Device 1 was a CE4 “top-coil” tank-style (Vision, Shenzhen, China). Three separate devices were used in this study, and from the same manufacturer, all virtually identical save for some variations in coil resistance. The three devices used in this study were determined to have coil resistance of 2.2, 2.8 and 3.4 Ω (average was 2.8 Ω, with standard deviation of 0.5 Ω). In this device, the liquid is held inside a tank, and silica strings acting as wicks descend from a ceramic cup containing the coil into the liquid, which is fed to the coil through the wicks. “CE4” refers to the general design, using a ceramic coil cup, fourth version of this type of tank system. Air flow travels up through a center tube to under the coil, and then to the mouth. Adequate wetting of any EC coil depends on the ability of the wick to feed the liquid as fast as the coil vaporizes it. It should be noted that this style of atomizer is largely out of favor now in the vaping community, due to the difficulty of wicking with some liquids, and the propensity for dry-puff to occur. It should also be noted that this was the atomizer style chosen recently by previous researchers who reported high aldehyde and acrolein content of EC aerosol using 5 V or more (
Jensen et al., 2015).
Device 2 was a Protank 1 (KangerTech, Shenzhen, China) with a replaceable 2.7 Ω bottom single-coil-head. A single tank and three separate coils were used in this study. In this device the liquid is held in a tank and gravity fed to the coil, which is positioned at the bottom of the tank, through short silica wicking threads which the coil is wrapped around and oriented horizontally if the tank is held tip-up. It was expected that this design would allow more consistent wetting of the coil compared to Device 1.
Device 3 was a Gladius (Innokin, Shenzhen, China) bottom coil tank system with a replaceable dual-coil-head and a total resistance of 2.8 Ω. A single tank and three unique coil-heads were used in this study. The overall design with respect to liquid feed is very similar to the Protank, but here there are two coils in parallel, at 5.6 Ω each, each wrapped horizontally around short silica wicks, stacked vertically on top of each other and across the central air-flow, which travels through a center tube to the mouth. The two coils in parallel have the effect of spreading the heat out evenly over the coils, compared to one coil when the same wattage is applied, assuming total resistance and all other factors are identical.
Device 4 was bottom single coil Nautilus (Aspire USA, Kent, WA) with 2.2 Ω resistance. The overall design is visually similar to the Protank, but the replaceable coil-head is larger and the coil is vertically oriented, longer and of thicker gauge, and in contact with more wicking material (poly-fill). A single tank and three unique coil-heads were used in this study.
Device 5 was a SubTank (KangerTech) with a 0.72 Ω bottom-coil-head. Since wattage is inversely proportional to coil resistance, reducing coil resistance will increase the wattage for a given battery voltage proportionally, allowing very high wattage from typical 3.7 V Li-ion batteries. The coil is vertically oriented, similar to the Nautilus coil-head, but the wicking material is cotton. A single atomizer was used with each device. In all cases, samples were collected from lowest power to highest power levels. All tanks were maintained at a minimum of 50% of the maximum liquid level. Where adjustment was possible for a device, airflow was set to maximum
