Spaced vs Contact coils, in theory...

[Raindance]

Read some thoughts on the forum on comparisons between contact and spaced coils recently. Thought I would investigate a bit further on my own.
I postulate (Always wanted to use that phrase) that a coils purpose it to heat wick containing a liquid which is in turn vaporised. The amount of juice available for this purpose in relation to heat provided is thus the deciding factor when it comes to supply and concentration of flavor.

So here's some of the math. I kept it to the essential and this is not perfect. Did not see the real necessity to work out real loop length of a spiral etc. just wanted to get the basic references right at ballpark level.


So, in conclusion based on the above, spaced coils hold more juice per mm of resistance wire and as a result reduce the risk of dry hits and theoretically should be able of higher temperatures for long drags and provide a more flavorful vape. At least according to the little cogs and gears spinning around in my head.

Discussion and debate on this theory is hereby invited and most welcome!

Cheers!

(Edit, fixed distorted spreadsheet image.)

 

[blujeenz]

Just speculating here, but I think a certain amount of backpressure, due to compressed coil wraps not venting the vaporised juice quick enough, could lead to reduced flow for the incoming juice to the wicking area enclosed by wire.
Spaced coils wont have this anomaly seeing as the coil wrap inter distance vents vapour adequately.

 

[Raindance]

Just speculating here, but I think a certain amount of backpressure, due to compressed coil wraps not venting the vaporised juice quick enough, could lead to reduced flow for the incoming juice to the wicking area enclosed by wire.
Spaced coils wont have this anomaly seeing as the coil wrap inter distance vents vapour adequately.

You may have a point there... Gears are turning again...

May be part of the cause of the popping some closed coilers have mentioned?

 

[RichJB]

I don't know what's up with that popping thing. Both my RDTAs do it, the Avo intermittently and the Limitless Plus constantly. It doesn't result in spitback or any other ill effects, it just pops like a wood fire in the grate. But I have had zero spitback from either atty. My dripper, on the other hand, refuses to make any noise at all other than a swooshy airflow noise. Yet I occasionally get spitback for a few draws before it settles down and behaves again. That's with simple contact coils in everything.

In his Avo24 review, Rip said that the pop, pop, pop is a sign that it's wicking well. I don't know about that but he seems to think that wicking rather than coil is the cause. I've heard it a lot in YouTube reviews and it never seems to faze the reviewer so it's never bothered me. It would be interesting to know what causes it, though.

 

[Jono90]

Today i did a spaced 20g KA1 4mm 7 wrap dual coil in my twisted messes 24 and without any doubt the flavor is intense and cloud production is better than any other exotic build i have done to date. I have always been a fan of contact coils especially with claptons but all my 20g contact coils sucked. its made me rethink my buillds. I think people of put off of spaced because its not as simple as contact and if you dont know how to space it, then most of the time you end up with an ugly coil, which may work well but i guess people are O.C.D about having a clean build.

 

[blujeenz]

You may have a point there... Gears are turning again...

May be part of the cause of the popping some closed coilers have mentioned?

Possible.
Also thinking fast wicking could cause micro pools of juice to form with contact coils.
Once the coils heats the entire micro pool up to its flash point, it lets go with the combined vapour of the whole pool popping out.
No real way to peer closely at the coils to see.
In theory popping could occur under certain conditions, contact coils with very wet wicks, so if the wicks are glossy wet with juice then perhaps popping would occur, whereas not so much with coils that are just satin wet.

Anyhow, my beard now feels rather stiff after all the rubbing and pulling while pondering.
Y'all know its hard to fall asleep with a stiff beard.

 

[KZOR]

I still prefer spaced coils. Plain old fused claptons spaced 5 or 6 wraps is what I use the most in my builds.

 

[JB1987]

I had some heavy popping in the Limitless Plus on a dual spaced 3mm 24g 0.35ohm setup at about 50 watts, going above that the popping reduces but the vape gets a bit hot for me. I rewicked it after a few days with the wick sitting much tighter in the coil and it seems as if the popping has basically disappeared. Still exceptional wicking with no dry hits.

Just a guess but maybe a loose wick in the coil allows juice to gather and then pop on the first few fires.

Edit: I found spaced coils to wick much better in rdta's with no dry hit problems compared to compact coils.

 

[Anneries]

Calling all engineers, preferably with access to SolidWorks. Please do a heat transfer/distribution simulation based on a compressed coil and a spaced coil. Lets see what that looks like, might give us another hint in this subject.
Wish I paid more attention in class.

 

[KZOR]

@Anneries
You can do it at home. Make two clone coils and just space the one. Wick them both exactly the same and do a dry burn test for 3 seconds. Remove the cotton and examine for burnt areas.
Replace the cotton and moisten them both the same amount of fluid then place a sheet of carlton towel in a upright position in close proximity to your mod and push button for another 3 seconds. Examine spray stains on the paper towel.

 

[blujeenz]

Heres my MS Paint simulation.

Cross section of coil and wick with the orange halo around the wire being the intense vapourising heat.
More cotton puffing up through the inter wire spacings on the spaced coil exposes more juice to heat.
However the heat is uniform at the wick surface with slightly cooler midway areas between the wire cross sections.


the compressed version.
Darker shaded green areas indicate flash heated juice due to combined heating of 2 wire cross sections.

 

[Chukin'Vape]

I don't know what's up with that popping thing. Both my RDTAs do it, the Avo intermittently and the Limitless Plus constantly. It doesn't result in spitback or any other ill effects, it just pops like a wood fire in the grate. But I have had zero spitback from either atty. My dripper, on the other hand, refuses to make any noise at all other than a swooshy airflow noise. Yet I occasionally get spitback for a few draws before it settles down and behaves again. That's with simple contact coils in everything.

In his Avo24 review, Rip said that the pop, pop, pop is a sign that it's wicking well. I don't know about that but he seems to think that wicking rather than coil is the cause. I've heard it a lot in YouTube reviews and it never seems to faze the reviewer so it's never bothered me. It would be interesting to know what causes it, though.

Exactly that - As the juice gets sucked out of your RDTA tank - it creates a vacuum, when that vacuum becomes stronger it sucks air through the wicking ports - creating those pop sounds.

 

[blujeenz]

Exactly that - As the juice gets sucked out of your RDTA tank - it creates a vacuum, when that vacuum becomes stronger it sucks air through the wicking ports - creating those pop sounds.

I should probably have been a bit more specific regards the popping, I was referring to a sound more akin to a game of "Lavender Hill" hide and seek played with 357's and 38 specials.

I agree with your conclusions regards the more muted sounds from the tank, not quite a gurgle or a gloeb, but a popping will do for now.

 

[Raindance]

@blujeenz, Awesome paintwork!

Today i did a spaced 20g KA1 4mm 7 wrap dual coil in my twisted messes 24 and without any doubt the flavor is intense and cloud production is better than any other exotic build i have done to date. I have always been a fan of contact coils especially with claptons but all my 20g contact coils sucked. its made me rethink my buillds. I think people of put off of spaced because its not as simple as contact and if you dont know how to space it, then most of the time you end up with an ugly coil, which may work well but i guess people are O.C.D about having a clean build.

I had some heavy popping in the Limitless Plus on a dual spaced 3mm 24g 0.35ohm setup at about 50 watts, going above that the popping reduces but the vape gets a bit hot for me. I rewicked it after a few days with the wick sitting much tighter in the coil and it seems as if the popping has basically disappeared. Still exceptional wicking with no dry hits.

Just a guess but maybe a loose wick in the coil allows juice to gather and then pop on the first few fires.

Edit: I found spaced coils to wick much better in rdta's with no dry hit problems compared to compact coils.

I also found the spaced coils wick better, especially with thinner (2.5mm D) coils. More wick acting as a reservoir for juice. I also found loose wicks to create popping and am tempted to agree that the surface wetness of the wick creates pools of juice that "explode" on heating as there is reduced contact between wick and wire which would otherwise dissipate some of the heat to a larger amount of juice within the coil. The coil thus gets hotter without actually transferring its energy for the purpose of vaporizing juice. Also found loose wicks to degrade quickly requiring replacement much sooner, probably for exactly the same reason.

Not mentioned in the initial post is that the figures also prove that larger diameter coils also provide a larger percentage of saturated wick per similar length of heating wire. This further reduces the possibility of dry hitting and increases the potential for vape production.

New questions arising are:
1. Just how tight must a wick fit for optimal performance,
2. Is it possible to determine (Reliably) the wicking speed of various types and brands of wicking material and
3. Would this information be useful or is my OCD taking me for a walk in the park again?

Cheers!

 

[blujeenz]

@blujeenz, Awesome paintwork!

New questions arising are:
1. Just how tight must a wick fit for optimal performance,
2. Is it possible to determine (Reliably) the wicking speed of various types and brands of wicking material and
3. Would this information be useful or is my OCD taking me for a walk in the park again?

Cheers!

Had to change my vote to a "like", so thanks.
1 no clue
2 somewhat easier, the equally sized samples dipped at the same time into a water dye solution should be an indication of wicking speed.
3 usefull indeed.

revisiting 1 again, perhaps 3 glass tubes with a 2.5mm ID threaded with varying wick densities and again dipped at the same time into a water dye solution might be a fairly good indication of when too much wick density is reached.

 

[Jono90]

i have also noticed that the spacing matters. uneven to wide spacing seems to give me less density and less flavor.so i personally like to make it as tight as possible spacing. a good example of a benefit from spaced is i couldn't push contact 20g coils past 100w without a dry hit with spaced coils of the same ID and wraps i can easily go up to 180w. which with 20g it truly shines, I have a DIY dessert coffee mix which the flavor is almost too much which it was never as intense with a contact coil.
as far as wicking it seems to me like spaced seem to fit more wick naturally? just from the feel of it? i still do like slight resistance when pulling my wick though, Any tighter and i feel i get less flavor. too me it makes sense if theres an excess of cotton then therefore less space for juice.
thats also why i never really like the Scottish roll method.

 

[Raindance]

Had to change my vote to a "like", so thanks.
1 no clue
2 somewhat easier, the equally sized samples dipped at the same time into a water dye solution should be an indication of wicking speed.
3 usefull indeed.

revisiting 1 again, perhaps 3 glass tubes with a 2.5mm ID threaded with varying wick densities and again dipped at the same time into a water dye solution might be a fairly good indication of when too much wick density is reached.

Great idea on how to test wicking. Thinking of using some tubes from the Nick bottle drippers for just this purpose. Will keep you posted!

Cheers!

 

[RichJB]

I don't know if this is going to help you, @Raindance, but Phil Busardo did several tests on different types of wicking some time back.

 

[Greyz]

I don't know if this is going to help you, @Raindance, but Phil Busardo did several tests on different types of wicking some time back.

Surprised to see how Organic cotton wicked so poorly compared to JC, Rayon and Hemp. My move to use JC over OC seems to have been the right move