Heat exchange – With coated – roughened or polished surface
Reexamination Certificate
1993-11-12
2001-10-16
Leo, Leonard (Department: 3743)
Heat exchange
With coated, roughened or polished surface
C165S184000, C122S00600B
Reexamination Certificate
active
06302194
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a pipe having ribs on its inner surface forming a multiple thread, and steam generators and heat transfer systems using the pipe.
Pipes that are ribbed on the inner surface have been used for some time in steam generators, in order to control major thermal strains in the combustion chamber. For instance, an article entitled “Zwangdurchlaufkessel für Gleitdruckbetrieb mit Vertikaler Brennkammerberohrung” [Forced Circulation Boiler for Sliding Pressure Operation with Vertical Combustion Chamber Piping] by H. Juzi, A. Salem and W. Stocker, published in VGB Kraftwerkstechnik [VGB Power Plant Industry] 64, pages 292-302, describes on page 294 thereof, among other things, that on one hand in a region of high combustion chamber thermal strain with smooth evaporator pipes, film evaporation must be expected within a wide range of subcritical pressures, yet on the other hand with pipes which are ribbed on the inner surface, the film evaporation is limited to a pressure range between approximately 206 bar and the critical pressure.
Due to the film of vapor between the metal pipe wall and the liquid phase of the heat absorption medium, the film evaporation hinders the heat transfer, so that the pipe wall temperature rises sharply in the region of the film evaporation. In steam generators with forced circulation of a coolant, the film evaporation occurs practically only in the region in which both the liquid and the vapor phase of the coolant occur simultaneously. Tests have confirmed that with smooth-walled pipes, film evaporation must be expected even with low steam content, and that the evaporation shifts to higher steam contents when pipes that are ribbed on the inner surface are used. This shift simultaneously reduces the extent of the undesired temperature increase in the metal pipe wall.
As can be found both in the above-cited article and in a report presented to The International Heat Transfer Conference in Tokyo, September 1974, paper PGTP 73-54, pages 14-21, the desired shift in the film boiling in commercially available internally grooved pipes, occurs only at relatively high mass flow densities and high coolant speeds.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a pipe with ribs on its inner surface forming a multiple thread and a steam generator for using the pipe, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which have an improved geometry that enables their use independently of the mass flow rate density.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a pipe, comprising a pipe wall having an inner wall surface, and ribs disposed on the inner wall surface forming a multiple thread, the ribs defining a mean inside pipe diameter measured in meters, and the ribs having a lead measured in meters and being equal to between 0.6 and 0.9 times the square root of the mean inside pipe diameter and, preferably between 0.8 and 0.9 times the square root.
In accordance with another feature of the invention, the ribs have a radial height being at least substantially 0.04 times the mean inside pipe diameter.
In accordance with a further feature of the invention, the mean inside pipe diameter is greater than substantially 27 mm.
In accordance with an added feature of the invention, the pipe wall defines a pipe axis, the ribs have sides, as seen in radial direction, and the sides form an angle of substantially from 80 to 90° with the pipe axis.
In accordance with an additional feature of the invention, the pipe wall has an interior, the ribs have sides as seen in radial direction, the ribs have free surfaces facing the interior, the ribs have a rounded transition from the sides to the inner wall surface, and the free surfaces have sharp edges.
In accordance with yet another feature of the invention, the pipe wall encloses a space having a circular cross section except for the ribs, and the pipe wall has an outer jacket with an elliptical or polygonal cross section or an outer jacket with at least one longitudinal rib to be welded to a neighboring pipe or to a longitudinal rib of a neighboring pipe or to another structural part.
In accordance with yet a further feature of the invention, the pipe wall is formed of ferritic material.
In accordance with yet an added feature of the invention, the pipe wall has a pipe axis, the ribs have sides as seen in radial direction, and the sides form a lead angle of less than substantially 60° with a plane perpendicular to the pipe axis.
In accordance with yet an additional feature of the invention, the mean inside pipe diameter is substantially from 30 to 40 mm.
In accordance with again another feature of the invention, the mean inside pipe diameter is substantially 40 mm, the pipe wall has a pipe axis, the ribs have sides as seen in radial direction, and the sides form a lead angle of substantially 55° with a plane perpendicular to the pipe axis.
With the objects of the invention in view, there is also provided a fossil-fuel steam generator, comprising a plurality of pipes being constructed according to the invention, functioning the same and being welded to walls of a combustion chamber.
In accordance with again a further feature of the invention, the pipes are disposed vertically.
With the objects of the invention in view, there is additionally provided a solar-heated steam generator, comprising pipes being constructed according to the invention and being disposed horizontally or at an incline.
With the objects of the invention in view, there is furthermore provided a heated steam generator serving as a waste-heat steam generator, a heat exchanger or a steam generator for absorbing after-heat in a nuclear power plant.
Pipes which are constructed and used in accordance with the invention are highly advantageous, because they permit low axial flow speeds without the harmful occurrence of film boiling, so that the pressure loss of the coolant in the pipe from friction is quite low, with a virtually unchanged geodetic pressure loss. As a result, in an unexpectedly advantageous way, there is a simultaneous reduction in the temperature differences at the end of the pipe occurring between spatially parallel pipes from the unavoidably unequal thermal output. As tests have shown, this effect ensues to a satisfactory extent if a coolant which ideally follows the rib shape and flows at a slow axial speed of 1 m/s, is exposed on its outside to a calculated centrifugal acceleration that is 2½ times greater than the acceleration due to gravity, because of the swirl motion imposed upon it.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a pipe with ribs on its inner surface forming a multiple thread and a steam generator for using the pipe, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
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Les chaudiéres de 700 MW de la centrale de Cordemais, Revue Générale de Ther
Kastner Wolfgang
Kohler Wolfgang
Wittchow Eberhard
Greenberg Laurence A.
Leo Leonard
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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