On Monday night on VTTV Monday I said I'd blog to explain why using multiple coils and higher wattage can have a sort of "milligrammage multiplying" effect. That is to say, how a 3mg liquid can satisfy a 24mg vaper, and why eight coils in an octocore with 6mg juice can keep me happy when I was using 45mg and higher e-liquid.
So, the basics. First, what is all this "mg/ml" stuff?
Well, simply put, if you have 1 millilitre of 6mg e-liquid, you have 6mg of nicotine. So a single ml of 24mg (2.4%) juice has 24mg of nicotine in it.
Next uo, how do we get the nicotine into us?
Again, not hard - a single coil in any e-cig is, basically, acting like a tiny kettle. It pumps heat into the liquid, and once enough heat is pumped into the liquid, it will evaporate. For us, this happens quite quickly, because we're talking small amounts of liquid and reasonably high power levels. Now, this is where the physics comes in, and where people start to get confused.
Latent heat of vaporisation/Boiling point.
Every liquid requires a different amount of heat to boil (become a vapour). It can be measured by the number of Joules per unit of volume it takes to do the deed. It's explained clearly here and is the basis for how multiple coil cores and atties work.
So, if one single coil can vaporise, let's say, 1ml of 6mg eliquid per minute at any given wattage (trying to keep it simple here!), then it will release 6mg of nicotine for someone to enjoy in that single minute. If you have eight coils, all at that same wattage, then, between them, they can vaporise eight times as much eliquid in that same minute - so between them would release 48mg of nicotine to be used and enjoyed.
Now this is where it gets interesting. A single Mouth to Lung draw has a volume of between 50ml and 100ml, so, even if you were using eight coils, you could only draw in a finite "volume" of vapour. Because those coils in the core produce a vapour that is "up to" eight times denser than the single coil (and this is very, very dependent on airflow - it's gonna be airy) you might think that you'd be getting eight times the 6mg - but, in all honestly, the likelihood it that you wouldn't.
Take the same setup, though, and get increased airflow, and then take it direct to lung, and, all of a sudden you're likely to have a system that has each of those eight coils producing at full capacity for long enough to allow you you suck nearly a litre of vapour into your lungs. And you will get close to achieving and eightfold increase in the amount of nicotine that's presented to your body.
This is why very few "Cloud Chasers" or DTL vapers use anything much beyond 6mg - the throat hit on 24mg juice in an octocore device would be tremendous. I could handle that on a dual coil, but, after trying it out a few times on higher numbers of coils, I can tell you it gets quite rough!!
So, to sum up, by multiplying the number of coils you use, you can make more nicotine available - it requires that each coil is being driven at the same wattage (power, actually, but it'll do) as it would be as a single coil, so if your single coil was running at 15 watts, the octocoil device would need to be at 8x15=120 watts in order to get close to an eightfold increase in nicotine availability.
And, in practice, that's pretty much what occurs. The more coils and power, the greater the availability of nicotine. Now, how it's absorbed is another question, and we're going to need someone like Lynne Dawkins or Konstantinos Farsalinos to do some applied research to answer that one.