Abstract:
A liquid dispensing device for dispensing a liquid into the surrounding atmosphere employs a forced airflow through a small cross-section outlet nozzle ( 48 ) to draw the liquid from an adjacent exit nozzle ( 50 ) into the airflow. The air outlet nozzle preferably has a cross-section less than that of the liquid exit nozzle. The liquid exit nozzle may partially overlie the airflow path from the air outlet nozzle. The nozzle may be formed in or carried by a unit ( 24 ) having sealed connections with the airflow source ( 16 ) and a container holding the liquid.

Description:
FIELD OF THE INVENTION 
     This invention relates to devices for the dispensing of liquids into a carrier fluid. 
     BACKGROUND 
     Our patent application PCT/GB99/00998 describes apparatus for dispensing a volatile liquid into a surrounding atmosphere in which a driving airflow is used to draw the liquid from a conduit by producing a pressure drop in the region of an outlet from the conduit in the manner of a jet pump or venturi. The liquid conduit may be formed as a capillary tube and the airflow may be directed past the conduit outlet region through an air delivery nozzle having a similar size cross-section. 
     By the use of such devices with small cross-section nozzles, it is possible to achieve rapid dispersal of the liquid into the atmosphere using low mass air flows and to do this by means of a compact device with only a small power requirement. The present invention is concerned with further improvements of devices of this nature. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, there is provided a liquid dispensing device comprising an air pump, a vessel for the liquid to be dispensed, a syphon tube extending from a lower region of the vessel to an exit nozzle, an air outlet conduit for said pump provided with an outlet nozzle for directing a stream of pumped air past the liquid exit nozzle, the air outlet nozzle having an effective cross-sectional area not more than twice that of the liquid exit nozzle. 
     The liquid conduit is preferably a capillary tube with a cross-sectional area about 10 mm 2  or less. The liquid exit nozzle is no larger and can have a substantially smaller cross-section eg. equivalent to a diameter of approximately 1–2 mm. 
     The air outlet nozzle preferably has a cross-sectional area not substantially more than that of the liquid exit nozzle, or even up to about 40% less than the liquid exit nozzle. It is also possible to form the air outlet nozzle as an orifice of a size similar to or greater than the liquid exit nozzle but with a smaller effective cross-sectional area by virtue of a baffle or other obstacle to the issuing flow immediately downstream of the orifice. For example the liquid exit nozzle structure may project into and partly block the flow path from the orifice in the air flow path. This both reduces the effective cross-sectional area to increase the air flow velocity and generates unsteady flow conditions which will enhance the dispersal of the liquid drawn into the flow. 
     Thus, according to another aspect, the invention provides a liquid dispensing device comprising a vessel for the liquid to be dispensed, an outlet passage extending from a lower region of the vessel to a liquid exit nozzle, a conduit provided with an outlet nozzle for directing a stream of air past the liquid exit nozzle, the liquid exit nozzle extending into a projection of the air outlet nozzle axially thereof to partially overlie said projection, the portion of the nozzle projection not so overlain having a cross-sectional area not substantially greater than the cross-section of the liquid exit nozzle. 
     In the case in which the air outlet nozzle has an orifice substantially equal to or smaller than the liquid exit nozzle, a baffle or the like obstacle may be located downstream of the liquid exit nozzle to promote unsteady flow conditions for accelerating the dispersal of the liquid in the airflow. 
     It is desirable to ensure that the outlet opening of the liquid exit nozzle of a liquid dispensing device according to the invention, at its closest to the air outlet nozzle opening, is spaced not more that four times the mean cross-sectional dimension of the air outlet nozzle from that nozzle, in order to limit the degree of diffusion of the airstream before it flows across the liquid exit nozzle outlet, and preferably the spacing is not substantially more than twice that dimension. 
     The invention is also concerned with arrangements of liquid dispensing devices in a manner suitable for large scale production. 
     Thus, in one arrangement according to a further aspect of the invention, a liquid dispensing device is provided comprising a vessel for a liquid to be dispensed, a conduit extending upwardly from a lower region of the vessel to a liquid exit nozzle, and an air pump connected to an outlet conduit having an air outlet nozzle opening adjacent said liquid exit nozzle to draw liquid therefrom by a flow of air through said outlet nozzle, said air and liquid nozzles being formed by a pair of elements having opposed faces at which the elements are sealed together, said nozzles comprising depressions in at least one of said faces. 
     In an alternative arrangement, the liquid dispensing device comprises a vessel for a liquid to be dispensed, a conduit extending upwardly from a lower region of the vessel to a liquid exit nozzle, and an air pump connected to an outlet conduit having an air outlet nozzle opening adjacent said liquid exit nozzle, at least the liquid exit nozzle being defined by a separately formed insert. The air outlet nozzle may comprise a further insert and, to control their relative location, the inserts may be arranged to lie in contact with each other. 
     In accordance with yet another aspect of the invention, a liquid dispensing device is provided comprising a pump for generating a carrier fluid flow, a replaceable vessel removably connected to a mounting communicating with a fluid flow exit from said generating means, said vessel providing a container for the liquid to be dispensed, an outlet passage for said liquid extending between the mounting and a lower region of the vessel, said mounting of the device containing coacting nozzles for the flow from said generating means and the liquid from said outlet passage to entrain the liquid in suspension in said fluid flow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Examples of the invention will be described with reference to the accompanying drawings in which: 
         FIG. 1  is a cross-section in a central vertical plane of one form of device according to the invention, 
         FIGS. 2 and 3  are, respectively, an oblique exploded view and a front view of the device of  FIG. 1  with the portions of the main body mouldings to one side of the central vertical plane of symmetry omitted, 
         FIG. 4  is a detail sectional view in the plane of  FIG. 1  of the air and liquid outlet in the device of  FIGS. 1–3 , 
         FIG. 5  is a detail sectional view illustrating an alternative arrangement of the liquid and air conduit outlets in the liquid container of another form of device according to the invention, 
         FIG. 6  is a view to a larger scale of the circled region in  FIG. 5 , 
         FIG. 7  is an exploded oblique illustration of the nozzle assembly of the device of  FIGS. 5 and 6 , 
         FIG. 8  is a sectional view similar to  FIG. 5  showing a further modified form of device according to the invention with half of the nozzle unit removed, 
         FIGS. 9 and 10  are front and oblique views of a unitary moulding that provides the air and liquid outlet nozzles in the device of  FIG. 8 , 
         FIG. 11  is a sectional view similar to  FIG. 5  illustrating a yet further modified form of device according to the invention, and 
         FIGS. 12 and 13  are, respectively, a larger scale view of the circled region in  FIG. 11  and an exploded view from below of the air and liquid outlet nozzles in the device of  FIGS. 11 and 12 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Referring to  FIGS. 1 to 4 , the dispensing device is in the form of a plug-in unit intended to be mounted on an electrical supply socket by a 3-pin connection plug  12  at the rear of the device. The device has a casing comprising a rear body moulding  14  from which the plug pins project. A pumping unit  16  comprising an electric motor and an air pump is mounted on the rear moulding and is enclosed by a front cover moulding  18  permanently secured to the rear moulding  14 . At the bottom of the air pump is a centrically located spigot  20  on which a socket  22  of a nozzle unit  24  fits closely. The nozzle unit  24  projects into a container  26  which is detachably held in the unit casing by securing means (not shown) between it and the rear moulding  14 . 
     The nozzle unit  24  in this and the later examples may form an integral part of the air pump spigot  20  or of the container  26  and comprise a mating part that seals releasably with the container or the pump spigot respectively. However, it may alternatively be a separate adaptor that, as shown in this example, fits as a sealing plug into the neck of the container  26  and, through the socket  22  in its top face, that similarly seals with the spigot. 
     Also mounted on the rear moulding is a printed circuit board  32  providing electrical connection between the plug connection  12  and the pump motor and comprising a variable time circuit which is controlled by a timer switch  34  slidably mounted on the front cover  18 . 
     The nozzle unit  24  comprises a nozzle block  42  integral with the main body of the unit or formed as a plug-in member inserted into a side face of the unit, as illustrated in  FIG. 2  in particular. The nozzle block  42  has a through bore  44  communicating with the air pump outlet through a vertical passage  46  in the nozzle unit. An air nozzle  48  is located in the entry end of the bore  44  and abuts a liquid nozzle  50  which projects into the bore from below. Secured to the lower end of the liquid nozzle  50  is a capillary tube  52  which extends downwards to the bottom of the container  26 . 
     The capillary tube diameter may be about 3 mm. The bore of the liquid nozzle  50  is considerably smaller, eg. not substantially more than 1 mm diameter and possibly as small as 0.5 mm or less. The bore of the air nozzle  48  may be of a similar size, or possibly smaller than the liquid nozzle bore, eg. with about half the cross-sectional area of the liquid nozzle bore. In addition, the illustrated example shows effective size of the air nozzle exit further reduced because it is overlapped by the tip of the liquid nozzle. 
     In operation, the air pump produces an air jet from the air nozzle  48 . The jet velocity is relatively high although the small size of the air nozzle means the volumetric flow is relatively small. A reduced pressure is thereby produced over the exit from the liquid nozzle  50  and liquid is drawn from the nozzle as fine droplets which, because of the high air velocity, are rapidly dispersed in the air flow. 
     To employ the high velocity, low volume airflow from the air outlet nozzle efficiently the liquid exit nozzle should be located close to the air nozzle because the airstream will diffuse rapidly as it flows away from the air nozzle. If this effect is not controlled, a much greater mass flow of air would be required to take up the liquid. In the example of  FIG. 4 , the air nozzle outlet is located some two diameters of the nozzle diameter from the liquid nozzle exit opening and the distance is preferably no more than twice that. 
     The overlap of the liquid nozzle  50  with the air nozzle  48  has a further effect in forming an impingement surface disturbing the flow exiting from the air nozzle. This effect promotes the mixing of liquid into the air flow and helps to inhibit the formation of large liquid droplets which would hinder rapid dispersal in the airflow. 
     The resulting flow of air with liquid vapour and droplets is dispersed into the surrounding atmosphere through exit openings  54  in the front wall of the container. The exit openings  54  are at an angle to the flow path from the nozzle unit bore  44  so the container front wall forms a further barrier for any larger liquid droplets in the flow. If such droplets strike the front wall they return into the main body of liquid in the container. 
     In the example of  FIGS. 5 to 7  the dispensing device may be a plug-in unit with a casing and a pumping unit arranged in the same manner as in the preceding example. The drawings show a modified air-liquid mixing arrangement in which a nozzle unit  62  between the air pump outlet spigot  20  and the liquid container  26  has an integral air nozzle. As in the first example, the spigot  20  is received in a socket  64  in the unit  62 , and a conduit  66  communicating with the air pump outlet leads downwards from the socket. At its lower end the conduit  66  joins a deep but narrow slit-like passage  68  in the unit  62  providing an air outlet nozzle. 
     At the bottom of the nozzle unit  62 , into a tubular extension  70  opening into the narrow passage  68  is inserted the capillary liquid tube  52 . Above the tube  52  and projecting into the passage  68  is a liquid outlet nozzle  72  with a diameter over most of its height greater than the width of the passage  68 . 
     The liquid outlet nozzle has a conical cap  74  with a central outlet opening  76  of a similar diameter to the outlet nozzle of  FIG. 4 , eg. 0.5 mm to 1 mm. It will be noted that the air conduit  66 , which may have a circular bore, is considerably larger and, although it opens into the smaller cross-section nozzle passage  68 , the divergent rectangular cross-section of that passage is still considerably larger than the liquid nozzle outlet opening  76 . However, the projection of the liquid outlet nozzle  72  into the air passage  68  reduces the free cross-section for the air flow substantially. Since the diameter of the base of the conical tip  74  is greater than the width of the passage  68 , air can only flow past the liquid outlet nozzle close to the upper end of the conical tip. A nozzle throat is thus formed with an air flow cross-section which is preferably not substantially greater than the liquid outlet opening  76 , and which in the illustrated example is smaller than that outlet opening. 
     Immediately downstream of the liquid nozzle the cross-section of the passage  68  increases sharply, so that there is a similarly sharp increase of static pressure which intensifies the mixing of the liquid drawn from the liquid outlet nozzle into the air flow. In the illustrated example, as is shown in  FIG. 7 , there is a step  78  in the passage wall at or adjacent the liquid nozzle outlet which promotes disturbance of the air flow and further increases the rate of mixing with the liquid drawn from the liquid nozzle. 
     The formation of flow passages of 1 mm diameter or less with the accuracy required to control the pressure changes at the point of mixing is difficult to achieve economically in large scale production. To some extent the use of nozzle inserts, as in the first-described example, and the control of their relative location by abutting the inserts against each other is able to reduce the extent to which precision manufacturing techniques are required. However,  FIGS. 8–10  illustrate another way in which the cost of manufacture can be substantially reduced. 
     In this example, again, only the container  26  and a nozzle unit  82  are shown and the remainder of the device may take the same form as in the first example. The air and liquid nozzles are integral parts of the nozzle unit  82  between the air pump spigot  20  and the liquid container  26 . The unit  82  itself is a unitary plastics moulding having two opposed parts  84 , 86  joined by an integral hinge element  88  about which the two parts can be folded together to bring their opposed planar faces  84   a , 86   a  together, these mating faces being sealed together at their areas of contact. The socket  88  receiving the air pump spigot is formed as two semicircular recesses  88   a , 88   b  in the two parts  84 , 86  and conduits  90 , 92  respectively for the air and liquid flows to the nozzles are also divided to be formed by semi-circular grooves in the faces  84   a , 86   a . In the abutting faces  84   a , 86   a  dowelling projections  94  are formed in the one part  84  for engagement with depressions  96  in the other part  86  to locate the matching recesses in the two parts together accurately. 
     The two parts of the moulding also share between them corresponding recesses forming a divergent exit passage  98  for the mixed flow of air and liquid droplets. However, the air and liquid nozzles between the conduits  90 ,  92  and the exit passage  98  are formed as recesses  102 ,  104  respectively in only one of the parts because of their small cross-sectional size. Thus from one of the recesses forming the air supply conduit  90  the air nozzle  102  extends to intersect the liquid exit nozzle  104  which has a similar or somewhat larger cross-section and which extends from one of the recesses forming the liquid supply conduit  92 . At the downstream side of the liquid outlet nozzle  104  is a baffle  106  which reduces the outlet cross-section abruptly at the beginning of the divergent exit passage  98  to promote mixing in a similar manner to the preceding examples. This baffle adjacent the nozzle exits disturbs the mixed flow of air and liquid from the nozzles. 
     The manufacture of a unitary moulding of the kind shown in  FIGS. 8–10  can be further simplified by forming further features, such as the conduits  90 , 92  and the exit passage  98 , in a face of one of the parts, the other part then having a mainly or wholly planar mating face. 
       FIGS. 11–13  show a further modified form of nozzle unit  110  devised with a view to simplifying manufacture of the dispensing device. Only part of the device is illustrated and the remainder of the device may be as shown in  FIGS. 1–4 . The nozzle unit  110  has a socket  112  receiving the air pump spigot  20  and it fits sealingly on the neck of the container  26  as in the earlier examples, but in this case the unit  110  carries a plug insert  114  into which respective air and liquid nozzles  116 , 118  are in their turn fitted. The nozzle unit has upper and lower entry conduits  120 , 122  for the air and liquid flows respectively, the liquid capillary tube  52  being inserted into the lower conduit  122 . Both conduits lead to a cross-passage  126  in which the plug insert  114  is a sealing fit. 
     The plug insert  114  has a through-bore  128  coaxial with the cross-passage  126  in the nozzle unit  110 . A flat  130  on the insert  114  locates against a corresponding flat in the passage  126  to ensure that the plug insert is held in the nozzle unit with the liquid nozzle  118  aligned with the liquid entry conduit  122 . Both nozzles  116 , 118  are rotationally symmetrical and can be produced with a high accuracy using simple dies. The plug insert  114  is similarly able to be produced economically with high dimensional accuracy, but it is only necessary to control the dimensions of the main body of the adaptor to ensure it makes fluid-tight seals with the parts to which it is attached. 
     Each nozzle has a locating flange  116   a , 118   a  that sets the depth of insertion into the plug insert  114 . When fully entered, as shown in the  FIG. 12  conical end face  116   b  of the air nozzle abuts the end face  118   b  of the liquid nozzle. The liquid nozzle outlet has a diameter of 0.5 mm and the air nozzle outlet diameter is smaller at 0.3 mm, but in addition the air nozzle outlet is partly blocked by the overlapping tip of the liquid nozzle, analogously to the first-described example. The effective exit flow area is thus reduced and, moreover, the facing side wall of the liquid nozzle forms a baffle that promotes unsteadiness in the exiting air flow.