Patent Publication Number: US-2022232885-A1

Title: Aerosol-generating article comprising an aerosol-cooling element with an elongated protrusion

Description:
The present disclosure relates to an aerosol-cooling element for use in an aerosol generating article comprising an aerosol-generating substrate and adapted to produce an inhalable aerosol upon heating, and an aerosol-generating article comprising such an aerosol-cooling element. 
     Aerosol-generating articles in which an aerosol-generating substrate, such as a tobacco-containing substrate, is heated rather than combusted, are known in the art. Typically in such heated smoking articles, an aerosol is generated by the transfer of heat from a heat source to a physically separate aerosol-generating substrate or material, which may be located in contact with, within, around, or downstream of the heat source. During use of the aerosol-generating article, volatile compounds are released from the aerosol-generating substrate by heat transfer from the heat source and are entrained in air drawn through the aerosol-generating article. As the released compounds cool, they condense to form an aerosol. 
     A number of prior art documents disclose aerosol-generating devices for consuming aerosol-generating articles. Such devices include, for example, electrically heated aerosol-generating devices in which an aerosol is generated by the transfer of heat from one or more electrical heater elements of the aerosol-generating device to the aerosol-generating substrate of a heated aerosol-generating article. 
     Substrates for heated aerosol-generating articles have, in the past, typically been produced using randomly oriented shreds, strands, or strips of tobacco material. More recently, alternative substrates for aerosol-generating articles to be heated rather than combusted have been disclosed, such as rods formed from gathered sheets of tobacco material. By way of example, the rods disclosed in international patent application WO-A-2012/164009 have a longitudinal porosity that allows air to be drawn through the rods. As a further alternative, international patent application WO-A-2011/101164 discloses rods for heated aerosol-generating articles formed from strands of homogenised tobacco material, which may be formed by casting, rolling, calendering or extruding a mixture comprising particulate tobacco and at least one aerosol former to form a sheet of homogenised tobacco material. In another embodiment, the rods of WO-A-2011/101164 may be formed from strands of homogenised tobacco material obtained by extruding a mixture comprising particulate tobacco and at least one aerosol former to form continuous lengths of homogenised tobacco material. 
     Substrates for heated aerosol-generating articles typically further comprise an aerosol former, that is, a compound or mixture of compounds that, in use, facilitates formation of the aerosol and that preferably is substantially resistant to thermal degradation at the operating temperature of the aerosol-generating article. Examples of suitable aerosol-formers include, but are not limited to: polyhydric alcohols, such as propylene glycol, triethylene glycol, 1,3-butanediol and glycerin; esters of polyhydric alcohols, such as glycerol mono-, di- or triacetate; and aliphatic esters of mono-, di- or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. 
     It is also common to include in an aerosol-generating article for producing an inhalable aerosol upon heating one or more additional elements that are assembled with the substrate in a same wrapper. Examples of such additional elements include a mouthpiece filtration segment, a support element adapted to impart structural strength to the aerosol-generating article. 
     It has also been proposed to include in an aerosol-generating article for producing an inhalable aerosol upon heating a cooling element adapted to favour cooling of the aerosol prior to reaching the mouthpiece. By way of example, WO 2013/120565 discloses an aerosol-generating article an aerosol-forming substrate and an aerosol-cooling element located downstream from the aerosol-forming substrate within the rod. In an embodiment, the aerosol-cooling element comprises a crimped sheet of polylactic acid (PLA) that has been gathered to define a plurality of longitudinally extending channels. As the stream of aerosol is drawn through the aerosol-cooling element, heat may be transferred from the aerosol to the sheet of PLA. 
     When an aerosol-generating article of the type described above is used under particularly hot and humid weather conditions, such as those frequently encountered in countries characterised by a tropical climate, the temperature reached by the mouthpiece of the article may be as high as in the range from 42 degrees Celsius to 45 degrees Celsius. These temperatures may be associated with a feeling of discomfort or mild pain for some consumers, as sensitive tissues such as lips, mouth, tongue and mucosae in general may come into direct contact with a surface of the mouthpiece during use. Without wishing to be bound by theory, this is understood to be because warm thermoreceptors, which respond to increases in skin temperature, are most responsive at approximately 45 degrees Celsius. By contrast, when the temperature of the skin is from about 30 degrees Celsius to about 36 degrees Celsius, warm thermoreceptors are spontaneously active, but there is generally no awareness of warmth (neutral thermal region). In addition, the skin also contains thermally sensitive receptors known as thermal nociceptors that lead to a painful sensation when the temperature of the skin rises above 45 degrees Celsius. This is because nociceptors responsive to temperature are meant to signal to the central nervous system that tissue damage may be imminent and that the affected body part should be promptly withdrawn from the heat source. 
     Thus, it would be desirable to provide a novel and improved aerosol-cooling element for an aerosol-generating article adapted to optimise cooling of the aerosol being delivered to the consumer. It would also be desirable to provide a novel and improved aerosol-cooling element for an aerosol-generating article adapted to optimise cooling of surfaces of the mouth end of the article that may come into contact with sensitive tissues of the consumer during use. At the same time, it would be desirable to provide one such aerosol-generating article that can be manufactured efficiently and at high speed without requiring major modifications or existing equipment and apparatus. 
     The present disclosure relates to an aerosol-cooling element configured for use in an aerosol-generating article. The aerosol-cooling element may comprise a hollow tubular segment comprising a peripheral wall. The hollow tubular segment may extend along a longitudinal axis and may have a downstream end in fluid communication with an upstream end. The hollow tubular segment may comprise at least one elongated protrusion extending from the peripheral wall into the interior of the hollow tubular segment. The at least one elongated protrusion may extend longitudinally from an upstream position on the peripheral wall to a downstream position on the peripheral wall downstream of the upstream position. 
     According to a first aspect of the present disclosure, there is provided an aerosol-cooling element configured for use in an aerosol-generating article. The aerosol-cooling element comprises a hollow tubular segment comprising a peripheral wall. The hollow tubular segment extends along a longitudinal axis and has a downstream end in fluid communication with an upstream end. The hollow tubular segment comprises at least one elongated protrusion extending from the peripheral wall into the interior of the hollow tubular segment. The at least one elongated protrusion extends longitudinally from an upstream position on the peripheral wall to a downstream position on the peripheral wall downstream of the upstream position. 
     The term “aerosol generating article” is used herein with reference to the invention to describe an article wherein an aerosol generating substrate is heated to produce and deliver an aerosol to a consumer. As used substrate capable of releasing volatile compounds upon heating to generate an aerosol. 
     A conventional cigarette is lit when a user applies a flame to one end of the cigarette and draws air through the other end. The localised heat provided by the flame and the oxygen in the air drawn through the cigarette causes the end of the cigarette to ignite, and the resulting combustion generates an inhalable smoke. By contrast, in heated aerosol generating articles, an aerosol is generated by heating a flavour generating substrate, such as tobacco. Known heated aerosol generating articles include, for example, electrically heated aerosol generating articles and aerosol generating articles in which an aerosol is generated by the transfer of heat from a combustible fuel element or heat source to a physically separate aerosol forming material. For example, aerosol generating articles according to the invention find particular application in aerosol generating systems comprising an electrically heated aerosol generating device having an internal heater blade which is adapted to be inserted into the rod of aerosol generating substrate. Aerosol generating articles of this type are described in the prior art, for example, in EP 0822670. 
     As used herein, the term “aerosol generating device” refers to a device comprising a heater element that interacts with the aerosol generating substrate of the aerosol generating article to generate an aerosol. 
     During use, volatile compounds are released from the aerosol-generating substrate by heat transfer and entrained in air drawn through the aerosol generating article. As the released compounds cool they condense to form an aerosol that is inhaled by the consumer. 
     As used herein, the term “tubular element” denotes an elongate element defining a lumen or airflow passage along a longitudinal axis thereof. In the context of the present specification, the term “tubular” is intended to encompass any tubular element having a substantially cylindrical cross-section which defines at least one airflow conduit establishing fluid communication between an upstream end of the tubular element and a downstream end of the tubular element. As used herein with reference to the present invention, the term “hollow” is used to describe a tubular element that defines an internal empty space, such as a chamber or cavity. 
     As used herein, the term “longitudinal” refers to the direction corresponding to the main longitudinal axis of the aerosol-generating article, which extends between the upstream and downstream ends of the aerosol-generating article. As used herein, the terms “upstream” and “downstream” describe the relative positions of elements, or portions of elements, of the aerosol-generating article in relation to the direction in which the aerosol is transported through the aerosol-generating article during use. During use, air is drawn through the aerosol-generating article in the longitudinal direction. The term “transverse” refers to the direction that is perpendicular to the longitudinal axis. Any reference to the “cross-section” of the aerosol-generating article or a component of the aerosol-generating article refers to the transverse cross-section unless stated otherwise. 
     The term “length” denotes the maximum dimension of a component of the aerosol-generating article in the longitudinal direction. For example, it may be used to denote the dimension of the rod or of the tubular element in the longitudinal direction. In particular, in the context of the present invention, the term “length of the tubular element” is used to denote the maximum distance between the upstream and downstream ends of the tubular element. 
     The term “peripheral wall” refers to a wall defining the periphery of the hollow tubular segment. The term “peripheral” refers to elements or features located at such a periphery. 
     The term “elongated protrusion” refers to a protrusion or projection that is long in relation to its width and thickness. For example, the elongated protrusion may comprise a flattened surface. The height, circumferential and radial position of the elongated protrusion are taken with reference to the base of the elongated protrusion. The elongated protrusion is connected at its base to the inner surface of the peripheral wall of the hollow tubular segment. The base of the elongated protrusion refers to the portion of the elongated protrusion which is connected to the inner surface of the peripheral wall of the hollow tubular segment. The base of the elongated protrusion defines the longitudinal or axial position, circumferential position and radial position of the elongated protrusion. For example, the radial position of the upstream position of the elongated protrusion refers to the radial position of the upstream position of the base of the elongated protrusion. 
     The term “radial position” refers to a direction along a radius from the centre of an object, which, in the present disclosure, is the hollow tubular element, the aerosol-cooling element or the aerosol-generating article. In other words, a particular radial position of the elongated protrusion, or a portion of the elongated protrusion, refers to a position and distance of the elongated protrusion, or portion thereof, relative to the central axis of the hollow tubular segment. 
     The term “circumferential position” refers to a direction following a circumference defined relative to the centre (or central axis) of an object, which, in the present disclosure, is the hollow tubular element, the aerosol-cooling element or the aerosol-generating article. In other words, a particular circumferential position of the elongated protrusion, or a portion of the elongated protrusion, refers to a position and distance of the elongated protrusion, or portion thereof, along a circumference defined relative to the central axis of the hollow tubular segment. 
     The term “thickness of a peripheral wall of the tubular element” is used in the present specification to denote the minimum distance measured between the outer surface and the inner surface of a wall of a tubular element. In practice, the distance at a given location is measured along a direction locally substantially perpendicular to opposite sides of the wall of the tubular element. For a substantially cylindrical tubular element, that is, a tubular element having a substantially circular cross-section, the thickness of the peripheral wall is assessed as the distance between the outer surface and the inner surface of the peripheral wall measured along a substantially radial direction of the tubular element. 
     The expression “air-impervious material” is used throughout this specification to mean a material not allowing the passage of fluids, particularly air and smoke, through interstices or pores in the material. If the tubular support element is formed of a material impervious to air and aerosol particles, air and aerosol particles drawn through the support element are forced to flow through the airflow conduit, but cannot flow across a wall of the support element. 
     By contrast, the term “porous” is used herein to refer to a material that provides a plurality of pores or openings that allow the passage of air through the material. 
     As used in the present specification, the term “homogenised tobacco material” encompasses any tobacco material formed by the agglomeration of particles of tobacco material. Sheets or webs of homogenised tobacco material are formed by agglomerating particulate tobacco obtained by grinding or otherwise powdering of one or both of tobacco leaf lamina and tobacco leaf stems. In addition, homogenised tobacco material may comprise a minor quantity of one or more of tobacco dust, tobacco fines, and other particulate tobacco by-products formed during the treating, handling and shipping of tobacco. The sheets of homogenised tobacco material may be produced by casting, extrusion, paper making processes or other any other suitable processes known in the art. 
     In aerosol-generating articles in accordance with the present invention, the aerosol-cooling element is adapted to lower the temperature of the aerosol flowing through the article, whilst at the same time homogenising the flow of aerosol and finely controlling how the aerosol flow is delivered to the consumer&#39;s mouth. 
     In more detail, it has been found that the structure and features of the aerosol-cooling element are such as to consistently lower the temperature of the gaseous flow in the article below the threshold values which may be associated with a sensation of discomfort or pain for the consumer. Without wishing to be bound by theory, it is understood that in aerosol-cooling elements and aerosol-generating articles in accordance with the invention, heat from the aerosol flowing through the article is conveniently dissipated as the material of the aerosol-cooling element is heated by conduction and convection. At the same time, the at least one elongated protrusion extending into the interior of the aerosol-cooling element increases the inner surface area of the aerosol-cooling element. Increasing the inner surface area of the aerosol-cooling element means that there is more surface area for heat transfer between the flow of aerosol and the material of the aerosol-cooling element to occur. Thus, the temperature of the flowing aerosol is reduced and overheating of the outer surfaces of the article that may come into contact with the consumer&#39;s lips during use is advantageously prevented, even when the article is used under particularly hot and humid weather conditions. 
     In addition to enhancing heat transfer of the aerosol-cooling element with the flowing aerosol, the at least one elongated protrusion partially blocks and diverts the heated aerosol entering and flowing through the aerosol-cooling element. The at least one elongated protrusion creates turbulence in the flowing aerosol, which encourages the mixing of the aerosol with the cooler air which is already present in the aerosol-cooling element. Therefore, such an effect further improves the cooling function of the aerosol-cooling element. 
     Further, aerosol-cooling elements and aerosol-generating articles in accordance with the present invention may be manufactured in a continuous process, and their production may conveniently be implemented at high speed and incorporated into existing production lines for the manufacture of heated aerosol-generating articles without requiring extensive modifications of the manufacturing equipment. 
     The aerosol-cooling element may be made of a material having a relatively high heat capacity, such that the aerosol-cooling element is capable of absorbing the thermal energy carried by the aerosol flowing through the article without this causing a major increase in the temperature of the aerosol-cooling element. By way of example, the aerosol-cooling element may be made of a cellulose-based compound, including a thermoplastic paper compound. By way of another example, the aerosol-cooling element may be made of polylactic acid (PLA) or a polyhydroxyalkanoate (PHA). 
     The at least one elongated protrusion may be made of the same material as the rest of the aerosol-cooling element. By way of example, at least one elongated protrusion may be made of a cellulose-based compound, including a thermoplastic paper compound. By way of another example, the at least one elongated protrusion may be made of polylactic acid (PLA) or a polyhydroxyalkanoate (PHA). The at least one elongated protrusion may be made by injection moulding or other extrusion techniques. 
     A length of the aerosol-cooling element may be from about 5 millimetres to about 35 millimetres. In some embodiments, a length of the aerosol-cooling element is from about 5 millimetres to about 25 millimetres or from about 5 millimetres to about 20 millimetres or from about 5 millimetres to about 19 millimetres. 
     Preferably, a length of the aerosol-cooling element is at least about 8 millimetres. More preferably, a length of the aerosol-cooling element is at least about 9 millimetres. A length of the aerosol-cooling element is preferably less than or equal to about 30 millimetres or from about 8 millimetres to about 25 millimetres or from about 8 millimetres to about 20 millimetres or from about 8 millimetres to about 19 millimetres. More preferably, a length of the aerosol-cooling element is less than or equal to about 25 millimetres. Even more preferably, a length of the aerosol-cooling element is less than or equal to about 20 millimetres. In particularly preferred embodiments, a length of the aerosol-cooling element is less than or equal to 19 millimetres. 
     In preferred embodiments, a length of the aerosol cooling element is from about 8 millimetres to about 30 millimetres or from about 8 millimetres to about 25 millimetres or from about 8 millimetres to about 20 millimetres or from about 8 millimetres to about 19 millimetres, more preferably from about 9 millimetres to about 30 millimetres or from about 9 millimetres to about 25 millimetres or from about 9 millimetres to about 20 millimetres or from about 9 millimetres to about 19 millimetres. 
     Preferably, a thickness of a peripheral wall of the hollow tubular segment is at least about 0.2 millimetres. More preferably, a thickness of the peripheral wall of the hollow tubular segment is at least about 0.5 millimetres. Even more preferably a thickness of the peripheral wall of the hollow tubular segment is at least about 1 millimetre. A thickness of the peripheral wall of the hollow tubular segment is preferably less than or equal to 3.5 millimetres. More preferably, a thickness of the peripheral wall of the hollow tubular segment is less than or equal to 3 millimetres. Even more preferably, a thickness of the peripheral wall of the hollow tubular segment is less than or equal to about 2.5 millimetres. 
     In some embodiments, a thickness of a peripheral wall of the hollow tubular segment is from about 0.2 millimetres to about 3.5 millimetres or from about 0.2 millimetres to about 3 millimetres or from about 0.2 millimetres to about 2.5 millimetres. In other embodiments, a thickness of a peripheral wall of the hollow tubular segment is from about 0.5 millimetres to about 3.5 millimetres or from about 0.5 millimetres to about 3 millimetres or from about 0.5 millimetres to about 2.5 millimetres. In further embodiments, a thickness of a peripheral wall of the hollow tubular segment is from about 1 millimetre to about 3.5 millimetres or from about 1 millimetre to about 3 millimetres or from about 1 millimetre to about 2.5 millimetres. 
     In some preferred embodiments, a thickness of the peripheral wall of the hollow tubular segment is from about 0.2 millimetres to about 3.5 millimetres, more preferably from about 0.5 millimetres to about 3 millimetres, even more preferably from about 1 millimetre to about 2.5 millimetres. 
     Preferably, an outer diameter of the hollow tubular segment is at least about 3 millimetres. More preferably, an outer diameter of the hollow tubular segment is at least about 4 millimetres. Even more preferably, an outer diameter of the hollow tubular segment is at least about 5 millimetres. An outer diameter of the hollow tubular segment is preferably less than or equal to about 13 millimetres. More preferably, an outer diameter of the hollow tubular segment is less than or equal to about 10 millimetres. Even more preferably, an outer diameter of the hollow tubular segment is less than or equal to about 8 millimetres. 
     In some embodiments, an outer diameter of the hollow tubular segment is from about 3 millimetres to about 13 millimetres or from about 3 millimetres to about 10 millimetres or from about 3 millimetres to about 8 millimetres. In other embodiments, an outer diameter of the hollow tubular segment is from about 4 millimetres to about 13 millimetres or from about 4 millimetres to about 10 millimetres or from about 4 millimetres to about 8 millimetres. In further embodiments, an outer diameter of the hollow tubular segment is from about 5 millimetres to about 13 millimetres or from about 5 millimetres to about 10 millimetres or from about 5 millimetres to about 8 millimetres. 
     In preferred embodiments, an outer diameter of the hollow tubular segment is from about 3 millimetres to about 13 millimetres, more preferably from about 4 millimetres to about 10 millimetres, even more preferably from about 5 millimetres to about 8 millimetres. In some embodiments, an outer diameter of the hollow tubular segment is from about 4 millimetres to about 8 millimetres. 
     Preferably, an inner diameter of the hollow tubular segment is at least about 2 millimetres. More preferably, an inner diameter of the hollow tubular segment is at least about 3 millimetres. Even more preferably, an inner diameter of the hollow tubular segment is at least about 4 millimetres. An inner diameter of the hollow tubular segment is preferably less than or equal to about 10 millimetres. More preferably, an inner diameter of the hollow tubular segment is less than or equal to about 7.5 millimetres. Even more preferably, an inner diameter of the hollow tubular segment is less than or equal to about 6 millimetres. 
     In some embodiments, an inner diameter of the hollow tubular segment is from about 2 millimetres to about 10 millimetres or from about 2 millimetres to about 7.5 millimetres or from about 2 millimetres to about 6 millimetres. In other embodiments, an inner diameter of the hollow tubular segment is from about 3 millimetres to about 10 millimetres or from about 3 millimetres to about 7.5 millimetres or from about 3 millimetres to about 6 millimetres. In further embodiments, an inner diameter of the hollow tubular segment is from about 4 millimetres to about 10 millimetres or from about 4 millimetres to about 7.5 millimetres or from about 4 millimetres to about 6 millimetres. 
     In preferred embodiments, an inner diameter of the hollow tubular segment is from about 2 millimetres to about 10 millimetres, more preferably from about 3 millimetres to about 7.5 millimetres, even more preferably from about 4 millimetres to about 6 millimetres. In some embodiments, an inner diameter of the hollow tubular segment is from about 3 millimetres to about 7.5 millimetres. 
     In some preferred embodiments, the at least one elongated protrusion extends along a radial direction from the peripheral wall towards the central axis of the hollow tubular segment. By extending along a radial direction of the hollow tubular segment of the aerosol-cooling element, the at least one elongated protrusion disturbs and obstructs the incoming flowing aerosol as much as possible in order to encourage turbulence in the flowing aerosol. As discussed above, turbulence assists in the cooling effects provided by the aerosol-cooling element. 
     In some preferred embodiments, a height of the at least one elongated protrusion varies between the upstream position and the downstream position. Such “a height of the at least one elongated protrusion” refers to a perpendicular distance from the interior of the peripheral wall of the hollow tubular segment by which the elongated protrusion extends. In such embodiments, the at least one elongated protrusion may have any profile where the protrusion may extend further into the interior of the hollow tubular segment at certain portions of the protrusion than other portions of the protrusions. 
     In some preferred embodiments, the height of the at least one elongated protrusion decreases between one of the upstream position and the downstream position and the other. 
     In some preferred embodiments, the ratio of the greatest height of the at least one elongated protrusion to the inner diameter of the aerosol-cooling element is at least 0.1. More preferably, the ratio of the greatest height of the at least one elongated protrusion to the inner diameter of the aerosol-cooling element is at least 0.25. Even more preferably, the ratio of the greatest height of the at least one elongated protrusion to the inner diameter of the aerosol-cooling element is at least 0.33 (a third). The term “greatest height” refers to the height of the portion of the at least one elongated protrusion having a height greater than any other portion of the at least one elongated protrusion. 
     In some preferred embodiments, the ratio of the greatest height or me at least one elongated protrusion to the inner diameter of the aerosol-cooling element is less than or equal to 0.75. More preferably, the ratio of the greatest height of the at least one elongated protrusion to the inner diameter of the aerosol-cooling element is less than or equal to 0.6. Even more preferably, the ratio of the greatest height of the at least one elongated protrusion to the inner diameter of the aerosol-cooling element is less than or equal to 0.5. 
     In some preferred embodiments, the ratio of the greatest height of the at least one elongated protrusion to the inner diameter of the aerosol-cooling element is between 0.1 and 0.75. More preferably, the ratio of the greatest height of the at least one elongated protrusion to the inner diameter of the aerosol-cooling element is between 0.25 and 0.6. Even more preferably, the ratio of the greatest height of the at least one elongated protrusion to the inner diameter of the aerosol-cooling element is between 0.33 (a third) and 0.5. 
     The at least one elongated protrusion may have a fin-like profile, a tapered profile, a curved profile or an undulated profile when viewed from the side. 
     In some preferred embodiments, the at least one elongated protrusion comprises (or is) a deflecting fin configured to change a direction of flow of an aerosol flowing from the upstream end to the downstream end of the hollow tubular segment. A “fin” refers to a flattened, thin protruding surface. 
     In preferred embodiments, the at least one elongated protrusion comprises a plurality of deflecting fins. In such preferred embodiments, the plurality of deflecting fins comprises at least two deflecting fins. More preferably, the plurality of deflecting fins comprises at least four deflecting fins. Even more preferably, the plurality of deflecting fins comprises at least six deflecting fins. 
     In some preferred embodiments, the deflecting fin comprises first and second opposing surfaces, wherein an angle formed between a reference plane, the reference plane parallel to the longitudinal axis and bisecting the internal volume of the hollow tubular segment, and the first surface of the deflecting fin at the upstream position is different from an angle formed between the reference plane and the first surface of the deflecting fin at the downstream position. 
     In some preferred embodiments, the deflecting fin is twisted along the length of the hollow tubular segment. The term “twisted” refers to the fact that the profile of the deflecting fin is bent or curled about a reference point or line along the length of the deflecting fin. The deflecting fin may take a helicoidal or spiral form or shape as it extends along the length of the aerosol-cooling element. Such a helicoidal or spiral shape is optimal for imparting turbulence in the flowing aerosol, which in turn enhances the cooling effect provided by the aerosol-cooling element. The term “helicoidal” refers to an element having the profile or shape of a helix or spiral. 
     In some preferred embodiments, the radial position or the circumferential position of the at least one elongated protrusion, or a portion thereof, varies between its upstream position and its downstream position. In such embodiments, the at least one elongated protrusion may not follow a straight line when viewed from above, or below. In such embodiments, the base of the at least one elongated protrusion may trace along the inner surface of the peripheral wall a curved profile, an undulated profile, or any other profile that diverts from being parallel with the longitudinal axis of the hollow tubular segment of the aerosol-cooling element. 
     In some preferred embodiments, a height of the at least one elongated protrusion is less than a radius of the hollow tubular segment. Such a radius of the hollow tubular segment preferably refers to the inner radius of the hollow tubular segment, which is half of the inner diameter of the hollow tubular segment discussed above. 
     In some preferred embodiments, the upstream position is located between the upstream end of the hollow tubular segment and a midpoint of the hollow tubular segment and wherein the downstream position is located between the midpoint of the hollow tubular segment and the downstream end of the hollow tubular segment. The midpoint of the hollow tubular segment refers to the middle of the hollow tubular segment, at a position halfway between the upstream and downstream ends of the hollow tubular segment. 
     In some preferred embodiments, the upstream position is located at a quarter of the length of the aerosol-cooling element away from the upstream end. In some other preferred embodiments, the upstream position is located at a third of the length of the aerosol-cooling element away from the upstream end. In some other preferred embodiments, the upstream position is located at half of the length of the aerosol-cooling element away from the upstream end. 
     In some preferred embodiments, the downstream position is located at a quarter of the length of the aerosol-cooling element away from the downstream end. In some other preferred embodiments, the downstream position is located at a third of the length of the aerosol-cooling element away from the downstream end. In some other preferred embodiments, the downstream position is located at half of the length of the aerosol-cooling element away from the downstream end. 
     In some preferred embodiments, the at least one elongated protrusion extends longitudinally from the upstream end of the hollow tubular segment to the downstream end of the hollow tubular segment. 
     In some preferred embodiments, the length of the at least one elongated protrusion is between about 8 mm and about 30 mm. More preferably, the length of the at least one elongated protrusion is between about 9 mm and about 19 mm. Even more preferably, the at least one elongated protrusion is between about 10 mm and about 15 mm. 
     In some preferred embodiments, the ratio of the length of the at least one elongated protrusion to the length of the aerosol-cooling element is at least 0.25. More preferably, the ratio of the length of the at least one elongated protrusion to the length of the aerosol-cooling element is at least 0.33 (a third). Even more preferably, the ratio of the length or the at least one elongated protrusion to the length of the aerosol-cooling element is at least 0.5. 
     In some preferred embodiments, the ratio of the length of the at least one elongated protrusion to the length of the aerosol-cooling element is less than or equal to 1. More preferably, the ratio of the length of the at least one elongated protrusion to the length of the aerosol-cooling element is less than or equal to 0.75. Even more preferably, the ratio of the length of the at least one elongated protrusion to the length of the aerosol-cooling element is less than or equal to 0.5. 
     In some preferred embodiments, the ratio of the length of the at least one elongated protrusion to the length of the aerosol-cooling element is between 0.25 and 1. More preferably, the ratio of the length of the at least one elongated protrusion to the length of the aerosol-cooling element is between 0.25 and 0.75. 
     In some preferred embodiments, the thickness of the at least one elongated protrusion is between about 0.1 mm and about 1 mm. More preferably, the thickness of the at least one elongated protrusion is between about 0.25 mm and about 0.75 mm. Even more preferably, the thickness of the at least one elongated protrusion is between about 0.4 mm and about 0.6 mm. 
     In some preferred embodiments, the thickness of the at least one elongated protrusion is about 0.1 mm. More preferably, the thickness of the at least one elongated protrusion is about 0.25 mm. Even more preferably, the thickness of the at least one elongated protrusion is about 0.4 mm. In some preferred embodiments, the thickness of the at least one elongated protrusion is about 0.6 mm. More preferably, the thickness of the at least one elongated protrusion is about 0.75 mm. Even more preferably, the thickness of the at least one elongated protrusion is about 1 mm. 
     Preferably, the thickness of the at least one elongated protrusion is less than 20 percent of the length of the at least one elongated protrusion. More preferably, the thickness of the at least one elongated protrusion is less than 10 percent of the length of the at least one elongated protrusion. Even more preferably, the thickness of the at least one elongated protrusion is less than 5 percent of the length of the at least one elongated protrusion. 
     In some preferred embodiments, the at least one elongated protrusion comprises a plurality of elongated protrusions radially distributed on the peripheral wall. In such preferred embodiments, the plurality of elongated protrusions are evenly (or uniformly) distributed on the peripheral wall in such a manner that the elongated protrusions are equally spaced amongst each other. 
     In some preferred embodiments, the at least one elongated protrusion comprises a plurality of elongated protrusions. Preferably, the plurality of elongated protrusions comprises at least two elongated protrusions. More preferably, the plurality of elongated protrusions comprises at least four elongated protrusions. Even more preferably, the plurality of elongated protrusions comprises at least six elongated protrusions. 
     In some preferred embodiments, the at least one elongated protrusion comprises a plurality of elongated protrusions axially distributed at a same radial position or circumferential position on the peripheral wall. 
     In some preferred embodiments, the plurality of elongated protrusions are evenly (or uniformly) distributed on the peripheral wall. This means that the plurality of elongated protrusions are evenly (or uniformly) spaced on the peripheral wall. In other embodiments, the plurality of elongated protrusions are spaced from each other by varying distances. 
     In some preferred embodiments, the elongated protrusions substantially have the same shape as each other. 
     The present invention relates to an aerosol-generating article for producing an aerosol upon heating. The aerosol-generating article comprises a rod of aerosol-generating substrate. The aerosol-generating article may comprise a first aerosol-cooling element according to the first aspect of the present disclosure, as described above, positioned downstream of the rod of aerosol-generating substrate. 
     According to a second aspect of the present disclosure, there is provided an aerosol-generating article for producing an aerosol upon heating. The aerosol-generating article comprises a rod of aerosol-generating substrate. The aerosol-generating article comprises a first aerosol-cooling element according to the first aspect of the disclosure, as described above, positioned downstream of the rod of aerosol-generating substrate. 
     In some embodiments, the aerosol-generating article may further comprise a hollow tubular support element positioned immediately downstream of the rod of aerosol-generating substrate. 
     In some embodiments, the aerosol-generating article may further comprise a second aerosol-cooling element downstream of the hollow tubular support element, wherein the first aerosol-cooling element is positioned downstream of the second aerosol-cooling element and extends all the way to a downstream end of the aerosol-generating article. 
     In preferred embodiments, the cavity defined by the first aerosol-cooling element defines a mouth-end cavity at the downstream end of the aerosol-generating article. 
     As described briefly above, the aerosol-generating article may comprise an additional component between the hollow tubular support element and the aerosol-cooling element, In some embodiments, the additional component may be a further aerosol-cooling element (also referred herein as a ‘secondary’ or ‘second’ aerosol-cooling element) adapted to initiate cooling of the gaseous flow incoming from the aerosol-generating substrate so as to facilitate condensation of the compounds released from the substrate such that they condense to form the aerosol. In some embodiments, the secondary aerosol-cooling element may be in the form of a gathered, optionally crimped sheet of a polymeric material, such as polylactic acid (PLA), that defines a plurality of longitudinally extending channels. In practice, a sheet of PLA may be ‘crimped’ to form substantially parallel ridges or corrugations. Then, the crimped PLA sneer may be gathered, convoluted, pleated or folded, or otherwise compressed or constricted substantially transversely to the longitudinal axis such that the substantially parallel ridges or corrugations extend in the longitudinal direction. Without wishing to be bound by theory, one such gathered, crimped sheet of polymeric material may act substantially as a heat exchanger. 
     Preferably, a length of the further aerosol-cooling element is at least about 4 millimetres. More preferably, a length of the further aerosol-cooling element is at least about 6 millimetres. Even more preferably, a length of the further aerosol-cooling element is at least about 9 millimetres. A length of the further aerosol-cooling element is preferably less than or equal to about 25 millimetres. More preferably, a length of the further aerosol-cooling element is preferably less than or equal to about 20 millimetres. Even more preferably, length of the further aerosol-cooling element is preferably less than or equal to about 15 millimetres. 
     In some embodiments, a length of the further aerosol-cooling element is from about 4 millimetres to about 25 millimetres or from about 4 millimetres to about 20 millimetres or from about 4 millimetres to about 15 millimetres. In other embodiments, a length of the further aerosol-cooling element is from about 6 millimetres to about 25 millimetres or from about 6 millimetres to about 20 millimetres or from about 6 millimetres to about 15 millimetres. In further embodiments, a length of the further aerosol-cooling element is from about 9 millimetres to about 25 millimetres or from about 9 millimetres to about 20 millimetres or from about 9 millimetres to about 15 millimetres. 
     In some preferred embodiments, a length of the further aerosol-cooling element is from about 4 millimetres to about 25 millimetres, more preferably from about 6 millimetres to about 20 millimetres, from about 9 millimetres to about 15 millimetres. 
     As briefly described above, an aerosol generating article in accordance with the present invention incorporates a rod of aerosol-generating substrate and a hollow tubular support element positioned immediately downstream of the rod of aerosol-generating substrate. Further, the aerosol-generating article of the invention may comprise an aerosol-cooling element downstream of the hollow tubular support element. 
     In contrast with existing aerosol-generating articles, in articles in accordance with the present invention the aerosol-cooling element may extend all the way to a downstream end of the aerosol-generating article. In other words, the aerosol-cooling element may define the mouth-end portion of the article and, during use, may be drawn on by a consumer. 
     An overall length of the aerosol-generating article is preferably at least about 35 millimetres. More preferably, an overall length of the aerosol-generating article is at least about 40 millimetres. Even more preferably, an overall length of the aerosol-generating article is at least about 45 millimetres. In addition, or as an alternative, an overall length of the aerosol-generating article is preferably less than or equal to about 100 millimetres. More preferably, an overall length of the aerosol-generating article is less than or equal to about 80 millimetres. Even more preferably, an overall length of the aerosol-generating article is less than or equal to about 75 millimetres. Most preferably, an overall length of the aerosol-generating article is less than or equal to about 70 millimetres. 
     In some embodiments, an overall length of the aerosol-generating article is from about 35 millimetres to about 100 millimetres or from about 35 millimetres to about 80 millimetres or from about 35 millimetres to about 75 millimetres or from about 35 millimetres to about 70 millimetres. In other embodiments, an overall length of the aerosol-generating article is from about 40 millimetres to about 100 millimetres or from about 40 millimetres to about 80 millimetres or from about 40 millimetres to about 75 millimetres or from about 40 millimetres to about 70 millimetres. In further embodiments, an overall length of the aerosol-generating article is from about 45 millimetres to about 100 millimetres or from about 45 millimetres to about 80 millimetres or from about 45 millimetres to about 75 millimetres or from about 45 millimetres to about 70 millimetres. 
     In particularly preferred embodiments, an overall length of the aerosol-generating article is from about 35 millimetres to about 80 millimetres, more preferably from about 40 millimetres to about 75 millimetres, even more preferably from about 45 millimetres to about 70 millimetres. 
     Aerosol generating articles in accordance with the present invention comprise an aerosol generating substrate, which may be provided in the form of a rod circumscribed by a wrapper. 
     The rod of aerosol generating substrate preferably has an external diameter that is approximately equal to the external diameter of the aerosol generating article. 
     Preferably, the rod of aerosol generating substrate has an external diameter of at least 5 millimetres. The rod of aerosol generating substrate may have an external diameter of between about 5 millimetres and about 12 millimetres, for example of between about 5 millimetres and about 10 millimetres or of between about 5 millimetres and about 8 millimetres or of between about 6 millimetres and about 12 millimetres or of between about 6 millimetres and 10 millimetres or of between about 6 millimetres and about 8 millimetres. In a preferred embodiment, the rod of aerosol generating substrate has an external diameter of 7.2 millimetres. 
     The rod of aerosol generating substrate may have a length of between about 5 millimetres and about 100 mm. Preferably, the rod of aerosol generating substrate has a length of at least about 5 millimetres, more preferably at least about 7 millimetres. In addition, or as an alternative, the rod of aerosol generating substrate preferably has a length of less than about 100 millimetres, more preferably less than about 80 millimetres, even more preferably less than about 65 millimetres, most preferably less than or equal to about 50 millimetres. In particularly preferred embodiments, the rod of aerosol generating substrate has a length of less than or equal to about 35 millimetres, more preferably less than or equal to 25 millimetres, even more preferably less than or equal to about 20 millimetres. In one embodiment, the rod of aerosol generating substrate may have a length of about 10 millimetres. In a preferred embodiment, the rod or aerosol generating substrate has a length of about 12 millimetres. 
     In some embodiments, the rod of aerosol generating substrate has a length of from about 5 millimetres to about 80 millimetres or from about 5 millimetres to about 65 millimetres or from about 5 millimetres to about 50 millimetres. In other embodiments, the rod of aerosol generating substrate has a length of from about 7 millimetres to about 100 millimetres or from about 7 millimetres to about 80 millimetres or from about 7 millimetres to about 65 millimetres or from about 7 millimetres to about 50 millimetres. In further embodiments, the rod of aerosol generating substrate has a length of from about 10 millimetres to about 100 millimetres or from about 10 millimetres to about 80 millimetres or from about 10 millimetres to about 65 millimetres or from about 10 millimetres to about 50 millimetres. 
     Preferably, the rod of aerosol generating substrate has a substantially uniform cross-section along the length of the rod. Particularly preferably, the rod of aerosol generating substrate has a substantially circular cross-section. 
     In preferred embodiments, the aerosol-generating substrate comprises one or more gathered sheets of homogenised tobacco material. Preferably the one or more sheets of homogenised tobacco material are textured. As used herein, the term ‘textured sheet’ denotes a sheet that has been crimped, embossed, debossed, perforated or otherwise deformed. Textured sheets of homogenised tobacco material for use in the invention may comprise a plurality of spaced-apart indentations, protrusions, perforations or a combination thereof. According to a particularly preferred embodiment of the invention, the rod of aerosol-generating substrate comprises a gathered crimped sheet of homogenised tobacco material circumscribed by a wrapper. 
     As used herein, the term ‘crimped sheet’ is intended to be synonymous with the term ‘creped sheet’ and denotes a sheet having a plurality of substantially parallel ridges or corrugations. Preferably, the crimped sheet of homogenised tobacco material has a plurality of ridges or corrugations substantially parallel to the cylindrical axis of the rod according to the invention. This advantageously facilitates gathering of the crimped sheet of homogenised tobacco material to form the rod. However, it will be appreciated that crimped sheets of homogenised tobacco material for use in the invention may alternatively or in addition have a plurality of substantially parallel ridges or corrugations disposed at an acute or obtuse angle to the cylindrical axis of the rod. In certain embodiments, sheets of homogenised tobacco material for use in the rod of the article of the invention may be substantially evenly textured over substantially their entire surface. For example, crimped sheets of homogenised tobacco material for use in the manufacture of a rod for use in an aerosol-generating article in accordance with the invention may comprise a plurality of substantially parallel ridges or corrugations that are substantially evenly spaced-apart across the width of the sheet. 
     Sheets or webs of homogenised tobacco material for use in the invention may have a tobacco content of at least about 40 percent by weight on a dry weight basis, more preferably of at least about 60 percent by weight on a dry weight basis, more preferably or at least about 70 percent by weight on a dry basis and most preferably at least about 90 percent by weight on a dry weight basis. 
     Sheets or webs of homogenised tobacco material for use in the aerosol-generating substrate may comprise one or more intrinsic binders that is tobacco endogenous binders, one or more extrinsic binders, that is tobacco exogenous binders, or a combination thereof to help agglomerate the particulate tobacco. Alternatively, or in addition, sheets of homogenised tobacco material for use in the aerosol-generating substrate may comprise other additives including, but not limited to, tobacco and non-tobacco fibres, aerosol-formers, humectants, plasticisers, flavourants, fillers, aqueous and non-aqueous solvents and combinations thereof. 
     Suitable extrinsic binders for inclusion in sheets or webs of homogenised tobacco material for use in the aerosol-generating substrate are known in the art and include, but are not limited to: gums such as, for example, guar gum, xanthan gum, arabic gum and locust bean gum; cellulosic binders such as, for example, hydroxypropyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose and ethyl cellulose; polysaccharides such as, for example, starches, organic acids, such as alginic acid, conjugate base salts of organic acids, such as sodium-alginate, agar and pectins; and combinations thereof. 
     Suitable non-tobacco fibres for inclusion in sheets or webs of homogenised tobacco material for use in the aerosol-generating substrate are known in the art and include, but are not limited to: cellulose fibres; soft-wood fibres; hard-wood fibres; jute fibres and combinations thereof. Prior to inclusion in sheets of homogenised tobacco material for use in the aerosol-generating substrate, non-tobacco fibres may be treated by suitable processes known in the art including, but not limited to: mechanical pulping; refining; chemical pulping; bleaching; sulphate pulping; and combinations thereof. 
     Preferably, the sheets or webs of homogenised tobacco material comprise an aerosol former. As used herein, the term “aerosol former” describes any suitable known compound or mixture of compounds that, in use, facilitates formation of an aerosol and that is substantially resistant to thermal degradation at the operating temperature of the aerosol-generating article. 
     Suitable aerosol-formers are known in the art and include, but are not limited to: polyhydric alcohols, such as propylene glycol, triethylene glycol, 1,3-butanediol and glycerine; esters of polyhydric alcohols, such as glycerol mono-, di- or triacetate; and aliphatic esters of mono-, di- or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. 
     Preferred aerosol formers are polyhydric alcohols or mixtures thereof, such as propylene glycol, triethylene glycol, 1,3-butanediol and, most preferred, glycerine. 
     The sheets or webs of homogenised tobacco material may comprise a single aerosol former. Alternatively, the sheets or webs of homogenised tobacco material may comprise a combination of two or more aerosol formers. 
     The sheets or webs of homogenised tobacco material have an aerosol former content of greater than 10 percent on a dry weight basis. Preferably, the sheets or webs of homogenised tobacco material have an aerosol former content of greater than 12 percent on a dry weight basis. More preferably, the sheets or webs of homogenised tobacco material have an aerosol former content of greater than 14 percent on a dry weight basis. Even more preferably the sheets or webs of homogenised tobacco material have an aerosol former content of greater than 16 percent on a dry weight basis. 
     The sheets of homogenised tobacco material may have an aerosol former content of between approximately 10 percent and approximately 30 percent on a dry weight basis. Preferably, the sheets or webs of homogenised tobacco material have an aerosol former content of less than 25 percent on a dry weight basis. 
     In a preferred embodiment, the sheets of homogenised tobacco material have an aerosol former content of approximately 20 percent on a dry weight basis. 
     Sheets or webs of homogenised tobacco for use in the aerosol-generating article of the present invention may be made by methods known in the art, for example the methods disclosed in International patent application WO-A-2012/164009 A2. In a preferred embodiment, sheets of homogenised tobacco material for use in the aerosol-generating article are formed from a slurry comprising particulate tobacco, guar gum, cellulose fibres and glycerine by a casting process. 
     Alternative arrangements of homogenised tobacco material in a rod for use in an aerosol-generating article will be known to the skilled person and may include a plurality of stacked sheets of homogenised tobacco material, a plurality of elongate tubular elements formed by winding strips of homogenised tobacco material about their longitudinal axes, etc. 
     As a further alternative, the rod of aerosol-generating substrate may comprise a non-tobacco-based, nicotine-bearing material, such as a sheet of sorbent non-tobacco material loaded with nicotine (for example, in the form of a nicotine salt) and an aerosol-former. Examples of such rods are described in the international application WO-A-2015/052652. In addition, or as an alternative, the rod of aerosol-generating substrate may comprise a non-tobacco plant material, such as an aromatic non-tobacco plant material. 
     In the rod of aerosol-generating substrate of articles in accordance with the invention, the aerosol-generating substrate is preferably circumscribed by a wrapper. The wrapper may be formed of a porous or non-porous sheet material. The wrapper may be formed of any suitable material or combination of materials. Preferably, the wrapper is a paper wrapper. 
     As discussed above, a tubular support element may be provided at a location downstream of the rod of aerosol-generating substrate. The tubular support element comprises a cylindrical peripheral wall and defines an airflow conduit extending longitudinally from an upstream end or the tubular support element to a downstream end of the tubular support element. Thus, the tubular support element establishes a fluid communication between the rod of aerosol-generating substrate and the one or more components of the article located further downstream. 
     In more detail, the tubular support element is longitudinally aligned with the rod, and is arranged immediately downstream of the rod. In the context of the present invention, the expression “immediately downstream of the rod” means that the tubular support element and the rod are in contact with one another or very close to one another, such that when the article is received for use in an aerosol-generating device adapted to heat the aerosol-generating substrate (for example, one including a heating element that is inserted into the rod) the tubular support element effectively provides support for the rod, with little to no deformation of the aerosol-generating article, or with little to no displacement of the rod, or both. Thus, in practice, as used herein with reference to the present invention, the expression “immediately downstream of the rod” is used to indicate that a minimum longitudinal distance between a downstream end surface of the rod and an upstream end surface of the peripheral wall of the tubular support element is less than 1 millimetre, preferably less than 0.5 millimetres, even more preferably less than 0.25 millimetres. In particularly preferred embodiments, an upstream end surface of the peripheral wall of the tubular support element directly contacts the downstream end surface of the rod of aerosol-generating substrate. 
     Thus, the tubular support element may effectively maintain the rod of aerosol-generating substrate at a predetermined distance from a downstream end of the aerosol-generating article. In addition, the tubular support element imparts structural strength to the aerosol-generating article, such that it can easily be handled by the consumer and that it may conveniently be inserted into an aerosol-generating device for use. 
     The tubular support element may be made of a porous material or of an air-impervious material. Suitable examples of porous material include, but are not limited to, cellulose acetate as well as a number of other porous polymeric materials, which will be known to the skilled person. Suitable examples of air-impervious materials include, but are not limited to, non-porous polymeric materials, with particular preference for bioplastics. 
     In a preferred embodiment, the tubular support element is a hollow tube of cellulose acetate. 
     During use, a thermal gradient is established along the airflow conduit of the tubular support element. In practice, a temperature differential is provided, such that a temperature of the volatilised aerosol components entering the tubular support element at the downstream end of the rod of aerosol-generating substrate is generally greater than a temperature of the volatilised aerosol components exiting the tubular support element at the downstream end of the tubular support element. However, this is generally not enough to sufficiently cool the volatilised aerosol components. 
     A thickness of the cylindrical peripheral wall of the hollow tubular support element is preferably less than or equal to 2 millimetres. More preferably, a thickness of the cylindrical peripheral wall is less than or equal to 1.5 millimetres. Even more preferably, a thickness of the cylindrical peripheral walls is less than or equal to 1 millimetre. 
     A thickness of the cylindrical peripheral wall of the hollow tubular support element is at least 0.2 millimetres. More preferably, a thickness of the cylindrical peripheral wall is at least 0.4 millimetres. Even more preferably, a thickness of the cylindrical peripheral wall is at least 0.6 millimetres. 
     In some embodiments, a thickness of the cylindrical peripheral wall of the hollow tubular support element is preferably from about 0.2 millimetres to about 2 millimetres, more preferably from about 0.4 millimetres to about 1.5 millimetres, even more preferably from about 0.6 millimetres to about 1 millimetre. 
     Thus, at the upstream end, the cylindrical peripheral wall presents an end surface adapted to abut a peripheral portion of the rod of aerosol-generating substrate. In some embodiments, the upstream end surface of the peripheral wall may have a substantially flat profile. Thus, it may contact substantially in its entirety the downstream end surface of the rod. In alternative embodiments, the upstream end surface of the peripheral wall has a non-flat profile, for example a slanted profile or a curved profile, such that the peripheral wall contacts the rod only at its outermost peripheral edge, whereas some spacing is provided between the downstream end surface of the rod and the end surface of the peripheral wall at the inner periphery of the peripheral wall. 
     Preferably, a length of the hollow tubular support element is at least about 10 millimetres. More preferably, a length of the hollow tubular support element is at least about 15 millimetres. Even more preferably, a length of the hollow tubular support element is at least about 20 millimetres. 
     A length of the hollow tubular support element is preferably less than or equal to about 60 millimetres. More preferably, a length of the hollow tubular support element is less than or equal to about 50 millimetres. Even more preferably, a length of the hollow tubular support element is less than or equal to about 40 millimetres. 
     In some embodiments, a length of the hollow tubular support element is from about 10 millimetres to about 60 millimetres or from about 10 millimetres to about 50 millimetres or from about 10 millimetres to about 40 millimetres. In other embodiments, a length of the hollow tubular support element is from about 15 millimetres to about 60 millimetres or from about 15 millimetres to about 50 millimetres or from about 15 millimetres to about 40 millimetres. In further embodiments, a length of the hollow tubular support element is from about 20 millimetres to about 60 millimetres or from about 20 millimetres to about 50 millimetres or from about 20 millimetres to about 40 millimetres. 
     In some preferred embodiments, a length of the hollow tubular support element is from about 10 millimetres to about 60 millimetres, more preferably from about 15 millimetres to about 50, even more preferably from about 20 millimetres to about 40 millimetres. 
     As described briefly above, an aerosol-generating article in accordance with the present invention comprises an aerosol-cooling element longitudinally aligned with the rod and the hollow tubular support element and positioned downstream of the hollow tubular support element. 
     In some embodiments, the aerosol-cooling element is positioned immediately downstream of the hollow tubular support element. As used herein with reference to the invention, the expression “immediately downstream of the hollow tubular support element” means that the aerosol-cooling element are in contact with one another or very close to one another. In practice, the expression “immediately downstream of the hollow tubular support element” is used to indicate that minimum longitudinal distance between a downstream end surface of the hollow tubular support element and an upstream end surface of the peripheral wall of the aerosol-cooling element is less than 1 millimetre, preferably less than 0.5 millimetres, even more preferably less than 0.25 millimetres. In particularly preferred embodiments, an upstream end surface of the aerosol-cooling element directly contacts the downstream end surface of the peripheral wall of the hollow tubular support element. 
     In other embodiments, the aerosol-generating article may comprise one or more additional components between the hollow tubular support element and the aerosol-cooling element. 
     By way of example, the aerosol-generating article may comprise a plug of filtration material capable of removing particulate components, gaseous components or a combination thereof. Suitable filtration materials are known in the art and include, but are not limited to: fibrous filtration materials such as, for example, cellulose acetate tow, viscose fibres, polyhydroxyalkanoates (PHA) fibres, polylactic acid (PLA) fibres and paper; adsorbents such as, for example, activated alumina, zeolites, molecular sieves and silica gel; and combinations thereof. In addition, the plug of filtration material may further comprise one or more aerosol-modifying agent. Suitable aerosol-modifying agents are known in the art and include, but are not limited to, flavourants such as, for example, menthol. A length of the plug of filtration material may be from about 4 millimetres to about 25 millimetres. Preferably, a length of the plug of filtration material is at least about 6 millimetres, more preferably at least about 8 millimetres. A length of the plug of filtration material is preferably less than or equal to about 25 millimetres, more preferably less than or equal to about 20 millimetres, even more preferably less than or equal to about 15 millimetres. In particularly preferred embodiments, a length of the plug of filtration material is less than or equal to about 10 millimetres. In an exemplary embodiment, a length of the plug of filtration material is about 5 millimetres. In another exemplary embodiment, a length of the mouthpiece is about 7 millimetres. 
     Components of an aerosol-generating article in accordance with the invention may be individually circumscribed by such a wrapper. The wrapper may be formed of a porous or non-porous sheet material. The wrapper may be formed of any suitable material or combination of materials. Preferably, the wrapper is a paper wrapper. Two or more components may, however, also be circumscribed by a same wrapper. Further, the rod of aerosol-generating substrate and the other components are typically assembled within a single wrapper. For example, in an embodiment, the aerosol-generating article comprises, in linear sequential arrangement, a rod of aerosol-generating substrate, a tubular support element, an aerosol-cooling element as described above, and an outer wrapper circumscribing the rod, the support element and the aerosol-cooling element. In another embodiment, the aerosol-generating article comprises, in linear sequential arrangement, a rod of aerosol-generating substrate, a tubular support element, a secondary aerosol-cooling element, an aerosol-cooling element as described above, and an outer wrapper circumscribing the rod, the support element and the aerosol-cooling elements. 
     In some embodiments, the aerosol-generating articles comprises a ventilation zone at a location along the aerosol-cooling element. Preferably, the aerosol-generating article comprises a ventilation zone at a location along the length of the aerosol-cooling element. 
     In some embodiments, the ventilation zone is provided at a location along the cavity of the hollow tubular segment. Thus, a fluid communication is established between the outer environment and the cavity such that, when the consumer draws upon the aerosol-generating article, some environment air is drawn into the cavity through ventilation holes formed through the peripheral wall of the hollow tubular segment. This is advantageous in that by mixing environment air with the incoming flow of aerosol may lower the temperature of the aerosol and favour condensation or growth of aerosol particles or both. At the same, the flow of environment air through the peripheral wall of the aerosol-cooling element may further facilitate maintaining the temperature of the peripheral wall below the desired threshold value. 
     In particularly preferred embodiments, the ventilation zone comprises a plurality of holes extending through the peripheral wall, such that slanted airflow conduits are formed that connect the outer environment with the cavity of the hollow tubular segment. This may particularly facilitate keeping the temperature of the peripheral wall of the aerosol-cooling element below the desired threshold value. 
     Aerosol-generating articles as described above may be used in an electrically operated aerosol generating device as part of an aerosol-generating system in accordance with another aspect of the present disclosure, or invention. One such aerosol-generating system comprises an aerosol generating article as described above and an electrically operated aerosol generating device comprising a heating element and an elongate heating chamber configured to receive the aerosol generating article so that the rod of aerosol-generating substrate is heated in the heating chamber. Preferably, the heating element comprises a heater blade or a heater pin adapted to be inserted into the rod of aerosol-generating substrate when the aerosol generating article is received into the heating chamber. 
    
    
     
       The invention will now be further described with reference to the figures in which: 
         FIG. 1  shows a front perspective view of an aerosol-cooling element in accordance with the invention; 
         FIG. 2  shows a schematic side sectional view of an aerosol-cooling element in accordance with the invention; 
         FIG. 3  shows a schematic cross-sectional view of the aerosol-cooling element of  FIG. 2  taken along the plane T-T, which is located at the middle of the aerosol-cooling element; 
         FIG. 4  shows a side sectional view of an aerosol-generating article including an aerosol-cooling element in accordance the invention; and 
         FIG. 5  shows a schematic side sectional view of an aerosol-generating system comprising an electrically operated aerosol-generating device and the aerosol-generating article shown in  FIG. 4 . 
     
    
    
     An aerosol-cooling element  16  shown in  FIG. 1  comprises a hollow tubular segment  8  comprising a peripheral wall  24  having a thickness of about 0.5 millimetres and defining a cavity  28 . Further, the hollow tubular segment  8  comprises a plurality of elongated protrusions  26  extending from the peripheral wall  24  into the interior of the hollow tubular segment  22 . Each of the elongated protrusions  26  extend from an upstream end of the hollow tubular segment  8  to a downstream end of the hollow tubular segment  8  and into the interior of the hollow tubular segment  23 . 
     As shown in  FIG. 1 , the plurality of elongated protrusions  26  comprises four deflecting fins. The four deflecting fins  26  are evenly radially distributed within the interior of the aerosol-cooling element. This means that the deflecting fins  26  are radially, evenly spaced amongst each other. The deflecting fins  26  twist between the upstream end of the hollow tubular segment  8  and the downstream end of the hollow tubular segment  8 , as shown in  FIG. 2 . As shown in  FIG. 2 , the circumferential positions of the elongated protrusions  26  vary along the length of the aerosol-cooling element. As shown in  FIG. 2 , the circumferential positions of the elongated protrusions at the midpoint of the aerosol-cooling element are different to the circumferential positions of the elongated protrusions at the downstream end of the aerosol-cooling element, as indicated by the cross-sections of the deflecting fins in dotted lines. 
     The aerosol-generating article  10  shown in  FIG. 4  comprises a rod of aerosol-generating substrate  12 , a tubular support element  14 , and an aerosol-cooling element  16  in accordance with the first embodiment of the invention. These three elements are arranged sequentially and in coaxial alignment and are circumscribed by a wrapper  18  to form the aerosol-generating article  10 . The aerosol-generating article  10  has a mouth end or downstream end  20 , and an upstream end  22  located at the opposite end of the article to the mouth end  20 . The aerosol-generating article  10  shown in  FIG. 4  is particularly suitable for use with an electrically operated aerosol-generating device comprising a heater for heating the rod of aerosol-generating substrate. 
     The rod of aerosol-generating substrate  12  has a length of approximately 12 millimetres and a diameter of approximately 7 millimetres. The rod  12  is cylindrical in shape and has a substantially circular cross-section. 
     The tubular support element  14  is provided as a hollow tube of cellulose acetate. It has a length of approximately 8 millimetres. An external diameter of the tubular support element  14  is approximately 7 millimetres. A peripheral wall of the tubular support element  14  has a thickness of about 1.85 millimetres. 
       FIG. 5  shows a portion of an electrically operated aerosol-generating system  200  that utilises a heater blade  210  to heat the rod of aerosol-generating substrate  12  of the aerosol-generating article  10  shown in  FIG. 4 . The heater blade  210  is mounted within an aerosol-generating article chamber within a housing of an electrically operated aerosol-generating device  212 . The aerosol-generating device  212  defines a plurality of air holes  214  for allowing air to flow to the aerosol-generating article  10 , as illustrated by the arrows in  FIG. 5 . The aerosol-generating device  212  comprises a power supply and electronics, which are not shown in  FIG. 5 . 
     The aerosol-generating article  10  shown in  FIG. 4  is designed to engage with the aerosol-generating device  212  shown in  FIG. 5  in order to be consumed. 
     The user inserts the aerosol-generating article  10  into the aerosol-generating device  212  so that the heater blade  210  is inserted into the rod of aerosol-generating substrate  12 . The aerosol-cooling element  16  projects outwards from the mouth end of the device  212 . Once the aerosol-generating article  10  is engaged with the aerosol-generating device  212 , the user draws on the aerosol-cooling element  16  defining a mouthpiece of the aerosol-generating article  10  and the rod of aerosol-generating substrate  12  is heated by the heater blade  210  to a temperature sufficient to generate an aerosol from the rod of aerosol-generating substrate  12 . The aerosol is drawn through the aerosol-cooling element  16  and into the user&#39;s mouth. 
     It will be appreciated that the aerosol-generating article  10  shown in  FIG. 4  may also be suitable for use with other types of aerosol-generating devices.