Abstract:
An improved spray nozzle assembly for use in a steam desuperheating device that is adapted to spray cooling water into a flow of superheated steam. The nozzle assembly is of simple construction with relatively few components, and thus requires a minimal amount of maintenance. In addition, the nozzle assembly is specifically configured to, among other things, prevent thermal shock to prescribed internal structural components thereof, to prevent “sticking” of a valve element thereof, and to create a substantially uniformly distributed spray of cooling water for spraying into a flow of superheated steam in order to reduce the temperature of the steam.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. patent application Ser. No. 13/644,049 entitled IMPROVED NOZZLE DESIGN FOR HIGH TEMPERATURE ATTEMPERATORS filed Oct. 3, 2012. 
    
    
     STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains generally to steam desuperheaters or attemperators and, more particularly, to a uniquely configured spray nozzle assembly for a steam desuperheating or attemperator device. The nozzle assembly is specifically adapted to, among other things, prevent thermal shock to prescribed internal structural components thereof, to prevent “sticking” of a valve stem thereof, and to create a substantially uniformly distributed spray of cooling water for spraying into a flow of superheated steam in order to reduce the temperature of the steam. 
     2. Description of the Related Art 
     Many industrial facilities operate with superheated steam that has a higher temperature than its saturation temperature at a given pressure. Because superheated steam can damage turbines or other downstream components, it is necessary to control the temperature of the steam. Desuperheating refers to the process of reducing the temperature of the superheated steam to a lower temperature, permitting operation of the system as intended, ensuring system protection, and correcting for unintentional deviations from a prescribed operating temperature set point. Along these lines, the precise control of final steam temperature is often critical for the safe and efficient operation of steam generation cycles. 
     A steam desuperheater or attemperator can lower the temperature of superheated steam by spraying cooling water into a flow of superheated steam that is passing through a steam pipe. By way of example, attemperators are often utilized in heat recovery steam generators between the primary and secondary superheaters on the high pressure and the reheat lines. In some designs, attemperators are also added after the final stage of superheating. Once the cooling water is sprayed into the flow of superheated steam, the cooling water mixes with the superheated steam and evaporates, drawing thermal energy from the steam and lowering its temperature. 
     A popular, currently known attemperator design is a probe style attemperator which includes one or more nozzles or nozzle assemblies positioned so as to spray cooling water into the steam flow in a direction generally along the axis of the steam pipe. In many applications, the steam pipe is outfitted with an internal thermal liner which is positioned downstream of the spray nozzle attemperator. The liner is intended to protect the high temperature steam pipe from the thermal shock that would result from any impinging water droplets striking the hot inner surface of the steam pipe itself. 
     One of the most commonly encountered problems in those systems integrating an attemperator is the addition of unwanted water to the steam line or pipe as a result of the improper operation of the attemperator, or the inability of the nozzle assembly of the attemperator to remain leak tight. The failure of the attemperator to control the water flow injected into the steam pipe often results in damaged hardware and piping from thermal shock, and in severe cases has been known to erode piping elbows and other system components downstream of the attemperator. Along these lines, water buildup can further cause erosion, thermal stresses, and/or stress corrosion cracking in the liner of the steam pipe that may lead to its structural failure. 
     In addition, the service requirements in many applications are extremely demanding on the attemperator itself, and often result in its failure. More particularly, in many applications, various structural features of the attemperator, including the nozzle assembly thereof, will remain at elevated steam temperatures for extended periods without spray water flowing through it, and thus will be subjected to thermal shock when quenched by the relatively cool spray water. Along these lines, typical failures include spring breakage in the nozzle assembly, and the sticking of the valve stem thereof. Further, in probe style attemperators wherein the spray nozzle(s) reside in the steam flow, such cycling often results in fatigue and thermal cracks in critical components such as the nozzle holder and the nozzle itself. Thermal cycling, as well as the high velocity head of the steam passing the attemperator, can also potentially lead to the loosening of the nozzle assembly which may result in an undesirable change in the orientation of its spray angle. 
     With regard to the functionality of any nozzle assembly of an attemperator, if the cooling water is sprayed into the superheated steam pipe as very fine water droplets or mist, then the mixing of the cooling water with the superheated steam is more uniform through the steam flow. On the other hand, if the cooling water is sprayed into the superheated steam pipe in a streaming pattern, then the evaporation of the cooling water is greatly diminished. In addition, a streaming spray of cooling water will typically pass through the superheated steam flow and impact the interior wall or liner of the steam pipe, resulting in water buildup which is undesirable for the reasons set forth above. However, if the surface area of the cooling water spray that is exposed to the superheated steam is large, which is an intended consequence of very fine droplet size, the effectiveness of the evaporation is greatly increased. Further, the mixing of the cooling water with the superheated steam can be enhanced by spraying the cooling water into the steam pipe in a uniform geometrical flow pattern such that the effects of the cooling water are uniformly distributed throughout the steam flow. Conversely, a non-uniform spray pattern of cooling water will result in an uneven and poorly controlled temperature reduction throughout the flow of the superheated steam. Along these lines, the inability of the cooling water spray to efficiently evaporate in the superheated steam flow may also result in an accumulation of cooling water within the steam pipe. The accumulation of this cooling water will eventually evaporate in a non-uniform heat exchange between the water and the superheated steam, resulting in a poorly controlled temperature reduction. 
     Various desuperheater devices have been developed in the prior art in an attempt to address the aforementioned needs. Such prior art devices include those which are disclosed in Applicant&#39;s U.S. Pat. No. 6,746,001 (entitled Desuperheater Nozzle), U.S. Pat. No. 7,028,994 (entitled Pressure Blast Pre-Filming Spray Nozzle), U.S. Pat. No. 7,654,509 (entitled Desuperheater Nozzle), and U.S. Pat. No. 7,850,149 (entitled Pressure Blast Pre-Filming Spray Nozzle), the disclosures of which are incorporated herein by reference. The present invention represents an improvement over these and other prior art solutions, and provides a nozzle assembly for spraying cooling water into a flow of superheated steam that is of simple construction with relatively few components, requires a minimal amount of maintenance, and is specifically adapted to, among other things, prevent thermal shock to prescribed internal structural components thereof, to prevent “sticking” of a valve stem thereof, and to create a substantially uniformly distributed spray of cooling water for spraying into a flow of superheated steam in order to reduce the temperature of the steam. Various novel features of the present invention will be discussed in more detail below. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided an improved spray nozzle assembly for an attemperator which is operative to spray cooling water into a flow of superheated steam in a generally uniformly distributed spray pattern. The nozzle assembly comprises a nozzle housing and a valve element which is movably interfaced to the nozzle housing. The valve element, also commonly referred to as a valve pintle or a valve plug, extends through the nozzle housing and is axially movable between a closed position and an open (flow) position. The nozzle housing defines a generally annular flow passage. The flow passage itself comprises three identically configured, arcuate flow passage sections, each of which spans an interval of approximately 120°. One end of each of the flow passage sections extends to a first (top) end or end portion of the nozzle housing. The opposite end of each of the flow passage sections fluidly communicates with a fluid chamber which is also defined by the nozzle housing and extends to a second (bottom) end of the nozzle housing which is disposed in opposed relation to the first end thereof. A portion of the second end of the nozzle housing which circumvents the fluid chamber defines a seating surface of the nozzle assembly. The nozzle housing further defines a central bore which extends axially from the first end thereof. The central bore may be fully or at least partially circumvented by the annular flow passage collectively defined by the separate flow passage sections, the central bore thus being concentrically positioned relative to the flow passage sections. That end of the central bore opposite the end extending to the first end of the nozzle housing terminates at the fluid chamber. 
     The valve element comprises a valve body or nozzle cone, and an elongate valve stem which is integrally connected to the nozzle cone and extends axially therefrom. The nozzle cone has a tapered outer surface. In one embodiment, the junction between the nozzle cone and the valve stem may be defined by a continuous, annular groove or channel formed within the valve element. The valve stem is advanced through the central bore of the nozzle housing. 
     In one embodiment, disposed within the central bore of the nozzle housing is a biasing spring which circumvents a portion of the valve stem, and normally biases the valve element to its closed position. In another embodiment, the biasing spring, though also circumventing a portion of the valve stem, is operatively captured between the nozzle housing and a nozzle shield movably attached or interfaced to a portion of the nozzle housing. 
     In the nozzle assembly, cooling water is introduced into each of the flow passage sections at the first end of the nozzle housing, and thereafter flows therethrough into the fluid chamber. When the valve element is in its closed position, a portion of the outer surface of the nozzle cone thereof is seated against the seating surface defined by the nozzle housing, thereby blocking the flow of fluid out of the fluid chamber and hence the nozzle assembly. An increase of the pressure of the fluid beyond a prescribed threshold effectively overcomes the biasing force exerted by the biasing spring, thus facilitating the actuation of the valve element from its closed position to its open position. When the valve element is in its open position, the nozzle cone thereof and the that portion of the nozzle housing defining the seating surface collectively define an annular outflow opening between the fluid chamber and the exterior of the nozzle assembly. The shape of the outflow opening, coupled with the shape of the nozzle cone of the valve element, effectively imparts a conical spray pattern of small droplet size to the fluid flowing from the nozzle assembly. In that embodiment wherein the biasing spring is disposed within the central bore of the nozzle housing, fluid flow through the nozzle assembly normally bypasses the central bore, and thus does not directly impinge the biasing spring therein. In that embodiment wherein the biasing spring is captured between the first end of the nozzle housing and the nozzle shield, the biasing spring is disposed within the interior of the nozzle shield which effectively shields or protects the biasing spring from any directly impingement from fluid flowing through the nozzle assembly. In any embodiment of the present invention, prescribed portions of the valve stem of the valve element may include grooves formed therein in a prescribed pattern, such grooves being sized, configured and arranged to prevent debris accumulation in the central bore which could otherwise result in the sticking of the valve element during the reciprocal movement thereof between its closed and open positions. 
     The present invention is best understood by reference to the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These, as well as other features of the present invention, will become more apparent upon reference to the drawings wherein: 
         FIG. 1  is a bottom perspective view of a nozzle assembly constructed in accordance with a first embodiment of the present invention, depicting the valve element thereof in a closed position; 
         FIG. 2  is a top perspective view of the nozzle assembly shown in  FIG. 1 ; 
         FIG. 3  is a bottom perspective view of the nozzle assembly of the first embodiment, depicting the valve element thereof in an open position; 
         FIG. 4  is a top perspective view of the nozzle assembly shown in  FIG. 3 ; 
         FIG. 5  is a cross-sectional view of the nozzle assembly of the first embodiment, depicting the valve element thereof in its closed position; 
         FIG. 6  is a cross-sectional view of the nozzle assembly of the first embodiment, depicting the valve element thereof in its open position; 
         FIG. 7  is a top perspective view of the nozzle housing of the nozzle assembly of the first embodiment; 
         FIG. 8  is a cross-sectional view of the nozzle housing shown in  FIG. 7 ; 
         FIG. 9  is cross-sectional view of a variant of the nozzle assembly of the first embodiment wherein the valve element thereof is provided with debris grooves in a prescribed arrangement therein; 
         FIG. 10  is a bottom perspective view of the nozzle assembly of the first embodiment as partially inserted into a complementary nozzle holder and retained therein via a tab washer; 
         FIG. 11  is a top perspective view of the tab washer shown in  FIG. 10  in an original, unbent state; 
         FIG. 12  is a cross-sectional view of a nozzle assembly constructed in accordance with a second embodiment of the present invention, depicting the valve element thereof in a closed position; 
         FIG. 13  is a top perspective view of the nozzle housing of the nozzle assembly of the second embodiment; and 
         FIG. 14  is cross-sectional view of a variant of the nozzle assembly of the second embodiment wherein the valve element thereof is provided with debris grooves in a prescribed arrangement therein. 
     
    
    
     Common reference numerals are used throughout the drawings and detailed description to indicate like elements. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings wherein the showings are for purposes of illustrating preferred embodiments of the present invention only, and not for purposes of limiting the same,  FIGS. 1-6  depict a nozzle assembly  10  constructed in accordance with a first embodiment of the present invention. In  FIGS. 1 ,  2  and  5 , the nozzle assembly  10  is shown in a closed position which will be described in more detail below. Conversely, in  FIGS. 3 ,  4  and  6 , the nozzle assembly  10  is shown in an open position which will also be described in more detail below. As indicated above, the nozzle assembly  10  is adapted for integration into a desuperheating device such as, but not necessarily limited to, a probe type attemperator. As will be recognized by those of ordinary skill in the art, the nozzle assembly  10  of present invention may be integrated into any one of a wide variety of different desuperheating devices or attemperators without departing from the spirit and scope of the present invention. 
     The nozzle assembly  10  of the present invention comprises a nozzle housing  12  which is shown with particularity in  FIGS. 7 and 8 . The nozzle housing  12  has a generally cylindrical configuration and, when viewed from the perspective shown in  FIGS. 1-8 , defines a first, top end  14  and an opposed second, bottom end  16 . The nozzle housing  12  further defines a generally annular flow passage  18 . The flow passage  18  comprises three identically configured, arcuate flow passage sections  18   a ,  18   b ,  18   c , each of which spans an interval of approximately 120°. One end of each of the flow passage sections  18   a ,  18   b ,  18   c  extends to the top end  14  of the nozzle housing  12 . The opposite end of each of the flow passage sections  18   a ,  18   b ,  18   c  fluidly communicates with a fluid chamber  20  which is also defined by the nozzle housing  12  and extends to the bottom end  16  thereof. A portion of the bottom end  16  of the nozzle housing  12  which circumvents the fluid chamber  20  defines an annular seating surface  22  of the nozzle housing  12 , the use of which will be described in more detail below. 
     As is most easily seen in  FIGS. 5-8 , the nozzle housing  12  defines a tubular, generally cylindrical outer wall  24 , and a tubular, generally cylindrical inner wall  26  which is concentrically positioned within the outer wall  24 . The inner wall  26  is integrally connected to the outer wall  24  by three (3) identically configured spokes  28  of the nozzle housing  12  which are themselves separated from each other by equidistantly spaced intervals of approximately 120°. As best seen in  FIG. 8 , one end of each of the spokes  28  terminates at the top end  14  of the nozzle housing  12 , with the opposite end of each spoke  28  terminating at the fluid chamber  20 . The inner wall  26  of the nozzle housing  12  defines a central bore  30  thereof. The central bore  30  extends axially within the nozzle housing  12 , with one end of the central bore  30  being disposed at the first end  14 , and the opposite end terminating at but fluidly communicating with the fluid chamber  20 . Due to the orientation of the central bore  30  within the nozzle housing  12 , the same is circumvented by the annular flow passage  18  collectively defined by the separate flow passage sections  18   a ,  18   b ,  18   c , i.e., the central bore  30  is concentrically positioned within the flow passage sections  18   a ,  18   b ,  18   c.    
     As further seen in  FIG. 8 , the central bore  30  is not of a uniform diameter. Rather, when viewed from the perspective shown in  FIG. 8 , the inner wall  26  is formed such that the central bore  30  defines a top section which is of a first diameter and a bottom section which is of a second diameter less than the first diameter. As a result, the top and bottom sections of the central bore  30  are separated by a continuous, annular shoulder  32  of the inner wall  26 . In the nozzle assembly  10 , the flow passage sections  18   a ,  18   b ,  18   c  are each collectively defined by the outer and inner walls  24 ,  26  and an adjacent pair of the spokes  28 , with the fluid chamber  20  being collectively defined by the outer wall  24  and that portion of the inner wall  26  which defines the shoulder  32  thereof. As is most apparent from  FIGS. 1-4  and  7 , a portion of the outer surface of the outer wall  24  is formed to define a multiplicity of flats  34 , the use of which will be described in more detail below. In the nozzle assembly  10 , it is contemplated that the nozzle housing  12  having the structural features described above may be fabricated from a direct metal laser sintering (DMLS) process in accordance with the teachings of Applicant&#39;s U.S. Patent Publication No. 2009/0183790 entitled Direct Metal Laser Sintered Flow Control Element published Jul. 23, 2009, the disclosure of which is also incorporated herein by reference. Alternatively, the nozzle housing  12  may be fabricated through the use of casting process, such as die casting or vacuum investment casting. 
     The nozzle assembly  10  further comprises a valve element  36  which is moveably interfaced to the nozzle housing  12 , and is reciprocally moveable in an axial direction relative thereto between a closed position and an open or flow position. The valve element  36  comprises a valve body or nozzle cone  38 , and an elongate valve stem  40  which is integrally connected to the nozzle cone  38  and extends axially therefrom. The nozzle cone  38  defines a tapered outer surface  42 , with the junction between the nozzle cone  38  and the valve stem  40  being defined by a continuous, annular groove or channel  44  formed in the valve element  36 . As is best seen in  FIGS. 5 and 6 , the valve stem  40  of the valve element  36  is not of uniform outer diameter. Rather, when viewed from the perspective shown in  FIGS. 5 and 6 , the valve stem  40  includes a top flange portion  46  and a bottom flange portion  48  which each protrude radially outward relative to the remainder thereof. The top and bottom flange portions  46 ,  48  are separated from each other by a prescribed distance, with the bottom flange portion  48  extending to the channel  44 . As also seen in  FIGS. 5 and 6 , the outer diameter of the bottom flange portion  48  is substantially equal to, but slightly less than, the diameter of the bottom section of the central bore  30 . 
     In the nozzle assembly  10 , the valve stem  40  of the valve element  36  is advanced through the central bore  30  such that the nozzle cone  38  predominately resides within the fluid chamber  20 . The nozzle assembly  10  further comprises a helical biasing spring  50  which is disposed within the central bore  30  and circumvents a portion of the valve stem  40  extending therethrough. More particularly, as seen in  FIGS. 5 and 6 , the biasing spring  50  circumvents that portion of the outer surface of the valve stem  40  which extends between the top and bottom flange portions  46 ,  48  thereof. The biasing spring  50  is operative to normally bias the valve element  36  to its closed position shown in  FIGS. 1 ,  2  and  5 . A preferred material for both the nozzle housing  12  and the biasing spring  50  is Inconel 718, though other materials may be used without departing from the spirit and scope of the present invention. 
     The nozzle assembly  10  further comprises a nozzle guide nut  52  which is cooperatively engaged to the valve stem  40  of the valve element  36 . When viewed from the perspective shown in  FIGS. 2 ,  5  and  6 , the nozzle guide nut  52  includes a generally cylindrical first, top portion  54  and a generally cylindrical second, bottom portion  56 . The outer diameter of the top portion  54  exceeds that of the bottom portion  56 , with the top and bottom portions  54 ,  56  being separated from each other by a continuous, annular groove or channel  58 . The outer diameter of the bottom portion  56  is substantially equal to, but slightly less than, the diameter of the top section of the central bore  30 . As such, the bottom portion  56  of the nozzle guide nut  52  is capable of being slidably advanced into the top section of the central bore  30 . 
     The nozzle guide nut  52  further includes a bore which extends axially therethrough, and is sized to accommodate the advancement of a portion of the valve stem  40  through the nozzle guide nut  52 . More particularly, as seen in  FIGS. 5 and 6 , the nozzle guide nut  52  is advanced over that portion of the valve stem  40  extending between the top flange portion  46  and the distal end of the valve stem  40  disposed furthest from the nozzle cone  38 . Such advancement is limited by the abutment of a distal, annular rim  60  defined by the bottom portion  56  of the nozzle guide nut  52  against a complimentary shoulder defined by the top flange portion  46  of the valve stem  40 . When such abutment occurs, the bore of the nozzle guide nut  52 , the central bore  30  of the nozzle housing  12 , and the valve stem  40  of the valve element  36  are coaxially aligned with each other. 
     In the nozzle assembly  10 , the nozzle guide nut  52  is maintained in cooperative engagement to the valve stem  40  through the use of a locking nut  62  and a complimentary pair of lock washers  64 . As seen in  FIGS. 2 ,  5  and  6 , the annular lock washers  64  are advanced over the valve stem  40 , and effectively compressed and captured between the locking nut  62  and an annular end surface  65  defined by the top portion  54  of the nozzle guide nut  52 . In this regard, a portion of the valve stem  40  proximate the distal end thereof is preferably externally threaded, thus allowing for the threadable engagement of the locking nut  62  thereto. The tightening of the locking nut  62  facilitates the compression and capture of the nozzle guide nut  52  between the lock washers  64  and top flange portion  46  of the valve stem  40 . 
     As indicated above, the valve element  36  of the nozzle assembly  10  is selectively moveable between a closed position (shown in  FIGS. 1 ,  2  and  5 ) and an open or flow position (shown in  FIGS. 3 ,  4  and  6 ). When the valve element  36  is in either of its closed or open positions, the biasing spring  50  is confined or captured within the top section of the central bore  30 , with one end of the biasing spring  50  being positioned against the shoulder  32  of the inner wall  26 , and the opposite end of the biasing spring  50  being positioned against the rim  60  defined by the bottom portion  56  of the nozzle guide nut  52 . Irrespective of whether the valve element  36  is in its closed or opened positions, at least the bottom portion  56  of the nozzle guide nut  52  remains or resides in the top section of the central bore  30  defined by the inner wall  26  of the nozzle housing  12 . Similarly, at least a portion of the bottom flange portion  48  of the valve stem  40  remains within the bottom section of the central bore  30 . 
     When the valve element  36  is in its closed position, a portion of the outer surface  42  of the nozzle cone  38  is firmly seated against the complimentary seating surface  22  defined by the nozzle housing  12 , and in particular the outer wall  24  thereof. At the same time, a substantial portion of the bottom flange portion  48  of the valve stem  40  resides within the bottom section of the central bore  30 , as does approximately half of the width of the channel  44  between the valve stem  40  and nozzle cone  38 . Still further, while the bottom portion  56  of the nozzle guide nut  52  resides within the top section of the central bore  30 , the channel  58  between the top and bottom sections  54 ,  56  of the nozzle guide nut  52  does not reside within the central bore  30 , and thus is located exteriorly of the nozzle housing  12 . As previously explained, the biasing spring  50  captured within the top section of the central bore  30  and extending between the rim  60  of the nozzle guide nut  52  and the shoulder  32  of the nozzle housing  12  acts against the nozzle guide nut  52  (and hence the valve element  36 ) in a manner which normally biases the valve element  36  to its closed position. 
     In the nozzle assembly  10 , cooling water is introduced into each of the flow passage sections  18   a ,  18   b ,  18   c  at the first end  14  of the nozzle housing  12 , and thereafter flows therethrough into the fluid chamber  20 . When the valve element  36  is in its closed position, the seating of the outer surface  42  of the nozzle cone  36  against the seating surface  22  blocks the flow of fluid out of the fluid chamber  20  and hence the nozzle assembly  10 . An increase of the pressure of the fluid beyond a prescribed threshold effectively overcomes the biasing force exerted by the biasing spring  50 , thus facilitating the actuation of the valve element  36  from its closed position to its open position. More particularly, when viewed from the perspective shown in  FIG. 6 , the compression of the biasing spring  50  facilitates the downward axial travel of the nozzle guide nut  52  further into the top section of the central bore  30 , and hence the downward axial travel of the valve element  36  relative to the nozzle housing  12 . The downward axial travel of the nozzle guide nut  52  is limited by the abutment of a distal rim  66  of the inner wall  26  located at the top end  14  of the nozzle housing  12  against a complimentary shoulder  68  defined by the top portion  54  of the nozzle guide nut  52  proximate the channel  58 . 
     When the valve element  36  is in its open position, the nozzle cone  38  thereof and that portion of the nozzle housing  12  defining the seating surface  22  collectively define an annular outflow opening between the fluid chamber  20  and the exterior of the nozzle assembly  10 . The shape of such outflow opening, coupled with the shape of the nozzle cone  38 , effectively imparts a conical spray pattern of small droplet size to the fluid flowing from the nozzle assembly  10 . When the valve element  36  is in its open position, the bottom flange portion  48  of the valve stem  40  still resides within the bottom section of the central bore  30 , though the channel  44  resides predominantly within the fluid chamber  20 . Further, both the bottom portion  56  and channel  58  of the nozzle guide nut  52  reside within the top section of the central bore  30 . As will be recognized, a reduction in the fluid pressure flowing through the nozzle assembly  10  below a threshold which is needed to overcome the biasing force exerted by the biasing spring  50  effectively facilitates the resilient return of the valve element  36  from its open position shown in  FIG. 6  back to its closed position as shown in  FIG. 5 . 
     Importantly, fluid flow through the nozzle assembly  10 , and in particular the flow passage sections  18   a ,  18   b ,  18   c  and fluid chamber  20  thereof, normally bypasses the central bore  30 . As previously explained, the top section of the central bore  30  is effectively cut off from fluid flow by the advancement of the bottom portion  56  of the nozzle guide nut  52  into the top section of the central bore  30  proximate the rim  66  of the inner wall  26  irrespective of whether the valve element  36  is in its closed or open positions, and the positioning of the bottom flange portion  48  of the valve stem  40  within the bottom section of the central bore  30  irrespective of whether the valve element  36  is in its open or closed positions. As a result, fluid flowing through the nozzle assembly  10  does not directly impinge the biasing spring  50  residing within the top section of the central bore  30 . Thus, even when the nozzle assembly  10  heats up to full steam temperature when no water is flowing and is shocked when impinged with cold water, the level of thermal shocking of the biasing spring  50  will be significantly reduced, thereby lengthening the life thereof and minimizing occurrences of spring breakage. Further, as is most apparent from  FIGS. 2 ,  4  and  7 , the inflow ends of the flow passage sections  18   a ,  18   b ,  18   c  at the first end  14  of the nozzle housing  12  are radiused, which increases the capacity thereof. This shape of the inflow ends is a result of the use of the DMLS or casting process described above to facilitate the fabrication of the nozzle housing  12 . 
     In addition, in the nozzle assembly  10 , the travel of the valve element  36  from its closed position to its open position is limited mechanically by the abutment of the shoulder  68  of the nozzle guide nut  52  against the rim  66  of the inner wall  26  of the nozzle housing  12  in the above-described manner. This mechanical limiting of the travel of the valve element  36  eliminates the risk of compressing the biasing spring  50  solid, and further allows for the implementation of precise limitations to the maximum stress level exerted on the biasing spring  50 , thereby allowing for more accurate calculations of the life cycle thereof. Still further, the aforementioned mechanical limiting of the travel of the valve element  36  substantially increases the pressure limit of the nozzle assembly  10  since it is not limited by the compression of the biasing spring  50 . This also provides the potential to fabricate the nozzle assembly  10  in a smaller size to function at higher pressure drops, and to further provide better primary atomization with higher pressure drops. The mechanical limiting of the travel of the valve element  36  also allows for the tailoring of the flow characteristics of the nozzle assembly  10 , with the cracking pressure being controlled through the selection of the biasing spring  50 . 
     Referring now to  FIG. 9 , it is contemplated that the valve element  36  and the nozzle guide nut  52  of the nozzle assembly  10  may optionally be provided with additional structural features which are specifically adapted to prevent any undesirable sticking of the valve element  36  during the reciprocal movement thereof between its closed and open positions. More particularly, it is contemplated that the bottom flange portion  48  of the valve stem  40  of the valve element  36  may include a series of elongate debris grooves  70  formed in the outer peripheral surface thereof, preferably in prescribed, equidistantly spaced intervals. As is apparent from  FIG. 9 , the debris grooves  70  circumvent the entire periphery of the bottom flange portion  48 , and each extend in spaced, generally parallel relation to the axis of the valve stem  40 . 
     Similarly, the bottom portion  56  of the nozzle guide nut  52  may include a series of debris grooves  72  within the peripheral outer surface thereof, preferably in prescribed, equidistantly spaced intervals. The debris grooves  72  circumvent the entire periphery of the bottom portion  56 , and each extend in spaced, generally parallel relation to the axis of the bore of the nozzle guide nut  52 , and hence the axis of the valve stem  40  of the valve element  32 . 
     When the valve element  36  is in either its closed position (as shown in  FIG. 9 ) or its open position, the debris grooves  70 ,  72  effectively reduce the contact area between the nozzle guide nut  52  and the nozzle housing  12 , and further between the valve element  36  and the nozzle housing  12 , as reduces the likelihood of the valve element  36  sticking as a result of foreign particles. Though the debris grooves  70 ,  72  may allow for some measure of the flow of cooling water into the top section of the central bore  30  and hence into contact with the biasing spring  50  therein, the amount of cooling water flowing into the top section of the central bore  30  is still insufficient to thermally shock the biasing spring  50 . The inclusion of the debris grooves  70 ,  72  is particularly advantageous in those applications wherein the nozzle assembly  10  may be integrated into a system wherein large amounts of particulates are present in the cooling water. 
     Referring now to  FIGS. 10 and 11 , in a conventional application, the nozzle assembly  10  is cooperatively engaged to a complimentary nozzle holder  74 . As indicated above, thermal cycling, as well as the high velocity head of steam passing through an attemperator including the nozzle assembly  10 , can potentially lead to the loosening thereof within the nozzle holder  74  resulting in an undesirable change in the orientation of the spray angle of cooling water flowing from the nozzle assembly  10 . To prevent any such rotation of the nozzle assembly  10  relative to the nozzle holder  74 , it is contemplated that the nozzle assembly  10  may be outfitted with a tab washer  76  which is shown in  FIG. 11  in an original, unbent state. The tab washer  76  has an annular configuration and defines a multiplicity of radially extending tabs  78  which are arranged about the periphery thereof. As is apparent from  FIG. 11 , one diametrically opposed pair of the tabs  78  is enlarged relative to the remaining tabs  78 . 
     When used in conjunction with the nozzle assembly  10 , the tab washer  76 , in its originally unbent state, is advanced over a portion of the nozzle housing  12  and rested upon an annular shoulder  80  which is defined thereby and extends in generally perpendicular relation to the above-described flats  34 . Thereafter, upon the advancement of the nozzle assembly  10  into the nozzle holder  74 , the enlarged tabs  78  of the tab washer  76  are bent in the manner shown in  FIG. 10  so as to extend partially along and in substantially flush relation to respective ones of a corresponding pair of flats  82  formed in the outer surface of the nozzle holder  74  in diametrically opposed relation to each other. Of the remaining tabs  78  of the tab washer  76 , every other such tab  78  is bent in a direction opposite those engaged to the flats  82  so as to extend along and in substantially flush relation to corresponding ones of the flats  34  defined by the nozzle housing  12 . The bending of the tab washer  76  into the configuration shown in  FIG. 10  effectively prevents any rotation of loosening of the nozzle assembly  10  relative to the nozzle holder  74 . Along these lines, though not shown in  FIGS. 1-9 , it is contemplated that the portion of the outer surface of the housing  12  extending between the shoulder  80  and the first end  14  will be externally threaded as allows for the threadable engagement of the nozzle assembly  10  to complementary threads formed within the interior of the nozzle holder  74 . In this regard, the nozzle assembly  10  and the nozzle holder  74  are preferably threadably connected to each other, with the loosening of this connection as could otherwise be facilitated by the rotation of the nozzle assembly  10  relative to the nozzle holder  74  being prevented by the aforementioned tab washer  76 . 
     Referring now to  FIGS. 12-14 , there is shown a nozzle assembly  100  constructed in accordance with a second embodiment of present invention. In  FIG. 12 , the nozzle assembly  100  is shown in a closed position which will be described in more detail below. Like the nozzle assembly  10  described above, the nozzle assembly  100  is adapted for integration into a desuperheating device such as, but not necessarily limited to, a probe type attemperator. 
     The nozzle assembly  100  comprises a nozzle housing  112  which is shown with particularity in  FIG. 13 . The nozzle housing  112  has a generally cylindrical configuration and, when viewed from the perspective shown in  FIG. 13 , defines a first, top end  114  and an opposed second, bottom end  116 . The nozzle housing  112  further defines a generally annular flow passage  118 . The flow passage  118  comprises three identically configured, arcuate flow passage sections  118   a ,  118   b ,  118   c , each of which spans an interval of approximately 120°. One end of each of the flow passage sections  118   a ,  118   b ,  118   c  extends to an annular shoulder  119  disposed below the first end  114  of the nozzle housing  112  when viewed from the perspective shown in  FIG. 12 . The opposite end of each of the flow passage sections  118   a ,  118   b ,  118   c  fluidly communicates with a fluid chamber  120  which is also defined by the nozzle housing  112  and extends to the bottom end  116  thereof. A portion of the bottom end  116  of the nozzle housing  112  which circumvents the fluid chamber  120  defines an annular seating surface  122  of the nozzle housing  112 , the use of which will be described in more detail below. 
     The nozzle housing  112  defines a tubular, generally cylindrical outer wall  124 , and a tubular, generally cylindrical inner wall  126 , a portion of which is concentrically positioned within the outer wall  24 . The inner wall  126  is integrally connected to the outer wall  124  by three (3) identically configured spokes  128  of the nozzle housing  112  which are themselves separated from each other by equidistantly spaced intervals of approximately 120°. As best seen in  FIG. 13 , one end of each of the spokes  128  terminates at the shoulder  119  of the nozzle housing  112 , with the opposite end of each spoke  128  terminating at the fluid chamber  120 . The inner wall  126  of the nozzle housing  112  defines a central bore  130  thereof. The central bore  130  extends axially within the nozzle housing  112 , with one end of the central bore  130  being disposed at the first end  114 , and the opposite end terminating at but fluidly communicating with the fluid chamber  120 . Due to the orientation of the central bore  130  within the nozzle housing  112 , a portion thereof is circumvented by the annular flow passage  118  collectively defined by the separate flow passage sections  118   a ,  118   b ,  118   c , i.e., the central bore  130  is concentrically positioned relative to the flow passage sections  118   a ,  118   b ,  118   c.    
     As further viewed from the perspective shown in  FIG. 12 , the inner wall  126  includes a first, upper section which protrudes from the outer wall  124 , and a second, lower section which is concentrically positioned within and therefore circumvented by the outer wall  126 , and hence the flow passage  118  collectively defined by the flow passage sections  118   a ,  118   b ,  118   c . The upper section defines the first end  114  of the nozzle housing  122 , as is separated from the second section by a continuous groove or channel  131  which is immediately adjacent the shoulder  119 . 
     In the nozzle assembly  100 , the flow passage sections  118   a ,  118   b ,  118   c  are each collectively defined by the outer and inner walls  124 ,  126  and an adjacent pair of the spokes  128 , with the fluid chamber  120  being collectively defined by the outer wall  124  and that end of the inner wall  26  opposite the end defining the first end  114  of the nozzle housing  112 . As is most apparent from  FIG. 13 , a portion of the outer surface of the outer wall  124  is formed to define a multiplicity of flats  134 , the use of which will be described in more detail below. In the nozzle assembly  100 , it is contemplated that the nozzle housing  112  having the structural features described above may be fabricated from a direct metal laser sintering (DMLS) process in accordance with the teachings of Applicant&#39;s U.S. Patent Publication No. 2009/0183790 referenced above. Alternatively, the nozzle housing  112  may be fabricated through the use of a casting process, such as die casting or vacuum investment casting. 
     The nozzle assembly  100  further comprises a valve element  136  which is moveably interfaced to the nozzle housing  112 , and is reciprocally moveable in an axial direction relative thereto between a closed position and an open or flow position. The valve element  136  comprises a valve body or nozzle cone  138 , and an elongate valve stem  140  which is integrally connected to the nozzle cone  138  and extends axially therefrom. The nozzle cone  138  defines a tapered outer surface  143 . The valve stem  140  of the valve element  136  is not of uniform outer diameter. Rather, when viewed from the perspective shown in  FIG. 12 , the upper end portion of the valve stem  140  proximate the end disposed furthest from the nozzle cone  138  includes a continuous groove or channel  141  formed therein and extending thereabout. The use of the channel  141  will be described in more detail below. The maximum outer diameter of the valve stem  140  is substantially equal to, but slightly less than, the diameter of the central bore  130 . 
     In the nozzle assembly  100 , the valve stem  140  of the valve element  136  is advanced through the central bore  130  such that the nozzle cone  138  predominately resides within the fluid chamber  120 . The length of the valve stem  140  relative to that of the bore  130  is such that when the nozzle cone  138  resides within the fluid chamber  120 , a substantial portion of the length of the valve stem  140  protrudes from the inner wall  126 , and hence the first end  114  of the nozzle housing  112 . 
     The nozzle assembly  100  further comprises a helical biasing spring  150  which circumvents a substantial portion of that segment of the valve stem  140  protruding from the first end  114  of the nozzle housing  112 . The biasing spring  150  resides within the interior of a nozzle shield  142  of the nozzle assembly  100  which is movably attached to the nozzle housing  112 , and in particular that first section of the inner wall  126  thereof. The nozzle shield  142  has a generally cylindrical, tubular configuration. When viewed from the perspective shown in  FIG. 12 , the nozzle shield  142  includes a side wall portion  144  which has a generally circular cross-sectional configuration, and defines a distal end or rim  146 . That end of the side wall portion  144  opposite the distal rim  146  transitions to an annular flange portion  148  which extends radially inward relative to the side wall portion  144 , and defines a circumferential inner surface  150 . 
     In the nozzle assembly  100 , the nozzle shield  142  is cooperatively engaged to both the nozzle housing  112  and the valve stem  136 . More particularly, the flange portion  148  is partially received into the channel  141  of the valve stem  140  which preferably has a complementary configuration. At the same time, the first section of the inner wall  126  of the nozzle housing  112  is slidably advanced into the interior of the nozzle shield  142  via the open end thereof defined by the distal rim  146 . In this regard, the inner diameter of the side wall portion  144  is sized so as to only slightly exceed the outer diameter of the first section of the inner wall  126 , thus providing a slidable fit therebetween. When the nozzle shield  142  assumes this orientation relative to the nozzle housing  112  and valve stem  136 , the biasing spring  150  circumvents that portion of the outer surface of the valve stem  140  which extends between the first end  114  and the flange portion  148 . In this regard, as also viewed from the perspective shown in  FIG. 12 , the top end of the biasing spring  150  is abutted against the interior surface of the flange portion  148 , with the opposite, bottom end of the biasing spring  150  being abutted against the first end  114 . As such, the biasing spring  150  is effectively captured between the nozzle shield  142  and the nozzle housing  112  within the interior of the nozzle shield  142 . The biasing spring  50  is operative to normally bias the valve element  136  to its closed position shown in  FIG. 12 . In this regard, when the valve element  136  is in its closed position, a gap is defined between the distal rim  146  of the nozzle shield  142  and the shoulder  119  defined by the nozzle housing  112 . As will be described in more detail below, the abutment of the distal rim  146  against the shoulder  119  functions as a mechanical stop in the valve assembly  100  as governs the orientation of the nozzle cone  138  of the valve element  136  relative to the valve housing  112  when the valve element  136  is actuated to its fully open position. A preferred material for both the nozzle housing  112  and the biasing spring  150  is Inconel 718, though other materials may be used without departing from the spirit and scope of the present invention. 
     In the nozzle assembly  100 , the valve element  136  is maintained in cooperative engagement to the nozzle housing  112  and the nozzle shield  142  through the use of a locking nut  162  and a complimentary pair of lock washers  164 . As seen in  FIG. 12 , the annular lock washers  164  are advanced over that portion of the valve stem  140  which normally protrudes from the flange portion  148  of the nozzle shield  142 , and effectively compressed and captured between the locking nut  162  and the exterior surface  65  defined by the flange portion  148 . In this regard, that portion of the valve stem  140  protruding from the flange portion  148  is preferably externally threaded, thus allowing for the threadable engagement of the locking nut  162  thereto. 
     As indicated above, the valve element  136  of the nozzle assembly  100  is selectively moveable between a closed position (shown in  FIG. 12 ) and an open or flow position similar to that shown in  FIGS. 3 ,  4  and  6  corresponding to the valve assembly  10 . When the valve element  136  is in either of its closed or open positions, the biasing spring  150  is confined or captured within the interior of the nozzle shield  142 , and thus covered or shielded thereby. Irrespective of whether the valve element  136  is in its closed or opened positions, at least a portion of the upper section of the inner wall  126  remains or resides in the interior of the nozzle shield  142 . 
     When the valve element  136  is in its closed position, a portion of the outer surface  143  of the nozzle cone  138  is firmly seated against the complimentary seating surface  122  defined by the nozzle housing  112 , and in particular the outer wall  124  thereof. At the same time, the aforementioned gap is defined between the distal rim  146  of the nozzle shield  142  and the shoulder  119  defined by the valve housing  112 . The biasing spring  150  captured within the interior of the nozzle shield  142  and extending between the flange portion  148  thereof and the first end  114  of the nozzle housing  112  acts against the valve element  136  in a manner which normally biases the valve element  136  to its closed position. In this regard, the biasing spring  150  normally biases the nozzle shield  142  in a direction away from the nozzle housing  112 , which in turn biases the valve element  136  to its closed position relative to the nozzle housing  112  by virtue of the partial receipt of the flange portion  148  into the complimentary channel  141  of the valve stem  140 . 
     In the nozzle assembly  100 , cooling water is introduced into each of the flow passage sections  118   a ,  118   b ,  118   c  at the ends thereof disposed closest to the first end  114  of the nozzle housing  112 , and thereafter flows therethrough into the fluid chamber  120 . When the valve element  136  is in its closed position, the seating of the outer surface  143  of the nozzle cone  136  against the seating surface  122  blocks the flow of fluid out of the fluid chamber  120  and hence the nozzle assembly  100 . An increase of the pressure of the fluid beyond a prescribed threshold effectively overcomes the biasing force exerted by the biasing spring  150 , thus facilitating the actuation of the valve element  136  from its closed position to its open position. More particularly, when viewed from the perspective shown in  FIG. 12 , the compression of the biasing spring  150  facilitates the downward axial travel of the valve element  136  relative to the nozzle housing  112 . As indicated above, the downward axial travel of the valve element  136  is limited by the abutment of a distal rim  146  of the nozzle shield  142  against the shoulder  119  defined by the nozzle housing  112 . 
     When the valve element  136  is in its open position, the nozzle cone  138  thereof and that portion of the nozzle housing  112  defining the seating surface  122  collectively define an annular outflow opening between the fluid chamber  120  and the exterior of the nozzle assembly  100 . The shape of such outflow opening, coupled with the shape of the nozzle cone  138 , effectively imparts a conical spray pattern of small droplet size to the fluid flowing from the nozzle assembly  100 . As will be recognized, a reduction in the fluid pressure flowing through the nozzle assembly  100  below a threshold which is needed to overcome the biasing force exerted by the biasing spring  150  effectively facilitates the resilient return of the valve element  136  from its open position back to its closed position as shown in  FIG. 12 . 
     Importantly, fluid flow through the nozzle assembly  100 , and in particular the flow passage sections  118   a ,  118   b ,  118   c  and fluid chamber  120  thereof, normally bypasses the central bore  130  and is further prevented from directly impinging the biasing spring  150  by virtue of the same residing within the interior of and thus being covered by the nozzle shield  142  in the aforementioned manner. Thus, even when the nozzle assembly  100  heats up to full steam temperature when no water is flowing and is shocked when impinged with cold water, the level of thermal shocking of the biasing spring  150  will be significantly reduced, thereby lengthening the life thereof and minimizing occurrences of spring breakage. Further, as is most apparent from  FIG. 13 , the inflow ends of the flow passage sections  118   a ,  118   b ,  118   c  at the first end  114  of the nozzle housing  112  are radiused, which increases the capacity thereof. This shape of the inflow ends is a result of the use of the DMLS or casting process described above to facilitate the fabrication of the nozzle housing  112 . 
     In addition, in the nozzle assembly  100 , the travel of the valve element  136  from its closed position to its open position is limited mechanically by the abutment of the shoulder  119  of the nozzle housing  112  against the rim  146  of the nozzle shield  142  in the above-described manner. This mechanical limiting of the travel of the valve element  136  eliminates the risk of compressing the biasing spring  150  solid, and further allows for the implementation of precise limitations to the maximum stress level exerted on the biasing spring  150 , thereby allowing for more accurate calculations of the life cycle thereof. Still further, the aforementioned mechanical limiting of the travel of the valve element  136  substantially increases the pressure limit of the nozzle assembly  100  since it is not limited by the compression of the biasing spring  150 . This also provides the potential to fabricate the nozzle assembly  100  in a smaller size to function at higher pressure drops, and to further provide better primary atomization with higher pressure drops. The mechanical limiting of the travel of the valve element  136  also allows for the tailoring of the flow characteristics of the nozzle assembly  100 , with the cracking pressure being controlled through the selection of the biasing spring  150 . 
     Referring now to  FIG. 14 , it is contemplated that the valve element  136  of the nozzle assembly  100  may optionally be provided with additional structural features which are specifically adapted to prevent any undesirable sticking of the valve element  136  during the reciprocal movement thereof between its closed and open positions. More particularly, it is contemplated that the valve stem  140  of the valve element  136  may include a series of elongate debris grooves  170  formed in and extending partially along the outer peripheral surface thereof, preferably in prescribed, equidistantly spaced intervals. As is apparent from  FIG. 14 , the debris grooves  170  circumvent the entire periphery of and each extend in spaced, generally parallel relation to the axis of the valve stem  140 . One end of each of the grooves  170  terminates proximate the nozzle cone  138 , with the opposite end terminating at approximately the central region of the valve stem  140 . 
     When the valve element  136  is in either its closed position (as shown in  FIG. 12 ) or its open position, the debris grooves  170  effectively reduce the contact area between the valve element  136  and inner wall  126  of the nozzle housing  112 , as reduces the likelihood of the valve element  136  sticking as a result of foreign particles. Though the debris grooves  170  may allow for some measure of the flow of cooling water into the interior of the nozzle shield  142  and hence into contact with the biasing spring  150  therein, the amount of cooling water flowing into the nozzle shield  142  is still insufficient to thermally shock the biasing spring  150 . The inclusion of the debris grooves  170  is particularly advantageous in those applications wherein the nozzle assembly  100  may be integrated into a system wherein large amounts of particulates are present in the cooling water. 
     In a conventional application, the nozzle assembly  100  is cooperatively engaged to the complimentary nozzle holder  74  shown in  FIG. 10 . Thermal cycling, as well as the high velocity head of steam passing through an attemperator including the nozzle assembly  100 , can potentially lead to the loosening thereof within the nozzle holder  74  resulting in an undesirable change in the orientation of the spray angle of cooling water flowing from the nozzle assembly  100 . To prevent any such rotation of the nozzle assembly  100  relative to the nozzle holder  74 , it is contemplated that the nozzle assembly  100  may be outfitted with the tab washer  76  shown in  FIGS. 10 and 11 , and described above. When used in conjunction with the nozzle assembly  100 , the tab washer  76 , in its originally unbent state, is advanced over a portion of the nozzle housing  112  and rested upon the annular shoulder  80  which is defined thereby and extends in generally perpendicular relation to the above-described flats  134 . Thereafter, upon the advancement of the nozzle assembly  100  into the nozzle holder  74 , the enlarged tabs  78  of the tab washer  76  are bent so as to extend partially along and in substantially flush relation to respective ones of a corresponding pair of flats  82  formed in the outer surface of the nozzle holder  74  in diametrically opposed relation to each other. Of the remaining tabs  78  of the tab washer  76 , every other such tab  78  is bent in a direction opposite those engaged to the flats  82  so as to extend along and in substantially flush relation to corresponding ones of the flats  134  defined by the nozzle housing  112 . The bending of the tab washer  76  into the configuration shown in  FIG. 10  effectively prevents any rotation of loosening of the nozzle assembly  100  relative to the nozzle holder  74 . Along these lines, it is contemplated that the portion of the outer surface of the housing  112  extending between the shoulder  80  and the first end  114  will be externally threaded as allows for the threadable engagement of the nozzle assembly  100  to complementary threads formed within the interior of the nozzle holder  74 . In this regard, the nozzle assembly  100  and the nozzle holder  74  are preferably threadably connected to each other, with the loosening of this connection as could otherwise be facilitated by the rotation of the nozzle assembly  100  relative to the nozzle holder  74  being prevented by the aforementioned tab washer  76 . 
     This disclosure provides exemplary embodiments of the present invention. The scope of the present invention is not limited by these exemplary embodiments. Numerous variations, whether explicitly provided for by the specification or implied by the specification, such as variations in structure, dimension, type of material and manufacturing process may be implemented by one of skill in the art in view of this disclosure.