# Some scientific speculation on coil cooling in an atomizer + evaluation metric



## Ezekiel (31/3/16)

Mods: Don't know if this is the right place to put this? It is more general than temp-sensing, RDA or RBA... eitherway, move it where you feel it is the most appropriate!


Hello gentlefolk!

Disclaimer: This is a long wall-of-text (again!) of some very technical speculations I’ve been musing about the last couple of weeks. The first post is mostly an introduction to a problem I have, and then some very opinionated speculation. The second post has a few preliminary results on something I’ve been experimenting and working with. If you want, you can read the first few paragraphs, then skip to the second post which has some interesting results. Secondly, I mostly write these type of things out for my own sake - it helps clarify thinking. I figure I share it because maybe someone persistent enough to read through all of this will get a bit of clarification, or at least an idea. So either way, read at your own risk!


So one of the little (not so little) vaping puzzles which continues to boggle me is the relationship between coil size and wicking, airflow (direct and indirect), power output and juice composition. Specifically, how the coil-masters can get practically any atty to vape fantastically first try, whereas for the rest of us it involves multiple videos, opinions and a hell of a lot of experimentation with different builds to get certain attys to work. The master builders can seemingly guess how many wraps, what ID, and how much wick to give any new atty. I on the other hand, have to play around with different builds before finally stumbling (usually mostly accidently) onto something I like, and then I’m usually not sure how I did it. In fact, quite often a very small adjustment - such as changing coil position a little bit - seems to go a very long way. Now, maybe I just don’t have the touch - certain people, like the artists they are, can look at an atty and tell you what type of build it wants. Luckily for me, and everybody who lacks this magical gift, we have the wonders of Science! Unfortunately, science is surprisingly lacking in this area... hence this post (and hopefully, others to follow).

I’ve talked before about all the different factors which influence the final temperature of a vape, and these four factors (coil size and wicking, airflow, power output and juice composition) are far-and-by the biggest players. However, the _effect_ of most of these factors are generally not quantifiable. Sure, we know how big our coils are, and we know what power we deliver, and we can even measure airflow holes and whatnot, but these factors still interplay in a complex fashion to give the final vape.

There is a simple reason why these things bug me, and why I want to know more. Whenever I watch a review of a new atomizer, the general comments are in the line of “Oh, the build deck is really large - you can throw massive 3.0 mm double-Zuma claptons on there.” This is only part of the picture though. We all know each atty _likes_ certain builds over others. For instance, when you install identical builds on different atomizers and run it at the same power, you often get massively different vapes. Therefore, build deck size and airflow hole sizes (and features such as vortexing) are not enough to determine the output of an atty - you need to build/vape on one yourself before you get an idea of how it performs. Now, usually, you either a) google to find builds which work for most for a specific atty, or b) try different builds until you find one which works for you. This approach annoys the scientist within me, since I’m always thinking I might still stumble on an even better build, or, in the worst case scenario, I spent large amounts of time trying different builds on an atty trying to “fix” the vape to no avail. As an example, I have a Fishbone Plus RDA an a Crius v3 RTA which I have finally given up on - I know it works for a lot of vapers, but it just doesn’t fit my build-style. And for that matter, some attys just work, and some don’t. Some airy attys are great for flavour, whereas some surprisingly restricted attys blow great clouds. Some just work for certain people, whereas others find them horrible. And some builds are horribly hot on some attys, while unvapebly cold on others.

Now why is that, I wonder? I mean, in the age of powerful hybrid mods, building low/high resistance isn’t the biggest governing factor any more, since you can get wonderful and cloudy vapes at practically any resistance you choose. On the other hand, things like surface area and heat flux is a great guiding tool for the interested builder (and especially for dedicated flavour or cloud chasers), but it doesn’t always pan out - you can have a high surface area build and still not get a great vape. Finally, airflow control is also a funny thing. Sometimes, you get more clouds, or more flavour, with the airflow not fully open or minimally closed. Indirect airflow (such as on the drip tip, or on the atty itself) also changes the vape in sometimes unexpected ways - too much indirect airflow and you get almost no vape at all despite practically burning up your coil, but a little indirect airflow can occasionally work wonders.

Before I go on, as with almost everything I write, I know that these things don’t bother the average vaper. Tinkering with different builds, feeding the CUD, and generally playing around with all things vape-related is _fun_, and the reward of getting a great vape when not expecting it is very fulfilling. All of us also have our favourite builds for specific attys, which we don’t mess around with since it _works_. In the way that DIY E-juice isn’t chemistry, RBA-ing isn’t physics - and generally, so much the better for it. If everything vape-related were quantifiable, cloud chasing competitions would be more a thing of large-lunged engineers than us vapers. 


But with that all said, every time I try a new build (regardless of whether it works well or not) I’m thinking of how these factors - coil, airflow, power output and juice composition - plays together to make or break a vape. And its begun to be a bit of an obsession - I’ve got a large spreadsheet of all the builds I’ve done thus far in 2016, including the calculated properties - surface area, heat flux and heat capacity - as well as some notes and thoughts on how it vaped. And I haven’t been able to find enough trends to satisfy my curiosity.


TL;DR: I need more quantifiable information on how coil build, airflow, power output and juice composition affects your final vape experience. To that purpose, I’ve created a new metric which I’m quite happy with. First a short premise on airflow


Airflow, and heat capacity

I’m not going to talk about surface area and heat flux here - I’ve got a few paragraphs on these in my TC guide, which you can go check out (in the signature). Generally though, a higher surface area means a lower heat flux - which generally means the coil can take more power, which generally means you’ll get more e-juice evaporated quicker. Ergo, more surface area = more vapour production, both clouds + flavour. 

However, the surface area goes hand in hand with the airflow. And not just the direct (or indirect) airflow holes you can see on the side of an atty. Rather, the combined airflow within the atty - how it hits the coil, how easy it is to move around the coil & wick, and how long it actually stays in contact with the coil. In this regard, you cannot just maximize your surface area. Sometimes, a lower surface area build coupled with the correct atty and airflow produces a better vape! (I’m looking at you, Goblin Mini). 

These two factors (surface area and total airflow) can be somewhat condensed into the effective heat capacity of a coil. Heat capacity is the amount of energy which is needed to heat your coil. High heat capacity (such as is typical for Clapton coils) need much more energy (power in W from your mod) to heat up than a small high-gauge micro coil. For fancy-ass mods and TC, this type of heat capacity isn’t a problem, since you can have a ramp-up power output to quickly get your coil hot.

However, this heat capacity (the one calculated on sites like www.steam-engine.org) is the heat capacity of your coil on its own - without air travelling over it, without wick and e-juice covering it, and without the energy which is absorbed when e-juice is evaporated. These things change the _effective_ heat capacity of your coils while vaping.

For instance, consider juice composition. Each component of an e-juice has a heat capacity - in other words, how much heat is absorbed in chemical terms by each molecule. We can simplify this by just looking at the boiling points of each component. PG has a boiling point of ~188 deg C, whereas VG has a boiling point of ~290 deg C. Therefore, a high VG juice will need more energy - therefore higher power - to evaporate. So if you have a high VG juice in your atty, the _effective _heat capacity (henceforth EHC) of the coils will be slightly higher than if you had a high PG juice in the same atomizer, and you’ll need more power to give the same amount of vape (even though the clouds will be different due to different chemical properties of these components).

So to clear things up a bit, lets break down the physical processes which happen at each coil a bit:


a) Electricity travels through a coil, causing the coil the heat up
b) Heat is absorbed by the e-juice, causing evaporation
c) Air travels over the coils, taking away any vaporized juice and cooling the coil/juice.

And some other minor things, such as new (cooled) juice entering the wicks, and the atty itself absorbing heat, etc. 

From the above list, only (a) increases the heat of the coil - both (b) and (c) decreases the heat. In the absence of (b) and (c) - in other words, an unwicked coil heating without pulling air over it- will continue heating up as much as it is physically feasible when we apply power to it. The tempo at which the coil heats up will be determined by the build, and the amount of power we apply. When we add (b) and (c) - in other words, when we vape on a wicked coil - we reduce the heat at the coil surface. Therefore, the tempo at which the coil heats up will be lowered. And this is where it gets interesting. The amount of heat absorbed by the airflow and the juice is dependent on the amount of heat already produced. As a result, when you just hit the fire button, the heat of a coil will increase at a fast tempo. As the heat of the coil increases, the heat absorbed by the juice and air will increase proportionally, decreasing the rate at which the coil’s temperature increases. Finally, a type of equilibrium will be reached - when the heat produced by the coil is evenly matched by the heat absorbed by the juice and airflow. At this stage, the coil’s temperature will remain constant. In reality, this never really happens, but rather the factors are _almost _balanced, resulting in the coil’s temperature increasing at a very small tempo. This temperature I’m calling the Max Equilibrium Temperature (MET). When we increase or decrease the power output, we are effectively changing the MET value. More power will result in the MET being higher. The MET will remain more or less constant until the juice in the wick runs out. Note that all of this discussion (including the MET value) is what happens _at the coil_ - not the temperature you are experiencing at the drip-tip.

As an example, consider the following figures:





Follow the red line (temperature) in these figures. The first one is at 20 W. You can see a sharp, initial increase and then a general plateau at 221 deg C. Initially, the cooling effect (airflow + juice evaporation) isn’t large, and the coil only heats from the electron movement. As it heats up, the cooling effects become bigger, and an almost equilibrium is reached at the MET value of 221 deg C. The next picture is at 40 W. Here, the MET occurs at 254 deg C. The third at 50 W, with an MET of 273 deg C. Finally, the last one (at 60 W) has an MET above 300 deg C - where the cotton starts to singe. Cotton burning adds to the heat of the coil rather than subtracts from it, and a large spike in resistance is seen (and a large spike in lung pain for me).

To illustrate this concept even more, look at the following picture:




Here, vaping at 30 W, we arrive at an initial equilibrium of 245 deg C. Then I paused pulling air, and immediately the heating effects were dominant, resulting in an increase in temperature. Then I started drawing air again, and the equilibrium re-established itself.


These graphs clearly illustrate how heating is balanced against airflow (and juice evaporation). More heating (higher watts) resulted in the balance being shifted upward, as did a lapse in airflow. Specifically, the physical property which governs where the MET sits is the combination of the heat capacity of the coil and the power output - in other words, how quickly a coil is heated - and the cooling effects in play (evaporation and airflow) - in other words, how quickly a coil is cooled. I like to combine these two effects to give the effective heat capacity (EHC) which tells us how quickly a coil heats up when it has reached equilibrium.

So all of the above-mentioned factors (airflow, coil build, e-juice composition and power output) combine to give the EHC (effective heat capacity) for the current setup, which gives the tempo of how quickly a coil (of a specific material and build) heats up in a specific environment (in terms of airflow, ejuice composition and power output). It should be apparent that the EHC and MET are more or less inversely proportional - a setup with a high EHC (in other words, takes long to heat up in a specific environment) will have a lower MET (it will reach equilibrium between the heat produced by the coil and the heat absorbed by the juice + airflow at a low temperature) than a setup with a low EHC.

So why is the EHC and MET important? In principle, it takes into account all of the events happening at a coil. More power, less direct airflow, less surface area and higher PG content will _decrease_ the EHC, and result in a higher MET. On the other hand, less power, more airflow, more surface area and higher VG content will _increase_ the EHC, and decrease the MET. Therefore, if there was any way in which we could measure or estimate the EHC or MET, we would be able to use that to optimize and fix any builds we might consider, together with the holy grail of surface area.

For instance, suppose you have a vape which is generally weak, but slightly hot - you want to add more power, but doing so starts burning your coils. That means your MET is very close (or even above) the singing temperature of your wick, and your EHC is generally quite low. To get more vape you want to increase the surface area, but doing so might increase your coil size, blocking more airflow and decreasing your EHC even further. Therefore, considering a smaller, but twisted/claptonned coil will give you higher surface area with the same airflow (given sufficient wicking). Alternatively, doing compressed coils instead of spaced coils will give more or less the same surface area but taking less space, resulting in more airflow and a higher EHC and thereby lowering your MET. Or finally, if the coil is too close to the airflow holes, it might be blocking them somewhat - raising your coils can give more airflow, increasing the EHC and lowering MET.

Makes sense? I hope it does. At this stage, thinking in these terms already helps diagnosing a few atty problems you might encounter. Of course, we have no real way to estimate the EHC at the moment except qualitatively (in other words, how it ‘feels’), and therefore, everything above is untested speculation. A more measurable statistic would definitely be desirable! And to that end, I’ve experimented with a new metric which I hope would prove helpful - in the next post!


Side note: Temperature Control (TC) and Maximum Equilibrium Temperature (MET)

To some of you, the MET which I’ve described above might sound like the temperature limit you impose when doing TC vaping. In principle however, the MET is a naturally occurring temperature limit - and in practice, it doesn’t remain completely constant. With TC, we are enforcing our own limit on the atty, through wattage control. Therefore, if the MET and TC-limit are more or less in the same ball park, then you’ll have a _great_ vape, since you are effectively keeping the temperature which results from the perfect balance of coil heating and airflow cooling exactly constant. However, most TC problems I’ve encountered myself or heard from others are when the TC limit you apply is very far from the MET - in other words, one element (whether it is power/coil or airflow) is off-balance with the rest of the setup.

Furthermore, TC and Kanthal works slightly different when cooling/airflow is discussed. In a Kanthal build, if you increase the cooling on a coil (either through internal airflow or an attys AFC, or whatever), you’ll generally get a colder vape, and you’ll need to up the power to keep up. On a TC build, on the other hand, if you increase the cooling but don’t change the temperature limit, you’ll get a stronger vape (since more power is needed to keep the temperature constant). On the other hand, the reverse is also true: less cooling on a Kanthal build will give a hotter vape, but in a TC build, it’ll just result in a weaker vape - since it reaches the temp limit quicker and less power is needed to sustain it.

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## Ezekiel (31/3/16)

Estimating a coefficient of cooling

The tempo through which a coil heats up is more or less known when you build the coil by using something like Steam-Engine.org, through the heat capacity, heat flux and power output on your mod. The largest unknown factors in a build, on the other hand, is how quickly your coil is cooled through airflow and juice evaporation. These vary greatly from atty to atty and build to build, and there is no direct way to quantify or even approximate these factors. They play a massive role though, and will determine whether the same build in different atty’s is weak, piffy and aneamic or hot, cloudy and flavourful in another.

The factors which cools your coil (and effectively reduce the tempo at which it heats up)

So I’ve been playing around with different ways to estimate how strong the cooling factors is in a specific build and atty setup. While I haven’t found any way to do so directly and absolutely, I did figure out a decent way to estimate how much a coil is cooled relative to another, or how much a coil is cooled in different environments. 

It is very simple, but unfortunately only applicable to TC coils. First, in order to establish a baseline, I measure how long it takes a wicked and juiced coil to heat up from room temperature to 300 deg C, _without pulling on it_. I use Escribe and a DNA200, which can give me the data accurately in a CSV file, but you can use any TC mod and a stopwatch. I use a moderately high wattage (round about the maximum I can vape comfortably on the build), and repeat the process a few times (letting it cool a bit between runs) for accuracy. This time is in other words the time it takes for a wicked and juiced coil to heat up from RT to max temperature without any airflow.




Next, I repeat the process, but pulling on it. I measure the same time, and repeat a few times to get an averaged measurement.




So now I have two time values - one for the baseline without any airflow, and one with full airflow. By taking the ratio of the two (full airflow divided by the baseline), we get a coefficient which gives a degree of cooling:



Lets just call it a Cooling Coefficient (CC). If the CC is larger than one, it tells us that yes, cooling did indeed happen, and the coil takes 1.55 times as long to fully heat up as the baseline. A larger CC therefore indicates more cooling. A value less than one, on the other hand, tells us that the cooling was reduced instead, and that the coil heats up faster than the baseline.


Now, with this value we can compare the same coil in different setups. For instance, if I built the exact same coil in a different atty with a bigger deck, I might get slightly different values:




This tells us that the same coil - with the exact same physical properties in terms of dimensions, surface area etc., will give a different kind of vape in different attys. In the second atty, more cooling takes place, and the vape will most likely be considerably cooler. Alternatively, you’ll need to pump through more power to give the same kind of vape.


Anyway, you can compare the two cases directly, through a normalization procedure. (Not going into this, but you can normalize the baselines to each other, and then recalculate the CC’s, and compare to each other). In this way, I can calculate that the second atty cools the same coil 1.34 times more than in the first atty.


This is now a mostly useless example, but it does give us an independent metric which can be used to compare a whole list of various vaping factors. Since the intrinsic components of two coils or setups can be compared directly (heat flux, heat capacity, surface area, etc.) this gives a way to evaluate the indeterminable factors (airflow, efficiency of juice evaporation, internal airflow, etc.). 

Btw, the degree of cooling is actually damn important in any build. Much like wicking, it doesn’t matter whether you have a super-ridiculous-build which took 3 years to make in an atty if you don’t have _just_ the right amount of cooling (not too much nor too little). In addition, the cooling can be maximized much the same way as the surface area or heat flux, since more cooling will allow for more power will allow for more vape!


I will be using this to do some experimentation across my atty’s, and with different builds. However, to give you a taste of the type of results you can get, consider the following short experiment:



Evaluation of effect of direct vs indirect airflow in the SteamCrave Aromamizer

I’ve got a dual microcoil in my Aromamizer at the moment. 2.0 mm ID, 8 wraps, Titanium 1, vertical coil and wicked with CottonBacon. I’ve been playing around with different builds on the Aromamizer, since the last few I did turned out meh.

Anyway, using the above method, I wanted to evaulate how the airflow holes affect the coils. It is an easy experiment, as you don’t have to build different coils, but gives an indication of how the method works. For those who are not familiar with the aromamizer, it has 4 large airflow holes. 2 of these hit the coil directly (and really directly - it doesn’t pass through any type of channel or pressure changer), and the other 2 hits the posts directly. With the included vape-band, you can close either the direct or indirect airflow holes.


Anyway, I established baselines through wicked coil heating without pulling, at 60 W. I did this for the fully open case, the indirect case, and the direct case. I repeated a few times, letting the coil cool in between. The juice was 70:30 VG, with 0 nic.

I then repeated the above step, but pulling on the atty at the same time. I then calculated all the CC values. They are represented below, all relative to the fully open baseline.



Consider the first line. Closing some of the airflow holes, even with no directed air moving through them, decreases the CC somewhat. In other words, the coils heat up considerably quicker when some of the available airflow is closed. This is a general trend I’ve seen anyway, in other attys as well. I find it interesting that the values for the direct and indirect airflow is the same though.

When we start actively cooling the coil (through drawing air through the atty - ya’know, vaping), we see a CC of 1.6. In other words, the coil takes 1.6 times as long to heat up. We can use this value to compare to other attys and things. It is actually surprisingly high, and goes to show how big a difference airflow can make.

The real interesting gem though, is the final two cells in the bottom row. These values show the CC’s when vaping with either the direct airflow or the indirect airflow. When we use only the direct airflow (in other words, _less_ airflow than the fully open case, but with no access to the indirect channels), we get even more cooling - the coil takes 2.1 times to heat up. On the other hand, using only the indirect airflow, we get a slight cooling effect, but much less than the fully open case - the coil takes only 1.1 times longer to heat up than the baseline.

This tells us something very important. In this specific build, we get _more_ cooling on the coil when using _only_ the direct airflow holes, and using the fully open airflow setting the indirect airflow is actually reducing the overall cooling on the coil. In fact, the degree of cooling for the fully open airflow (1.6) is pretty much directly in between the CC’s for the direct (2.1) and indirect (1.1) cases. This means that we can actually produce the densest vape and most flavour (by maximizing cooling) by using only the direct case. Of course, we’ll get an actual cooler vape, and possibly bigger clouds, by using the fully open case, since the inclusion of the indirect airflow does help to enlarge clouds. Either way, it is quite a cool result!


We can arrange the data somewhat differently, by using the fully-open case (with drawing through the drip-tip) as a baseline, and comparing the direct and indirect cases:



Now we can see that the direct case cools the coils 1.3 times more than the fully open case, whilst using only the indirect airflow holes cools the coils 0.6 times less than the fully open case.

Finally, we can see a more real indication of the same effect by measuring the temperature at low wattage for a specific amount of time:



You can see here that the temperature of the only direct case is generally lower than the fully open case, whereas the temperature of the only indirect case is generally higher.


While not yet the most useful results, it does show that the method can provide some insight. Once I’ve used it a bit for different types of evaluations I’ll post my findings, if there is any interest!


Thanks for making it this far, and please leave comments and criticisms!

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## Mike (31/3/16)

*N*ever have I
*E*ver seen such
*R*eally cool
*D*ata


Looking forward to the read man. Not sure if I'll be done by the next time I see you

Reactions: Funny 8 | Thanks 1


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## Ezekiel (31/3/16)

Mike said:


> *N*ever have I
> *E*ver seen such
> *R*eally cool
> *D*ata
> ...



Pahaha, well done man.


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## Lord Vetinari (1/4/16)

Will take me a while to chew on...

Reactions: Like 1


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## Papa_Lazarou (1/4/16)

Very interesting insight. Unintuitive that direct air only would cool more efficiently than fully open, and the concept of MET is intriguing not only for regulated users looking for power/effect windows, but for mech users trying to dial in the vape characteristics.

(see, I read the whole thing )

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## Ezekiel (1/4/16)

Papa_Lazarou said:


> Very interesting insight. Unintuitive that direct air only would cool more efficiently than fully open, and the concept of MET is intriguing not only for regulated users looking for power/effect windows, but for mech users trying to dial in the vape characteristics.
> 
> (see, I read the whole thing )



Haha, thanks @Papa_Lazarou . I think you'll be the very first then. 

Glad you agree. Time will tell whether it will actually be useful or not. MET/EHC is definitely useful concepts for all styles of vaping, and maybe actually more so for mech users. Just a shame that you practically need TC just to figure these things out, if it doesn't come naturally.

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## Neal (1/4/16)

Just when I think I am finally learning a little I come across posts such as this and I realise I am not as clever as I think I am. I have bookmarked this thread for future reference. Another excellent contribution @Ezekiel, thanks for sharing your obviously vast knowledge with us lesser mortals. Damn, my brain is starting to hurt....

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## Silver (1/4/16)

My gosh @Ezekiel
Vaping Scientist of note!!

Those were two fabulous posts! Thank you for sharing your speculations, insights and outcomes of your first batch of tests. Very well written and so easy to follow. You sir have a great way of explaining things!

I have gone through it and it is extremely interesting.
It has helped me to appreciate that some builds just dont work even though one thinks they should.
And why it seems each device has a sort of "sweet spot" where all the variables are in harmony.

Would be really cool if everyone with a DNA200 could submit their coefficient of cooling test results according to a standard test on all their atties.

I too have a spreadsheet of coils i have tried on the RM2. It does amaze me how the vape changes with slight changes to the coil and its position. But my sheet is very simple - coil specs followed by words like "meh", "amazing" or phrases like "remember this build - have taken photo of it". But i never appreciated why these outcomes were the way they were. Now I am starting to appreciate it more. Oh no @Ezekiel, dont get me into all of this - I see many hours of experimentation staring me in the face....

But with a big smile nonetheless... 

Lovely!

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## CloudmanJHB (1/4/16)

Holy smoke ! Brilliantly researched and written, nicely done Ezekiel!

Interesting as hell, now my head hurts

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## Andre (1/4/16)

Great read, but only for a fresh mind early in the morning.

I lost the plot here "_This means that we can actually produce the densest vape and most flavour (by maximizing cooling) by using only the direct case. Of course, we’ll get an actual cooler vape, and possibly bigger clouds, by using the fully open case, since the inclusion of the indirect airflow does help to enlarge clouds.". _This sounds contradictory to me. Please elucidate.

I did try a practical application on my Aromamizer. With direct airflow only the flavour for me is noticeable better than with both direct and indirect flows. At the same wattage (50W). I could not discern any difference in clouds (size and density) and warmth of the vape between the 2 cases though. And I almost vaped myself into a Silver in the process.

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## WARMACHINE (1/4/16)

@Ezekiel Nice one NERD. Give this man a medal

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## Ezekiel (1/4/16)

Silver said:


> My gosh @Ezekiel
> Vaping Scientist of note!!
> 
> Those were two fabulous posts! Thank you for sharing your speculations, insights and outcomes of your first batch of tests. Very well written and so easy to follow. You sir have a great way of explaining things!
> ...



Haha, thanks for the kind words @Silver ! And yeah, my spreadsheet was more or less the same... just without the photos! Thats a good idea, should've done the same...

And yeah, maaaaany hours of experimentation ahead! Hopefully it turns out fruitful!

BTW, no DNA is needed - if you have a TC mod you're good to go! Just set it on 300, and stop vaping when you hit the limit. Most modern mods have a 'last puff time' display somehwere (I know the EVic VTC at least has), which is fairly accurate!

Thanks again! 



Andre said:


> Great read, but only for a fresh mind early in the morning.
> 
> I lost the plot here "_This means that we can actually produce the densest vape and most flavour (by maximizing cooling) by using only the direct case. Of course, we’ll get an actual cooler vape, and possibly bigger clouds, by using the fully open case, since the inclusion of the indirect airflow does help to enlarge clouds.". _This sounds contradictory to me. Please elucidate.
> 
> I did try a practical application on my Aromamizer. With direct airflow only the flavour for me is noticeable better than with both direct and indirect flows. At the same wattage (50W). I could not discern any difference in clouds (size and density) and warmth of the vape between the 2 cases though. And I almost vaped myself into a Silver in the process.



Thanks @Andre - appreciate it!

Mm... most of what I write always seems like gibberish to me the next morning... so I was at first just as stumped as you. However, I've noticed (when trying to build cloud-chasing builds) that some degree of indirect airflow (typically such as the additional holes on the Velocity Mini, or the top airflow on the Smok TFV4) 'loosens' clouds somewhat. It makes it slightly less dense, but really adds to the volume! Not 100% sure why yet though. On the flip side, it definitely diminishes the flavour somewhat.

On the aromamizer, I've noticed it is quite build specific. I always also get better flavour with only the direct airflow open, and slightly bigger but less dense clouds with airflow fully open. It might be something totally different, such as coil positioning or something... more testing awaits! I really want to spend some time trying to explore the factors and myths which supposedly makes a flavour or a cloud build.

Anyway, I vaped myself into a Silver and then some trying this stuff out. Full-blown vapers tongue today... I can't even taste the difference between @Mike's Ashy Bac and pure VGG today...

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## Silver (1/4/16)

Lol @Ezekiel - thanks
I didnt actually put the photos in my spreadsheet - just the date I took the photo - and then I could go look at it on my phone if I needed to. Hardly ever did though - haha


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## Andre (1/4/16)

Ezekiel said:


> Haha, thanks for the kind words @Silver ! And yeah, my spreadsheet was more or less the same... just without the photos! Thats a good idea, should've done the same...
> 
> And yeah, maaaaany hours of experimentation ahead! Hopefully it turns out fruitful!
> 
> ...


Lol, thanks. Just tried the Aromamizer with indirect flow only. Considerable less clouds, but (too) intense throat hit and good flavour.


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## Ezekiel (5/4/16)

I’ve run some more tests, mostly just to see the validity of using cooling constants and whether it actually means something. And I got a brand new Hastur v2 RDA from @Mike, and was so impressed with the thing that I just couldn’t resist overanalyzing the crap out of it and producing some super NERD data.

The new Hastur has a very interesting design, as it has very large cyclops airholes, controlled by a top airflow and AFC. Very small deck with velocity posts and a wide-bore drip tip with spitback protection. There is therefore no indirect airflow, and it is very easy to line up your coils directly in front of the air holes. Closing the airflow therefore still results in all the available air hitting the coils, just with less air. Finally, you can actually adjust the airholes to hit your coils from the side.





Anyway, I installed two simple builds on it while playing around with it, and figured I might as well collect some data to see how the approach works. There isn’t much which I can conclude from this, as we are not _really_ comparing apples with apples, but it is interesting none the less.

Build A is from the previous post: Dual 26 AWG Titanium 1, 2.0 mm ID, 9 wraps, compressed coil in the Aromamizer v1. Vertical. Wicked normally with Cotton Bacon v2.

Build B:



28 AWG Stainless Steel 316L (UD), 2.5 mm ID, 10 wraps, compressed coil, ohming at 0.5 Ohms. Horizontal. On the Hastur v2 RDA. Wicked Scottish with Cotton Bacon v2.

Build C:


26 AWG Stainless Steel 316L (UD), 2.5 mm ID, 10 wraps, _spaced coil_, ohming at 0.32 ohms. Horizontal. On the Hastur v2 RDA. Wicked Scottish with Cotton Bacon v2.

I did build B first, and wasn’t terribly impressed. I noticed that the coil, while directly in front of the air hole, was so small in comparison, that I guessed I was getting so much indirect airflow from the rest of the cyclops. Thats why I built Build C, and by spacing the coil I essentially covered most of the airhole. My first build I also felt that my wick was too tight.





You can see the difference between coil size and air holes very clearly from the above pictures.

As I said, I changed a lot of the variables, so the data isn’t particularly meaningful, but it adds to my small-but-growing library, which will hopefully deliver some trends one day!


Anyway, measured cooling constants as specified, at 60 W. I measured with the AFC fully open (Open), with half AFC (Half), with the coils directly aligned with the airflow (Direct), with the coils partly aligned with the airflow (Half-Indirect), and with the coils perpendicularly aligned to the airflow (Indirect). I also took a ‘Super-Pull’ - a draw where I’m sucking on the drip tip as if all life depended on me, just to get an idea of the max cooling the atty could achieve.

Build B: 28 AWG SS316L compressed





First of all, the trends for the baselines follow generally the same trends as for the Aromamizer: Closing of some of the airflow, or when the coils aren’t aligned, tends to reduce the cooling on the coils even when no air is actually drawn over them.

When vaping, I got a CC of 2.44 for this build - which is quite high it seems. Therefore, the larger cyclops air holes on the Hastur definitely cools the coils more! We can clearly see the effects of moving the coils away from the airholes, with the CC dropping down to only 1.15. The vape was cooler using this alignment as well, indicating that the drop in CC is definitely due to more indirect airflow within the atty. Finally, the semi-direct airflow gives a median of the two values, at 1.48. In addition, closing of the airflow resulted in an appropriate drop in CC, to 1.6. In this case I noticed a significantly hotter vape, indicating that the drop in CC is due to less airflow as opposed to changing the ratio of direct to indirect airflow. Finally, when increasing the airflow from my lungs, I get a massive CC of 3.36.

In the second table, the effects of different airflow can be seen directly in comparison to the fully open case. Using semi direct or half airflow gives more or less the same effect, with cooling constants of 0.61 and 0.66, respectively.

While interesting on its own, it does not tell us much, except that the method seems to be working, when compared to the Aromamizer results.

Build C: 26 AWG SS316L Spaced

With this build, I used a lower wire gauge, and a spaced coil, filling up much more space within the atty and specifically in front of the airflow holes. Otherwise, the builds are more or less the same.





Now, however, we have a massive 3.1 CC for the fully open case. As expected, with more of the coil exposed to the airflow, we get more cooling! With the maximum lung draw, I got a CC of 4.5 - in other words, the coil takes 4.5 times longer to heat up to maximum temperature than it would do without any airflow.

But here something quite interesting happened. With the coils aligned up half-way - in other words, with the airflow approaching the coil in an almost diagnoal way, we actually got slightly higher cooling, with a CC of 3.2. This is the direct opposite of what happened in Build B, where arranging the coils in this manner resulted in reduced cooling. Practically speaking, it means the coils are actually better arranged for maximum airflow - quite interesting, even if it is a bit difficult for me to visualize. I actually think I reinforced the vortex effect with this alignment, as the vape was very slightly cooler this way as well. All other trends remain the same as for Build B.

When I looked at this data, I took a few vapes, and realized the flavour was considerably better using this alignment than full-on direct airflow. Whether this is due to vortexing, or just more air across the coils (as the increased CC seems to suggest), I’m not really sure, and will have to investigate further. Either way, I started playing around, and switched up the drip tip for a normal (smaller) drip tip, and reduced the AFC to about half. This setup gave me by far the best flavour, and I found it had a CC of 2.5 - a bit less than the fully open case of 3.1 or the semi-alinged case of 3.2. From all of this I can surmise the following: The best airflow across the coils I managed to get by aligning the coils partly with the airholes, since it gives me the best CC. But with this arrangement, I managed to get the best flavour by reducing the overall airflow to give a CC of 2.5. For this atty + build, this CC seems to give me the sweet spot for flavour!


Finally, here are some comparisons between the three builds I’ve tested this method with:



A: Aromamizer RDTA v1, 26 AWG Ti 1 x2, 2.0 mm ID, 9 wraps, 0.16 Ohms, compressed @ 0.05 mm
B: Hastur RDA v2, 28 AWG SS 316L x2, 2.5 mm ID, 10 wraps, 0.5 Ohms, compressed @ 0.05 mm
C: Hastur RDA v2, 26 AWG SS 316L x2, 2.5 mm ID, 10 wraps, 0.32 Ohms, spaced @ 0.5 mm

First of all, compare the final column titled ‘Baseline comparison’. This is the ratio of the times it takes to heat up the coils without any airflow, relative to build A (the quickest ramp-up time). It is nice to see that these values correctly reflect the Heat capacities of the coils, with build C having the highest capacity also showing the longest ramp-up time. However, the values are quite small, suggesting that the differences in heat capacities aren’t all that large, and therefore allow us to compare the final CC’s pretty much directly.

Build A has the smallest CC of the lot, with 1.6. In comparison, build B - a very similar build in terms of surface area and heat flux, but in a different atty, has a CC of 2.4. Build C, on the other hand, has much larger dimensions and surface area, and this is reflected in its CC of 3.1.

Interestingly, whereas 60 W was generally too much for Build A and B, it was a little bit on the light side for build C. More importantly, for Build A, I found the best vaping spot at 40 W, and for build B at 50 W, despite otherwise similar physical properties of these two builds. This means that the CC’s, which are largely atty dependent, accurately predicts which build will be able to take more power by virtue of increased cooling.

Finally, the flavour and vapour production and final vape temperature takes a bit more in-depth study, by looking at how the CC’s change when different airflow options are considered. As an example, in both builds A and C, increasing the amount of direct airflow relative to indirect airflow resulted in a higher CC, and more flavour production. From that point onwards I could optimize the flavour even more by adjusting the amount of direct airflow. I don’t think I’m ready to tackle that hurdle just yet, as it will take more precise experimentation - but I’m quite confident about the ability of CC’s to help evaluate and benchmark different builds and atty’s!

This will now be my last post with NERD data for a while, as I have to start focussing on some other things. Very clearly, this excursion has been my main procrastination from work that I really don't want to do. I've got other vaping related things in the works which I'm quite excited about, so this will have to take a bit of a back seat.

For those who've read through it, hope you enjoyed!

Reactions: Like 4


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## Stosta (5/4/16)

Wow @Ezekiel ! How you even begin a quest like this I don't know! Interesting point about the diagonally-placed coils increasing the cooling effect, wonder if you should share that with some of the manufacturers?  I would agree that that would seem to come from inadvertantly aiding a vortex.

What's your next vaping-related mission then?! Tell us!

Reactions: Thanks 1


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