Abstract:
A nozzle for discharging finely atomized fluids comprises a vortex-mixing-module with a mixing chamber along with at least one liquid inlet tangentially communicating with the chamber and at least one gas inlet axially communicating with the liquid inlet prior to their injection into the mixing chamber, wherein the mixed fluid of liquid/gas from the liquid inlet is setting vortex flow, re-mixing with each other and forming bubble-laden fluid. An impingement member positioned at the downstream of a substantially concentric-mounted pintle stem of the module provides the function of metering flow and forming the spray angle while maintaining the flow distribution to be axial-symmetric in both mass and velocity plus forming a flow field with non-disturbed angular momentum. A gas passage prepared in the pintle stem and exiting to the downstream side of the deflector provides the feature of cleaning the pintle surface, which eliminates the coarse drops on the pintle surface, stops any undesired residual hard layer from accumulation, and provides surface cooling for required high temperature applications.

Description:
FIELD OF INVENTION  
         [0001]    The present invention relates to atomizing nozzles and, more particularly, to twin-fluid atomizers comprising features of double-dipped fuel/gas mixing and pintle self-cleaning for creating sprays with extremely fine drops.  
         BACKGROUND OF THE INVENTION  
         [0002]    Liquid atomization is one of the most effective methods in preparing liquid with maximized total surface area for various industrial applications, such as agricultural spraying, evaporation cooling, slurry drying, scrubbing of stack gases, dust collectors and oil-burner combustion processes. There are two kinds of atomizing schemes being used in nozzle design: pressure atomizers (single-fluid) and twin-fluid atomizers. The pressure atomizer, single-fluid, achieves droplet atomization by transforming pressure energy of the liquid to form high velocity liquid jet/film as it is injecting out of the atomizer. The exiting high velocity-jet/film is further sheared into small drops by the ambient airfield that contains induced-turbulent energy adjacent to the atomizer exit. This atomizer is widely used in low flow rate applications. In high flow rate requirements, however, the high velocity jet/film from a pressure atomizer becomes much thicker, which makes it harder to be atomized by the ambient air only. A remedy is to use a twin-fluid nozzle, which introduces pressurized gas to mix with the liquid prior to its injection, thus improving atomization at higher flow rate conditions. While in its operation, in the microscopic view point, gas is introduced under pressure to stir and mix with the liquid in the nozzle chamber to generate numerous tiny bubbles of gas entrapped into the liquid, which causes the viscosity and surface tension of the liquid to be much reduced (bubble-laden fluid) and results in much finer sprays. Technically, there are two atomization mechanisms involved in this liquid break-up process. The primary atomization is achieved at the nozzle exiting port by the sudden expansion of those entrapped-bubbles in the liquid as they experience pressure reduction, thus forming a fast moving dense spray of fine drops. The secondary atomization is subsequently introduced by the turbulent shear force from ambient air that breaks the high velocity moving drops into even finer sprays. The latter process shares the same spirit of the atomization mechanism with the pressure atomizer as described above. In general, the twin-fluid nozzle has broader usage in industrial applications in light of its much higher flow rate capacity and its much finer drops generated over a fairly wide operating range (also called turndown ratio).  
           [0003]    On the twin-fluid nozzle, a fairly effective design of the prior art is shown in FIG. 8. This nozzle utilizes a nozzle cap  1000  to assist in the production of liquid drops. In FIG. 8, the nozzle cap  1000  includes an outer frame  1005 , a pintle  1010  and support spokes  1015  to support and couple the pintle  1010  to the outer frame  1005 . The pintle comprises an inlet splash plate  1020 , a tapered shaft  1025  and an outlet deflector plate  1040  (FIG. 9). The function of the prior art is to make a liquid stream injecting on the splash plate  1020  perpendicularly to form liquid films on both surfaces of plate  1020  and spokes  1015 . The swirling atomization air introduced from the upstream of the splash plate (not shown) is then mixed with the liquid films in the passage between the spokes as well as the downstream annular passage defined by the outer surface of the pintle  1025  and the inner surface  1035  of the frame  1005 . Another example of prior art is shown in FIG. 10. This design modifies the prior art of FIG. 8 by positioning dams  1051  on spokes  1052  to improve the nozzle performance by reducing the amount of liquid flowing on the spokes while the liquid and air is mixing in the nozzle.  
           [0004]    These designs are fairly effective in achieving gas/liquid mixing and atomization, nonetheless, subject to several limitations.  
           [0005]    1. When the nozzle is used for injecting liquid with abrasive particles or contamination, erosion on the spokes  1015  or  1052  can occur, resulting in the damage of the pintle leading to failure of the nozzle.  
           [0006]    2. As the swirling air being introduced into the mixing chamber of the nozzle (not shown) mixes with the liquid on the surface of both the splash plate  1020  and the spokes  1015 , several aerodynamic wakes could be generated at the downstream of these spokes. In the wake region of the nozzle chamber (downstream of the spokes  1015 ), both velocity and angular momentum of the mixed fluid are significantly reduced in quantity and their distributions could become non-axial-symmetrically skewed. The skewed flow pattern then propagates through the nozzle exit and results in non-uniform sprays. This outcome can severely compromise the nozzle performance in several widely used applications, for instance, in furnaces of industrial oil burners, given the fact that the uniformity of a spray as well as its well maintained angular momentum are vital factors to stable flames in the burner.  
           [0007]    3. As a spray is formulated after impinging on the deflect plate  1040 , an axially symmetric recirculation region with lower pressure will also be formed in the center of the spray adjacent to the surface  1040  of deflector  1039 . In this low-pressure recirculation zone, fine drops in the spray will be sucked back toward the downstream surface of the deflector and form large drops on the surface, called re-attachment. This process will compromise the spray quality quite severely in some cases. For example, in the applications of oil burner combustion or slurry heating processes, as the radiation heat in the furnace raises the surface temperature of the deflector, some recirculating fine drops in the spray accumulated on the downstream surface  1040  of the deflector can form layers of dried shells/cokings. Over time, the hardened slurry build-up, or coking layer in the oil burner cases, on top of the deflector edge can round and dull the sharp edge and cause the spray angle to be reduced, leading to more coarse drops in the spray. Nozzles under this limitation can compromise the quality of the powder-production in the slurry drying processes. Or it could severely damage the liner of a burner and cause unstable flames. The built-up coking layer on the pintle surface in the oil-burner will further cause hot spots on the pintle surface itself and eventually damage the pintle and cause the nozzle to fail.  
         SUMMARY OF THE INVENTION  
         [0008]    This design comprises a vortex-mixing-module containing two new features. First, liquid and gas streams are pre-mixed by injecting both into the same swirler slots prior to their entering the annular mixing chamber of the module. Second, a pintle is center-mounted, and is provided with a self-cleaning feature. With this double-dipped mixing arrangement, the effectiveness of mixing between liquid/gas is much enhanced and the size of the mixing module can be greatly reduced, in comparison to the prior art, to result in more uniform fine sprays of great turndown ratio. The center-mounted pintle concept totally eliminates the possibility of pintle damage caused by the spoke erosion as shown in the prior arts (FIGS. 8 &amp; 10) and provides a non-disturbed annular mixing chamber for generating well-mixed fluid with high angular momentum. The self-cleaning feature on the pintle serves to improve spray quality and increase the life span of the nozzle service, and is especially beneficial to a burner application where cooling of the hot surface of the deflector is needed. In more detail, the self-cleaning feature of the pintle is achieved with a center-drilled hole along the stem of the pintle to the downstream of the deflector plate, where a purge-disk is mounted substantially concentrically to the deflector downstream surface. This forms a passage which can tap part of the atomizing gas from the pressure source and turn it out to become purge gas to the downstream surface of the deflector plate. As the purge gas is exiting out of the slit on the deflector with extremely high velocity, it cleans the surface and prevents recirculated drops from forming the undesired hard-shell-accumulation on the surface that damages the pintle or compromises the nozzle performance. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is an exploded view of a preferred embodiment of dual-fluid nozzle with self-cleaning pintle system constructed to operate in accordance with the principle of the current invention.  
         [0010]    [0010]FIG. 2 is a front-perspective-exploded view of a preferred embodiment of the vortex-mixing-module  3  shown in FIG. 1.  
         [0011]    [0011]FIG. 3 is a rear-perspective-exploded view of a preferred embodiment of the vortex-mixing-module  3  shown in FIG. 1.  
         [0012]    [0012]FIG. 4 is a cross section view of a preferred embodiment of dual-fluid nozzle with self-cleaning pintle system constructed to operate in accordance with the principle of the current invention shown in FIG. 1.  
         [0013]    [0013]FIG. 5 is a front view of a preferred embodiment of dual-fluid nozzle showing the cross-section line that the view of FIG. 4 is taken from.  
         [0014]    [0014]FIG. 6 is an enlarged partial cross section view of the purging gas outlet shown in the dotted zone in FIG. 4.  
         [0015]    [0015]FIG. 7 is a cross section view of another embodiment of vortex-mixing-module assembly sharing the same spirit of the current invention combined with a converging-diverging (Venturi) orifice geometry coupling to a conical shape deflector head.  
         [0016]    [0016]FIG. 8 is a rear perspective view of a prior art nozzle cap.  
         [0017]    [0017]FIG. 9 is a front perspective view of a prior art nozzle cap.  
         [0018]    [0018]FIG. 10 is a rear perspective view of another prior art nozzle cap. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    A preferred embodiment of a nozzle, shown in FIG. 1, constructed to operate in accordance with the principles of this invention comprises a vortex-mixing-module  3 , a module adapter  1 , and a holder  9 .  
         [0020]    The Vortex-mixing-module  3  (FIGS.  2 , 3 , 4 ) comprises a swirler housing  30 , an orifice body  50 , a pintle body  60  and a disk  80 . The swirler housing  30  is substantially a cylindrical body on which a mixing chamber  32  is bored from the surface  34  to the surface  36 . On the end of surface  34  a conical convex-surface  38  is also formulated with an included angle, such as lying in the range of 90 to 150 degrees, to provide a self-aligned surface contact during the assembly with the mating surface of the orifice body  50 . On the other end of the swirler housing  30 , FIG. 3, a buffer chamber  40  is bored from the surface  42  to the surface  44 . Several equally spaced slots  35  are prepared, such as milled, on the cylindrical wall the of the mixing chamber side to provide communication conduits from the exterior of the housing to the mixing chamber  32 . These slots are substantially tangentially prepared on the wall, so that as the liquid from the exterior of the body is guided into the chamber  32  through these slots, a swirling vortex flow will be induced. In each slot, a hole  37  is also prepared, such as drilled, in parallel with the cylindrical axis of the swirler housing from the bottom of the slot through the ceiling, defined by the surface  36  and  44  of the swirler body, and up to a predetermined height of surface  46  on the wall of the buffer chamber  40 . As shown in FIG. 2, 3, the hole  37 , of diameter no larger than the width of the slot, are positioned in the slot and with its edge very close to the edge of the mixing chamber. The gas holes  37 , now looking from the buffer chamber side, are partially drilled into the wall of the buffer chamber and up to the height of surface  46 . The distance of surface  46  to surface  44  is predetermined to assure that the flow passage opening from the chamber  40  to hole  37  is larger than the cross-section area of the hole  37  itself. This arrangement is to use the exposed/interfered portion of hole  37  in the buffer chamber as a leading entrance to lead the gas through the hole into the slots of liquid to initiate mixing followed by generating a swirling vortex as the mixed fluid is entering the mixing chamber. In some other conditions, when the mixing chamber is designed to be smaller than the current layout shown or when the gas hole  37  is drilled at a slant angle (not shown) relative to the axis of the housing  30 , the holes  37  may not interfere with the wall of the buffer chamber and will end on the ceiling only, surface  44 . In these scenarios, the function of the mixing module will be identical as far as the spirit of this invention is concerned. This arrangement will provide the benefits of double-dipped liquid/gas mixing efficiency with very compact swirler geometry by allowing both fluids to pass through the same tangentially cut slots.  
         [0021]    In FIGS. 2 and 3, a cylindrical-shape orifice body  50  is made with a center-bored through-hole  52 , with a size no larger than the internal diameter of the mixing chamber  32 . The upstream surface  54  of the orifice body is a conical-concave shape with the same included angle as the surface  38  of the swirler housing  30 , such as lying between 90 to 150 degrees, in order to properly seal each other during the assembly. On the opposite side of the surface  54 , a flange surface  56 , substantially vertical to the axis of the body, is prepared for liquid sealing purpose when the vortex swirler module  3  is assembled to the nozzle adapter  1  (FIGS. 1, 4). The flange outer diameter, surface  59 , is sized for close clearance with the mating part of adapter  1  for alignment purposes in the nozzle assembly. In one possible embodiment sharing the same spirit of this invention, the through hole  52  of the orifice body is constructed in the shape of a Venturi (as the orifice surface  210  in FIG. 7), i.e., the internal diameter of the wall is progressively decreased along the passage of the orifice to a minimum dimension then gradually increased back. This embodiment is applied to the cases when the quantity of atomization gas is relatively low in supply and the uniformity of the mixed fluid will be determined mainly by the distribution of liquid flow; then the convergent and divergent passage design, Venturi, can maximize their distribution pattern.  
         [0022]    In FIGS. 2 and 3, a pintle body  60  comprising a substantially cylindrical stem  62  and a deflector head  64  of substantially disk-shape with a center hole  65  drilled through is shown. On the deflector head  64 , the upstream surface  66  is substantially vertical to the pintle axis with an outer diameter, head  64 , slightly smaller than the smallest diameter of orifice  52 . This arrangement is for accessibility while assembling the entire swirler-vortex module together. On the downstream side of the deflector head, an annular groove  68  is prepared concentrically on the surface to divide the remaining surface into two annular surfaces  70  and  72 . The annular surface  70  is machined to be lower than the annular surface  72  at a predetermined quantity. Multiple slots  74  are cut (FIG. 2),  4  slots as shown, on the annular surface  72  at a predetermined depth to provide the radial-conduits between the center hole  65  and the annular groove  68 . Finally, the surface  82  of the disk  80 , with no larger diameter than the diameter of the deflector head  64 , is sealed, such as welded, to the surface  72  substantially concentrically. With this arrangement, a gap  76 , FIG. 6, is formed between the annular surface  70  on the deflector head and the surface  82  of the disk  80 . On the assembly of pintle body  60  and disk  80 , in detail, a gas conduit is formulated which comprises the gas passages of hole  65 , slots  74 , annular groove  68  and annular gap  76 . This assembly is then coupled to the center-drilled hole  39  on the ceiling of the housing  30  at a predetermined axial location along the stem  62  of pintle body  60 . This forms a predetermined gap between the exiting edge  58  of the orifice body  50  and the deflector head surface  66  when they are assembled together. This predetermined gap is the nozzle metering passage, which serves to define the flow capacity for both gas and liquid as well as shape the spray angles. The methods of coupling the pintle body  60  and the housing  30  can be by welding or by other ways such as threading, which is not shown in the drawing.  
         [0023]    The holder  9  (FIGS. 1, 4) is made from a bar of drumstick shape with external threads  92  on one end and o-ring seal  94  the other. A center hole  98  is drilled-through on the holder. The o-ring seal  94  is to connect an external conduit for guiding gas into the nozzle through the center hole  98 . In some other applications, within the scope of the spirit of this invention, the o-ring seal can be replaced by either internal or external thread (not shown) for the connecting purpose. Two parallel-flat-surfaces  96  are prepared on the exterior surface  104  of the holder  9  for torque purposes during assembly. Several equally spaced slots  100  are cut axially through the thread  92  at a predetermined width and depth to provide liquid conduits for the assembled nozzle when it is in operation.  
         [0024]    The adapter  1  (FIGS. 1, 4), with both external threads  14  and internal threads  12 , is to host the vortex-mixing-module  3  and the holder  9 . At the downstream of the internal thread  12 , an annular groove  16  is bored to clear the thread  12  up to the surface  18  and a tight clearance hole  19  is also bored concentrically between surface  18  and surface  20  to fit with the flange diameter  59  of the orifice body  50 . As the vortex-mixing-module  3  is placed into the adapter  1  (FIGS. 1, 4 ), the flange surface  56  of the orifice body  50  will be bottomed-to and seal on the surface  15  of the adapter  1 . In the meantime, the swirler housing  30 , integrated with the pintle body  60  and purge disk  80 , is pressed from the back surface  42  of the body by the surface  102  of the holder  9 . Through the action of pressure force from the holder  9 , both the swirler housing  30  and the orifice body  50  will be closely-contacted and concentrically-aligned due to the conical mating surface provided on both parts. The same force also causes a tight seal between surface  56  of the orifice body  50  and surface  15  of the adapter  1 .  
         [0025]    One possible embodiment which shares the same spirit of this invention makes use of the orifice body  50  combined with the adapter  1  as an integrated part (not shown). In this case, the features on the orifice body  50  such as conical surface  54  and the through hole  52  are part of the adapter  1 . This arrangement is a very easy practice which can benefit from a reduced total number counts of the parts of this invention, but will limit the material variation capability between the adapter and the orifice. Sometimes the capability of material selection between the orifice body  50  and the adapter  1 , as the main embodiment shown, can be vital to the success of certain nozzle applications.  
         [0026]    Another possible embodiment, shown in FIG. 7, which shares the same spirit of this invention, is that the through hole  210  of the orifice body  200  is made into a convergent-divergent passage, Venturi type. This modification focuses the mixed fluid into a more confined cross-section area before exiting to the injector, making the spray distribution more uniform when the atomization gas consumption rate is limited.  
         [0027]    Another possible embodiment, shown in FIG. 7, which share the same spirit of this invention, is that the upstream surface  320  of the deflector head  310  on the pintle stem  300  is a conical shape. This modification provides alternative ways to shape the spray angle by the angle of the cone of the deflector head.  
         [0028]    After the detailed description of all the parts of this invention, it is believed that the spirit and advantage of the design can be presented more clearly by describing the function of the complete assembly shown in FIGS. 1 and 4. In this illustration, the vortex-mixing-module  3  is placed in the adapter  1  where the flange  56  of the orifice body  50  is to be bottomed at the surface  15  of the adapter  1 . The holder  9  is screwed into the internal thread  12  of the adapter  1  and seals on the surface  42  of the housing  30  with the surface  102 . By doing so, the flange  56  of the orifice body  50  will also be sealed by the surface  15  of the adapter  1 . During the nozzle operation, a liquid from an upstream source (not shown) is pumped to the conduits set between the thread  12  of the adapter and the exterior surface  104  of the holder  9 . It is then guided through the slots  100  on the holder  9  and goes between the threads  12  and the exterior surface of the housing  30  into the annular chamber defined by the groove  16  in the adapter  1  and the exterior surface of swirler housing  30 . The liquid will then be injected into the tangential cut slots  35  of the swirler housing.  
         [0029]    Meanwhile, a pressurized gas from the gas source (not shown) is conducted to the holder  9 , through the center hole  98  of the holder, to the baffle chamber  40  of swirler housing  30 . The majority of the gas, serving as atomization gas, is guided into the holes  37  on the ceiling of the housing  30  and impinges onto the liquid flowing through slots  35 . The pre-mixed liquid/gas fluid in the slots is then injected into the mixing chamber  32  forming vortex flows. During this process, numerous tiny gas bubbles are formed and entrapped in the fluid. The mixed fluid, bubble-laden-fluid, then moves from the mixing chamber through the annular passage defined by the hole  52  of the orifice body  50  and the exterior surface of stem  62  of the pintle  60 , and flows down to the metering section of the vortex-mixing-module defined by the distance between edge  58  of the orifice body  50  and the surface  66  of the deflector head  64 . As the bubble-laden-fluid is passing through the metering section of the module, the sudden expansion of gas bubbles in the fluid, induced by pressure reduction, will accelerate its velocity and break the liquid into fine drops. The high velocity drops in this stream then encounter a secondary atomization caused by the ambient turbulence-induced flow-field. A predetermined portion of gas, called purge gas, in the baffle chamber  40  of the swirler housing  30  is, in the meantime, guided as in FIG. 6 through the center hole  65  of the pintle body  60 , the slots  74 , the annulus groove  68  on the deflector head  64 , and the gap  76 , thoroughly cleaning the edge of the downstream surface  70  of the deflector head  64 .  
         [0030]    Looking through the description of the spirit and function related to the preferred embodiment of current invention, it has been found that the nozzle performance and its operation life span are greatly improved for the following reasons. First, the introduction of ducting both fuel and gas into the same tangentially cut slots on the mixing module not only enhances the mixedness of those two fluids with a more compact swirler design but also improves the turn-down ratio of the nozzle due to a more stable aerodynamic vortex flow forming at low flow rate conditions. Second, by introducing the pintle stem with gas-purging means directly to the ceiling of the housing  30  in this invention, both the potential of erosion-induced nozzle damage to the pintle spokes and the compromised spray quality by hard-coking layer on the pintle surface experienced in the prior arts are totally eliminated. It should also be noted that the shortcomings of nonsymmetrical spray distribution with compromised angular momentum of the spray caused by the spokes in the mixing chamber of prior arts are much improved as well.  
         [0031]    It should be understood that the preferred embodiment and some possible embodiments described above sharing the same spirit of the present invention are merely illustrative of some of the applications of the principles of the invention. Numerous modifications may also be made by those skilled in the art without departing from the true spirit and scope of the invention.