Dual enhanced tube for vapor generator

Abstract

A heat exchange assembly for generating steam from a second medium to be used to drive a steam turbine for generating electricity or for other process, includes a tube having a longitudinal axis and an inner wall and an outer wall. The outer wall includes a plurality of spaced fins oriented generally perpendicular to the longitudinal axis. The inner wall defines a preheat zone and a dual phase zone. The preheat zone defines a helical rib configured to provide swirling motion and increase heat transfer surface area to liquid entering the tube increasing heat transfer from the tube to the liquid. The dual phase zone is spaced from the preheat zone and defines a helical rib configured to provide swirling motion to steam and liquid passing through the dual phase zone increasing heat transfer from the tube to the steam and liquid while preventing vapor stagnation and film boiling.

1 . A heat exchange assembly for generating steam from a second medium comprising:
 a tube defining a longitudinal axis and having an inner wall and an outer wall, said outer wall including a plurality of spaced fins oriented generally perpendicular to said longitudinal axis of said tube;   said inner wall defining a preheat zone and a dual phase zone, said preheat zone defining a helical rib configured to provide swirling motion and increase heat transfer surface area to liquid entering said tube thereby increasing heat transfer from said tube to said liquid, and said dual phase zone being spaced from said preheat zone and defining a helical rib configured to provide swirling motion to steam and liquid passing through said dual phase zone thereby increasing heat transfer from said tube to said steam and liquid.   
     
     
         2 . The assembly set forth in  claim 1 , wherein said assembly includes a plurality of tubes configured in a bundle, each tube converting liquid to steam. 
     
     
         3 . The assembly set forth in  claim 1 , wherein said inner wall includes a smooth wall section separating said preheat zone and said dual phase zone. 
     
     
         4 . The assembly set forth in  claim 1 , wherein said spaced fins disposed upon said outer wall of said tube includes an average height of between about 0.6 mm and 0.7 mm. 
     
     
         5 . The assembly set forth in  claim 1 , wherein said spaced fins disposed upon said outer wall of said tube includes an average height of about 0.66 mm. 
     
     
         6 . The assembly set forth in  claim 1 , wherein said spaced fins disposed upon said outer wall of said tube include an average fin thickens of between about 0.2 mm and 0.4 mm. 
     
     
         7 . The assembly set forth in  claim 1 , wherein said spaced fins disposed upon said outer wall of said tube includes an average thickness of about 0.3 mm. 
     
     
         8 . The assembly set forth in  claim 1 , wherein said spaced fins include a density of between about 7 to 12 per centimeter. 
     
     
         9 . The assembly set forth in  claim 1 , wherein said rib includes an average height between about 0.5 mm and 1.0 mm. 
     
     
         10 . The assembly set forth in  claim 1 , wherein said rib includes an average rib thickness of between about 0.38 mm and 0.44 mm. 
     
     
         11 . The assembly set forth in  claim 1 , wherein said helical rib includes an apex angle with respect to tube radius of between about zero and thirty degrees. 
     
     
         12 . The assembly set forth in  claim 1 , wherein said helical rib includes a helix angle to said tube axis of between about ten and forty five degrees. 
     
     
         13 . A method of converting liquid to vapor using a heating fluid, comprising the steps of:
 providing a tube having a first zone, a second zone, and a third zone defined by an inner surface of said tube;   heating an exterior surface of said tube with the heating fluid;   preheating the liquid passing through said tube in said first zone while providing swirling motion the liquid thereby improving heat transfer from said tube to the liquid;   converting at least a portion of the liquid to vapor in said second zone; and   providing swirling motion to the vapor and liquid passing through said third zone thereby preventing film boiling from occurring on the surface of said third zone.   
     
     
         14 . The method set forth in  claim 13 , wherein said step of providing swirling motion to the liquid passing through said first zone is further defined by providing a helical rib to said inner surface of said tube at said first zone. 
     
     
         15 . The method set forth in  claim 13 , wherein said step of providing a tube is further defined by providing a tube with a second zone having a substantially smooth surface. 
     
     
         16 . The method set forth in  claim 13 , wherein said step of providing a tube is further defined by providing a tube having a two phase zone comprising vapor and liquid. 
     
     
         17 . The method set forth in  claim 13 , further including the step of providing sufficient heat energy to said third zone from the heating fluid to continuously maintain both vapor and liquid inside said tube. 
     
     
         18 . The method set forth in  claim 13 , wherein said step of providing swirling motion to the liquid passing through said third zone is further defined by providing a helical rib to said inner surface of said tube at said first zone. 
     
     
         19 . The method set forth in  claim 13 , wherein said step of providing a tube having a first zone, a second zone, and a third zone is further defined by providing a tube having a first zone comprising about 20% of a length of said tube, a second zone comprising about 60% of a length of said tube and a third zone comprising about 20% of a length of said tube. 
     
     
         20 . The method set forth in  claim 13 , further including the step of providing a different swirling motion to the liquid passing through said first zone than the swirling motion provided to the vapor and liquid passing through said third zone. 
     
     
         21 . The method set forth in  claim 13 , further including the step of providing a helical rib to said inner surface of said tube thereby increasing the surface area of said inner surface of said tube providing improved heat transfer from the heating fluid to the liquid passing through said tube. 
     
     
         22 . The method set forth in  claim 21 , wherein said step of providing a helical rib to said inner surface of said tube is further defined by providing a helical rib to said first and said second zones. 
     
     
         23 . A heat exchange assembly for converting water to steam, comprising:
 a housing having an inlet and an outlet;   a plurality of baffle plates oriented in a predetermined fixed relationship, spaced apart creating a serpentine path inside said housing providing a route for a heating medium flowing from said inlet to said outlet;   a plurality of tubes defining an inner wall and an outer wall, said tubes being disposed in said housing in a substantially vertical orientation, each of said plurality of tubes being received by at least some of said baffle plates providing contact to said outer wall with the heating medium flowing along said serpentine path;   said outer wall of said tubes defining fins thereby increasing the surface area of said outer wall and said inner wall defining helical ribbing, said helical ribbing providing swirling motion to water entering said tube and swirling motion to water and steam passing through said tube thereby reducing film boiling associated with converting water to steam while increasing heat transfer through increased surface area of said inner wall associated with said helical ribbing.   
     
     
         24 . The assembly set forth in  claim 23 , wherein said housing includes an inlet plenum for delivering water to said plurality of tubes and outlet plenum for evacuating steam from said plurality of tubes. 
     
     
         25 . The assembly set forth in  claim 23 , wherein said inner wall of said tubes include a first zone, a second zone, and a third zone, said first zone being positioned adjacent said inlet plenum, said third zone being positioned adjacent said outlet plenum and said second zone being positioned between said first zone and said third zone. 
     
     
         26 . The assembly set forth in  claim 25 , wherein said first, second, and third zones each include helical ribbing thereby providing swirling motion to the water and the steam passing through said plurality of tubes. 
     
     
         27 . The assembly set forth in  claim 25 , wherein said second zone comprises a substantially smooth surface of said inner wall and said first zone and said third zone comprise helical ribbing for providing swirling motion to the water adjacent said inlet plenum and swirling motion to the steam adjacent said exit plenum. 
     
     
         28 . The assembly set forth in  claim 23 , wherein said fins are oriented in a substantially perpendicular relationship to the orientation of said tubes. 
     
     
         29 . The assembly set forth in  claim 23 , wherein said fins disposed upon said outer wall of said tube includes an average height of between about 0.6 mm and 0.7 mm. 
     
     
         30 . The assembly set forth in  claim 23 , wherein said fins disposed upon said outer wall of said tube includes an average height of about 0.66 mm. 
     
     
         31 . The assembly set forth in  claim 23 , wherein said fins disposed upon said outer wall of said tube include an average fin thickens of between about 0.2 mm and 0.4 mm. 
     
     
         32 . The assembly set forth in  claim 23 , wherein said fins disposed upon said outer wall of said tube includes an average thickness of about 0.3 mm. 
     
     
         33 . The assembly set forth in  claim 23 , wherein said fins include a density of between about 7 to 12 per centimeter. 
     
     
         34 . The assembly set forth in  claim 23 , wherein said helical ribbing includes an average height between about 0.5 mm and 1.0 mm. 
     
     
         35 . The assembly set forth in  claim 23 , wherein said helical ribbing includes an average rib thickness of between about 0.38 mm and 0.44 mm. 
     
     
         36 . The assembly set forth in  claim 23 , wherein said helical ribbing defines an apex angle relative to a tube radius of between about zero and thirty degrees. 
     
     
         37 . The assembly set forth in  claim 23 , wherein said helical ribbing includes a helix angle to said tube axis of between about ten and forty five degrees.