Abstract:
An aerosol inhalator of the invention has an inner tube ( 22 ) forming part of a suction path, a capillary tube ( 40 ) extending within the inner tube ( 22 ) and configured to discharge a solution therefrom in conjunction with a user&#39;s inhalation, and a heater ( 56 ) extending in a direction perpendicular to the axis of the inner tube ( 22 ) so as to traverse the inner tube ( 22 ) and configured to receive the solution discharged from the capillary tube ( 40 ), wherein the heater ( 56 ) atomizes the received solution by heating to generate, inside the inner tube ( 22 ), an aerosol to be inhaled by the user.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an aerosol inhalator capable of generating an aerosol as a user inhales, to supply the user with the generated aerosol. 
       BACKGROUND ART 
       [0002]    This type of aerosol inhalator is disclosed, for example, in Patent Documents 1 to 4 identified below. 
         [0003]    The aerosol inhalator disclosed in Patent Document 1 includes a suction pipe provided with a mouthpiece, a solution supply source incorporated into the suction pipe and storing a solution to be aerosolized, a dispenser capable of supplying a fixed amount of the solution at a time from the solution supply source to a dispensing position within the suction pipe, and an electric heater for heating and thereby atomizing the solution supplied to the dispensing position, to generate an aerosol inside the suction pipe. 
         [0004]    The aerosol inhalator disclosed in Patent Document 2 includes an electric heater and a high-frequency generator, in order to aerosolize a liquid fed by a pump. 
         [0005]    The aerosol inhalator disclosed in Patent Document 3 includes an ink jet unit for aerosolizing a liquid. 
         [0006]    The aerosol inhalator disclosed in Patent Document 4 includes a liquid supply path utilizing capillarity, and an electric heater arranged at the outlet of the liquid supply path. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Document 1: PCT International Publication No. WO 2008/105918 A1 
         Patent Document 2: PCT International Application-Japanese Translation No. JP 2006-524494 A 
         Patent Document 3: PCT International Application-Japanese Domestic Re-publication No. WO 97/48293 
         Patent Document 4: Unexamined Japanese Patent Publication No. JP H11(1999)-89551 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0011]    The aerosol inhalator of Patent Document 1 requires that the user manually operate the dispenser before inhaling through the mouthpiece, or that the dispenser automatically operate simultaneously with the user&#39;s inhalation. The use of the dispenser directly leads to increase in the size of the aerosol inhalator, and also the need for manual operation of the dispenser is a hindrance to the user&#39;s easy inhalation of the aerosol. 
         [0012]    Automatic operation of the dispenser enables the user to inhale the aerosol with ease, but in this case, the dispenser not only requires a complicated structure but consumes electrical energy for the automatic operation. Consequently, a high-capacity power supply is indispensable for the dispenser and the electric heater, resulting in further increase in the size of the aerosol inhalator. 
         [0013]    In the case of the aerosol inhalators of Patent Documents 2 and 3, it is difficult to reduce the sizes of the aerosol inhalators because of their complicated structures, like the aerosol inhalator of Patent Document 1. The aerosol inhalator of Patent Document 4, on the other hand, has a simple structure, compared with the aerosol inhalators of Patent Documents 1 to 3. However, like the aerosol inhalators of Patent Documents 1 to 3, the liquid is aerosolized not by causing the liquid to collide directly with the electric heater, and thus reliable aerosolization is not guaranteed. 
         [0014]    An object of the present invention is to provide a small-sized aerosol inhalator which enables a user to inhale an aerosol with ease and also guarantees reliable aerosolization of liquid. 
       Solution to Problem 
       [0015]    The above object is achieved by an aerosol inhalator of the present invention, which comprises: 
         [0016]    a suction path connecting an atmosphere-exposed opening and a mouthpiece to each other and permitting air to flow from the atmosphere-exposed opening toward the mouthpiece; 
         [0017]    a solution supply device configured to supply a solution from which an aerosol is to be generated, the solution supply device including 
         [0018]    a solution supply source storing the solution, and 
         [0019]    a capillary tube connected to the solution supply source and having a discharge end located in the suction path and opening in a direction toward the mouthpiece, the capillary tube guiding the solution from the solution supply source to the discharge end and, when the flow of air is produced within the suction path, allowing the solution to be discharged from the discharge end; and 
         [0020]    a heater device configured to receive the solution discharged from the discharge end and atomize the received solution by heating, the heater device including 
         [0021]    a power supply, and 
         [0022]    an electric heater arranged immediately downstream of the discharge end and facing the discharge end at a predetermined distance from the discharge end while permitting the flow of air, the heater being configured to generate heat when applied with a voltage from the power supply. 
         [0023]    With the above aerosol inhalator, when the user inhales through the mouthpiece, the solution is discharged from the discharge end of the capillary tube. The discharged solution is received on the outer surface of the heater and at the same time is atomized in its entirety by heat generated by the heater, so that an aerosol is generated inside the suction path. The user can therefore inhale the aerosol through the mouthpiece. 
         [0024]    Specifically, the heater extends in a direction perpendicular to an axis of the suction path and traverses the suction path. Preferably, the capillary tube extends coaxially with the suction path. 
       Advantageous Effects of Invention 
       [0025]    In the aerosol inhalator of the present invention, the solution is discharged from the discharge end of the capillary tube in conjunction with the user&#39;s inhalation, and the discharged solution is received on the outer surface of the heater, so that a total amount of the discharged solution can be atomized on the outer surface of the heater, generating an aerosol inside the suction path. Accordingly, the user can easily and effectively inhale the aerosol. 
         [0026]    Details and other advantages of the aerosol inhalator of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0027]      FIG. 1  is a schematic longitudinal sectional view of an aerosol inhalator according to one embodiment of the present invention. 
           [0028]      FIG. 2  illustrates a specific example of a liquid tank appearing in  FIG. 1 . 
           [0029]      FIG. 3  is an enlarged sectional view of a heater appearing in  FIG. 1 . 
           [0030]      FIG. 4  illustrates the heater in  FIG. 1  along with a power feed circuit. 
           [0031]      FIG. 5  schematically illustrates part of the aerosol inhalator in a state before an aerosol is generated. 
           [0032]      FIG. 6  schematically illustrates part of the aerosol inhalator in a state in which an aerosol is being generated, as viewed in a longitudinal section of an inner tube taken along a longitudinal section of the heater. 
           [0033]      FIG. 7  schematically illustrates part of the aerosol inhalator in a state in which an aerosol is being generated, as viewed in a longitudinal section of the inner tube taken along a cross section of the heater. 
           [0034]      FIG. 8  illustrates a malfunction of the aerosol inhalator caused in cases where the distance between a capillary tube and the heater is too long. 
           [0035]      FIG. 9  illustrates a malfunction of the aerosol inhalator caused in cases where the distance between the capillary tube and the heater is too short. 
           [0036]      FIG. 10  schematically illustrates a heating test apparatus for determining an optimum heater. 
           [0037]      FIG. 11  is a graph showing measurement results obtained by the heating test apparatus. 
           [0038]      FIG. 12  illustrates a modification of a sheath element. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0039]    As illustrated in  FIG. 1 , an aerosol inhalator  10  according to one embodiment includes a cylindrical outer tube  12  opening at both ends, and a mouthpiece  14  detachably connected to a proximal end of the outer tube  12 . The outer tube  12  and the mouthpiece  14  are each made of heat-resistant synthetic resin. The outer tube  12  has a lid  16  located at its distal end, and the lid  16  is detachable from the outer tube  12 . 
         [0040]    The outer tube  12  contains a power supply unit  18  as a source of electricity, a liquid tank  20  as a solution supply source, and an inner tube  22 . The power supply unit  18 , the liquid tank  20  and the inner tube  22  are arranged sequentially in the mentioned order from the lid side coaxially with the outer tube  12 . The inner tube  22  communicates with the mouthpiece  14 . 
         [0041]    The power supply unit  18  and the liquid tank  20  are each replaceable, and with the lid  16  detached from the outer tube  12 , the power supply unit  18  and the liquid tank  20  are replaced with new ones. 
         [0042]    The power supply unit  18  includes a cell holder  24  and a commercially available battery cell, for example, an AA size cell  26 , held by the cell holder  24 . The cell  26  has a nominal voltage of 1.5 V and is arranged coaxially with the outer tube  12 . 
         [0043]    The liquid tank  20  is illustrated in detail in  FIG. 2 . 
         [0044]    The liquid tank  20  includes a cylindrical tank casing  28 . The tank casing  28  has a plurality of ribs formed on an outer peripheral surface thereof. The ribs are spaced from each other in a circumferential direction of the tank casing  28  and extend in an axial direction of the tank casing  28  except an end portion of the casing  28  close to the power supply unit  18 . 
         [0045]    The ribs serve to form a plurality of axial passages  27  (see  FIG. 1 ) between the outer surface of the tank casing  28  and an inner surface of the outer tube  12 , and also serve to secure an annular chamber  29  (see  FIG. 1 ) between the aforementioned end portion of the tank casing  28  and the inner surface of the outer tube  12 . The annular chamber  29  is connected to the axial passages  27 . 
         [0046]    A tube coil  30  is contained in the tank casing  28 . The tube coil  30  extends in the axial direction of the outer tube  12  and has opposite open ends. An inlet conduit  32  extends from one end of the tube coil  30  to the outer surface of the tank casing  28  and opens on the outer surface of the tank casing  28  to be connected to the annular chamber  29 . A check valve  34  is arranged in the inlet conduit  32  and opens only in one direction toward the one end of the tube coil  30 . 
         [0047]    An outlet conduit  36  extends from the other end of the tube coil  30  and is connected to a capillary tube  40  through a joint  38 . The capillary tube  40  projects from the tank casing  28  into the aforementioned inner tube  22  and is located coaxially with the inner tube  22 . The projecting end of the capillary tube  40  forms a discharge end  42 , which opens in a direction toward the mouthpiece  14 . Another check valve  44  is arranged in the outlet conduit  36  and opens only in one direction toward the capillary tube  40 . 
         [0048]    An internal flow channel (inlet conduit  32 , tube coil  30  and outlet conduit  36 ) of the liquid tank  22  and the capillary tube  40  are filled with a solution to be aerosolized, and the solution reaches the discharge end  42  of the capillary tube  40 . The solution may contain, for example, propylene glycol, glycerin or the like. 
         [0049]    As is clear from  FIG. 1 , the inner tube  22  extends from the liquid tank  20  toward the mouthpiece  14  and is connected to an absorbent sleeve  48 . The absorbent sleeve  48  is located in alignment with the inner tube  22  and has an inner diameter identical with that of the inner tube  22 . A portion of the outer tube  12  surrounding the inner tube  22  and the absorbent sleeve  48  has a larger thickness than a portion of the outer tube  12  surrounding the power supply unit  18  and the liquid tank  20 . 
         [0050]    Specifically, the inner tube  22  is made of stainless steel or ceramic, for example. On the other hand, the absorbent sleeve  48  is, for example, a paper tube or hollow tubular paper filter capable of absorbing the solution. The absorbent sleeve  48  has a volume sufficient to retain a required absorption amount of the solution. 
         [0051]    As illustrated in  FIG. 1 , the outer tube  12  has a plurality of atmospheric ports  50  formed therein. The atmospheric ports  50  adjoin the liquid tank  20 , for example, and are spaced from each other in the circumferential direction of the outer tube  12 . Each of the atmospheric ports  50  extends from the outer peripheral surface of the outer tube  12  and penetrates through the inner tube  22 . Thus, the atmospheric ports  50  provide atmosphere-exposed openings  52  that open on the outer peripheral surface of the outer tube  12 , and are connected to the annular chamber  29  through the axial passages  27 . 
         [0052]    Accordingly, the atmospheric ports  50  and the inner tube  22  form a suction path connecting the atmosphere-exposed openings  52  to the mouthpiece  14 . Also, the atmospheric ports  50  serve to keep the interior of the annular chamber  29  at atmospheric pressure, and as a consequence, the solution in the liquid tank  20  remains in a state such that the solution is always acted upon by the atmospheric pressure through the open end of the inlet conduit  32 . 
         [0053]    When the user inhales the air in the inner tube  22  through the mouthpiece  14 , a negative pressure is created in the inner tube  22 , so that ambient air is introduced into the inner tube  22  through the atmospheric ports  50 . Such introduction of the ambient air produces, within the suction path, a flow of air toward the mouthpiece  14 . 
         [0054]    The negative pressure created in the inner tube  22  causes the solution to be discharged from the discharge end  42  of the capillary tube  40  into the suction path, namely, into the inner tube  22 , and the amount of the solution discharged is determined by the intensity of the negative pressure. On the other hand, the capillary tube  40  is replenished with the solution from the liquid tank  20  in an amount corresponding to the discharge amount. Since the solution in the liquid tank  20  is always applied with the atmospheric pressure as stated above, the solution in the internal flow channel of the liquid tank  20  moves toward the capillary tube  40  accompanying the replenishment of the solution. 
         [0055]    A cylindrical heater  56  is arranged in the inner tube  22 . The heater  56  is located immediately downstream of the discharge end  42  of the capillary tube  40 , as viewed in the direction of the flow of air produced in the suction path. 
         [0056]    Provided that as shown in  FIG. 3 , the inner diameters of the inner tube  22  and capillary tube  40  are D IT  and D CT , respectively, the outer diameter D O  of the heater  56  is smaller than the inner diameter D IT  of the inner tube  22  and at the same time is larger than the inner diameter D CT  or outer diameter of the capillary tube  40 . 
         [0057]    That is, the outer diameter D O  satisfies the following relationship: 
         [0000]      D IT &gt;D O &gt;D CT   (1)
 
         [0058]    The heater  56  penetrates through the inner tube  22  in a diametrical direction of the tube  22  and has an axis intersecting perpendicularly with the axis of the inner tube  22 . The heater  56  is supported at both ends by the outer tube  12 . 
         [0059]    Considering that the capillary tube  40  is located coaxially with the inner tube  22  as stated above, the discharge end  42  of the capillary tube  40  is hidden by the heater  56  when the heater  56  is viewed from the downstream end of the inner tube  22 . In other words, the cross section of the discharge end  42  can be totally projected onto the outer surface of the heater  56 . 
         [0060]    Further, when the solution is discharged from the discharge end  42  in the aforementioned manner, the discharged solution forms a liquid droplet at the discharge end  42 , and a maximum diameter of the liquid droplet is determined by the inner diameter D CT  of the capillary tube  40 . Provided the maximum diameter of the liquid droplet is D MAX , a gap Z between the discharge end  42  and the heater  56  fulfills the following relationship: 
         [0000]      D MAX &gt;Z&gt;D CT   (2)
 
         [0061]    Thus, when the solution is discharged from the discharge end  42 , the discharged solution is received on the outer surface of the heater  56  without fail. 
         [0062]    Table 1 below shows the relationship observed where the solution is propylene glycol (PG; density: 1.036 g/mm 2 ), among the discharge amount and volume of the solution discharged in the form of a liquid droplet and the diameter of the liquid droplet with respect to the inner diameter D CT  of the capillary tube  40  and the flow rate of intake air flowing through the inner tube  22 . 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Capillary tube 
                   
               
             
          
           
               
                   
                   
                 Cross- 
                   
                   
                   
                   
               
               
                   
                   
                 sectional 
                   
                 Discharge 
                 Discharge 
                 Diam- 
               
               
                 Solu- 
                 D CT   
                 flow area 
                 Intake air 
                 amount 
                 volume 
                 eter 
               
               
                 tion 
                 (mm) 
                 (mm) 
                 flow rate 
                 (mg) 
                 (mm 3 ) 
                 (mm) 
               
               
                   
               
             
          
           
               
                 PG 
                 0.36 
                 0.1 
                 35 ml/2 sec 
                 2.58 
                 2.49 
                 0.84 
               
               
                   
                   
                   
                 55 ml/2 sec 
                 3 
                 2.90 
                 0.88 
               
               
                   
                 0.5 
                 0.2 
                 35 ml/2 sec 
                 5.5 
                 5.31 
                 1.08 
               
               
                   
                   
                   
                 55 ml/2 sec 
                 11 
                 10.62 
                 1.36 
               
               
                   
               
             
          
         
       
     
         [0063]    The liquid tank  20  illustrated in  FIG. 3  has a structure different from that of the liquid tank already explained above. Specifically, the liquid tank  20  in  FIG. 3  has an internal flow channel  30   a  extending in a zigzag, in place of the coil tube  30 . This means that the coil tube  30  is not indispensable to the liquid tank  20 . 
         [0064]    The structure of the heater  56  will now be described in detail. 
         [0065]    The heater  56  includes, for example, a Nichrome wire  58  as a resistance heating element, and a cylindrical sheath element  60  enclosing the Nichrome wire  58 . In this embodiment, as is clear from  FIG. 3 , the Nichrome wire  58  axially penetrates through the sheath element  60  three times and has two ends projecting from the respective opposite ends of the sheath element  60 . 
         [0066]    As illustrated in  FIG. 4 , the Nichrome wire  58  is connected in series with the aforementioned cell  26  via a power feed circuit  63 , and the power feed circuit  63  has a switch  64 . Although not illustrated in  FIG. 1 , the power feed circuit  63  and the switch  64  are arranged on the inner surface of the outer tube  12 , and the outer tube  12  is provided, on its outer surface, with a push button (not shown) for operating the switch  64 . 
         [0067]    The sheath element  60  is made of a ceramic such as alumina or silicon nitride, and constitutes the outer surface of the heater  56 . Further, as is clear from  FIG. 4 , an annular groove  62 , for example, is formed in part of the outer surface of the sheath element  60 , and a ring-shaped heat-resistant net  64 , which serves as a wetting enhancement element, is preferably fitted around the annular groove  62 . The net  64  directly faces the discharge end  42  of the capillary tube  40 , and the aforementioned gap Z is secured between the discharge end  42  and the net  64 . 
         [0068]    The sheath element  60  not only protects the Nichrome wire  58  but thermally connects the Nichrome wire  58  and the net  64 . Specifically, where the cell  26  is in a usable state and the Nichrome wire  58  is applied with a voltage of 1 to 1.5 V, the sheath element  60  performs the function of quickly transferring heat generated by the Nichrome wire  58  to the outer surface of the heater  56  and keeping the heating temperature of the outer surface of the heater  56  within a temperature range required to atomize the solution. That is, the Nichrome wire  58  and the sheath element  60  constitute an internal structure whereby the heating temperature of the outer surface of the heater  56  is kept within the required temperature range, and to this end, the sheath element  60  has a predetermined thickness and volume. 
         [0069]    Referring now to  FIGS. 5 to 9 , the principle of operation of the aerosol inhalator according to the embodiment will be explained. In  FIGS. 5 to 9 , the net  64  of the heater  56  is not illustrated. 
         [0070]      FIG. 5  illustrates a state in which the aerosol inhalator is ready for use with the switch  64  of the power feed circuit  63  turned on. The heating temperature of the outer surface of the heater  56  is quickly raised and kept within the required temperature range, and since the relationship indicated by the aforementioned expression (2) is fulfilled, the solution in the capillary tube  40  is not atomized by the radiant heat from the heater  56 . That is, no aerosol is generated. 
         [0071]    On the other hand, when the user inhales through the mouthpiece  14  of the aerosol inhalator in the state illustrated in  FIG. 5 , the solution is discharged from the discharge end  42  of the capillary tube  40  as mentioned above. Since the relationships indicated by the expressions (1) and (2) hold between the capillary tube  40  and the heater  56 , the discharged solution L is reliably received on the outer surface of the heater  56 , as shown in  FIGS. 6 and 7 . Where the net  64  is fitted around the outer surface of the heater  56 , the discharged solution is received by the net  64  and then spreads over the net  64 . 
         [0072]    At this time, since the heating temperature of the outer surface of the heater  56  is already kept within the required temperature range, the discharged solution L is immediately atomized by being heated by the heater  56 , generating an aerosol X inside the inner tube  22 . The user can therefore inhale the aerosol X through the mouthpiece  14 . 
         [0073]    Also, where the heater  56  is provided with the net  64 , the net  64  serves to enhance the wettability of the heater  56  with respect to the discharged solution L, so that the discharged solution L can be atomized over a wider area, enabling prompt generation of the aerosol. 
         [0074]    As soon as the user ceases breathing in, the discharge of the solution from the discharge end  42  of the capillary tube  40  stops immediately. As is clear from the above explanation, since the gap Z between the discharge end  42  and the outer surface of the heater  56  is greater than at least the inner diameter D CT  of the capillary tube  40 , the solution in the discharge end  42  is not atomized by the radiant heat from the heater  56  insofar as the heating temperature of the outer surface of the heater  56  is kept within the aforementioned temperature range. 
         [0075]    Accordingly, the generation of the aerosol stops at the same time as the cessation of the user&#39;s inhalation, so that the solution in the capillary tube  40  is not wasted. 
         [0076]    As a result, the user can inhale the aerosol without fail each time he/she breathes in, and the amount of the aerosol inhaled by the user is determined by the intensity and duration of the user&#39;s inhalation. 
         [0077]    On the other hand, even though the heating temperature of the outer surface of the heater  56  is kept within the required temperature range, the discharged solution L fails to be received on the outer surface of the heater  56  and drops to the inner surface of the inner tube  22 , as shown in  FIG. 8 , if the relationship indicated by the aforementioned expression (2) is not fulfilled and the gap Z is greater than the maximum diameter D MAX  of the liquid droplet of the solution. In such a case, the discharged solution L is not atomized, so that the user cannot inhale the aerosol. 
         [0078]    Conversely, if the gap Z is smaller than the inner diameter D CT  of the capillary tube  40 , the solution in the capillary tube  40  is possibly atomized by the radiant heat from the heater  56 , as shown in  FIG. 9 . In this case, the aerosol X is generated independently of the user&#39;s inhalation, with the result that the solution in the liquid tank  20  is wasted. 
         [0079]    Thus, in the case of the aerosol inhalator of this embodiment, the discharged solution L fails to be atomized, that is, the aerosol fails to be generated, or waste of the solution is unavoidable unless the relationships indicated by the expressions (1) and (2) are fulfilled and also the heating temperature of the outer surface of the heater  56  is kept within an appropriate temperature range. 
         [0080]    Specifically, it is necessary that the relationships indicated by the expressions (1) and (2) be fulfilled and also that, where the solution is propylene glycol, the heating temperature of the outer surface of the heater  56  be kept within a temperature range of 180 to 280° C. 
         [0081]    The aerosol inhalator of the embodiment does not include a control circuit for controlling the heat generated by the Nichrome wire  58 . Thus, in order to keep the heating temperature of the outer surface of the heater  56  within the above temperature range, the thickness (volume) of the sheath element  60  needs to be properly set. 
         [0082]    If the sheath element  60  has a larger thickness, it takes a longer time for heat to transfer from the Nichrome wire  58  to the outer surface of the heater  56  via the sheath element  60 , and since the area of the outside surface of the sheath element  60  increases, the amount of heat radiated from the sheath element  60  also increases. Thus, it is thought that the larger the thickness of the sheath element  60 , the lower the heating temperature of the outer surface of the heater  56  becomes. 
         [0083]    In order to confirm such lowering of the heating temperature of the outer surface of the heater  56 , the inventors hereof prepared heaters  56   A  to  56   G  which differed from one another only in the thickness of the sheath element  60 . The sheath elements  60  of the heaters  56   A  to  56   G  had thicknesses progressively increasing in order of  56   A  to  56   G  each by a fixed increment. 
         [0084]      FIG. 10  illustrates a heating test apparatus for a heater  56   X  (X represents any one of A to G). 
         [0085]    The heating test apparatus includes a power feed circuit  66  for applying a voltage to the heater  56   X , and the power feed circuit  66  includes a direct-current power supply  68  capable of varying the applied voltage, a shunt resistor  70  (1 mΩ), and a voltmeter  72 . The heater  56   X  is connected in series with the shunt resistor  70 . 
         [0086]    Further, the heating test apparatus includes a temperature sensor  74 , which is capable of measuring the temperature of the heater  56   X , that is, the temperature of the outer surface of the sheath element  60 . Specifically, the temperature sensor  74  includes a type K thermocouple. 
         [0087]    When the heater  56   X  is connected to the power feed circuit  66  as illustrated in  FIG. 10 , a voltage is applied from the direct-current power supply  68  to the Nichrome wire  58  of the heater  56   X , so that the Nichrome wire  58  generates heat. The heat generated by the Nichrome wire  58  is transferred through the sheath element  60 , thus increasing the temperature of the sheath element  60 , and on the other hand is released to the outside from the outer surface of the sheath element  60 . 
         [0088]    Consequently, the heating temperature of the outer surface of the sheath element  60  is determined by a difference between the amount of heat generated by the Nichrome wire  58  and the amount of heat released from the sheath element  60 , and the rate of temperature increase of the outer surface of the sheath element  60  is determined by the rate of heat transfer through the sheath element  60 . 
         [0089]    A heating test was conducted on the heater  56   X  in such a manner that with the applied voltage, applied to the Nichrome wire  58  from the direct-current power supply  68 , sequentially varied within a range of 0.8 V to 1.6 V, the heating temperature of the outer surface of the sheath element  60  was measured by the temperature sensor  74  with respect to each of the applied voltages of the Nichrome wire  58 . The measurement results are shown in  FIG. 11 . 
         [0090]    As is clear from  FIG. 11 , the outer surface of the sheath element  60  of the heater  56   X  is heated to a higher temperature as the voltage applied to the Nichrome wire  58  increases. 
         [0091]    Considering, however, ordinary use of the AA size cell  26  which is expected to apply a voltage of 1.0 V to 1.5 V, the heater  56   F  alone is capable of keeping the heating temperature of the outer surface of the sheath element  60  within the aforementioned temperature range (180 to 280° C.) 
         [0092]    This means that where the heater  56   F  is used as the heater  56  of the aerosol inhalator  10  of the embodiment, the heating temperature of the outer surface of the heater  56  can be kept within the required temperature range without the need to use a control circuit for controlling the voltage applied to the Nichrome wire  58 . 
         [0093]    Since the aerosol inhalator  10  need not be provided with such a control circuit, the load on the cell  26  is reduced, whereby the aerosol inhalator  10  can be used for a long period of time. Further, the use of the cell  26  serves to make the aerosol inhalator  10  smaller in size and slenderer, improving handiness of the aerosol inhalator  10 . 
         [0094]    If, on the other hand, the user inhales in a situation where the heating temperature of the outer surface of the heater  56  is lower than the aforementioned temperature range due to voltage reduction of the cell  26 , the solution discharged from the capillary tube  40  may be insufficiently atomized and part of the discharged solution may possibly adhere to the inner surface of the inner tube  22 . 
         [0095]    Further, it is also conceivable that even though the heating temperature of the outer surface of the heater  56  is kept within the aforementioned temperature range, the generated aerosol condenses on the inner surface of the inner tube  22 , with the result that the solution adheres to the inner surface of the inner tube  22 . 
         [0096]    In such cases, as the user inhales, the adherent solution may move toward the mouthpiece  14  and possibly flow into the user&#39;s mouth. 
         [0097]    However, since the absorbent sleeve  48 , which is a paper tube or paper filter, is arranged between the inner tube  22  and the mouthpiece  14 , the adherent solution, if moved toward the mouthpiece  14 , is reliably absorbed into the absorbent sleeve  48  and does not flow into the user&#39;s mouth. 
         [0098]    The present invention is not limited to the aerosol inhalator  10  of the foregoing embodiment and may be modified in various ways. 
         [0099]    As regards the heater  56 , for example, the resistance heating element is not limited to Nichrome wire, and the cross-sectional shape of the heater  56  is not limited to circle and may instead be ellipse, polygon or the like. 
         [0100]    The sheath element  60  may be made of metal and, as shown in  FIG. 12  by way of example, may have a rough outer surface  66  formed on at least a portion thereof where to receive the discharged solution, in place of the aforementioned net  64 . The rough outer surface  66  is constituted, for example, by a large number of narrow annular grooves spaced from each other in the axial direction of the sheath element  60 , and when the discharged solution is received on the outer surface  66  of the sheath element  60 , the annular grooves serve to spread the discharged solution, like the net  64 . 
         [0101]    Further, where the sheath element  60  of the heater  56  and the inner tube  22  are to be made of the same ceramic, the sheath element  60  and the inner tube  22  are preferably formed as a one-piece molded article, and in this case, the number of parts of the aerosol inhalator can be reduced. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               12 : outer tube 
               14 : mouthpiece 
               18 : power supply unit 
               20 : liquid tank 
               22 : inner tube 
               26 : cell 
               40 : capillary tube 
               42 : discharge end 
               48 : absorbent sleeve (paper tube, paper filter) 
               50 : atmospheric port 
               52 : atmosphere-exposed opening 
               56 : heater 
               58 : Nichrome wire (resistance heating element) 
               60 : sheath element 
               64 : net (wetting enhancement element)