "radiates" a lot of heat and will likely heat it's surroundings rather than the air you want to heat.

Air itself is somewhat of an insulator, especially if it is still. The molecules of air that touch the element get hot then conduct the heat to other air molecules. If the air flow is high enough so there is turbulence then mixing aids in the dispersion of the heat. If you heat the cylinder itself and there is no air flow then the temp is likely to settle at some uniform point in some amount of time. If air is flowing thru the cylinder then this won't be the case.

If your intent is to have some flow of air (or some other fluid) from one end to the other you might require a number of electric elements covering a cross section. Note that the air velocity may or may not be uniform and that might profoundly impact what you are doing.

This could get pretty involved depending on what you are doing.

Thank you both for your replies! Perhaps I should be a little more clear on the purpose of this device . My mother smokes medicinal cannabis from a clinic to ease certain conditions. I don't especially like the fact that she has to consume it anyway, but I really don't like how she has to smoke it. My idea with this was to create an environment where the active ingredients she needs can be activated and released with no plant matter being burnt in the process. The temperature doesn't have to be as uniform as I implied earlier, but rather for everything in the chamber to become active it needs to get to around 392ºF. I was a bit embarrassed to reveal this fact, but maybe now that you know the purpose, the heating process could be a bit simpler?

 

[Oznog]

That's called a "vaporizer". They use a nichrome heating element inside a glass tube to make hot air and the user will inhale and draw it over the cannabis at a temp that will vaporize the THC but not burn any material off. The one I saw had a power control but no way to read the temp or provide temp regulation.

Actually there are tons of vaporizer plans on the net. Also they can be had off of eBay. Many are based around a soldering iron stuck into the material itself which fills a chamber with vapor. I had to note that the air will probably cool below the temp at which the THC will condense back out. Anyways, just Google for "vaporizer plans" or "vaporizer design".