Cloud 9 (watts) challenge

[Nada Nix]

As an experiment, I want to see how I can maximize cloud production with 9 watts, i.e. about the maximum power using an ego/evod regulated battery. Not interested in flavor, just maximally dense billowy fluffy clouds... how would you do it?

What would be the optimum wire gauge, coil diameter, placement, single vs. dual, wick techniques and so on? Can it be done with a tank, or is a dripper a must? I don't usually do lung hits, but hopefully the principles are about the same. I'm not looking to enter a cloud chasing competition, in other words it's not about vaping technique, but to find out what atomizer parameters to tweak in order to optimize vapor production.

So far, I've arrived at a small RDA with a 30 gauge 1.5-1.6 ohm cotton microcoil on a non-VV evod battery. It's significantly - though not "massively" - better than my previous Protank mini. Wondering if I can take it farther from here, without jumping to a higher wattage variable mod or mech. Even if I do make the jump, I think doing this will be a good learning experience.

I'm looking more for general principles than specific atomizer recommendations, but those are welcome too - just try to explain what makes them better.

One question I want to answer is whether a variable voltage battery is necessary. I only use one kind of juice. Do you need to use a higher (or lower) voltage and resistance for maximum vapor, or is it possible to get optimal results for a given juice, just by tweaking the atomizer setup at the standard voltage?

Any thoughts?

 

[State O' Flux]

Interesting experiment... "what build will produce the highest level of performance, when you've got only 9 watts to play with?"
What you have now is not too far off the mark, Nada, but... you can save time by having a better understanding of how to optimize build specifics against available wattage output.

Read both part one and two of the Steam Engine User Guide (along with the Steam Engine modelling program - link one), found in the second hyperlink below... in particular, what I've written about "Heat Flux", wire surface area and mass. Learn the program - learn the important details of the program's features.

With output wattage set at 9 watts, what you're shooting for will be a single coil build. You can do dual parallel coils, but you'd be working with very thin wire - around 36 gauge - to obtain similar performance to a single coil.

A small diameter single coil RDA (with good air flow) is your best bet due to vapor density / heat concentration... and easy to fine tune as well. Obtain the highest heat flux value (radiant coil temperature as expressed in milliwatts per millimeter squared - "mW/mm2") you can obtain balanced against the largest net surface area / least net mass (the latter of which can be found when you click the "advanced" button).

Chances are, it will end up being something in the 1.2-1.5Ω range (depending on your maximum amperage capabilities), using 30-31 gauge wire. It's a bit of a trade off... as you decrease resistance, coil temp will increase, but... surface area (wick-to-coil exposure) decreases as well.

The idea is to expose the juice to the highest temperature, spread across the largest surface area with the least amount of coil mass (to reduce lag time to a minimum)... that your 9 watts can fully support. If you use a coil between 1.5 ~ 2mm ID, it should have a good wrap count / diameter to wick exposure.

As for what to buy... well, technically your can build coils that will run with 300 watts or more, but in the real world, if you can duplicate a dual parallel 18650 mech mod - at around 200-250 watts output - that's more than enough. Consider that typical single 18650 / 30A mech mod users peak out at the Ohm's Law values of 126 watts feeding a 0.17Ω build.

 

[Nada Nix]

Thanks... I've used the coil calculator a lot in the past, but haven't paid much attention to the Heat Flux numbers.

I guess a very basic question is, what is the relationship of coil temperature to vapor production? The hotter the better? In other words, should I focus on getting a temperature on the borderline of burning the wick, as opposed to getting more surface area contact?

I've been reading that most people are using 28 gauge for microcoils, so I thought I should buy some of that instead of 30 - maybe the larger surface area would produce more vapor, even though it's cooler overall. But according to the calculator, my current coil's HF is 199, and 28 gauge would double the surface area but cut the HF in half to 99. So maybe that's going in the wrong direction. I do have some 32 gauge, which doubles the HF to 399 - maybe I'll give that a try.

I tried to see what happens if you use the max voltage on a vv battery (which I don't have). So at 4.8 volts, I can go up to 2.56 ohms for my 9 watts. Using a thinner wire value of about 31.5 gauge to get the same HF of 199, with 12/11 wraps instead of 10/9, the surface area is basically the same. The heat capacity is slightly less, but probably not something you'd notice. So that seems to answer my question, that there's no advantage to a vv battery. That's assuming the current limit is on the battery side rather than the voltage-boosted side, not sure about that.

Also it seems that a dual-coil setup using thinner wire, with the same HF, doesn't really change anything other than the heat capacity. You actually get a bit less surface area, because there are more legs. But perhaps there are other factors involved in practice.

I was surprised that the coil geometry didn't have any effect, eg. a 4-wrap coil on a 4 mm wick with 1 mm spacing looks the same to the calculator as a 10-wrap microcoil. But I guess it would be very complicated to calculate all the other things that affect the actual temperature and performance, like coil spacing, wick mass, airflow, and so on... In the absence of a super vaping physics simulator, I'll keep on with trial and error, and asking the masters here on ECF!

 

[93gc40]

Vapor production is a result of a balance of air flow, and air volume, coil surface area and heat and juice supply or wicking.

Fact is a cold coil on a large surface may make more vapor than a HOT coil with little surface area. A hot coil in an airy atomizer may run cooler than a cool coil in a restriced atty.

 

[WattWick]

Part of what microcoils work well is -I believe - that they bring the entire coil closer to the edge of the coil. Which makes no sense... I know.

With a regular, spaced out coil; or any coil for that matter - the part of the wick that is inside the coil dries out. It is replenished from the sides. So - with a microcoil - you get less of a dry area in the center of the coil - that won't replenish until you stop heating the coil. You're only really heating liquids with the edge of your coil after the initial liquids are gone and wicking sets in. (...I think)

This may just be fantasy... But you may want to consider more than two 'wick legs' if you try for a non-microcoil. Which I believe should be able to produce pretty decent vapor. Not sure how it would compare. Just thinking out loud.

Great idea for a thread and experiment, by the way!

 

[Nada Nix]

Under what circumstances would a cold coil with more surface make more vapor? How do you find the right balance? It often feels like I'm just randomly tweaking things. I mean, I understand the theory of Ohm's law, heat flux / capacity, and so on, but sometimes it doesn't really translate into practice. Or maybe the setup I've got is already as good as it gets with 9 watts.

Today I swapped out an 8/7 wrap on 2 mm for an 11/10 on 1.3 mm. It seems like an improvement, but I can't really say why.

In terms of air flow, I have the coil pulled out on about 2 mm legs so it's sitting directly in front of the 1.5 mm air hole, almost touching the cap.

 

[93gc40]

Under what circumstances would a cold coil with more surface make more vapor? 31g twisted on 3mm at 1.74ohm run at 8 watts make more vapor and flavor than 29g on 2.5mm at 9 watts in my Kayfun
How do you find the right balance? Experimentation

The 31g coil has half the heat flux and almost 3x the surface area.
Just takes practice. Eventually you will find a build that suits you within the limitations of your device..
I find I like a much cooler vape that most build though. I run on a Mech mod with a 5-12watt kick module. I prefer builds in the 1.5-2ohm range. I do have a dripper I use on occasion that I run without the kick, in the .8-1.2 range, for taste testing.

 

[Nada Nix]

Thanks, good to know. I've never used twisted wire, I'll try some experiments.

The 31g coil has half the heat flux and almost 3x the surface area.

I don't see how that's possible. Heat flux is the watts divided by the surface area. So with 3x the surface area, you get only 1/3rd the heat flux. Going from 9 watts to 8 watts drops it another 1/9th. So the first coil would have only 29.6% of the heat flux, not 50%. In other words, to achieve half the heat flux of a 9-watt coil, an 8-watt coil would have 1.78 times the surface area, not 3 times.

 

[Nada Nix]

I've noticed that I seem to get better performance just when the wick is nearly dried out, right before I have to drip some more. When the wick is quite wet, eg. when there's a bit of liquid still sitting on the deck - I get more flavor (and nicotine), but the vapor isn't as thick and fluffy as when it's almost dry.

Also when I make the cotton a bit thicker so it's fairly snug in the coil, and it's just kind of "sizzling" when I vape, compared to making it thinner and getting a bit more snapping and popping. So the wick is kind of choking the liquid a bit. Both of these seem to indicate that limiting how wet the coil gets improves vapor production. I always read here that to get more vapor, you need to get lots of liquid wicking to the coil. So that seems to be the opposite of usual advice. Does that make any sense?

 

[93gc40]

Yes, small quantity of fluid heats faster and turns to steam faster than a large amount of fluid..
Think of adding water to a hot pan.. If you dump in a cup it sizzles for a second and slowly heats, and you have most of the water left.. What happens to the water, if you pour that same cup of water very slowly, onto the pan, say a dropper full at a time. Each dropper full will vaporize before you can add the next.