New Atomizer Prototype

[roadkilldeluxe]

Here's my idea for a heating element.


Pros:
-Safer: solder is inside, no direct metal-on-liquid contact
-Easier to clean, longer life, easily replaceable
-Smaller, more fragile Nichrome can be used (less power, more heat?)
-Coil should not oxidize much because bulb is sealed
-No flooding/drying out/etc

Cons:
-Longer heat-up time (due to heating of glass and air)
-Glass could pose a risk, some will crack under excessive heat
-Possible dangers of heating epoxy, unless we can melt the glass to seal it (but JB-Weld is supposedly non-toxic and can withstand high temps)

Needs more research:
-Melting the bulb at the bottom to seal it instead of using epoxy (like this)
-Cutting bulbs cleanly (this is how I do it)
-Optimal gage and length of Nichrome to use.

Specifications:
-Glass bulb (from "mini" christmas lights), about 5mm wide and 20mm long
-First test will use 1.5" of 36ga Nichrome (~3.4ohms)
-JB-Weld Epoxy to seal the bottom airtight

Current Progress:

I have misplaced my digital multimeter. Need more butane for glass melting experiments.

I'd appreciate any thoughts, concerns, or advice!

[jacko]

Looks promising. I have also been thinking about an improved design... you are well on the way though. Let me know how this turns out. I didn't think of the glass 'shell' though. Very nice.

[Scottbee]

You've already identified the major problem, and it's a show-stopper. The time-constant for this ting will be very long. In other words, you have a large thermal capacitance associated with that glass bulb and it will take a very long time for the element (running maybe 4 watts of power) to heat it up. And, as you mentioned, the heat transfer needs to be mostly convection with a bit of radiation (between the coil and the glass). Pretty poor conduction methods in this case.

And then there is one more problem.. the glass represents a large surface area. It will dissipate the power without having the same temperature increase as just the coil. And you need the temperature to vaporize the fluid.

[Lashes]

how is this going to connect to the battery?

[roadkilldeluxe]

Originally Posted by Scottbee

You've already identified the major problem, and it's a show-stopper. The time-constant for this ting will be very long. In other words, you have a large thermal capacitance associated with that glass bulb and it will take a very long time for the element (running maybe 4 watts of power) to heat it up. And, as you mentioned, the heat transfer needs to be mostly convection with a bit of radiation (between the coil and the glass). Pretty poor conduction methods in this case.

And then there is one more problem.. the glass represents a large surface area. It will dissipate the power without having the same temperature increase as just the coil. And you need the temperature to vaporize the fluid.

True, but the dry coil will be much hotter. StratOvation's tests indicate that a dry coil is more than twice as hot as a wet one under the same voltage.

Also, we have never been able to use higher-gage wire before because it would likely be too fragile. Losses in heating the glass might be made up by using real thin Nichrome, which should be safe within its glass shell.

[roadkilldeluxe]

Originally Posted by Lashes

how is this going to connect to the battery?

Not 100% sure yet, possibly similar to the way a (replaceable!) mini "christmas tree" light bulb clips into its socket.

[Scottbee]

Originally Posted by roadkilldeluxe

True, but the dry coil will be much hotter. StratOvation's tests indicate that a dry coil is more than twice as hot as a wet one under the same voltage.

Of course it is. Two reasons: A "wet coil" has more surface area and is therefore trying to reject heat across a larger interface. That yields lower temperatures. Secondly, as the liquid vaporizes you get the rough equivalent to evaporative cooling. Vaporizing literally sucks heat out of the system. Look up "latent heat of vaporization".

This is all just a thermo and heat-and-mass transfer experiment. But have fun and good luck!

[suhrim21]

I am glad to see someone trying to make these things better. in all theory the only thing I see is cooling down the glass after you get it heated up. if you fill the bulb with sand that will act as a conductor for the heat and keep it heated up longer which will result in wasted liquid. I do however think you are off to a great start.

[roadkilldeluxe]

Originally Posted by Scottbee

Of course it is. Two reasons: A "wet coil" has more surface area and is therefore trying to reject heat across a larger interface. That yields lower temperatures. Secondly, as the liquid vaporizes you get the rough equivalent to evaporative cooling. Vaporizing literally sucks heat out of the system. Look up "latent heat of vaporization".

This is all just a thermo and heat-and-mass transfer experiment. But have fun and good luck!

This is all true, I was just saying that having the dry coil (and possibly using a smaller gage of Nichrome) will make up for some of the heat loss to the glass/air. And we just got done with thermodynamics last week but 50% of it has already been forgotten

Anyway, I hope it will not be a complete show-stopper. I experimented it by wrapping NiCr around the bulb and dripping 2-3 drops inside the bulb. It was an extremely crude setup but within a few seconds I had a nice chimney going

If this is an issue, I might need to incorporate a "warm-up" switch to prepare the atomizer (like lighting a cigarette). If warmed up a few seconds in advance to just below vaporization temperature, pressing the 2nd button should bring it up to proper heat real fast.

Originally Posted by suhrim21

I am glad to see someone trying to make these things better. in all theory the only thing I see is cooling down the glass after you get it heated up. if you fill the bulb with sand that will act as a conductor for the heat and keep it heated up longer which will result in wasted liquid. I do however think you are off to a great start.

True, wasted liquid and energy, I suppose. Also, sand conducts heat better, but it takes more energy to heat up than air (and releases heat slower).

This thing actually has got me really interested in glass-blowing now. How about an all-glass ecig? It would be safer, and you could see the coil light up and the vapor flowing through...

[Bandit]

How do you get airflow with the bulb end being sealed?

I would think that this would be very fragile. Not only because of the glass, but the filament inside... if jarred enough it will fail. This is why you don't go shaking a light bulb before you put it in a lamp.