The wick has been used for thousands of years to provide lighting in darkness and has progressed in the past several centuries in kerosene lamps and candles. The operation of a wick, in its basic form, utilizes capillary action, in which a liquid is transported inside a small diameter passage, by attractive forces between the passage material and the liquid properties. For example, if a small diameter glass tube is inserted into a water container, the water will rise inside the tube, to a height which is proportional to the difference in surface tension, of the glass and water, and inversely proportional to the tube diameter and the liquids' viscosity. Capillary action is one of the fundamental processes in transporting water in trees from the ground to the leaves.
In a wick, the cohesive forces between the wick fibers and the liquid surface tension, transport the liquid material upwards, thus increasing the liquid materials' surface area and causing it to evaporate by a heat source such as a candle flame or electric powered wire filament. In a wire filament, such as that described in the U.S. Publication No. 2013/0213419A1, entitled “Electronic Smoking Article and Improved Heater Element”, by C. S. Tucker et al., a wire mesh, instead of a wire, is utilized as the heat source, vaporizing the liquid transported by the wick, from the liquid reservoir. The wire mesh, having a greater surface area, is thus more efficient in vaporizing the liquid in contact with the wick material, than a circular wire.
The concern with such vaporization methods, is that the heat source is in contact with the wick material, and one the liquid is depleted, the heater elements' temperature rises sufficiently to combust the wick material causing potentially toxic vapors to be generated. FDA and WHO regulators are concerned, but may be years away from issuing any regulations regarding e-cigarettes and vaporizers.