I have seen very different explanations of vapor production on ECF, sometimes quite weird. So, I decided to clarify a bit the process.
Disclaimer: I am not involved in any e-cig research, but I have some background in physics.
Aerosol – a cloud of tiny particles (for us – liquid droplets) in air. Each droplet is too small to be visible individually, but it reflects a tiny amount of light in odd directions and all droplets together look like a cloud or fog (clouds and fog are water aerosol).
Solubility. Solubility could be full (infinite), like PG in VG or alcohol in water, or limited, like salt in water. If solubility is limited, then saturation point exists – excess of salt will not dissolve in water, will stay on the bottom of the cap. If we leave a cap with solution, water will evaporate with time and more and more salt will settle on the bottom (like in Great Salt Lake). The same true for air. For example, water is soluble in air, but its solubility greatly depends on temperature. If after a hot humid day we have a cold night, amount of water which was good for air at high daytime temperature will become excessive for low night temperatures and excess of water dissolved in air should “settle” somehow; the result we usually see is dew or fog.
Human lungs are famous for their wetness and they provide exhaled air with a lot of water in gaseous state at the temperature of a human body. But when a human body is outside at low temperatures exhaled gases (warm air + gaseous water) are chilled and will contain excess of water, which will “settle” as tiny droplets, i.e. aerosol, and we will see clouds of exhaled breath. Nice evaporator, always with us (just add a cold room)…
Boiling. Easy explanation for single liquid system (like water). Heated to boiling point temperature water will boil and produce water vapor. A bit more complicated is boiling of two component liquid, like PG-VG mixture. Liquid will boil as a single system (no separate boiling of its components) at a temperature between boiling points of its components and it will produce vapor of both PG and VG.
Now to vaping. Coil heat liquid supplied by a wick and transfer it into gaseous state (by boiling). But this vaporized liquid can stay in gaseous state only in small area of hot air surrounding a coil. Air draw is chilling this gaseous mixture and PG and VG form tiny aerosol droplets, our beloved clouds.
What’s wrong in my simplified explanations. When multicomponent liquid boils it produces more vapor of its components with lower boiling point, sometimes much more. For example, if we vape 30/70 solution of PG/VG, then PG (boiling point 371 F) will evaporate much faster than VG (477). If things were going as I described above, pretty soon we will be vaping almost pure VG (PG will be gone). It could be even worse. Suppose we have a third component – raspberry ketone (raspberry flavor) with boiling point of just 284 F. It should be gone in no time and most of the tank will be left flavorless.
Fortunately things are a bit more complicated then were described (a bit more complicated than my ability to comprehend them fully). In reality we have a mild overheating and a mild undersupply of liquid by a wick, plus mostly unidirectional liquid movement along a wick. In these conditions boiling produce vapor which is much closer in it composition to composition of a juice.
Disclaimer: I am not involved in any e-cig research, but I have some background in physics.
Aerosol – a cloud of tiny particles (for us – liquid droplets) in air. Each droplet is too small to be visible individually, but it reflects a tiny amount of light in odd directions and all droplets together look like a cloud or fog (clouds and fog are water aerosol).
Solubility. Solubility could be full (infinite), like PG in VG or alcohol in water, or limited, like salt in water. If solubility is limited, then saturation point exists – excess of salt will not dissolve in water, will stay on the bottom of the cap. If we leave a cap with solution, water will evaporate with time and more and more salt will settle on the bottom (like in Great Salt Lake). The same true for air. For example, water is soluble in air, but its solubility greatly depends on temperature. If after a hot humid day we have a cold night, amount of water which was good for air at high daytime temperature will become excessive for low night temperatures and excess of water dissolved in air should “settle” somehow; the result we usually see is dew or fog.
Human lungs are famous for their wetness and they provide exhaled air with a lot of water in gaseous state at the temperature of a human body. But when a human body is outside at low temperatures exhaled gases (warm air + gaseous water) are chilled and will contain excess of water, which will “settle” as tiny droplets, i.e. aerosol, and we will see clouds of exhaled breath. Nice evaporator, always with us (just add a cold room)…
Boiling. Easy explanation for single liquid system (like water). Heated to boiling point temperature water will boil and produce water vapor. A bit more complicated is boiling of two component liquid, like PG-VG mixture. Liquid will boil as a single system (no separate boiling of its components) at a temperature between boiling points of its components and it will produce vapor of both PG and VG.
Now to vaping. Coil heat liquid supplied by a wick and transfer it into gaseous state (by boiling). But this vaporized liquid can stay in gaseous state only in small area of hot air surrounding a coil. Air draw is chilling this gaseous mixture and PG and VG form tiny aerosol droplets, our beloved clouds.
What’s wrong in my simplified explanations. When multicomponent liquid boils it produces more vapor of its components with lower boiling point, sometimes much more. For example, if we vape 30/70 solution of PG/VG, then PG (boiling point 371 F) will evaporate much faster than VG (477). If things were going as I described above, pretty soon we will be vaping almost pure VG (PG will be gone). It could be even worse. Suppose we have a third component – raspberry ketone (raspberry flavor) with boiling point of just 284 F. It should be gone in no time and most of the tank will be left flavorless.
Fortunately things are a bit more complicated then were described (a bit more complicated than my ability to comprehend them fully). In reality we have a mild overheating and a mild undersupply of liquid by a wick, plus mostly unidirectional liquid movement along a wick. In these conditions boiling produce vapor which is much closer in it composition to composition of a juice.
