Abstract:
The invention relates to a nozzle ( 10 ) for mixing a gaseous fluid such as air and a liquid such as water and for ejecting an atomize mist of liquid droplets. The nozzle includes a nozzle body defining first ( 60 ), second ( 44 ) and third ( 52 ) annular passages along the length thereof. Pressurized fluid is introduced into the first annular passage ( 60 ) and a first restricted annular orifice ( 68 ) leads from the first annular passage ( 60 ) to the third annular passage ( 52 ). Liquid is introduced into the second annular passage ( 44 ) and a second restricted annular orifice ( 48 ) leads from the second annular passage ( 44 ) to the third annular passage ( 52 ). Liquid and gaseous fluid are aggressively mixed in the third annular passage ( 52 ). A third restricted annular orifice ( 72 ) leads from the third annular passage ( 52 ) to atmosphere such that mixed liquid and gaseous fluid are forcibly ejected from the nozzle through the third restricted annular orifice ( 72 ), the liquid being atomized in small controlled droplets in the ejected gaseous fluid.

Description:
[0001]    The present invention relates to a nozzle device for atomizing liquid for fine spray and misting applications. In particular the invention relates to a nozzle meeting criteria for air humidification in ducts used commercially in Heating Ventilating and Air Conditioning (HVAC) systems as well as in other humidification applications including localized spatial humidification for process and printing plant operations and greenhouse humidification.  
         BACKGROUND OF THE INVENTION  
         [0002]    There are existing atomizer designs for the applications described above, the designs typically providing a spray that is dynamically controlled to vary air humidity level. Usually an array of nozzles is mounted within a duct or other area and the required humidification supply is varied by adjusting air and water pressures to suit the desired bulk vaporization rate. The existing nozzles suffer from a number of shortcomings, such as high air consumption, the collection of large droplets on external components of the assembly, relatively high cost, difficulty in providing a limited or controlled droplet size distribution, and high noise levels due to high air consumption.  
           [0003]    Many current nozzle designs are configured Dr optimized for only one flow condition or the operating range is very limited for achieving consistent, unchanged droplet size. Also, many of the present designs that use air atomization are designed with one or more impactor plates that produce fine spray (typically less that 50 μm mean size) but the mounting for each plate interferes with the spray and often results in a fraction of the spray comprising course droplets resulting from an accumulation of liquid on the impactor-mounting components. Another problem associated with prior art nozzles, as indicated above, is the noise level produced by the nozzles since they are used in commercial building air conditioning. The high noise level of the prior art nozzles is usually attributed to high air consumption—thus a low air consumption is desirable.  
           [0004]    U.S. Pat. No. 4,483,482 of Nov. 20, 1984 is representative of prior art designs. It utilizes a convergent/divergent tube-path to accelerate gaseous fluid into an annular mixing chamber where the fluid mixes with liquid entering downstream of the gaseous fluid inlet. The mixed fluid and liquid flow along an annular path towards the nozzle exit from which the fluid and liquid are sprayed in a fan-like pattern from the flared end of the nozzle. This nozzle suffers from all of the drawbacks enumerated hereinabove.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention addresses the shortcomings associated with the prior art humidification nobles as discussed above. The present nozzle was designed so that it can be incorporated in new construction and so that it will work with existing lines of commercial products to replace older nozzle designs. To improve the humidification equipment, the present invention also involves refinement of supporting equipment for the spray system including: (a) controls for air and water flow for a distributed array of nozzles installed in ducting, with flow dumping for shutoff without duct contamination; (b) nozzle mounting support structures for installation in ducting; and (c) piping and feed-tubing header assemblies to supply air and water to the nozzles mounted in ducting.  
           [0006]    The atomization device of this invention is unique in that the design incorporates a 2-phase flow conditioning chamber downstream of the mixing of gas and liquid phases. Air flow is limited by an orifice built into the nozzle body assembly, which orifice serves to limit air flow and deliver the air at near sonic conditions as it mixes with the liquid flow (i.e., in the 2-phase flow conditioning chamber). The nozzle uses 2-stage atomization: the 1 st  stage provides for sonic flow through a chamber; and the 2 nd  stage is in the cavity formed by a deflector disc or plate mounted at the nozzle exit. This design produces a spray droplet distribution which is bimodal and can have advantages in humidification for gradual evaporation of the water stream into a flow of air in HVAC duct applications. The nozzle of this invention can be connected to a dynamic feed control system for operating the nozzle over a range of conditions suited to the desired delivery rate of liquid for the nozzle (i.e., the humidification rate) without significant change in the spray shape and droplet size. Typically the mass-mean of the bimodal distribution of droplet sizes can be maintained in the range of 10 to 15 μm with a flow turndown ratio of 3 or greater.  
           [0007]    The nozzle of this invention uses less than half the air consumption for equivalent spray performance in comparison to existing atomizers typically used in HVAC applications.  
           [0008]    Water flow in typical nozzles used for HVAC applications is regulated by an adjustable needle (or other type). The new design uses a fixed orifice to meter the flow.  
           [0009]    The nozzle of this invention uses an optional impact surface held by a center supporting rod. Such a design is not typically used for nozzles that have a two phase (water and air) flow.  
           [0010]    The supporting mechanism for the center pin used in this invention is unique in nozzles used for humidification.  
           [0011]    The atomizer or nozzle of this invention achieves a narrow and controlled droplet size distribution with low air consumption and fine atomization without dripping. The reduction of air consumption is very advantageous in some applications where limits are placed on the size of compressor that can be used in the installation.  
           [0012]    In summary, the present invention may be considered as providing a nozzle for mixing a gaseous fluid and a liquid and for ejecting an atomized mist of liquid droplets comprising: a nozzle body defining first, second, and third annular passages along the length thereof; means for introducing pressurized gaseous fluid into the first annular passage; means defining a first restricted annular orifice leading from the first annular passage to the third annular passage; means for introducing pressurized liquid into the second annular passage; a second restricted annular orifice leading from the second annular passage to the third annular passage, whereby liquid and gaseous fluid are aggressively mixed in the third annular passage; and a third restricted annular orifice leading from the third annular passage to atmosphere, whereby mixed liquid and gaseous fluid are forcibly ejected from the nozzle through the third restricted annular orifice, the liquid being atomized in small controlled droplets in the ejected gaseous fluid. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 shows a cross-sectional view of a nozzle constructed in accordance with the present invention.  
         [0014]    [0014]FIG. 2 shows an enlarged cross-sectional view of the outlet end of the nozzle, illustrating preferred dimensional relationships  
         [0015]    [0015]FIG. 3 is an enlarged cross-sectional view illustrating the flow paths for introducing, mixing and shearing liquid for atomization.  
         [0016]    [0016]FIGS. 4A to  4 D shows cross-sectional views of several alternative shapes for the deflector plate of this invention.  
         [0017]    [0017]FIG. 5 illustrates the use of nozzles according to the invention in a typical HVAC duct. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    The present invention provides a nozzle  10  which includes a main nozzle body  12 , which body may be of any suitable external cross-section, such as cylindrical, rectangular, or square, for example, depending on the particular application in which it will be used. The main body has a rearmost block portion and is stepped down at the forward end to create a cylindrical projection  14  that has a frustoconical end surface  16 . A central bore  18  extends through the main body, the bore being stepped as well so as to define a main central section  20 , a proximal section  22  of a diameter greater than that of the central section, and a short distal section  24  of a diameter smaller than that of the central section. The distal section  24  and a portion of the central section  20  reside within the projection  14 . A radially directed inlet port or bore  26  extending through the main body communicates the bore  18  at the central section  20  with a source of pressurized air (not shown).  
         [0019]    The main body  12  mounts thereon a body cap  28  which has the same external configuration as the main body. The body cap has a stepped cylindrical bore  30  that includes a first section  32  that receives the projection  14 , a second section  34  of a smaller diameter than that of section  32 , and a third section  36  of a diameter smaller than that of section  34 . An O-ring seal  38  provided in an annular recess  40  in the projection  14  effects a seal between the main body and the body cap. A radially directed inlet port or bore  42  extending through the body cap communicates the bore  30 , at section  32 , with a source (not shown) of liquid such as water.  
         [0020]    It will be noted that the bore section  32  and the frustoconical end  16  of the projection  14  define a first annular chamber  44 , which chamber contains the outlet of the bore  42 . The sloping forward end transitional wall  46  of the chamber  44  defines with the end edge  48  of the projection  14  a first narrow liquid accelerating annulus or orifice  50  (see FIG. 3) which opens into a 2-phase conditioning or second annular chamber  52 . The chamber  44  serves to evenly distribute the liquid into the orifice  50  for even flow to the chamber  52 .  
         [0021]    A flow throttle pin  54  resides in the bore  18  of diameter head  56  at the proximal end thereof, which head is press fit so as to be in the largest diameter proximal end section  22  of the bore  18  The pin  54  has a reduced diameter shaft section  58  which extends forwardly, the outer surface of the shaft section defining with the inner surface of the central bore section  20  a first annular gap or passage  60  into which the air is directed via the inlet port  26 . In order to ensure that the pin  54  is fixed in place within the bore  18  so that there will be no off-axis movement at the distal end thereof there is provided a support member  62  intermediate the length of the shaft section, having longitudinally extending grooves  64  therethrough to permit air flow therepast. The support member is in the shape of a spider, with the grooves  64  located between radial arms  66 . The outer edges of the support member arms  66  have a sliding fit with the interior wall of the bore  18 .  
         [0022]    The shaft section  58  of the pin extends forwardly to the end of the projection  14  and defines with the inner surface of the reduced diameter distal bore section  54  a very narrow first annular air flow orifice  68 . Air enters the gap or passage  60  via the inlet port  26  and flows forwardly therethrough, past the support member  62  and then through the orifice  68  into the second or mixing chamber  52  where it aggressively mixes with the liquid that was introduced via the inlet port  42  and entered the chamber  52  via orifice  50 .  
         [0023]    A distal projection or extension  70  on the pin  54  passes through the mixing chamber  52 , meaning that that chamber actually has a generally annular configuration defined between the inner surface of the bore section  34  and the outer surface of the extension  70 . The extension  70  has a diameter smaller than that of the shaft section  58  and passes through the smallest diameter portion  36  of the bore  30  at the end of the body cap  28 , defining with the inner surface of that bore section a third annular 1 st  stage or primary atomization orifice  72 . Liquid and air that is aggressively mixed in the mixing chamber  52  is evenly distributed from that chamber into the orifice  72 , in which the liquid is formed into tiny ligaments dispersed within the flowing air. Those ligaments are projected outwardly from the end of the body cap as a spray of atomized droplets.  
         [0024]    An optional and desirable addition to the structure of this nozzle is a 2 nd  or secondary stage atomization zone  74  defined in part by the end face of the extension  70 , a small diameter button pin  76  extending forwardly from that face, and a small diameter deflector plate or button  78  at the distal end of the pin  76 . The deflector plate serves to further disperse the spray exiting the nozzle and also acts as a shield to prevent the spray from collecting on the nozzle components at the distal end thereof. The flow dynamics of the spray exiting the nozzle are such that there will be a build-up of turbulent air between the button pin  76  and the inner face  80  of the button pin  78 . That turbulent flow tends to impart a radial component to the exiting flow, causing it to deflect outwardly at a greater conical angle, of 90 degrees or more, than the conical spray angle would be without the button plate in place, usually less than 90 degrees. Because of the flow dynamics created by the button plate there will be very little impingement of water droplets on the button plate, and furthermore there will be a reduced tendency of water droplets to form at the end face of the nozzle.  
         [0025]    A further feature of the invention is the frustoconical or sculpted end face  82  of the body cap  28  which helps to control the spray flow as it exits the nozzle. As seen in the drawing the spray  84  is generally conical, its size and shape being controlled by the sizing of the nozzle components. Since the nozzle of this invention is typically used in HVAC ductwork, along which air will be flowing, such flowing air will follow the frustoconical end surface  82  to meet the spray exiting the nozzle, creating a back-swirling effect at the atomization zone  74  and causing the spray to dissipate more quickly into the ambient atmosphere at a still greater conical angle.  
         [0026]    The size of the components used in the invention and the flow rates provided or achieved will of course determine the physical properties of the resulting spray. For example, the resulting spray will be influenced by: the velocity of the liquid flowing from the inlet  42  to the chamber  44  and through the acceleration annulus; the air velocity through the second annular orifice  48 ; the length and volume of the second annular mixing chamber  52 ; the dimensions of the 1 st  stage atomization orifice  72 ; and the geometry of the 2 nd  stage atomization zone  74 . The orifice  48  is preferably designed so that the air velocity therethrough is critical at the operating pressure of the nozzle. The 1 st  stage atomization orifice  72  is preferably designed for choked flow conditions.  
         [0027]    The basic arrangement for use in duct humidification application involves an array of nozzles installed on boom assemblies  86  with associated feed manifolds  88 ,  88 ′ to distribute and supply each nozzle with air and water. The typical installation for nozzles in accordance with this invention is for water flow up to 200 mL/min with a mass ratio of air-to-liquid of 0.45-0.50 (i.e., 2.5 scfm air flowrate). For this operating target condition there can be a liquid-flow turndown up to 3 or an operating range from 70 mL/min up to 200 mL/min. The nozzle design is scalable to larger or smaller operating ranges through careful design modification of the components used to create the flow through channels and external paths.  
         [0028]    The geometry of the “button” or deflector plate  78  is selected: (a),to avoid wetting of the pin holding the button in place; and (b) to provide a cavity between the primary atomization orifice  72  and the “button” itself, thereby creating a length for the spray to establish and disperse in the vicinity of the button face for secondary atomization. The size, shape and position of the “button” relative to the geometry of the primary atomization orifice can be varied to accommodate the requirements of droplet size and spray shape for the particular application (i.e., droplet size can be made finer or coarser by varying the button geometry).  
         [0029]    In order to ensure that the button or deflector plate will achieve the desired level of secondary atomization without accumulation of liquid on the structure thereof the plate  78  should have a desired geometry that will control the hydrodynamic and aerodynamic nature of the spray impinging thereon. The key geometric dimensions are illustrated in FIG. 2 which shows the nozzle tip on an enlarged scale. The preferred interrelated geometries of the nozzle elements are summarized in Table 1 below.  
                                     TABLE 1                       Ratio or Parameter   Typical Range   Preferred                                B/A   1.3-1.5   1.4       A/C   &gt;2   2.25       L/B   0.25-0.4    0.34       T/L   &lt;2   1.01       β   &gt;35 degrees   37 degrees       D/A   1.5-2     1.6       D/B   1.0-1.3   1.15                                                                                          
 
         [0030]    The atomizer as shown can be used with or without a “button” component depending on the requirements for end use. Typically the button is used in applications where the spray is to be mixed quickly and in a small volume of space near the nozzle exit; if the spray is to be displaced to some location far away from the nozzle tip, the button may be removed to improve projection of the spray but a slightly coarser spray will result. Compensation to maintain droplet size when the button is removed can be achieved by modifying the air-to-liquid feed ratio for the nozzle with change to the flow rates as outlined for the critical geometric dimension ratio provided above. In general, droplet size is determined by the geometry of nozzle components  44 ,  48 ,  52  and  72  to establish sonic flow conditions for the spray at the exit of orifice  72 . The addition of the button therefore serves not only as a secondary atomization component of the nozzle but also as a deflector that can be positioned in the spray to control or limit spray dispersion.  
         [0031]    [0031]FIG. 3 illustrates the nozzle tip in an enlarged view, indicating the flow channels used for introducing, mixing and shearing the liquid for optimum atomization. The flow through from feed to final stage of atomization and the associated criteria for design are as follows in Table 2 and with reference to the elements as defined in FIG. 3:  
                                 TABLE 2                           Description and criteria for design of flow channels of nozzle            Location                   or Flow       Criteria Range       Channel   Description   (typical operation)   Preferred               [44]   Annular inlet chamber   sized for axial velocity   empirical           for distribution of   less than 1 m/s   design           water feed           chamber must be           large enough to           distribute liquid to           annular entrance to           second chamber [52A]       [48]   Annular orifice for   liquid velocity   0.65 m/s           liquid flow to acceler-   criterion:           ate liquid into the gas   U liquid  = 0.3-0.7 m/s           flow entering through           orifice [68]       [68]   Annular entrance for   gas velocity as   0.6 mach           air flow metered   criterion:           through the annulus   U air  = 0.5 to 1.0 mach           (i.e. air flow is limited           to choked flow when           liquid feed is shut off)       [52A]   Entrance and annular   geometry depends on   residence           flow channel for   gas-to-liquid ratio used   time of at           mixing of gas and   design for a differen-   least 25 ms           liquid streams to pro-   tial superficial velocity   slip           duce a fine bubbly 2-   (slip velocity) between   velocity at           phase mixture   air and water of at   the between           good contacting and   least 6 m/s and as high   liquid and           relatively high-shear   as 25 m/s; superficial   gas of at           2-phase flow is devel-   liquid velocity esti-   least 20 m/s           oped to promote small   mated to be 0.3 m/s   for fine           bubble formation and   and superficial gas of   spray           dispersion in the   about 21 m/s   application           liquid flow       [52]   Chamber for accelerat-   channel has hydro-           ing the 2-phase flow   dynamic shape to           (finely dispersed   promote gradual tran-           bubbles in the liquid   sition to flow from           stream) into the   [9a] through to [10]           primary atomization           orifice           [52] is configured to           provide choked flow           conditions (i.e. flow           limited by sonic           conditions) for the 2-           phase mixture       [72]   Primary atomization   geometry configured   residence           orifice   empirically for choked   time of           flow accelerates   flow based on maxi-   liquid to be           through [72] under   mum throughput   3 ms or           choked flow condi-   criteria for gas and   more (based           tions to shear the   liquid streams   on estimated           liquid and provide   feed pressure and   superficial           intense mixing with   desired droplet size   velocity)           the gas phase bubbles   criteria are used to               empirically determine               the appropriate               dimensions of this               channel       [74]   geometry and criteria   atmospheric or near-           defined above for   atmosphenc conditions           “button” configuration   design criteria is for           as in FIG. 2   geometry that provides           the 2-phase mixture   impingement of spray           exits the nozzle orifice   without accumulation           [72] and liquid is   on the “button” or its           promptly atomized.   supporting post           due to the sudden           pressure reduction to           near-atmospheric           conditions       [74A]   geometry and criteria   atmospheric or near-           defined above for   atmospheric conditions           “button” configuration           as in FIG. 2           shape of spray plume           is relatively main-           tained over the entire           operating range due to           configuration of the           “button”with spray           impinging on the           outer edge to perform           secondary atomization                  
 
         [0032]    The preferred button  78  is that shown in FIGS. 1, 2 and  3 , being in the form of a circular plate with a diameter slightly greater than that of the distal end of the throttle pin extension  70 . Alternative “buttons” that were evaluated and found to provide varying degrees of atomization and produce a range of spray shapes are shown in FIGS. 4A to  4 D. The button of FIG. 4A is generally in the form of a cylindrical rod  90  having a concave inner end surface  92  and a convex or rounded outer end surface  94 . The button of FIG. 4B is in the form of a cylindrical rod  96  having chamfered end edges  98 ,  98 . The button of FIG. 4C is in the form of a cylindrical rod  100  having a small diameter concave inner end surface portion  102  and a flat outer end surface  104  with chamfered end edges  106 . The button of FIG. 4D is in the form of a cylindrical rod  108  having a tapered or chamfered inner end surface  110  leading to an inwardly tapered or chamfered inner surface  112  and a rounded outer end surface  114 . Shapes shown as example, but not limited the ones shown, were tested.  
         [0033]    These shapes functioned satisfactorily but were not the preferred “button” described as the preferred embodiment. The “button” of the preferred embodiment was easy to manufacture and install in the atomizer assembly. Dimensions of the “button” prescribed both the final droplet size distribution and general shape of spray. The preferred shape of spray was a hollow cone. Mean size of the spray was less than 50 μm for effective evaporation rates in humidification applications.