METHOD OF CONTROLLING AEROSOL PRODUCTION TO CONTROL AEROSOL PROPERTIES

Abstract

There is provided a method of controlling aerosol production in an aerosol-generating device including a heater including at least one heating element, an aerosol-forming substrate disposed and configured to be heated by the heating element, and a power source configured to provide power to the heating element; the method including providing a period of gas flow over the substrate, the gas flow rate varying during the period, providing power to the heating element such that the substrate is heated and volatile components of the substrate are entrained in the gas flow, thereby forming an entrained gas flow, and allowing the entrained gas flow to cool such that the volatile components condense and form an aerosol, wherein the power provided to the heating element during the period is controlled such that one or more physical and/or chemical characteristics of the aerosol are maintained at a substantially constant value during the period.

Claims

1.-8. (canceled)

9. A method of controlling aerosol production in an aerosol-generating device, the device comprising: a heater comprising at least one heating element, an aerosol-forming substrate disposed and configured to be heated by the heating element, and a power source configured to provide power to the heating element; and the method comprising: providing a period of gas flow over the aerosol-forming substrate, the gas flow rate varying during the period of the gas flow, providing power to the heating element such that the aerosol-forming substrate is heated and volatile components of the aerosol-forming substrate are entrained in the gas flow, thereby forming an entrained gas flow, and allowing the entrained gas flow to cool such that the volatile components condense and form an aerosol, wherein the power provided to the heating element during the period of the gas flow is controlled such that one or more physical characteristics and/or one or more chemical characteristics of the aerosol are maintained at a substantially constant value during the period of gas flow.

10. The method according to claim 9, wherein the power provided to the heating element during the period of gas flow is controlled such that a mixing efficiency of the volatile components in the entrained gas flow and/or a cooling rate of the volatile components in the entrained gas flow are maintained at a steady state during the period of the gas flow.

11. The method according to claim 9, wherein the one or more physical characteristics of the aerosol include at least one characteristic of a concentration of a volatile component, a droplet number density, and a droplet size, and wherein the one or more physical characteristics of the aerosol are maintained at a constant value during the period of the gas flow.

12. The method according to claim 11, wherein values representative of the one or more physical characteristics of the aerosol are measured or calculated in real time and are used to control the power provided to the heating element during the period of the gas flow.

13. The method according to claim 9, wherein the power provided to the heating element is reduced to zero for at least one period of time during the period of the gas flow.

14. A method of controlling aerosol production in an aerosol-generating device, the device comprising: a heater comprising at least one heating element, an aerosol-forming substrate disposed and configured to be heated by the heating element, and a power source configured to provide power to the heating element; and the method comprising: providing a period of gas flow over the aerosol-forming substrate, the gas flow rate varying during the period of the gas flow, providing power to the heating element such that the aerosol-forming substrate is heated and volatile components of the aerosol-forming substrate are entrained in the gas flow, thereby forming an entrained gas flow, and allowing the entrained gas flow to cool such that the volatile components condense and form an aerosol, wherein the power provided to the heating element is controlled with reference to the gas flow rate so as to control physical properties of the aerosol and/or chemical properties of the aerosol, and wherein the provided power to the heating element is switched off before an end of the period of the gas flow.

15. The method according to claim 9, wherein the aerosol-generating device is an electrically-operated aerosol-generating device and the period of the gas flow is provided by a user puffing on the aerosol-generating device.

16. An electrically-operated aerosol-generating device, comprising; a heater comprising at least one heating element; an aerosol-forming substrate disposed and configured to be heated by the heating element; a power source configured to provide power to the heating element; at least one sensor configured to sense one or more parameters to enable real-time characterization of an aerosol generated by the aerosol-generating device; and a controller configured to control a power provided to the heating element based on the real time characterization of the aerosol generated.

Description

[0039] The invention will be further described, by way of example only, with reference to the accompanying drawings, in which:

[0040] FIG. 1 shows one example of an electrically operated aerosol-generating device;

[0041] FIG. 2 is a graph illustrating a variation in cooling rate during a puff for a number of aerosol-generating devices;

[0042] FIG. 3 is a graph illustrating a variation in mixing efficiency during a puff for a number of aerosol-generating devices; and

[0043] FIG. 4 provides schematic diagrams illustrating desirable aerosol properties over a puff duration and an example heating profile to achieve those properties.

[0044] FIG. 1 shows one example of an electrically heated aerosol generating device. In FIG. 1, the device is a smoking device having a liquid storage portion. The smoking device 100 of FIG. 1 comprises a housing 101 having a mouthpiece end 103 and a body end 105. In the body end, there is provided an electric power supply in the form of battery 107 and electric circuitry in the form of hardware 109 and a puff detection device 111. In the mouthpiece end, there is provided a liquid storage portion in the form of cartridge 113 containing liquid 115, a capillary wick 117 and a heater 119 comprising at least one heating element. Note that the heater is only shown schematically in FIG. 1. One end of the capillary wick 117 extends into the cartridge 113 and the other end of the capillary wick 117 is surrounded by the heater 119. The heater is connected to the electric circuitry via connections 121. The housing 101 also includes an air inlet 123, an air outlet 125 at the mouthpiece end and an aerosol-forming chamber 127.

[0045] In use, operation is as follows. Liquid 115 is transferred or conveyed by capillary action from the cartridge 113 from the end of the wick 117 which extends into the cartridge to the other end of the wick 117 which is surrounded by the heater 119. When a user draws on the device at the air outlet 125, ambient air is drawn through air inlet 123. In the arrangement shown in FIG. 1, the puff detection device 111 senses the puff and activates the heater 119. The battery 107 supplies energy to the heater 119 to heat the end of the wick 117 surrounded by the heater. The liquid in that end of the wick 117 is vaporized by the heater 119 to create a supersaturated vapour. At the same time, the liquid being vaporized is replaced by further liquid moving along the wick 117 by capillary action. (This is sometimes referred to as “pumping action”.) The supersaturated vapour created is mixed with and carried in the airflow from the air inlet 123. In the aerosol-forming chamber 127, the vapour condenses to form an inhalable aerosol, which is carried towards the outlet 125 and into the mouth of the user.

[0046] The capillary wick can be made from a variety of porous or capillary materials and preferably has a known, pre-defined capillarity. Examples include ceramic- or graphite-based materials in the form of fibres or sintered powders. Wicks of different porosities can be used to accommodate different liquid physical properties such as density, viscosity, surface tension and vapour pressure. The wick must be suitable so that the required amount of liquid can be delivered to the heating element. The wick and heating element must be suitable so that the required amount of aerosol can be conveyed to the user.

[0047] In the embodiment shown in FIG. 1, the flow rate during a puff and the temperature of the heater are monitored during a puff. Values representative of cooling rate and mixing efficiency are generated and a controller controls power to the heater. This allows a heating profile for the duration of the puff to be managed such that cooling rate and mixing efficiency are maintained at approximately constant levels.

[0048] FIG. 1 shows one example of an electrically heated aerosol generating device which may be used with the present invention. Many other examples are usable with the invention, however. The electrically heated aerosol generating device simply needs to include or receive an aerosol forming substrate which can be heated by at least one electric heating element, powered by a power supply under the control of electric circuitry. For example, the device need not be a smoking device. For example, the aerosol forming substrate may be a solid substrate, rather than a liquid substrate. Alternatively, the aerosol forming substrate may be another form of substrate such as a gas substrate. The heating element may take any appropriate form. The overall shape and size of the housing could be altered and the housing could comprise a separable shell and mouthpiece. Other variations are, of course, possible.

[0049] FIG. 2 is a graph illustrating variations in cooling rate of air drawn through an aerosol-generating device over the duration of a puff. FIG. 3 is a graph illustrating variations in mixing efficiency of air drawn through an aerosol-generating device over the duration of a puff. Results in both FIG. 2 and FIG. 3 are representative of four different aerosol-generating devices having different geometries. All aerosol-generating devices were controlled such that the heating element was maintained at constant temperature. It can be clearly seen that, despite the constant temperature of the heating element, the cooling rate and mixing efficiency vary greatly over the puff profile. Thus, the properties of the aerosol generated vary over the puff profile.

[0050] FIG. 4 illustrates a desired situation in which characteristics such as species concentration, cooling rate, and mixing efficiency are maintained at a quasi-steady state during the puff duration, despite significant variation in puff profile.

[0051] An example thermal profile is illustrated aimed at achieving the desired result. The desired result may be achieved by designing a specific thermal profile for a particular device structure and geometry, and then implementing the thermal profile based on measurement of flow rate through the device. Alternatively, the desired result may be achieved by monitoring parameters representative of mixing efficiency and/or cooling rate and controlling the power supplied to the heater based on those parameters. By use of one of these methods it is possible to produce a uniform aerosol over the duration of a puff.