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TSRC, Tob. Sci. Res. Conf., 2023, 76, abstr. 49

A model of the transfer of species from the e-liquid to the aerosol during vaporization in an ENDS product

Juul Labs, Inc., Washington, DC, USA

Electronic nicotine delivery systems (ENDS) that vaporize an e-liquid to produce an aerosol are observed experimentally to transfer nicotine, glycerol, and propylene glycol to the aerosol at concentrations nearly proportional to their e-liquid concentration. However, because vaporization is the primary mechanism for transfer of compounds to the aerosol, proportional transfer (PT) does not occur for larger, less volatile compounds under similar conditions.

This report presents a model for e-liquid vaporization in ENDS based on the energy and mass balance in the vaporization region (VR), the heated area at the interface between the e-liquid and air. In the VR, e-liquid components are vaporized at rates proportional to their equilibrium vapor pressures and concentrations. The model demonstrates that initially vaporization rates for the e-liquid components are not proportional to their e-liquid concentrations, but over time within a puff, and over successive puffs, the VR concentrations of the less volatile components increase, resulting in higher vaporization rates and eventually leading to PT. For the major e-liquid components this occurs within 0.1-0.3s, while for less volatile and dilute compounds it takes significantly longer to reach PT, and in some cases it will not occur before the ENDS runs out of e-liquid.

A series of polyethylene glycols (PEG) with 4-8 repeating units has been used to test the model. The model predicts nearly 100% transfer for the major constituents and accurately predicts the measured device mass loss. The model also predicts a decrease in transfer efficiency due to decreasing vapor pressure for the PEGs, from 98% for PEG4 to 54% for PEG8 in qualitative agreement with the experimentally observed trend. This work supports the observation that larger compounds have limited transfer efficiencies into the aerosol.