On 2017 Sep 26, Clive Bates commented:

So again, we have a study that ignores the central feature of vaping: namely, that it is a human behaviour in which the human user regulates variables like the choice of device and hence coil and wicking configuration, voltage and power settings during operation, and the rate of liquid consumption according to their preferences.

The formation of volatile aldehydes (VAs) is largely temperature dependent (they are products of thermal decomposition), and increasingly vaping devices include temperature control. But the ultimate control is with the user. A high volume of liquid consumption combined with greater coil surface area can still allow for operation at a moderate temperature even at high power, as the liquid transfers heat away from the coil surface.

Users will operate the equipment in a way that does not lead to harsh dry puff conditions, with associated high VA formation. This is a key human control feedback that does not exist in laboratory equipment. So experiments that just standardise power settings or volume consumption must take care to validate these are realistic proxies for human use for a particular device. In this paper, many of the coil, power and volume settings combinations were not realistic. That could have been avoided through engaging with people with real practical expertise.

On 2017 Sep 26, Clive Bates commented:

I would like to recommend that the authors (and anyone attempting similar experiments) consult experienced users about the way these products are used in practice in order to ensure their work is relevant and realistic. I am posting a critical review of this paper by an experienced vaper, Paul Barnes, a trustee of the New Nicotine Alliance.

Paul Barnes' review starts here

An emerging category of electronic cigarettes (ECIGs) are sub-Ohm devices (SODs) that operate at ten or more times the power of conventional ECIGs

Sub-Ohming has been a feature of vaping for many years with advanced, or hobbyist, users utilising knowledge of Ohms Law and unregulated mechanical mods (“mech-mods”), along with user-made coils to provide an experience customised to suit the individual user.

As technology has improved, the need for mechanical mods has waned, bringing forth the era of the regulated devices. These contain a chipset to regulate power output (wattage), include safety cut-off (to prevent over-use), and control thermal safety (to prevent cell failures), among other features. These devices can produce similar, or greater, power output compared with the mechanical device.

Pre-made coils are now the norm for most users. The coils mentioned in this paper - Smok TF-Q4 (1), Smok V8-Q4 (2), Smok V8-T8 (3) and the Smok V8-T10 (4) - present a unique problem for researchers lacking in an understanding of both the technology and the consumer.

In this paper, all the chosen coils were used at a constant power of 50W, with the Smok V8-T8 coil head being used at varying power levels (50, 75, and 100 Watts).

Fundamentally, the design of the coil head is suitable for higher power usage, not low power.

One of the key problems with this approach is the misunderstanding of a) how these devices are used in the real world, and b) the particular user characteristics.

For example, the Smok TF-Q4 states (screen printed on the coil head itself) that the “best” range (determined by user experience, the resistance of the coil, and knowledge of consumer preferences) for power (in Watts) is between 80-120W - between the medium and the upper end of the coil-head maximum capability of 140 Watts.

The power ranges for the other coils are as follows (according to manufacturer specifications):

Smok V8-Q4: 50-180W and "best between" 90-150W

Smok V8-T8: 50-260W and "best between" 125-180W

Smok V8-T10: 50-300W and "best between" 130-190W

Considering that the coil head chosen for the variable power test (Smok V8-T8) has a “best” operating range of 125-180 W, testing at 100 demonstrates an imbalance between the cooling effects of the e-liquid, aerosol generation and airflow - a factor not directly considered in the paper.

At a measured resistance of 0.15 Ohms - the culmination of eight physical coils arranged in parallel - (assuming the Joyetech Cuboid used measured the resistance accurately), and a power setting of 100W, the voltage applied to the coil head is 5.33V (35.59A).

Finding a decrease in VA emissions is obvious, given the coil heads fundamental design and operating parameters. In comparison, the Vapor Fi (5) device used demonstrated high levels of VA emissions when used at 11 W (approximately 6.2V), far and above the power that would generate the "dry puff" phenomenon (6); as commonly seen in the older CE4/CE5 clearomisers favoured by some researchers (7).

The key difference between the VF coil and the Smok coil-heads is in the construction. The Smok coil-heads utilise multiple physical coils inside a single unit, conversely, the VF coil is a single coil unit. Therefore, the entirety of the 6.2V (at 11W) is being applied to a single resistance material. The unique construction of the Smok coil-heads negates this fundamental problem by providing up to 10 distinct coils within the head. The total effect is the same, 5.33V is being applied to the entirety of the head, but distributed across 4, 8 or 10 distinct paths.

Coupled with the larger surface area and substantially more wicking material, heat dissipation through the wick, aerosolisation and air inhalation, the Smok coil heads are capable of handling much higher voltage, while using substantially more e-liquid, without generating the dry-puff.

Prior research (8) on the various types of e-cig coil, including a common Sub-Ohm tank and coil, has previously been performed with a focus on nicotine aerosolisation, suggesting that the liquid consumed through vaping is not proportional to nicotine content.

In summary

The central point of this paper is to examine the relationship between increasing power applied to a coil or coil-head and increasing VA emissions. Fundamentally, with a coil-head containing multiple physical coils, the total heating area, relative to a single (or even a dual) coil is substantially greater. The amount of wicking material which, when soaked with e-liquid (with or without nicotine) provides a significant cooling effect, is also substantially greater. With more physical coils in the coil-head, the time taken for a coil-head to reach a temperature that is both a) satisfying for the user, and b) includes the possibility of inducing a dry-puff, is much longer. Further, the material used for the coil alters the overall heat capacity; as demonstrated by the "Coil Wrapping" calculator (9).

In reality, as power to the coil increases, liquid consumption also increases. In real-world scenarios, human users regulate both power and liquid flow to minimise the risk of dry-puff conditions and therefore avoiding increases in VA emissions.

References

(1) Smok TF-V4 Coil - UK ECIG Store: [link]

(2) Smok Tech Store V8-Q4 core: [link]

(3) Smok Tech Store V8-T8 core: [link]

(4) Smok Tech Store V8-T10 core: [link]

(5) VaporFi Platinum II Tank: [link]

(6) Farsalinos K, Voudris V, Poulas K - E-cigarettes generate high levels of aldehydes only in 'dry puff' conditions [link] Farsalinos KE, 2015

(7) CE5 Clearomizer Tank - VapeClub: [link]

(8) Farsalinos K et al - Protocol proposal for, and evaluation of, consistency in nicotine delivery from the liquid to aerosol of electronic cigarette atomizers: [link] Farsalinos KE, 2016

(9) For example, see Steam Engine Coil Wrapping Calculator [link]

On 2017 Sep 26, Clive Bates commented:

I would like to recommend that the authors (and anyone attempting similar experiments) consult experienced users about the way these products are used in practice in order to ensure their work is relevant and realistic. I am posting a critical review of this paper by an experienced vaper, Paul Barnes, a trustee of the New Nicotine Alliance.

Paul Barnes' review starts here

An emerging category of electronic cigarettes (ECIGs) are sub-Ohm devices (SODs) that operate at ten or more times the power of conventional ECIGs

Sub-Ohming has been a feature of vaping for many years with advanced, or hobbyist, users utilising knowledge of Ohms Law and unregulated mechanical mods (“mech-mods”), along with user-made coils to provide an experience customised to suit the individual user.

As technology has improved, the need for mechanical mods has waned, bringing forth the era of the regulated devices. These contain a chipset to regulate power output (wattage), include safety cut-off (to prevent over-use), and control thermal safety (to prevent cell failures), among other features. These devices can produce similar, or greater, power output compared with the mechanical device.

Pre-made coils are now the norm for most users. The coils mentioned in this paper - Smok TF-Q4 (1), Smok V8-Q4 (2), Smok V8-T8 (3) and the Smok V8-T10 (4) - present a unique problem for researchers lacking in an understanding of both the technology and the consumer.

In this paper, all the chosen coils were used at a constant power of 50W, with the Smok V8-T8 coil head being used at varying power levels (50, 75, and 100 Watts).

Fundamentally, the design of the coil head is suitable for higher power usage, not low power.

One of the key problems with this approach is the misunderstanding of a) how these devices are used in the real world, and b) the particular user characteristics.

For example, the Smok TF-Q4 states (screen printed on the coil head itself) that the “best” range (determined by user experience, the resistance of the coil, and knowledge of consumer preferences) for power (in Watts) is between 80-120W - between the medium and the upper end of the coil-head maximum capability of 140 Watts.

The power ranges for the other coils are as follows (according to manufacturer specifications):

Smok V8-Q4: 50-180W and "best between" 90-150W

Smok V8-T8: 50-260W and "best between" 125-180W

Smok V8-T10: 50-300W and "best between" 130-190W

Considering that the coil head chosen for the variable power test (Smok V8-T8) has a “best” operating range of 125-180 W, testing at 100 demonstrates an imbalance between the cooling effects of the e-liquid, aerosol generation and airflow - a factor not directly considered in the paper.

At a measured resistance of 0.15 Ohms - the culmination of eight physical coils arranged in parallel - (assuming the Joyetech Cuboid used measured the resistance accurately), and a power setting of 100W, the voltage applied to the coil head is 5.33V (35.59A).

Finding a decrease in VA emissions is obvious, given the coil heads fundamental design and operating parameters. In comparison, the Vapor Fi (5) device used demonstrated high levels of VA emissions when used at 11 W (approximately 6.2V), far and above the power that would generate the "dry puff" phenomenon (6); as commonly seen in the older CE4/CE5 clearomisers favoured by some researchers (7).

The key difference between the VF coil and the Smok coil-heads is in the construction. The Smok coil-heads utilise multiple physical coils inside a single unit, conversely, the VF coil is a single coil unit. Therefore, the entirety of the 6.2V (at 11W) is being applied to a single resistance material. The unique construction of the Smok coil-heads negates this fundamental problem by providing up to 10 distinct coils within the head. The total effect is the same, 5.33V is being applied to the entirety of the head, but distributed across 4, 8 or 10 distinct paths.

Coupled with the larger surface area and substantially more wicking material, heat dissipation through the wick, aerosolisation and air inhalation, the Smok coil heads are capable of handling much higher voltage, while using substantially more e-liquid, without generating the dry-puff.

Prior research (8) on the various types of e-cig coil, including a common Sub-Ohm tank and coil, has previously been performed with a focus on nicotine aerosolisation, suggesting that the liquid consumed through vaping is not proportional to nicotine content.

In summary

The central point of this paper is to examine the relationship between increasing power applied to a coil or coil-head and increasing VA emissions. Fundamentally, with a coil-head containing multiple physical coils, the total heating area, relative to a single (or even a dual) coil is substantially greater. The amount of wicking material which, when soaked with e-liquid (with or without nicotine) provides a significant cooling effect, is also substantially greater. With more physical coils in the coil-head, the time taken for a coil-head to reach a temperature that is both a) satisfying for the user, and b) includes the possibility of inducing a dry-puff, is much longer. Further, the material used for the coil alters the overall heat capacity; as demonstrated by the "Coil Wrapping" calculator (9).

In reality, as power to the coil increases, liquid consumption also increases. In real-world scenarios, human users regulate both power and liquid flow to minimise the risk of dry-puff conditions and therefore avoiding increases in VA emissions.

References

(1) Smok TF-V4 Coil - UK ECIG Store: [link]

(2) Smok Tech Store V8-Q4 core: [link]

(3) Smok Tech Store V8-T8 core: [link]

(4) Smok Tech Store V8-T10 core: [link]

(5) VaporFi Platinum II Tank: [link]

(6) Farsalinos K, Voudris V, Poulas K - E-cigarettes generate high levels of aldehydes only in 'dry puff' conditions [link] Farsalinos KE, 2015

(7) CE5 Clearomizer Tank - VapeClub: [link]

(8) Farsalinos K et al - Protocol proposal for, and evaluation of, consistency in nicotine delivery from the liquid to aerosol of electronic cigarette atomizers: [link] Farsalinos KE, 2016

(9) For example, see Steam Engine Coil Wrapping Calculator [link]