Aerosol generating system having means for handling consumption of a liquid subtrate

Abstract

There is provided an electrically operated aerosol generating system for receiving an aerosol-forming substrate. The system includes a liquid storage portion for storing liquid aerosol-forming substrate, an electric heater including at least one heating element for heating the liquid aerosol-forming substrate, and electric circuitry configured to monitor activation of the electric heater and estimate an amount of liquid aerosol-forming substrate remaining in the liquid storage portion based on the monitored activation. There is also provided a method in an electrically operated aerosol generating system including a liquid storage portion for storing liquid aerosol-forming substrate and an electric heater including at least one heating element for heating the liquid aerosol-forming substrate, the method including monitoring activation of the electric heater and estimating an amount of liquid aerosol-forming substrate remaining in the liquid storage portion based on the monitored activation.

Claims

1. An electrically operated aerosol generating system configured to receive an aerosol-forming substrate, the system comprising: a liquid storage portion configured to store a liquid aerosol-forming substrate; an electric heater comprising at least one heating element configured to heat the liquid aerosol-forming substrate; and electric circuitry configured to monitor activation of the electric heater, estimate an amount of the liquid aerosol-forming substrate remaining in the liquid storage portion based on the monitored activation, and estimate a consumed amount of the liquid aerosol-forming substrate based on a first equation relating heating element temperature or resistance to liquid aerosol-forming substrate consumption up to a first threshold of temperature or resistance, and based on a second equation relating heating element temperature or resistance to liquid aerosol-forming substrate consumption above the first threshold.

2. The electrically operated aerosol generating system according to claim 1, wherein the electric circuitry is further configured to estimate a consumed amount of the liquid aerosol-forming substrate, and to subtract the consumed amount from a known initial amount to provide an estimate of an amount of the liquid aerosol-forming substrate remaining in the liquid storage portion.

3. The electrically operated aerosol generating system according to claim 1, wherein the electric circuitry is further configured to monitor activation of the electric heater by monitoring a temperature or a resistance of the at least one heating element over time.

4. The electrically operated aerosol generating system according to claim 1, wherein the second equation is dependent on power applied to the at least one heating element.

5. The electrically operated aerosol generating system according to claim 1, wherein the first equation is independent of power applied to the at least one heating element.

6. The electrically operated aerosol generating system according to claim 1, wherein the first threshold is a boiling point of the liquid aerosol-forming substrate.

7. The electrically operated aerosol generating system according to claim 1, wherein the first and second equations are stored in the electric circuitry.

8. The electrically operated aerosol generating system according to claim 7, wherein a plurality of different first and second equations are stored in the electric circuitry for different compositions of liquid aerosol-forming substrate and for different power levels.

9. The electrically operated aerosol generating system according to claim 1, wherein the electric circuitry is further configured to measure an electrical resistance of the at least one heating element, and to ascertain a temperature of the at least one heating element from a measured electrical resistance.

10. The electrically operated aerosol generating system according to claim 1, further comprising a capillary wick configured to convey the liquid aerosol-forming substrate from the liquid storage portion to the electric heater.

11. A method, comprising: providing an electrically operated aerosol generating system comprising a liquid storage portion configured to store a liquid aerosol-forming substrate and an electric heater comprising at least one heating element configured to heat the liquid aerosol-forming substrate; monitoring, by electric circuitry, activation of the electric heater and estimating, by the electric circuitry, an amount of the liquid aerosol-forming substrate remaining in the liquid storage portion based on the monitored activation; and estimating, by the electric circuitry, a consumed amount of the liquid aerosol-forming substrate based on a first equation relating heating element temperature or resistance to liquid aerosol-forming substrate consumption up to a first threshold of temperature or resistance, and based on a second equation relating heating element temperature or resistance to liquid aerosol-forming substrate consumption above the first threshold.

Description

(1) The invention will be further described, by way of example only, with reference to the accompanying drawings, of which:

(2) FIG. 1 shows one example of an electrically operated aerosol generating system having a liquid storage portion;

(3) FIG. 2 is a plot of total particle mass versus power applied for two different liquid aerosol forming substrate compositions in a device of the type shown in FIG. 1;

(4) FIG. 3 is a plot of evaporation rate versus temperature of a liquid composition up to boiling point, together with a curve correlated to the plotted points;

(5) FIG. 4 is a plot showing the evaporation rate of a liquid composition versus temperature in a device of the type shown in FIG. 1, showing evaporation rate for two different power levels;

(6) FIG. 5 is a plot showing the evolution of temperature of a heating element during a puff, with different plots shown for different stages in the consumption of the liquid aerosol forming substrate;

(7) FIG. 6 is a plot showing the liquid evaporation rate during a puff and the corresponding temperature of the heating element;

(8) FIG. 7 is a plot showing the cumulative evaporated mass for a puff;

(9) FIG. 8 is a plot showing, on the y-axis, heating element resistance and, on the x-axis, heating element temperature of an electric heater of an electrically operated aerosol generating system; and

(10) FIG. 9 is a schematic circuit diagram, which allows heating element resistance to be measured, according to one embodiment of the invention.

(11) FIG. 1 shows one example of an electrically operated aerosol generating system having a liquid storage portion. In FIG. 1, the system is a smoking system. The smoking system 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 109. A puff detection system 111 is also provided in cooperation with the electric circuitry 109. 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. Note that the heater is only shown schematically in FIG. 1. In the exemplary embodiment shown in FIG. 1, one end of capillary wick 117 extends into cartridge 113 and the other end of capillary wick 117 is surrounded by the heater 119. The heater is connected to the electric circuitry via connections 121, which may pass along the outside of cartridge 113 (not shown in FIG. 1). The housing 101 also includes an air inlet 123, an air outlet 125 at the mouthpiece end, and an aerosol-forming chamber 127.

(12) In use, operation is as follows. Liquid 115 is 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 which is surrounded by heater 119. When a user draws on the aerosol generating system at the air outlet 125, ambient air is drawn through air inlet 123. In the arrangement shown in FIG. 1, the puff detection system 111 senses the puff and activates the heater 119. The battery 107 supplies electrical 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 air flow 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.

(13) In the embodiment shown in FIG. 1, the electric circuitry 109 and puff detection system 111 are preferably programmable. The electric circuitry 109 and puff detection system 111 can be used to manage operation of the aerosol generating system. This assists with control of the particle size in the aerosol.

(14) FIG. 1 shows one example of an electrically operated aerosol generating system according to the present invention. Many other examples are possible, however. In addition, note that FIG. 1 is schematic in nature. In particular, the components shown are not to scale either individually or relative to one another. The electrically operated aerosol generating system needs to include or receive a liquid aerosol-forming substrate contained in a liquid storage portion. The electrically operated aerosol generating system requires some sort of electric heater having at least one heating element for heating the liquid aerosol-forming substrate. Finally, the electrically operated aerosol generating system requires electric circuitry for determining an amount of liquid aerosol-forming substrate in the liquid storage portion. This will be described below with reference to FIGS. 2 to 9. It is emphasized that the system does not need to be a smoking system and a puff detection system does not need to be provided. Instead, the system could operate by manual activation, for example the user operating a switch when a puff is taken. For example, the overall shape and size of the housing could be altered. Moreover, the system may not include a capillary wick. In that case, the system may include another mechanism for delivering liquid for vaporization.

(15) However, in a preferred embodiment, the system does include a capillary wick for conveying the liquid from the liquid storage portion to the at least one heating element. 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 heater. Preferably, the heater comprises at least one heating wire or filament extending around the capillary wick.

(16) As discussed above, according to the invention, the electrically operated aerosol generating system includes electric circuitry for determining an amount of liquid aerosol-forming substrate in the liquid storage portion. Embodiments of the invention will now be described with reference to FIGS. 2 to 9. The embodiments are based on the example shown in FIG. 1, although they are applicable to other embodiments of electrically operated aerosol generating systems.

(17) FIG. 2 is a plot of the total particle mass (TPM) of aerosol generated in a user puff in a device as shown in FIG. 1, for two different aerosol forming substrates. Plot 200, with the plotted points drawn as larger squares, shows the results for Liquid 1 and plot 210, with the plotted points shown as smaller squares, shows the results for Liquid 2 The plots show the effect on aerosol generation of increasing power to the heater. It can be seen that increasing the power to the heater broadly increases aerosol generation. At very high power aerosol mass reduces, and this can be explained by the evaporated mass remaining in the gaseous phase rather than forming droplets.

(18) FIG. 2 also illustrates that the mass of aerosol generated is also dependent on the composition of the liquid aerosol-forming substrate. For example, different compositions will have different boiling points and different viscosities. Any model to accurately estimate liquid aerosol-forming substrate consumption must therefore account for liquid composition and power applied to the heater.

(19) The generation of aerosol requires supplying enough energy to the liquid to vaporise it. The energy required is called the enthalpy of vaporisation. The amount of energy supplied depends on the temperature of the heater element or elements: The higher the temperature the more energy is supplied to the liquid. So, up to the boiling point of the liquid, there is a relationship between the temperature of the heater elements and the evaporation rate. This is independent of the power supplied to the heater. FIG. 3 is a plot showing the evaporation rate of a liquid aerosol-forming substrate versus temperature up to its boiling point. The experimental data is plotted as diamonds 220. Also shown is a curve 230, drawn with square points, that is fitted to the experimental data 220. The curve 230 is of the form m=Ae.sup.BT, where m is the evaporated mass rate, A and B are calibration constants and T is the temperature of the heating element. The constants A and B depend on the liquid composition.

(20) Once the temperature of the heating element reaches the boiling point of the liquid the rate of evaporation no longer increases in the same manner. At this point further energy from the heating element does not increase the temperature of the liquid. However, as the temperature of the heating element increases beyond the boiling point thermal diffusion through the liquid substrate and more particularly through any medium holding the substrate, in this embodiment the capillary wick, becomes a significant factor. As the heating element temperature rises there is a greater rate of thermal diffusion so more liquid substrate is vaporised.

(21) FIG. 4 is a plot of two different evaporation rate curves as a function of temperature using a wick system as shown in FIG. 1. The two curves 240 and 250 correspond to two different amounts of power supplied to the heating element during a puff. In both curves 240 and 250, the first portion below the boiling point of the liquid corresponds to the curve 230 shown in FIG. 3. Above the boiling point the two curves diverge. Curve 240, corresponds to a lower power than curve 250. Both curves show a linear increase in evaporation rate with temperature, but the rate of increase is clearly dependent on power. The portion of curves 240 and 250 above the boiling point of the liquid substrate are of the form m=CT+D, where m is the rate of evaporation, C and D are calibration constants and T is temperature. Constants C and D are dependent on liquid composition, the power applied to the heater as well as the physical properties of the device, such as the composition and dimensions of the wick and the configuration of the heater.

(22) The curves of FIG. 4 provide a model that can be used to calculate the evaporation rate of the liquid substrate if the temperature of the heating element and the power applied to the heating element are known. For each design of aerosol generating system the constants A, B, C and D need to be empirically derived and constants C and D must be derived for the different power levels that the system can operate at.

(23) The temperature of the heating element changes during the course of each puff and changes as the amount of liquid in the liquid storage portion is reduced. FIG. 5 is a plot showing five averaged temperature profiles during a puff. The temperature, T of the heating element is shown on the y-axis and the puff time t is shown on the x-axis. Curve 501 is the median of a first set of puffs, each puff having a 2-second puff duration. Similarly, curve 503 is the median of a second set of puffs, curve 505 is the median of a third set of puffs curve 507 is the median of a fourth set of puffs and curve 509 is the median over a fifth set of puffs. In each curve, the vertical bars (for example shown at 511) indicate the standard deviation around the median for those puffs. Thus, the evolution of the measured temperature over the life of the liquid storage portion is shown. This behaviour was observed and confirmed for all liquid formulations vaporized and for all power levels used.

(24) As can be seen from FIG. 5, the temperature response of the heating element is reasonably stable over curves 501, 503 and 205. That is to say, the standard deviation around the median for the first three sets of puffs is reasonably small. The model illustrated in FIG. 4 is most accurate during this period when the temperature response is stable. During this period there is always sufficient aerosol-forming substrate being delivered to the heater through the wick. Once the wick begins to dry a different behaviour is observed.

(25) FIG. 6 is an illustration of the temperature profile of a heating element during a puff (averaged over a set of puffs), shown as curve 600 together with the corresponding evaporation rate calculated using the model shown and described with reference to FIG. 4, shown as curve 610.

(26) The total mass of liquid aerosol-forming substrate evaporated during a puff can be calculated by integrating under the evaporation rate curve 610. This integral can be performed by the electric circuitry using the trapezium method for example. The result of the integral is shown in FIG. 7. FIG. 7 again shows the temperature profile 600 of a heating element during a puff but also shows the cumulative evaporated mass over the puff as curve 700.

(27) The total amount of liquid aerosol-forming substrate consumed can be calculated by summing the totals calculated for each puff. This total consumed mass can be subtracted from a known initial mass of liquid in the liquid storage portion to provide an estimate of the amount of liquid aerosol-forming substrate remaining. The amount remaining can be indicated to the user as a meaningful quantity, such as an estimated number of puffs remaining or as a percentage value.

(28) Determining the amount of liquid aerosol-forming substrate in the liquid storage portion is advantageous because, when the liquid storage portion is empty or nearly empty, insufficient liquid aerosol-forming substrate may be supplied to the heater. This may mean that the aerosol created and inhaled by the user does not have the desired properties, for example, aerosol particle size. This may result in a poor experience for the user. In addition, it is advantageous to provide a mechanism whereby the user can be informed that the liquid storage portion is empty or nearly empty. Then the user can prepare to replace or refill the liquid storage portion.

(29) The electric circuitry may include a sensor which is able to detect the presence of a liquid storage portion and, moreover, to determine the characteristics of the liquid storage portion including, for example, how much liquid aerosol-forming substrate is contained in the liquid storage portion and the composition of the liquid aerosol-forming substrate. As described in the applicant's pending International application PCT/IB2009/007969, this may be based on identification information provided on the liquid storage portion. This information, together with information derived from monitoring activation of the heater, allows the electric circuitry to predict the amount of liquid aerosol-forming substrate in the liquid storage portion. Alternatively, the electric circuitry does not need to include a sensor. For example, the amount of liquid aerosol-forming substrate in each liquid storage portion may simply be of only one kind and set at a standard amount.

(30) A number of variations of the invention are possible. For example, the aerosol generating system does not need to include a puff detection system. Instead, the system could operate by manual activation, for example the user operating a switch when a puff is taken.

(31) According to the first embodiment of the invention, a temperature sensor is provided in the aerosol generating system close to the heating element. The electric circuitry can monitor the temperature measured by the temperature sensor and hence determine an amount of liquid in the liquid storage portion as described. The advantage of this embodiment is that no calculation or derivation is required, since the temperature sensor directly measures the temperature close to the heating element.

(32) According to the second embodiment of the invention, the amount of liquid in the liquid storage portion is determined by measuring the resistance of the electric heating element. If the heating element has suitable temperature coefficient of resistance characteristics (for example, see equation (5) below), then the resistance may provide a measure of the temperature of the electric heating element.

(33) FIG. 8 is a plot showing the resistance, R of the heating element of the electric heater on the y-axis, versus the temperature, T of the heating element on the x-axis. As can be seen in FIG. 8, as the temperature T of the heating element increases, so does the resistance R. Within a selected range (between temperatures T1 and T2 and resistances R1 and R2 in FIG. 4), the temperature T and resistance R may be proportional to one another.

(34) As discussed above in relation to the first embodiment of the invention, if the liquid storage portion is empty or nearly empty, insufficient liquid aerosol-forming substrate will be supplied to the heater. This will mean that any capillary wick will become dry, and the temperature of the heating element will increase. FIG. 8 shows that such a temperature increase may be determined by measuring the resistance of the heating element because, as the temperature increases, the measured resistance will increase as well.

(35) FIG. 9 is a schematic electric circuit diagram showing how the heating element resistance may be measured according to the second embodiment of the invention. In FIG. 9, the heater 901 is connected to a battery 903 which provides a voltage V2. The heater resistance to be measured at a particular temperature is R.sub.heater. In series with the heater 901, an additional resistor 905, with known resistance r is inserted and connected to voltage V1. The voltage V1 has an intermediate value between ground and voltage V2. In order for microprocessor 907 to measure the resistance R.sub.heater of the heater 901, the current through the heater 901 and the voltage across the heater 901 can both be determined. Then, the following well-known formula can be used to determine the resistance:
V=IR  (1)

(36) In FIG. 9, the voltage across the heater is V2−V1 and the current through the heater is I. Thus:

(37) $\begin{array}{cc}{R}_{\mathrm{heater}}=\frac{V2-V1}{I}& \left(2\right)\end{array}$

(38) The additional resistor 905, whose resistance r is known, is used to determine the current I, again using (1) above. The current through the resistor 905 is I and the voltage across the resistor 905 is V1. Thus:

(39) $\begin{array}{cc}I=\frac{V1}{r}& \left(3\right)\end{array}$

(40) So, combining (2) and (3) gives:

(41) $\begin{array}{cc}{R}_{\mathrm{heater}}=\frac{\left(V2-V1\right)}{V1}r& \left(4\right)\end{array}$

(42) Thus, the microprocessor 907 can measure V2 and V1, as the aerosol generating system is being used and, knowing the value of r, can determine the heater's resistance at a particular temperature, R.sub.heater.

(43) Then, the following formula can be used to determine the temperature T from the measured resistance R.sub.heater at temperature T:

(44) $\begin{array}{cc}T=\frac{R_{\mathrm{heater}}}{\alpha R_0}+T_0-\frac{1}{\alpha }& \left(5\right)\end{array}$
where α is the thermal resistivity coefficient of the heating element material and R.sub.0 is the resistance of the heating element at room temperature T.sub.0.

(45) An advantage of this embodiment is that no temperature sensor, which can be bulky and expensive, is required.

(46) Thus, a measure of the temperature of the heating element can be derived. This can be used to determine when the amount of liquid in the liquid storage portion has decreased to a threshold and to estimate an absolute amount of aerosol-forming substrate remaining in the liquid storage portion.

(47) In the embodiments described above, once it has been determined when the amount of liquid aerosol-forming substrate in the liquid storage portion has decreased to a threshold, one or more actions may be taken. The electric heater may be deactivated. For example, a system may be triggered to render the liquid storage portion unusable. For example, the electric circuitry, on determining that the amount of liquid aerosol-forming substrate in the liquid storage portion, has decreased to a threshold, may blow an electrical fuse between the at least one heating element of the electric heater and an electric power supply. The electrical fuse may be provided as part of a removable component including the liquid storage portion. Alternatively, the electric circuitry, on determining that the amount of liquid aerosol-forming substrate in the liquid storage portion, has decreased to a threshold, may switch off a switch between the at least one heating element of the electric heater and an electric power supply. Alternative methods of deactivating the electric heater are, of course, possible. An advantage of deactivating the electric heater is that it is then impossible to use the aerosol generating system. This renders it impossible for a user to inhale an aerosol which does not have the desired properties.

(48) Once it has been determined when the amount of liquid in the liquid storage portion has decreased to a threshold, the user may be advised. For example, the electric circuitry, on determining that the amount of liquid aerosol-forming substrate in the liquid storage portion, has decreased to a threshold, may indicate this to a user. For example, if the aerosol generating system includes a user display, it may be indicated to the user, via the user display, that the liquid storage portion is empty or nearly empty. Alternatively or additionally, an audible sound may indicate to the user that the liquid storage portion is empty or nearly empty. Alternative methods of indicating to the user that the liquid storage portion is empty or nearly empty are, of course, possible. An advantage of advising the user is that the user is then able to prepare to replace or refill the liquid storage portion.

(49) Thus, according to the invention, the electrically operated aerosol generating system includes electric circuitry for determining when the amount of liquid aerosol-forming substrate in the liquid storage portion has decreased to a predetermined threshold. Features described in relation to one embodiment may also be applicable to another embodiment.