The efficiency of an electronic cigarette changes with the delivered power but also with inhalation behaviour.The harder you breathe, the more a device is made efficient.

Currently, the tests carried out on electronic cigarettes are based on standard reference documents. In order to reproduce user behaviour, a vaping regimen is defined. For example, it describes the duration or volume of air of a puff. A standard puff corresponding to a 3-second inhalation and a volume of 55 mL. 55 mL is approximately the volume of a mouth. Just over half the electronic cigarettes commercially available are intended for non-beginner consumers. These vapers have a behaviour during inhalation which is close to natural breathing. When you breathe, the lungs are filled with air and not just the mouth. The volumes of air inhaled are closer to 500 mL even 2L litres of air if you force. In this case, the vaping regimen defined in the standards is not in step with reality.  Not only inconsistent but according to this publication[1] leads to an under-estimation of the efficiency of these

74% efficiency

The efficiency of an electronic cigarette can be defined as the ratio between the energy required to heat and vaporise the liquid (determined from the amount of liquid vaporised) and the delivered energy. Thus, an efficient device approaches 100%. The efficiencies of five atomisers including Cubis (reference atomiser) are evaluated. They are tested at different powers and use two vaping regimens. These have a puff volume of 55 mL for the low regimen and 500 mL for the intense one. The use of an intense regimen leads in almost all cases to a significant increase in the efficiency of an atomiser. This increase seems to be all the greater for strong powers. Items of equipment with resistance greater than 1 Ω have efficiency exceeding 50%. It succeeds even in reaching 74% in intense regimen while it barely exceeds 46% with a low regimen. For atomisers with resistances less than 1 Ω, the efficiencies do not exceed 50%. It also seems that thanks to using an intense vaping regimen, devices tolerate higher powers.

Cold coffee or hot coffee?

When an air flow is passed over something hot, its cooling is forced. This is why we blow on hot coffee to drink it. In the case of electronic cigarettes, the air flow would then lead to losing more energy when using an intense profile. It would consequently reduce the efficiency of an atomiser. Contradictory? One reason that can be seen is found in the clearance of the vapour. A current of air also leads to cooling the vapour generated and to condensing it. At low regimen, the current of air is weaker and leaves more time for condensation of the liquid in the device. With a high flow rate, the vapour will also be cooled but as it is trapped in a stronger current of air, it has less time to condense in the device. This is why, with an intense regimen, we find that atomisers are more efficient.

There should then be the puff volume necessary for clearing all the vapour generated. It should be just as strong as the amount of liquid vaporised is large.

5 Soulet, S.; Duquesne, M.; Toutain, J.; Pairaud, C.; Mercury, M. Impact of Vaping Regimens on Electronic Cigarette Efficiency. Int. J. Environ. Res. Public Health 2019, 16, 4753.