Abstract
In electronic nicotine delivery systems (ENDS), coil resistance is an important factor in the generation of heat energy used to change e-liquid into vapor. An accurate and unbiased method for testing coil resistance is vital for understanding its effect on emissions and reporting results that are comparable across different types and brands of ENDS and measured in different laboratories. This study proposes a robust, accurate and unbiased method for measuring coil resistance. An apparatus is used which mimics the geometric configuration and assembly of ENDS reservoirs, coils and power control units. The method is demonstrated on two commonly used ENDS devices—the ALTO by Vuse and JUUL. Analysis shows that the proposed method is stable and reliable. The two-wire configuration introduced a positive measurement bias of 0.086 (Ω), which is a significant error for sub-ohm coil designs. The four-wire configuration is far less prone to bias error and is recommended for universal adoption. We observed a significant difference in the coil resistance of 0.593 (Ω) (p < 0.001) between the two products tested. The mean resistance and standard deviation of the reservoir/coil assemblies was shown to be 1.031 (0.067) (Ω) for ALTO and 1.624 (0.033) (Ω) for JUUL. The variation in coil resistance between products and within products can have significant impacts on aerosol emissions.
Highlights
Coil resistance test fixtures are built for two pod-style products: ALTO and JUUL
The commonly employed two-wire lead configuration is demonstrated to introduce a positive bias, the magnitude of which is dependent upon the laboratory testing apparatus and impedes reproducing results between independent laboratories
The constant current four-wire lead method is recommended as the standard method for measuring the resistance of electronic cigarette coil assemblies
Summary
Typical pod-style electronic nicotine delivery systems (ENDS) consist of three subsystems: the reservoir, power control unit (PCU) and lithium battery. The reservoir includes a mouthpiece, e-liquid storage compartment, a heating element called the coil, sometimes a wick, and an aerosol generation chamber, sometimes referred to as the atomizer. Reservoirs designed for re-use, permitting users to refill the reservoir with e-liquids, are sometimes called “open systems.”. Reservoirs designed to be disposable, not intended to permit e-liquid refills by the user, are sometimes called “closed systems.”. Most pod-style ENDS reservoirs are designed with the heating element, or “coil”, fully integrated with a wick to deliver e-liquid from the reservoir to the heating element such that thermally generated aerosol mixes with inhaled air for delivery through the mouthpiece to the user Reservoirs designed for re-use, permitting users to refill the reservoir with e-liquids, are sometimes called “open systems.” Reservoirs designed to be disposable, not intended to permit e-liquid refills by the user, are sometimes called “closed systems.” Most pod-style ENDS reservoirs are designed with the heating element, or “coil”, fully integrated with a wick to deliver e-liquid from the reservoir to the heating element such that thermally generated aerosol mixes with inhaled air for delivery through the mouthpiece to the user
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