Abstract:
In a metering unit ( 10 ) having at least one outlet ( 20 ) for dispensing an aerosol with a defined concentration, with at least one inlet ( 180 ) for a carrier gas, at least one inlet for a liquid, preferably for a hydrogen peroxide solution, and a buffer container ( 30 ) for the liquid, it is provided that the metering unit ( 10 ) has at least one liquid flow controller ( 90 ) on the outflow side.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a metering unit for dispensing an aerosol that preferably contains a hydrogen peroxide solution as liquid component. 
       BACKGROUND 
       [0002]    Aerosols are used in the food industry, for example for sterilising packaging. 
         [0003]    In metering devices for dispensing an aerosol having a defined liquid concentration, flow measurements of the liquid are frequently carried out and the opening time of a switching valve is adjusted to the determined flow values. 
         [0004]    Hydrogen peroxide solutions, which are usually used for sterilisation purposes with a concentration of 35%, tend to decompose at least partially into oxygen and water, especially at such high concentrations, so that apart from the liquid phase, a gaseous phase will always be present as well. 
         [0005]    This gaseous component can have an adverse effect on the flow measurement of the liquid, so that the metering will subsequently become inaccurate and unreliable. However, it is especially in the food industry that very accurate metering processes are necessary, because it has to be avoided at all costs that either in the case of an overdosage food is contaminated with chemicals such as disinfectants or that in the case of an underdosage the packaging is not sterile and as a result, food will become infested with germs. 
         [0006]    It is therefore the object of the invention to provide a metering unit that does not have these disadvantages and that allows an exact metering of an aerosol to be accomplished. 
       SUMMARY 
       [0007]    The invention provides a metering unit having at least one outlet for dispensing an aerosol with a defined concentration, at least one inlet for a carrier gas, at least one inlet for a liquid, preferably a hydrogen peroxide solution, a buffer container for the liquid as well as at least one liquid flow controller on its outflow side. Liquid flow controllers have the advantage that they comprise a flow meter and a proportional valve in one unit, which means that the required valve is directly integrated in the liquid flow controller and therefore separate lines with pipes or tubes between the flow meter and the valve are eliminated. Different suitable flow metering units are known as components of a liquid flow controller, which are based on various measurements principles such as ultrasound, calorimetric, Coriolis, magnetically-inductive (MID), floating body or differential pressure, and which may be used in the invention. Moreover it is favourable if a proportional valve is integrated in the liquid flow controller. In the case of proportional valves, the opening degree of the valve can be open-loop controlled or even closed-loop controlled, which allows very fine adjustments to be made. As a result, the accuracy of the open-loop and/or closed-loop control and the metering is substantially increased. 
         [0008]    In one embodiment, the at least one liquid flow controller has two absolute pressure measuring cells and operates according to the differential pressure method. This method can be used to determine very accurate flow measurements with particularly low tolerances. 
         [0009]    The buffer container is e.g. mounted between a first and a second carrier module and each carrier module is preferably also fluidically and/or mechanically connected to at least one liquid flow controller. The carrier modules are formed to be substantially plate shaped. The first carrier module forms a bottom and the second carrier module a cover for the buffer container. By means of the carrier modules, the individual components of the metering unit are fluidically and/or mechanically connected to each other. To this end, the carrier modules include on a lateral surface fastening means for fastening the at least one liquid flow controller. Moreover, channels for fluidically connecting the components are arranged in the carrier modules. This allows a very compact and stable design of the metering unit to be achieved. In this way, the buffer container may be integrated in the metering unit in a compact and simple manner. 
         [0010]    In one embodiment, a channel is provided in the first carrier module, which is formed as an inflow for the buffer container. Via this inflow, the buffer container can be filled with the liquid that is a component in the aerosol to be metered. Advantageously, liquid is continuously supplied to the buffer container and the buffer container is permanently kept under pressure. As a result, a continuous supply of the at least one liquid flow controller with liquid is ensured, whilst no significant amounts of gas can get to the liquid flow controller. 
         [0011]    In the first carrier module, at least one fluid connection can be provided between the buffer container and an inlet of the at least one liquid flow controller. This design measure results in a fluid path as short as possible between the two components to be connected to each other and thus in a short dwell time of the liquid in connection lines of the metering unit. As a result, especially in the case of applications with hydrogen peroxide solutions, the interfering gas proportion is kept as low as possible as a result of the decomposition of hydrogen peroxide, as described above. Further, this measure also provides for a compact design. 
         [0012]    In a further embodiment, a connection for a pressure relief valve for controlling the pressure in the buffer container is provided in the first carrier module. Thus, a desired maximum pressure in the buffer container will not be exceeded. However, the connection for the pressure relief valve may also be positioned directly on the buffer container. 
         [0013]    The liquid exiting from the pressure relief valve can return to the buffer container. As a result, liquid consumption and thus costs can be reduced. 
         [0014]    In an embodiment of the metering unit, all of the fluid connections are implemented in a piping-free manner, which means that no pipes or tubes are present as a fluid connection between the individual components. This has the advantage that the contact surfaces wetted with liquid within the metering unit are reduced and thus the liquid volume is kept as small as possible, which in the case of hydrogen peroxide solution again has a positive effect on the degree of decomposition and the gas proportion occurring during the metering process. 
         [0015]    It is contemplated to connect an outlet of the at least one liquid flow controller with a mixing device for mixing the liquid with the carrier gas. The mixing device may also be connected directly to the outlet of the liquid flow controller in a piping-free manner. 
         [0016]    All of the liquid-carrying connections from the inlet for liquid (in particular hydrogen peroxide) to the outlet of the aerosol can be free of piping. All channels are seated in units that are flanged together. 
         [0017]    The mixing device has a feed line for the carrier gas for forming the aerosol. Thus, the aerosol in the mixing device is formed directly at the outlet of the liquid flow controller. This, too, contributes towards keeping the dwell time of the liquid within the metering unit as short as possible. 
         [0018]    In one embodiment, the mixing unit is provided on the second carrier module as well as the at least one outlet for dispensing the aerosol. Also as a result of this measure, all of the fluid connections are realised in a piping-free manner and the liquid volume within the metering unit is reduced. This has the advantage that the outlet on the second carrier module can be adapted to a desired connector, depending on the requirements of the further use of the aerosol. However, the outlet for dispensing the aerosol can also be provided directly on the mixing device. 
         [0019]    In one embodiment, the at least one liquid flow controller is vertically provided in the metering unit. This has the advantage that the gas proportion that may be formed immediately flows in the direction of the outlet of the liquid flow controller and a gas bubble that would distort the flow measurement cannot develop at any other location in the metering unit. 
         [0020]    In one embodiment, the buffer container has overflow means for adjusting the level of the hydrogen peroxide solution. Thus, a constant liquid level is ensured at all times during the metering process. 
         [0021]    The overflow means can be formed as a riser pipe. This constitutes a cost-effective and simple solution for adjusting the level of the liquid in the buffer container. 
         [0022]    A discharge of the overflow means is fluidically connected to the first carrier module and an outlet provided there. If the first carrier module forms the bottom for the buffer container, the overflow means can be connected directly at one end to the first carrier module in a simple manner, for example by inserting or screwing the overflow means into a recess provided for this purpose, which opens outwards into a channel in the first carrier module. 
         [0023]    In one embodiment, a valve for the application of a defined pressure onto the buffer container is connected to the buffer container. This valve is above all important during the start-up phase of the metering unit, as long as the buffer container is filled with liquid. As a result of an initial pressure application by means of the valve, the at least one liquid flow controller is therefore supplied with liquid at an early stage, which means even before the desired liquid level has been reached, so that the metering unit will be ready for operation sooner. 
         [0024]    In a further embodiment, a plurality of liquid flow controllers are mounted next to each other in a block-like manner on the first and/or second carrier module(s), the inlets of which are all fluidically connected to the buffer container and the outlets of which are respectively connected to a mixing device for dispensing aerosol. Thus, by means of one single metering unit, aerosol can be dispensed in parallel in a metered manner to a buffer container and a first and second carrier module on several outlets. As a result, a very compact and cost-effective metering unit is provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  shows a three-dimensional representation of a metering unit according to the invention; 
           [0026]      FIG. 2  shows an exploded view of the metering unit according to  FIG. 1 ; and 
           [0027]      FIG. 3  shows a lateral view of the metering unit with a cross-sectional view in a sub-region; 
           [0028]      FIG. 3   a  shows a detailed view of the flow meter of the metering unit according to  FIG. 1 ; 
           [0029]      FIG. 4  shows a three-dimensional representation of a second embodiment of a metering unit according to the invention; 
           [0030]      FIG. 5  shows a top view of the metering unit according to  FIG. 4 ; 
           [0031]      FIG. 6  shows a cross-sectional view through the metering unit according to  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0032]      FIG. 1  shows a metering unit  10  having three outlets  20  for dispensing an aerosol. A common buffer container  30  for receiving a liquid, a component of the aerosol to be metered, is provided between a first, lower carrier module  40  and a second, upper carrier module  50 . 
         [0033]    The two carrier modules  40 ,  50  are substantially rectangular, one-piece parts that are formed so as to be parallel to each other. 
         [0034]    A carrier gas is supplied via connectors  60  on the carrier module  50 , to which the liquid for forming the aerosol is admixed (detailed description in  FIG. 3 ). 
         [0035]    The first carrier module  40  has a port  80  to which a pressure relief valve  70  for controlling the pressure in the buffer container  30  is connected. 
         [0036]    Three liquid flow controllers  90 , which are each formed as constructional units, respectively having a fluid block  95 , are mechanically fixedly connected, for example by screwing, to one end  100  of the fluid block  95  with the first carrier module  40  and on the other end  110  with the second carrier module  50 . 
         [0037]    The liquid flow controllers  90  are disposed vertically within the metering unit  10  with respect to the liquid flow direction. Liquid flow controllers  90  usually comprise a fluid block  95 , through which a main channel  96  extends, a flow sensor  97  and a proportional valve  98  (see  FIG. 3 ). At the end  100  of the fluid block  95 , a fluid inlet of the liquid flow controller  90  is provided, and at the end  110  a fluid outlet, which both open into the main channel  96  extending through said fluid block  95 . Of course, other embodiments of the metering unit  10  may also be implemented, which have a different number of outlets  20  and liquid flow controllers  90 , and it is also possible to provide more outlets  20  than liquid flow controllers  90  in the metering unit  10 . 
         [0038]      FIG. 2  shows an exploded view of the metering unit  10  having the three adjacent liquid flow controllers  90  corresponding to  FIG. 1 . The buffer container  30  is formed as a pipe section, axially open on both sides, between the first carrier module  40  as the bottom and the second carrier module  50  as the cover, and two sealing elements  120 . The carrier modules  40 ,  50  have indentation bores which are adjusted to the outside diameter of the buffer container  30  and which receive the respective end of said buffer container  30 . 
         [0039]    The carrier modules  40 ,  50  have openings  130 ,  140  for fluid connections on lateral surfaces  45 ,  55 . In the metering unit  10 , each opening  130  in the carrier module  40  is fluidically connected to a fluid inlet at the end  100  of the liquid flow controller  90 , and each opening  140  in the carrier module  50  is connected to a fluid outlet at the end  110  of the liquid flow controller  90 . 
         [0040]    The openings  130  provide fluid connections to the inside of the buffer container  30 . They may be implemented as simple bores in the carrier module  40 . 
         [0041]    However, the buffer container  30  can also be formed as an integral unit with the carrier modules  40 ,  50  or as a container with a cover and a bottom that is adjacent to the carrier modules  40 ,  50 , and may include fluid connections as separate ports. 
         [0042]    A further opening  150  is provided in the carrier module  40 , which is implemented as a simple bore through the carrier module  40  and leads into the buffer container  30 . This opening  150  is used as a feed line for filling the buffer container  30  with a liquid that is a component of the aerosol to be metered. 
         [0043]    By means of an overflow device  160  provided in the buffer container  30 , the liquid level in the buffer container  30  is kept constantly at a desired level. The overflow device  160  is formed as a riser pipe and is fastened at the lower end thereof in the buffer container  30  parallel to the central axis thereof in the bottom, i.e. in the embodiment described here, in the carrier module  40  on a fluid outlet  165 , for example screwed in by means of threaded connections. 
         [0044]    A fluid connection leads from the fluid outlet  165  to an outlet  170  on a lateral surface of the carrier module  40 . The port  80  is provided at the outlet  170  and is connected to the pressure relief valve  70 . The riser pipe is formed to be open at the top and acts as an overflow pipe, into which the liquid flows when a certain level in the buffer container  30  is exceeded. 
         [0045]    Advantageously, the overflow device  160  is arranged so as to be adjustable in its height in the buffer container  30 , so that a desired level can be adjusted in the buffer container  30 . The liquid exiting via the overflow device  160  can be returned into the buffer container  30 . 
         [0046]    The pressure relief valve  70  can be used to control the pressure in the buffer container  30 . Of course it is insignificant for the functioning mode of the metering unit  10  on which lateral surface of the carrier module  40  the fluid connection is led out of the outlet  170 . The port  80  may also be provided on a lateral surface other than the one shown in  FIG. 2 . 
         [0047]    Apart from the openings  140  to connections with respectively one fluid outlet at the end  110  of a liquid flow controller  90 , the carrier module  50  also includes inlets  180  to be coupled to the ports  60  for supplying the carrier gas. 
         [0048]    The carrier modules  40 ,  50  are fixedly connected via a mounting plate  190 . The mounting plate  190  increases the mechanical stability of the metering unit  10  and is useful for mounting the metering unit  10  in a system. 
         [0049]    Since all of the fluid connections between the individual components are formed as channels within the carrier modules  40 ,  50  and the liquid flow controllers  90  are directly connected to the carrier modules  40 ,  50 , other types of fluid lines such as tube or pipe connections may be dispensed with in the metering unit  10 . The fluid connection paths are therefore implemented to be as short as possible. This piping-free design concerns in particular all the parts that carry liquid from the inlet of the liquid to the outlet  20  of the aerosol. 
         [0050]      FIG. 3  shows a lateral view of the metering unit  10  with a cross-sectional view of all components with the exception of the liquid flow controller  90 . Like  FIG. 2 ,  FIG. 3  shows the buffer container  30  with the overflow device  160 , the carrier module  40  with the opening  150  for supplying the liquid into the buffer container and the mounting plate  190 , plus additional details concerning the carrier module  50 . 
         [0051]    In the carrier module  50 , the opening  140  is connected to a fluid outlet at the end  110  of the liquid flow controller  90 . The opening  140  merges into a channel  200  in the carrier module  50 , which leads to a mixing device  210  that is also provided in the carrier module  50 . An exactly defined amount of liquid flows from the liquid flow controller  90  through the channel  200  into the mixing device  210 . The mixing device  210  is provided in the carrier module  50  in a channel-shaped recess starting from the inlet  180  and has a channel  220  that is in communication with the port  60  for supplying the carrier gas via the inlet  180 . 
         [0052]    A removable insert  230  is inserted in the recess downstream of the inlet  180 , which has the channel  220 . The channel  200  opens into a mixing chamber  240  in the channel  220  of the insert  230 , which mixing chamber narrows down in a nozzle-like manner. However, the use of an insert  230  is not absolutely necessary. 
         [0053]    As a result of the merging channels  200 ,  220 , the aerosol consisting of the liquid and the carrier gas is provided at the end of the mixing device  210 . To ensure that also a defined amount of carrier gas gets into the mixing device  210 , a gas flow controller, for example a mass flow controller, can be connected to the port  60 . 
         [0054]    The end of the mixing device  210  is fluidically connected to the outlet  20  of the metering unit  10 . This outlet  20  is adapted to a desired port, depending on the further use of the metered aerosol. 
         [0055]    Further, a valve  75  is connected to the buffer container  30 , which is only schematically shown in  FIG. 3 , through which valve a defined pressure can be applied onto the buffer container  30 . 
         [0056]    The functioning mode of the metering unit  10  will be briefly summarised again below. For forming an aerosol, a liquid is fed via an opening  150  forming an inlet of the metering unit  10  and a carrier gas is fed via the ports  60 . The opening  150  forms a channel that is used as an inflow for the buffer container  30 . The liquid initially fills the buffer container  30 . The liquid flows from the buffer container  30  via the carrier module  40  to the openings  130 . Each opening  130  is connected to a fluid inlet at the end  100  of the fluid block  95  of a liquid flow controller  90 , so that the liquid gets into the main flow channel  96 . 
         [0057]    Each main flow channel  96  has connected thereto respectively one flow sensor  97 , which measures the flow of liquid therethrough. The opening degree of the proportional valve  98  is adjusted accordingly, and a defined amount of liquid reaches the outlet at the end  110  of the fluid block  95  of the liquid flow controller  90 . 
         [0058]      FIG. 3   a  shows a schematic view of the design of a flow sensor  97 . The flow sensor  97  operates according to the differential pressure method. To this end, the flow sensor  97  has two absolute pressure measuring cells  101 ,  102  as well as an aperture  103  for pressure reduction, which is provided in the main flow channel  96  between the absolute pressure measurement cells  101 ,  102 . The flow rate of liquid flowing through the main flow channel  96  can be determined from the difference between the pressures measured by the two absolute pressure measuring cells  101 ,  102  as well as from further (known) parameters such as for example the liquid density. 
         [0059]    The fluid outlet of the liquid flow controller  90  is immediately next to the opening  140 , so that the liquid flows from the liquid flow controller  90  to the opening  140  in the carrier module  50  and there into the channel  200 . 
         [0060]    The liquid flows through the channel  200  further into the mixing chamber  240  of the mixing device  210 . Also the carrier gas flows into the mixing chamber  240  via the port  60 , the inlet  180  in the carrier module  50  and the channel  220  of the mixing device  210 , as a result of which the aerosol to be metered is produced in the mixing chamber  240 . 
         [0061]    That means that in the embodiment shown in  FIGS. 1 to 3 , the carrier gas flows through the mixing device  210  in the longitudinal direction completely through the channel  220 . The aerosol flows from the outlet of the mixing chamber  240  to the outlet  20  of the metering unit  10 . 
         [0062]    The embodiment shown in  FIGS. 4 to 6  differs from the embodiment shown in  FIGS. 1 to 3  in that the channel  200 , in which the liquid flows into the mixing device  210 , opens into the channel  220 . An annular channel  250  is provided on the mixing device  210 , into which the carrier gas is passed via the inlet  180  for the carrier gas to the mixing chamber  240 . 
         [0063]    Also the mixing device  210  shown in  FIGS. 1 to 3  may include such an annular channel. 
         [0064]    Moreover, the channel  200  has two sections  200   a,    200   b,  between which an additional valve  260  is provided, which is used as a shut-off valve. 
         [0065]    The port  60  or the inlet  180  for the carrier gas are here provided on the top surface of the carrier module  50 . 
         [0066]    The shut-off valve ensures for example that the supply of the liquid into the mixing device  210  can, if needed, be reliably stopped. 
         [0067]    Thus, the additional valve  260  can be regarded as a safety device. 
         [0068]    In  FIGS. 4 and 5 , the pressure relief valve  70  is connected via internal channels in the carrier module  40  to the overflow device  160  as well as the port  80 . The liquid exiting from the metering unit  10  via the flow device  160  is discharged via the port  80 .