How it works: coils, temperature, juice, etc.

[Alien Traveler]

E-liquid atomizer is a quite simple thing: coil, wick, airflow. But how it really works? I have seen some descriptions on ECF but was not satisfied with them, so I come out with my own theory. I am sure somewhere in a better world true explanation exists, but I did not come across it yet. I just hope my theory will not differ drastically from a true one.

Most explanations I have seen consider vaping process as a simple liquid boiling by submerged coil. If it were true then juice components with lower boiling temperature than VG (PG, ethanol) should evaporate at much greater proportion than VG, and at the time when tank is half full it should be strongly depleted with PG and enriched with viscous and tough on wicks VG. Some flavorings (like raspberry ketone) have considerable lower boiling point than both VG, and PG and so they should evaporate extensively at the beginning and fade with decreasing of a juice level – if, of course, vapor were produced by simple boiling. While vaping I have not observed described effects – nor increased viscosity, nor fading of flavors (if not for taste buds tiredness).

Now let’s imagine we have a hot plate and we are dripping a liquid on it. Of course droplets will evaporate completely without any separation of components. If a plate is really hot, droplets will evaporate on flight, not even touching the plate. Returning to a coil – if it is hot enough to overheat closest layer of liquid then liquid will evaporate fast enough to let any significant separation of components occur.

Now wicks. They are connecting big and (relatively) cold volume of liquid in tank with small hot coil. They are feeding coil with liquid. It is unidirectional feeding – when we are puffing we are sucking liquid from a tank to a coil. There are no backflow, at least not in worthy a consideration amounts.

In short: All juice evaporates “as is”, without enriching/depleting vapor by some components (exception: some burnt stuff from flavorings which gunks coils). There is no change in juice composition in a tank because of vaping.
All it happens because of some overheating of juice by coil and because of unidirectional coil feeding. What is more important I do not know. Hope somebody with better understanding of thermodynamics (especially non-equilibrium thermodynamics) can clarify vaping process better than I did. For years I was happily forgetting thermodynamics, reaching near zero state by now.

 

[rusirius]

As I've stated in a previous post, chemistry is NOT my strong point. However, my personal thoughts on this differ a bit. While not a common one, I'm still fairly confident that glycol and glycerin form an azeotrope. Which changes the boiling point of the combined liquid. Azeotropes form a fixed percentage. Meaning a certain amount of glycerin would combine with a fixed amount of glycol.

Now how does this explain the points in your post? For example, if a flavoring has a boiling point much lower than either PG or VG or any azeotrope they form, why doesn't the entire tank just empty of flavoring and leave us with tasteless VG/PG mixture?

There are two reasons in my opinion that this happens.

The first is because of the wicking action. Remember you aren't heating the ENTIRE contents of a tank... If you did, then yes, that's exactly what would happen... If the flavoring had the lowest boiling point, then it would vaporize first, followed by the next lowest boiling point component, etc... The nicotine, whatever is "left over" from the PG/VG azeotrope, etc... However, we aren't doing that... Instead we are wicking into the coil at a relatively slow rate at that.

Now let's think about this for a minute... Since I've used it before let's talk about distilling alcohol. Normally you heat up the mash... When it hits around 172 degrees the methanol and some other nasties boil off, then the azeotrope of water and ethanol (the good stuff... ) then eventually the temperature raises to 212 degrees and water starts boiling off.. We are heating an entire tank of mash though... So let's rewrap this same concept in a slightly different manner.

What if we had a large tank of mash... and fed a small hose out of the bottom of it which dripped a stream of drops of mash onto a hot plate as you describe in your post.... Are we still going to get the same product? No.... Why?

Because each drop that hits the hot plate is first going to boil off the methanol, then the ethanol, then the water... All before the next drop even gets there... The temperature of the hot plate where the drops of mash are hitting is going to be fluctuating. What comes out the other end is going to end up being a mixture that is exactly the same as what went in.... minus the impurities and solid matter. Anything in the original mash that can vaporize will vaporize. In the same respect, the mash in our tank isn't going to magically have all the ethanol boil off when only the droplets are in contact with the heat source.

Now on the other hand, if we were able to speed this mechanism up and feed mash onto the entire surface of this hotplate very quickly, i.e. flood it across very quickly.... what's going to happen then? We'll get methanol and other very low boiling point nasties coming out the other end... because the constant flood is going to keep the temperature of the hot plate surface down to the lowest boiling point. In fact, flood it too fast and you'll get the temperature of the hot plate below the boiling temp and get nothing.

In other words, in my opinion, what's going on here to help understand this phenomenon is that you have to shift your thinking... When you say "coil temperature" you're thinking of an average... But the entire surface of the coil isn't going to be the exact same temperature... It's constantly going to be fluctuating slightly over the entire surface.

As one very small area vaporizes the lower temperature elements it's temperature will rise and then vaporize the higher temperature elements. At the same time, the wick is slowly bringing in new juice to reset and replenish this cycle. To look at the "whole picture" doesn't give us an accurate way of being able to understand it. It's like looking at a car and trying to understand quantum physics... You have to look at a much smaller view to be able to do that.

Secondly there is one last piece to the puzzle. And that is atomization... As these components of the juice boil off, much energy is released as the vapor it releases has a MUCH larger volume than the juice it's created from. In doing this very rapid expansion, other portions of the juice, including those that are still below their boiling point are broken up into extremely small droplets, with light enough mass to get carried away in the vapor stream.

 

[rusirius]

You know... After reading over you post again, I think in a way we are saying the same thing.... There are a few things I take exception to... For example, your hot plate example, it sounds as though you are trying to say that the hot plate will somehow superheat the liquid vaporizing all of it at once. That I don't agree with... Will it vaporize all the liquid? Yes... But not because it's superheated. The liquid isn't staying in a liquid form above it's boiling point as it would in say a pressurized system. Instead the reason all of the liquid "seems" to vaporize all at once is simply because it's happening so fast.... But there is absolutely no doubt in my mind that the components in that liquid vaporize in the order of their boiling points. Drip a drop of mash on a hot plate and the methanol, ethanol, water etc will boil off in that order... it's just that it happens so quickly it seems like it happens all at once when in fact it's not.

I have no doubt this is exactly what's happening in our coils. The coils aren't reaching some ridiculous temperature where they just instantly superheat and vaporize all liquid at once. It's just because the amount being fed in is relatively slow combined with the atomization due to rapidly expanding gas, it seems to happen all at once, and efficiently enough to vaporize all the liquid or at least most of it before more can be fed in.

Do I believe this results in the temperature of the coil ever reaching a significantly higher temperature than the boiling point of the liquid? Absolutely not. Ask any dripper who's ever flooded their coils what happens... They get very little (and very crappy) vapor... In this case there is enough liquid that the lowest boiling point portion will be vaporized first.

Does that mean the coil will never reach a boiling point above the lowest boiling point component? Absolutely not. Because again as those components are boiled off the temperature can rise enough in small microsections of the coil to vaporize higher boiling point liquids before it can be replenished and cooled back down with more fresh liquid from the wick.

Exceed this too much (i.e. faster than the wick can supply) and you get a dry/burnt hit as the coil temperature skyrockets and scorches the wick and/or the solid matter built up on the coil.

It's just a nice happy medium in a good setup.

 

[Alien Traveler]

May I skip answering on your second post since you stated many times that you have no doubts that you are right? You see, discussion makes no sense if one of the sides has no doubts.

 

[Alien Traveler]

As I've stated in a previous post, chemistry is NOT my strong point. However, my personal thoughts on this differ a bit. While not a common one, I'm still fairly confident that glycol and glycerin form an azeotrope. Which changes the boiling point of the combined liquid. Azeotropes form a fixed percentage. Meaning a certain amount of glycerin would combine with a fixed amount of glycol.

Now how does this explain the points in your post? For example, if a flavoring has a boiling point much lower than either PG or VG or any azeotrope they form, why doesn't the entire tank just empty of flavoring and leave us with tasteless VG/PG mixture?

Let’s forget about azeotropes because:
1. Azeotropes are rather rare animal among liquids, and PG-VG (as far as I know) does not form one.
2. Azeotrope is a mixture of liquids of only of one defined concentration. For example water and ethyl alcohol form azeotrope only at 96% of alcohol and 4% of water. That’s it. All other concentrations of alcohol in water will not be azeotropic.

There are two reasons in my opinion that this happens.

The first is because of the wicking action. Remember you aren't heating the ENTIRE contents of a tank... If you did, then yes, that's exactly what would happen... If the flavoring had the lowest boiling point, then it would vaporize first, followed by the next lowest boiling point component, etc... The nicotine, whatever is "left over" from the PG/VG azeotrope, etc... However, we aren't doing that... Instead we are wicking into the coil at a relatively slow rate at that.

Now let's think about this for a minute... Since I've used it before let's talk about distilling alcohol. Normally you heat up the mash... When it hits around 172 degrees the methanol and some other nasties boil off, then the azeotrope of water and ethanol (the good stuff... ) then eventually the temperature raises to 212 degrees and water starts boiling off.. We are heating an entire tank of mash though... So let's rewrap this same concept in a slightly different manner.

It is a bit wrong understanding of boiling process. Liquid mixture boils at temperatures different of boiling temperatures of its components. All components are boiling together, all vaporize simultaneously, - only their proportions in vapor differ of their proportions in liquid. Methanol in mush does not boils out separately, it goes together with water and ethanol, only in higher proportion. The same with ethanol.

Secondly there is one last piece to the puzzle. And that is atomization... As these components of the juice boil off, much energy is released as the vapor it releases has a MUCH larger volume than the juice it's created from. In doing this very rapid expansion, other portions of the juice, including those that are still below their boiling point are broken up into extremely small droplets, with light enough mass to get carried away in the vapor stream.

While I disagree with you here, let’s leave the topic of aerosol formation for some other thread.

 

[rusirius]

May I skip answering on your second post since you stated many times that you have no doubts that you are right? You see, discussion makes no sense if one of the sides has no doubts.

Perhaps you are having a reading comprehension problem? As I recall, and can clearly see in the post, I only said there was one thing I had "no doubt" about. You don't want to discuss something simply because I don't agree with you? Funny, I always thought that was the core of a debate. To have two sides who don't agree with one another state their case and give examples for why they feel they are right? You'll note that my posts are full of examples to demonstrate the point(s) I'm trying to make, the terms "in my opinion", etc. Meanwhile yours are simply stating "This is how it is."

Now if you want to have a debate about this topic, I'm 100% for it. But let's not make ridiculous statements about the merits of having a discussion simply because I don't agree with you. In other words, let's not get snarky eh?

 

[rusirius]

Let’s forget about azeotropes because:
1. Azeotropes are rather rare animal among liquids, and PG-VG (as far as I know) does not form one.

As I stated in my post, I don't know that they do either, though I'm fairly certain they do, however what percentage they form I have no idea. Regardless it isn't a big factor in the discussion taking place either way.

2. Azeotrope is a mixture of liquids of only of one defined concentration. For example water and ethyl alcohol form azeotrope only at 96% of alcohol and 4% of water. That’s it. All other concentrations of alcohol in water will not be azeotropic.

Yes, but not exactly. Ethanol and water form an azeotrope just as you mention, though actually I believe it's closer to 95% if I remember correctly, but I'm not sure about that, and it really doesn't matter anyway. The point is, if I take a mixture of 50/50 water and ethanol I can't say it is or isn't an azeotrope. "Azeotrope" simply means one thing and one thing only... It's a combination of two or more components that can NOT be separated by distilling. Because they form a bond that has a different boiling point than the original liquids. What I do find a little ironic is that you made the point about how "Rare" azeotropes are, yet you claim that all liquids in a solution boil at exactly the same time, which is exactly what an azeotrope is! In other words, (and this is why it IS relevant to the discussion), they both vaporize at exactly the same moment when heated. It has nothing to do with the concentration of components in a vapor, etc. It simply means they can't be fractionalized by simple distilling BECAUSE they will both boil at the exact same time.

In fact, if what you were stating were true, then azeotropes wouldn't even exists. If all liquids when combined ALL boil together at the exact same boiling point then distilling wouldn't even exist. Think about it for a minute... How can you possibly have all liquids in a solution boil at the EXACT same time, and yet have varied amounts of their constituents in the vapor? Honestly if you break it down it just doesn't make sense. Distilling works because liquids with different boiling points DON'T boil at the same time... Meaning they don't vaporize at the same time... Which is what allows the entire process to even work.

It is a bit wrong understanding of boiling process. Liquid mixture boils at temperatures different of boiling temperatures of its components. All components are boiling together, all vaporize simultaneously, - only their proportions in vapor differ of their proportions in liquid.

See above. Again if ALL components were boiling together then how would you propose that proportions in vapor would differ? How can you have ALL liquids vaporizing at the exact same rate yet end up with different proportions?

Methanol in mush does not boils out separately, it goes together with water and ethanol, only in higher proportion. The same with ethanol.

Ok, so let's look at this a little closer... As the temperature of a mash starts to rise and approaches 172 degrees does ONLY methanol/ethanol come out of a still? No... absolutely not... There IS water contained in it right from the start... But do you honestly believe that's because the WATER is also boiling at 172 degrees at 1 atmosphere of pressure? Think about it... It just doesn't make any sense.... So... why if you're boiling a pot of mash at 172 degrees are you getting some water in the output? Because of 3 simple reasons...

1) As stated, ethanol and water form an azeotrope.More specifically they form a POSITIVE azeotrope. This means that the boiling point of the azeotrope is LESS than the boiling point of either of it's constituents. So even though the water doesn't boil until 212 degrees, a small portion of it (approximately 5% of the total volume of ethanol) will boil at 172 degrees (approx.) The rest of the water will NOT... This is exactly why no matter how many times you run "shine" through a still, you will never get more than 95% ethanol... Because the other 5% will always be water due to the azeotrope they form which again has a lower boiling point than EITHER the water or ethanol it is made up of.

2) Before the boiling point of any liquids is reached there will be energy constantly added (in the form of heat) to the mash... Since this is not an enclosed system this means some of the water will also evaporate until saturation reaches 100% (Assuming it does).

3) For the exact reason I stated in my previous post. You have to think on a very small scale. VERY small... You can't assume that in our mixture there is ALWAYS going to be a 100% even distribution of molecules. You're not going to have an ethanol molecule sitting beside each and every water molecule. There are going to be places where there are lots of water molecules and few if any ethanol molecules. If this happens very close to the heat source, then then energy transfer that takes place will vaporize the water as well. Think of it like this... If I take a tiny pin point of heat with unlimited potential and place it in the center of this mixture... A source that is only the size of a molecule itself... (we're throwing a lot of things out the window here but this is only a thought experiment). Now think about this... If you have a group of several ethanol molecules surrounding the point, they are going to absorb the heat and vaporize... When they do they are going to carry that heat away with them... The water molecules will NEVER reach 212 degrees, and therefore will never vaporize (boil) because the energy is being carried away by the ethanol vapor being produced... However, now after several of these ethanol molecules vaporize, there are only water molecules left surrounding this point, so they absorb the energy and DO reach 212 degrees and boil/vaporize...So in immediate contact (on a molecular scale) of this heat source, you're GOING to have fluctuations in heat and you're going to have some water that does in fact boil and vaporize... However the liquid as a whole is still only going to rise to the nominal temperature. Still this will leave traces of higher boiling point liquids (depending on the original ratio in the liquid) in the output of the still...

Which is why in this case if you want to concentrate and purify the ethanol you're going to have to distill it multiple times... Because each time you are going to remove more and more water... Because each time more and more of the ethanol is in contact with the heat source and eventually it becomes only the azeotrope that can no longer be distilled.

 

[Kurt]

I cannot find info on a PG/VG azeotrope, but there might be one.

The way I think about azeotropes is, in the example of ethanol/water, you cannot enrich the ethanol beyond 95% by distillation. In other words, you will never be able to remove all the water by distillation.

Water does not form an azeotrope with VG or with PG, but it does with ethanol. Why? I don't know.

Also, the idea that liquid moves only one direction in a wick (towards the coil) may not be true. I have noted that when using Ecowool (braided tube-form silica) as a wick, that juice moves towards the coil during coil activation, but then moves away from the coil when activation is off. Sort of a two steps forward, one step back behavior. One can see this with an RDA that is open.

Binary mixture phase-diagram behavior is at "reversible" conditions, very controlled, with heating coming from an external source, not an immersed coil. The liquid temp will not surpass the BP for a given mixture composition. But preliminary measurements are showing that the liquid in the wick near the coil can surpass the BP temp, meaning that system (or at least regions of that system) are deviating strongly from reversible conditions.

So the true nature of the vaporization in an atty is likely to be somewhere between reversible conditions and everything-goes conditions. Where exactly does this fall? I do not know, but it probably depends on the power, coil density, etc.

I still maintain that the viscosity of remaining liquid in my RTA increases over time. Saw this again last night, clearly by just tilting the tank and looking through the transparent tank tube. And flavors diminish too over time. Dripping the same flavor liquid on the coil directly brings the flavors back. This is not a taste-saturation flavor loss, I don't think, it is volatile flavor compounds getting evaporated faster than heavier VG. Probably not reversibly, but not everything at once, either.

 

[Israfil]

The fruits of your discussion, in my mind, are that (I believe) you've touched on the "gunk" on atomizers. I would suggest that once separated by a partially heated coil, the components are less likely to vaporize and some will, instead, burn and cook onto the coil. Repeated re-heatings would then gunk the coil quicker if it has a longer heating time. At the same time, a quicker heating coil would vaporize more effectively, therefore gunking up over a longer period.

Watch, if you will, a coil that hasn't heated up fully or doesn't have air blowing on it. It bubbles and boils off partially, changing to a darker color.

Seeing this has gotten me thinking that maybe the theory behind coilbuilding could be tweaked. Too fast of a wick and youve got yourself a bubbling coil that'll gunk too quickly, too slow and you get burned tasting juice. The objective would then be to make the coil quickly reach a temperature that all the constituent parts of the juice will vaporize at, and rather quickly, while at the same time allowing for a fast enough wicking action to continue supplying said coil, and enough power throughput from the batteries to keep the coil charged.

 

[rusirius]

I cannot find info on a PG/VG azeotrope, but there might be one.

The way I think about azeotropes is, in the example of ethanol/water, you cannot enrich the ethanol beyond 95% by distillation. In other words, you will never be able to remove all the water by distillation.

Water does not form an azeotrope with VG or with PG, but it does with ethanol. Why? I don't know.

Also, the idea that liquid moves only one direction in a wick (towards the coil) may not be true. I have noted that when using Ecowool (braided tube-form silica) as a wick, that juice moves towards the coil during coil activation, but then moves away from the coil when activation is off. Sort of a two steps forward, one step back behavior. One can see this with an RDA that is open.

Binary mixture phase-diagram behavior is at "reversible" conditions, very controlled, with heating coming from an external source, not an immersed coil. The liquid temp will not surpass the BP for a given mixture composition. But preliminary measurements are showing that the liquid in the wick near the coil can surpass the BP temp, meaning that system (or at least regions of that system) are deviating strongly from reversible conditions.

So the true nature of the vaporization in an atty is likely to be somewhere between reversible conditions and everything-goes conditions. Where exactly does this fall? I do not know, but it probably depends on the power, coil density, etc.

I still maintain that the viscosity of remaining liquid in my RTA increases over time. Saw this again last night, clearly by just tilting the tank and looking through the transparent tank tube. And flavors diminish too over time. Dripping the same flavor liquid on the coil directly brings the flavors back. This is not a taste-saturation flavor loss, I don't think, it is volatile flavor compounds getting evaporated faster than heavier VG. Probably not reversibly, but not everything at once, either.

Well stated.

One question... You stated that preliminary measurements are showing that the liquid in the wick near the coil can surpass the BP temp. Do you think this could actually be an artifact of the BP point rising rather than being exceeded? In other words, could the rapidly expanding gas be pressurizing the immediate area around (or at least between wick and) coil above 1 atmosphere hence raising the BP?

And I absolutely agree about the viscosity increasing over time. I've noticed this as well. Especially when using liquids which have a higher concentration of PG to begin with... 50/50 or 60/40 PG/VG seems to be most susceptible. While it seems to be less noticeable in 80/20 VG/PG, max VG, etc. Which makes sense given PG's lower BP and the much higher viscosity of VG. Particularly if there is bi-directional travel of liquid in the wick it only makes sense that over time the PG/VG ratio would shift to lower the PG levels slightly.

 

[Kurt]

Well stated.

One question... You stated that preliminary measurements are showing that the liquid in the wick near the coil can surpass the BP temp. Do you think this could actually be an artifact of the BP point rising rather than being exceeded? In other words, could the rapidly expanding gas be pressurizing the immediate area around (or at least between wick and) coil above 1 atmosphere hence raising the BP?

And I absolutely agree about the viscosity increasing over time. I've noticed this as well. Especially when using liquids which have a higher concentration of PG to begin with... 50/50 or 60/40 PG/VG seems to be most susceptible. While it seems to be less noticeable in 80/20 VG/PG, max VG, etc. Which makes sense given PG's lower BP and the much higher viscosity of VG. Particularly if there is bi-directional travel of liquid in the wick it only makes sense that over time the PG/VG ratio would shift to lower the PG levels slightly.

There could be something to this point you raise in your first question: it might be that the temperature probe is in a small trapped bubble, which could go to very high temps, and not in pure liquid. I do not know the answer yet, but it is an angle to consider carefully, especially if the probe itself is causing bubble nucleation.

If my Kayfun is fully filled, by the time I get to about 1/2-filled, the liquid is thick enough that it does not wick well, and I add maybe 0.5 mL of water to the tank, shake it up, and I am back to good flow and good vaping.

 

[Alien Traveler]

...
In fact, if what you were stating were true, then azeotropes wouldn't even exists. If all liquids when combined ALL boil together at the exact same boiling point then distilling wouldn't even exist. Think about it for a minute... How can you possibly have all liquids in a solution boil at the EXACT same time, and yet have varied amounts of their constituents in the vapor? Honestly if you break it down it just doesn't make sense. Distilling works because liquids with different boiling points DON'T boil at the same time... Meaning they don't vaporize at the same time... Which is what allows the entire process to even work.
...

I’d rather avoid any further discussion on azeotropes (which are rather exception among liquids with proper behavior – they even make distillation more difficult) and on boiling process, which I already outlined. If you still do not believe me, please read this (you made me google):
Vapor Pressure Diagrams and Boiling Diagrams

You may safely skip first half (about laws) and to do section “Boiling diagrams”.

 

[Alien Traveler]

Also, the idea that liquid moves only one direction in a wick (towards the coil) may not be true. I have noted that when using Ecowool (braided tube-form silica) as a wick, that juice moves towards the coil during coil activation, but then moves away from the coil when activation is off. Sort of a two steps forward, one step back behavior. One can see this with an RDA that is open.

Sure, I over simplified by using word “unidirectional” movement. Of course oscillations do exist. Main question: do amplitude of backward movement is big enough to push “used” liquid out of chamber, or length of wicks inside chamber is greater than the amplitude? Of course, tanks are different, so answer could be tank-dependent. And I do not accept example with RDA, since I was talking about tanks, and dynamics in RDA is quite different. Anyway, since RDAs are constantly replenished, changes in liquid composition are not as important for them.

Binary mixture phase-diagram behavior is at "reversible" conditions, very controlled, with heating coming from an external source, not an immersed coil. The liquid temp will not surpass the BP for a given mixture composition. But preliminary measurements are showing that the liquid in the wick near the coil can surpass the BP temp, meaning that system (or at least regions of that system) are deviating strongly from reversible conditions.

So, you have found a piece of super heated liquid in atty.

So the true nature of the vaporization in an atty is likely to be somewhere between reversible conditions and everything-goes conditions. Where exactly does this fall? I do not know, but it probably depends on the power, coil density, etc.

I still maintain that the viscosity of remaining liquid in my RTA increases over time. Saw this again last night, clearly by just tilting the tank and looking through the transparent tank tube. And flavors diminish too over time. Dripping the same flavor liquid on the coil directly brings the flavors back. This is not a taste-saturation flavor loss, I don't think, it is volatile flavor compounds getting evaporated faster than heavier VG. Probably not reversibly, but not everything at once, either.

For now I assume that viscosity of liquid is in the eye of the beholder. My eye does not see any changes in my 2.8 ml tank, ego-style (i.e. narrow and tall), which I routinely vape out almost to empty state.

 

[bman1977]

My brain hurts.

 

[Kurt]

Perhaps it is not really viscosity that is at issue, although I do see visibly thicker over time in my 4.5 mL Kayfun tank, and evidently others do too. Maybe it is increased surface tension that is leading to what I do observe: wicking becomes poorer over time. If VG unthinned wicked perfectly well, for me this would be a moot conversation. But it does not. It has to be thinned (reduce surface tension, increase capillary action), or else the coil starts to get dry. So another observable that higher volatiles are going faster than lower volatiles, since higher volatiles tend to break up surface tension.

I used the example of the RDA because both RDAs and RTAs use a wick, and wicks do not have a "valve" property of liquid spreading in only one direction. So my thinking is that if I see bidirectional character in an RDA, then there must also be that in an RTAs, like the Kayfun. I think some of the liquid in the wick is back tracking into the tank, its just that over time it is a tank-to-coil direction.

Point is this: if ANY of the liquid boils following the phase diagram composition, then over time the liquid MUST become more enriched in less volatile components. I guess how much this is true depends on how reversible the boiling actually is, and this might depend on the build itself. Of course the way to find this out is to measure the bp of the initial liquid, and then measure it over time as it is vaped, as in removing some liquid and directly doing a bp measurement. I agree visible viscosity changes could be subjective, but actual bp measurements would not be.

And yes, if a coil is going dry, then decomposition (gunking) will increase, since the coil temp is increasing a lot.

 

[rusirius]

Perhaps it is not really viscosity that is at issue, although I do see visibly thicker over time in my 4.5 mL Kayfun tank, and evidently others do too. Maybe it is increased surface tension that is leading to what I do observe: wicking becomes poorer over time. If VG unthinned wicked perfectly well, for me this would be a moot conversation. But it does not. It has to be thinned (reduce surface tension, increase capillary action), or else the coil starts to get dry. So another observable that higher volatiles are going faster than lower volatiles, since higher volatiles tend to break up surface tension.

I used the example of the RDA because both RDAs and RTAs use a wick, and wicks do not have a "valve" property of liquid spreading in only one direction. So my thinking is that if I see bidirectional character in an RDA, then there must also be that in an RTAs, like the Kayfun. I think some of the liquid in the wick is back tracking into the tank, its just that over time it is a tank-to-coil direction.

Point is this: if ANY of the liquid boils following the phase diagram composition, then over time the liquid MUST become more enriched in less volatile components. I guess how much this is true depends on how reversible the boiling actually is, and this might depend on the build itself. Of course the way to find this out is to measure the bp of the initial liquid, and then measure it over time as it is vaped, as in removing some liquid and directly doing a bp measurement. I agree visible viscosity changes could be subjective, but actual bp measurements would not be.

And yes, if a coil is going dry, then decomposition (gunking) will increase, since the coil temp is increasing a lot.

Another observable to support this. I've seen many occasions where a newer user using a clearomizer or tank with a very dirty coil would comment about their juice getting blacked/nasty throughout the tank... Even in my kayfuns if I've neglected the wick/coil for a while I've seen this happen. Which would again indicate bidirectional flow.

 

[Robino1]

To add to the theory of liquid getting thicker as time goes by. My observation, using a kayfun and 70/30 pg/vg, when the liquid gets to the point that I have to tilt the kayfun to see the liquid, it is very noticeably thicker than what I had started with. There is also a noticeable darkening. Since the kayfun draws the liquid to the coil by the wick, the liquid must be traveling back down the wick to mix with the liquid left in my tank.

There are many times that I am too lazy to take it apart and clean, at which point I will just refill and sometimes there about a ml left in the tank before the refill. When I tilt my device, I can see a clear separation of where the fresh liquid is and where the older stuff meets.

Don't know what that brings to the table, but just throwing my uneducated observations out here.

 

[Kurt]

Robino1, the layers are from difference in density, and thus viscosity. They do mix, but it does support that what remains becomes thicker over time, so not 100% vaporization from the coil. I have noted the same effect over time with protanks, evods, top coils, any tank system. Thanks for sharing!

 

[Alien Traveler]

Now I have to agree. Back flow can be an issue.