Vape Liquid Viscosity

blending your own custom e-juice, at the right viscosity…

…also, notes on rebuilding a Protank atomizer…

I recently got into the fascinating “e-cig” hobby, whereby one dumps the dirty, ashy smoking of tobacco products, with its 4,000 toxic, carcenogenic chemicals, and starts “vaping” (vaporizing) glycerin (glycerol) and nicotine, with one’s choice of favorite flavors. We’ve all seen the “water vapor, not smoke” e-cig ads on TV, but that’s but one of many options for vaping. A large and growing industry for vaping now exists, and clever people are offering many options for electrical devices and fluids that provide nicotine-laden vapors instead of tobacco smoke. Yup, it’s really better. 🙂

The advantages are many: (1) while nicotine is a potent and highly addictive toxin, it’s relatively safe in small, measured quantities, particularly when we eliminate the many other toxins in tobacco products, and (2) vaping is a lot cheaper than smoking, if you do it right. For example, you can get the hardware and about a 3-4 month supply of flavored nicotinic liquid for around $60, a small fraction of what one might pay for smoking highly-taxed and high-restricted cigarettes. Furthermore, you can vape almost anywhere, and if they complain, you just say, “Sorry, but this is a vaporizer, and it doesn’t contain any tobacco products.” How sweet! 🙂

The most cost-effective system is a “tankomizer” (tank-type atomizer) that holds ~ 1.5-3 milliliters (ml) of liquid, vaporizing it with a ~ 2.5 Ohm heater coil, powered by a ~ 3.7-volt lithium rechargeable battery unit. One can buy the liquid pre-mixed, or buy the components (glycerine, propylene glycol, nicotine, and flavor), and mix one’s own “juice”, as desired. One decides the base liquid blend, which determines the viscosity; the nicotine percentage (usually 12-24 mg/ml), and any of several hundred flavors. These need not be tobacco flavors, but can be anything from Dunhill to Cappuccino to Strawberry Cheesecake, as desired. Not to mention, good ol’ menthol.

Types of e-cigarettes

First is the cigarette-sized (mini) vaporizers like the Blu. These use disposable cartridges and small rechargeable batteries. Quite expensive. From there one moves up to the replaceable “cartomizer” type, where a replaceable liquid cartridge plugs into an atomizer, which screws onto a rechargeable battery. These are somewhat larger (about like a cigarillo), and last substantially longer than the mini-e-cig types. Beyond that are the clear tanks (clearomizers), which are designed to be refilled many times. Beyond that are the rebuildable tanks with replaceable atomizers. Atomizer heater coils typically last only a couple of months, and there’s really no point in throwing away a whole e-cig just because it needs a new atomizer. These initially cost more, but are cheaper in the long run.

In the clearomizer tank there is a vaporizer tube containing the atomizer heating coil. It is fed a thick liquid via either a fiber wick (top heater) or tiny holes (bottom heater), and the rate of liquid feed is largely determined by the viscosity of the liquid. Glycerine has a very high viscosity index (VI), while propylene glycol has a relatively low VI, and since both are safe for human consumption, they are blended to provide the correct viscosity. However, some people have allergies and/or objections to propylene glycol, so pure vegetable glycerine, thinned a bit with water, is used instead. I have determined experimentally that a mixture of glycerine and about 3.5% water (96.5% Aqueous Glycerine (AG)) has about the same viscosity profile as 50:50 glycerine:glycol, which is commonly used, and a 6% water in glycerine (94% AG) has about the same viscosity profile as 30:70 glycerine:glycol, also commonly used.

Viscosity Profiles

viscosity chart
click for large

I spent way too many dozen hours looking up all the available data on glycerine and propylene glycol, put it it all into a spreadsheet, and generated a Viscosity Profile chart:

Note that, in the chart, P.Glycol is hidden by 80% AG.

Note that the numbers for Aqueous Glycerine are accurate, from an old chemistry book, whilst the numbers for 50:50 and 30:70 glycerine:glycol mixtures are mathematically interpolated, and may or may not be accurate—I’m not a chemist, and I didn’t grind it right down to molecular weights, but I see no reason why they might not be close to reality.

From this data, we can see the interesting conclusions:

  • 97% AG nearly matches the profile of 50:50.
  • 94% AG nearly matches the profile of 30:70.
  • 80% AG nearly matches the profile of 100% PG.
  • A 20% water AG has a nearly flat profile from 60 to 3 cPs.s. This is probably too thin for most clearo/tankomizers.

The flow rate into an atomizer will initially be controlled by the Room Temp viscosity, but will increase rapidly as the atomizer heats up the tank – so, the flatter the curve, the better, but it must not be too low or the atty will flood and gurgle. The flow rate is also determined by the user’s draw—the air inlet is restricted, so when the use draws, it lowers the pressure in the atty, causing more liquid to flow into the wicks. Furthermore, a nearly empty tank will flow more (when drawn) than a nearly full one, because there’s more air-space in the tank. As the liquid level drops it creates a partial vacuum in the tank, reducing the flow, then, after the draw, a little bubble of air goes through the wicks and normalizes the pressure inside…and the lower the tank level, the less frequently this needs to happen (this applies to bottom-coil tanks).

From what I have read on many vaping forums, it seems that a lot of people are somewhat confused as to why their PV (personal vaporizer) performs so much differently with various pre-mixed fluids, and various coil powers (e.g., wattage = voltage × amperage, where amperage = voltage ÷ resistance — E=IR and P=EI). It seems to me that for a given room-temp (i.e., 25°C) viscosity, a certain amount of liquid will move into the heating coil (by osmosis), and for that amount of flow, a certain amount of power is required to vaporize it. Thus, if you’re gonna blend your own juice, you should understand its viscosity profile and the amount of power needed for said viscosity profile.

Back to the chart, it becomes apparent that the flatter the viscosity profile the better, since vaping warms up the whole carto/clearo/tanko, and the viscosity rapidly drops during a vaping session. And, as you can see, the higher the percentage of glycerine, the steeper the curve! Example: You start out vaping pure glycerine at 25C room temperature, and it has a viscosity of 995 centiPoise—about like honey. But after 2-3 minutes of vaping, it has warmed to 40°C and dropped to <300 cPs.s! But your atto coil is designed to vaporize at a certain rate and wattage. You start out with a light, dry vape, and end the session with a heavy, wet vape, and maybe even flooding and gurgle in the PV. All this is due to the drop in viscosity as the tank warms up. The vape becomes much more consistent as we add water (or, to a lesser extent, propylene glycol) and thin the glycerine, flattening it’s viscosity profile. But we can go too far: Though some recommend 20% water in glycerine, we see from the chart that this is ~= to straight PG, and is way too thin for tankos, but about right for cartos, which hold the liquid in a pack of fiber.

Empirical

I’ve just started testing these assertions, in a KangerTech Protank, and will in the future months provide results. Meanwhile, your feedback is both welcomed and appreciated! My goal is to help mature this hobby with better, scientifically-controlled information.

I therefore propose a standardized measure of viscosity, which I call 10-5, to be measured in a 10cc syringe body (plunger removed) with a #12 x 1/2" blunt needle, where the liquid drops from 10 to 5 ml in n seconds. This may be correlated to centiPoise if someone wants to drag out a multi-thousand-dollar lab-grade viscometer, or we can just use 10-5 cc drop (spec: through a #12x1/2" needle at 25°C) time to compare fluids. We probably don’t need to get into densities and measure things in centiStokes kinematic, as just knowing if it’s “honey” or “maple” will likely be sufficient to select and blend juices at ~ the proper vis for the popular clearos.

If you wanna participate in these viscosity experiments, I will be using as viscometers:

  • http://www.amazon.com/dp/B008MLV3NM/ is (6) Amico Stainless Steel Luer Lock Dispensing Needle Tip, 12 Gauge, 2.05mm ID x 2.8mm OD x 1/2" Length, $5.09 f/s.
  • http://www.amazon.com/dp/B002RUI8WS/ is (5) B-D Luer Lock 10ml syringes, $2.83 f/s.

…you’ll need to fabricate a 10cc B-D syringe holder, and acquire some 30ml catch bottles, etc. And a cheapo digital thermometer. And a stopwatch!

Hey, it might be fun! It might even help mature this hobby a bit.

Updates

May 8, 2013 — I finally received the #12 blunt needles, and have tested my current batch, which is 96.5 AG. It dropped from 10-5 cc in the B-D syringe in a reasonable 72 seconds, so it looks like the choice of the #12 needle was about right. My next batch will be 93% AG, which should bring the viscosity down to about same as 30:70 glycerol:glycol.

May 21, 2013 — Made the next 30ml batch at 7% water and 20mg/ml nic. Too thin! The Kanger Protank floods and gurgles, doesn’t vape well, and needs to be completely washed out every couple of days. The 10-5 drop time viscosity is 47 seconds. Looks like 4-5% water in glycerine is gonna be the right number for the next batch.

Jan 2, 2016 — Wow! I forgot I hadn't updated this for so long! After a year or so I got tired of all the above and just started using 100% VG, no water. It vapes OK, and without the water it doesn't crackle or spit.

To catch up, that first year I went through 2 Ego Twist batteries; they don't last nearly long enough. Then I discovered VisionSpinner batteries, much better! They cost less and last twice as long.

For juice, I get 1 liter of 10% (100mg/ml) nicotine in glycerine, mix that with 2 liters of glycerine, yielding 3 liters of 3.3% (33mg/ml) nicotine. About $75 at MyFreedomSmokes.com. Add to that a couple VisionSpinners and 10 protank coils, totals about $125 for 3+ years of vaping. Can't do better than that!

CAUTION: If you buy 10% bulk nicotine, handle and store it with all possible care — it's very toxic at that strength. Even with the 3.3% mix I always wash hands and wipe down the tanko and countertop after a refill. Just to be safe.

Another thing I do sometimes is drink my dose. Just keep some 3.3% in a little plastic eye-drop bottle and add 5 or so drops (~¼cc) to a liter water bottle and you're good for 2-3 hours. Not as satisfying as vaping, but keeps away cravings when/where you can't vape.

TIP: Keep some Q-tips next to your charger. Always swab out the battery contact in the end of the battery before screwing it onto the charger, else it'll corrode the charger contact.

Rebuilding an Atomizer Coil

My first 2.5-Ohm Protank heater burned out after 6 weeks. I had a spare, but decided to disassemble the bad one and see if it could be fixed. Indeed, the coil wire broke right where it goes into the little rubber bushing in the bottom, so I lost about ¼″ of wire. The coil and wick was encased in a load of black crud. I removed that and un-wound the coil wire and cleaned it. Then wound it around 3 new wicks, leaving two wire tails about ¼″ long, laid it in place, inserted the battery contact bushing and battery contact (one wire is pinched outside the bushing against the outer part; the other wire is pinched inside the bushing against the inner battery contact part). Then laid two wicks on top, trimmed the wicks close with small wire-cutters, installed the top stem and bushing, then tried it. It worked like new, but it quickly flooded and gurgled. Removed the top stem again and added two more wicks on top of the coil, trimmed, and reassembled. Now it works great!

See, the ends of the wicks stick out of two slots, and the upper rubber bushing pushes down over that, closing off the top of the slots above the wicks. If the remaining slot-space below the bushing isn’t full of wicks, it will leak around them, causing flooding of the air tube. So, if your tanko is flooding, you might be able to disassemble the atty and add 2-3 more wicks. That will both fill up the wick-slots, as well as compress the existing wicks some, slowing the flow. It is not necessary to re-wind the wire around more wicks, just lay them on top and don’t mess with trying to rebuild the coil, unless it’s broken or totally gunked in burned carbon crud.

—kv5r

2 thoughts on “Vape Liquid Viscosity
  1. Nice work! try a falling sphere viscometer. Get a stainless ballbearing at your local hardware store. Density is 7.84 g/cc.
    Size should be about 3 mm diameter for vape fluids. Put the juice in a small grad cylinder and time how long it takes for fall a given distance. That is the terminal velocity. Look up the equation. It’s not too bad!

    • Yeah, I was gonna do that but I didn’t have a graduated cylinder. I don’t measure the viscosity any more, I just vape 100% VG. It works OK in my Protank, and w/o the water it doesn’t crackle or spit. See Jan 2016 updates above.
      Thanks for stopping by!
      –kv5r

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