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]

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]

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]

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]

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.

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.

 

[roadkilldeluxe]

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.

Air flows around the sides of the bulb (which is contained in the atty housing). The diameter of the bulb is about half that of the 510. It will probably be centered in the housing somehow, poking into the cartridge material upon the cartridge's insertion.

The glass itself is not very fragile; for example, it would take an extremely hard pinch to break it. And it's not really a filament, just the same Nichrome coil as inside normal attys. I know that these bulbs (before I take them apart) are tough... Christmas lights are tossed around, taken out and repackaged every year, and can handle sub-zero temperatures outside for weeks.

 

[Carlos49]

The only problem I have had trying this system is that the glass gets so hot that it will shatter with contact to the juice.
Carlos

 

[roadkilldeluxe]

The only problem I have had trying this system is that the glass gets so hot that it will shatter with contact to the juice.
Carlos

This worries me as well, but I think the only way to know for sure is to test it out. So far, though, I have not broken any glass. This includes when I was heating a coil wrapped around a bulb with PG in it, running till it dried out, and dripping more onto it (all while power is being applied).

However, it will be important for the glass to not get scratched. Heat makes scratches in glass grow/spread (but i'm not sure if our attys reach that temp).

 

[Carlos49]

you might have some thing there ... keep testing

 

[jacko]

What if the coil could be wrapped around a ceramic, or a glass rod within the bulb to add stability?

 

[roadkilldeluxe]

What if the coil could be wrapped around a ceramic, or a glass rod within the bulb to add stability?

The coil should be pretty stable. I made a coil a few days ago and it's still sitting on my desk in the same shape. If it needs something though, I can definitely try that out. Although I don't know where to get ceramic or glass rods... I guess that's why my technique is kind of ghetto in the first place

Mostly playing around with glass tonight, trying to figure out how to get nice, clean cuts on the bulbs. Still need to find/buy a digital multimeter (and now more light bulbs to practice on).

 

[Vaporer]

Good thinking out of the box road.
I've actually considered using a Krypton bulb from a Mag Lite. I doubted to would get hot enough even if over driven on voltage.
Pyrex glass will take fast temp changes and smaller wire is actually the opposite way to go. IMHO 36ga NiCr is around 20 ohms per foot. 40ga jumps to whoppin 70ohms per foot.
The idea isnt nonfeasible. It will require more power and the loss mentioned of wasted juice will be minimal since no air is being drawn.
I'd looks for the coil to touch the glass surface inside keeping heat tranference as low as possible. Personally, I'd try with the sand out as this increases the mass requiring heat. If a longer warm up and cool down time was acceptable sand/cermaic would be fine.
In the instance of a PV you want it up to temp and back down as fast as possible with minimum power required. There are other mitigating factors and limits you will run into as your experiment proceeds.

Keep at it!

 

[Jason365]

Here is an idea..
Looking at cartomiser disection pics and such, I think You could wrap the bulb in Silica tape or put it in a silica sleeve. To help keep it in the center of the tube and it would help keep the liquid near the heat source. Basically making it a cartomiser. I may be going in a different direction than the OP, but it could work. I really hope this thing pans out.

Jason

 

[Bubo]

Wow - definitely 'outside of the box'!

You have stated all of the cons that I can think about;
My #1 concern would be the epoxy fumes... Perhaps a drop of molten glass on the end to seal it instead?

Thermal conductivity of air would take an extra second or two, I would think... but is it negligible? Smaller Christmas light.. Cut it closer to the top as time goes on and practice would make closer tolerances... Perhaps an On/Off switch to turn on a preheater? (This may be a bit dangerous, unless there is a timer in there)

Glass breakage.. not a biggie to me, just a pain in the tuckus....

Hey - wait a minute - what if we just dip the Nichrome coil in Pyrex glass?
That takes the air out of the picture, thermal transference is dropped, glass breakage is minimized, preheating is dropped, nickle foam around the heater is gone, bridge is gone, epoxy is gone... Electroplate the Nichrome leads with copper (in a thread somewhere) and the solder is gone too.

Make the glass/nichrome long enough to stick in the cartridge wadding and the only thing left is to figure out how to connect it to a battery.....

Okay... what am I missing - that's too simple....
(Oh yeah - how do you melt Pyrex....)

 

[jacko]

Hey - wait a minute - what if we just dip the Nichrome coil in Pyrex glass?
That takes the air out of the picture, thermal transference is dropped, glass breakage is minimized, preheating is dropped, nickle foam around the heater is gone, bridge is gone, epoxy is gone... Electroplate the Nichrome leads with copper (in a thread somewhere) and the solder is gone too.

Interesting idea... can you explain your thoughts? I am thinking that you are wanting to encase the coil in Pyrex. do you mean to have an enclosed coil where it is somewhat fused to the glass?