Measurement of heating coil temperature for e-cigarettes with a “top-coil” clearomizer

Abstract

ObjectivesTo determine the effect of applied power settings, coil wetness conditions, and e-liquid compositions on the coil heating temperature for e-cigarettes with a “top-coil” clearomizer, and to make associations of coil conditions with emission of toxic carbonyl compounds by combining results herein with the literature.MethodsThe coil temperature of a second generation e-cigarette was measured at various applied power levels, coil conditions, and e-liquid compositions, including (1) measurements by thermocouple at three e-liquid fill levels (dry, wet-through-wick, and full-wet), three coil resistances (low, standard, and high), and four voltage settings (3–6 V) for multiple coils using propylene glycol (PG) as a test liquid; (2) measurements by thermocouple at additional degrees of coil wetness for a high resistance coil using PG; and (3) measurements by both thermocouple and infrared (IR) camera for high resistance coils using PG alone and a 1:1 (wt/wt) mixture of PG and glycerol (PG/GL).ResultsFor single point thermocouple measurements with PG, coil temperatures ranged from 322 ‒ 1008°C, 145 ‒ 334°C, and 110 ‒ 185°C under dry, wet-through-wick, and full-wet conditions, respectively, for the total of 13 replaceable coil heads. For conditions measured with both a thermocouple and an IR camera, all thermocouple measurements were between the minimum and maximum across-coil IR camera measurements and equal to 74% ‒ 115% of the across-coil mean, depending on test conditions. The IR camera showed details of the non-uniform temperature distribution across heating coils. The large temperature variations under wet-through-wick conditions may explain the large variations in formaldehyde formation rate reported in the literature for such “top-coil” clearomizers.ConclusionsThis study established a simple and straight-forward protocol to systematically measure e-cigarette coil heating temperature under dry, wet-through-wick, and full-wet conditions. In addition to applied power, the composition of e-liquid, and the devices’ ability to efficiently deliver e-liquid to the heating coil are important product design factors effecting coil operating temperature. Precautionary temperature checks on e-cigarettes under manufacturer-recommended normal use conditions may help to reduce the health risks from exposure to toxic carbonyl emissions associated with coil overheating.

Accuracy of commercial electronic nicotine delivery systems (ENDS) temperature control technology

“…Enabling the TCM feature on fourth-generation ENDS, which are capable of supplying up to 300 W, may reduce the risk of inhaling harmful chemicals by preventing the heating coil from reaching extremely high temperatures. In a recent study [ 12 ], the maximum heating-coil temperature of a second-generation e-cigarette device was reported as high as 1008 °C for a dry coil (no e-liquid), using a power of 13.3 W. The devices also have a power control mode which is not addressed in the current study. The temperature control and monitoring features are based on the coil material’s variation of resistance with temperature.…”

“…Also, performing IR thermography is difficult to do while the ENDS device is in use with puff flow, since the coils cannot be exposed to the camera. In a recent study [ 12 ], the coil temperature of a second-generation e-cigarette device was measured, for different powers (2.4 W to 13.3 W), coil wetness, and e-liquid compositions. Thermocouple measurements were compared with values determined via IR thermography.…”

Potential for release of pulmonary toxic ketene from vaping pyrolysis of vitamin E acetate

“…Critically, the temperature of heating coils within vaping devices is highly variable and has been measured to range between 110 and 1,008°C. Several factors can contribute to the actual temperature(s) applied to the complex vape mixture, such as the heating coil resistance, voltage applied, composition of the mixture being vaporized, and the mode of user usage (9,10). In reality, a vaping device should be considered as a crude uncontrollable minipyrolysis apparatus capable of causing changes to the chemical composition of a vaping mixture in an unpredictable manner.…”

Does ‘Dry Hit’ vaping of vitamin E acetate contribute to EVALI? Simulating toxic ketene formation during e-cigarette use

“…Heating coil temperatures, however, can be highly variable, and strongly depend on the e-liquid fill level and composition. For instance, working temperatures as high as 1008˚C have been measured under dry-through-wick conditions [13].…”