Heat exchanger tube support bar

#The present invention relates generally to the field of heat exchanger tube supports, and in particular to a new and useful tube support bar for restraining and positioning the U-bends of water tubes within a nuclear steam generator.

#In a pressurized water nuclear power station, steam generators, which are large heat exchangers, transfer heat, produced via nuclear reactions in the reactor core, from a primary water coolant to a secondary water coolant that drives the steam turbine. The primary coolant is pressurized, which allows the primary water coolant to be heated in the reactor core with little or no boiling. For example, in a light water reactor, the primary coolant is pressurized to about 2250 psia and heated to about 600 deg F. in the reactor core. From the reactor, the primary water coolant flows to a steam generator, where it transfers heat to the secondary coolant. In a U-tube, or recirculating steam generator, the primary coolant enters at the bottom of the steam generator, flows through tubes having an inverted U-shape transferring heat to the secondary coolant, and then exits at the bottom of the steam generator. The secondary coolant is pressurized only to a pressure below that of the primary side, and boils as it flows along the outside of the tubes, thereby producing the steam needed to drive the turbine. Nuclear steam generators must be capable of handling large quantities of two-phase secondary coolant moving at high flow rates, and are therefore very large structures. For example, a nuclear U-tube steam generator can weigh more than 450 tons, with a diameter exceeding 12 feet and an overall length of greater than 70 feet. It may contain as many as 9,000 or more of the long, small diameter, thin-walled U-shaped tubes. For a general description of the characteristics of nuclear steam generators, the reader is referred to Chapters 47 and 52 of Steam/Its Generation and Use, 40th Edition, The Babcock & Wilcox Company, Barberton, Ohio, U.S.A., ©1992, the text of which is hereby incorporated by reference as though fully set forth herein.

#Heat exchangers such as nuclear steam generators require tube restraints or supports, to position the tubes and to restrain the tubes against flow induced vibration forces. In the U-bend region of a nuclear steam generator, a large flow of steam and water mixture passes upwards through the tube array, in a general direction which locally is normal to the axis of the individual U-bend tubes. This large two phase flow is able to cause excitation of the U-bend tubes via the turbulent and other flow forces imparted by the flow. As a result, the tubes tend to vibrate in both the out-of-plane and in-plane directions relative to the U-bend plane. Typically this restraint function is provided by an array of flat U-bend support bars. While such flat bars provide positive restraint in the U-bend out-of-plane direction, they provide restraint only by friction in the in-plane direction.

#In the accompanying drawings, forming a part of this specification, and in which reference numerals shown in the drawings designate like or corresponding parts throughout the same:

#FIG. 1 is a sectional front elevation view of a nuclear steam generator where the pocketed tube support bars of the invention may be used;

#FIG. 2 is a partially cut away perspective view of a known U-bend support assembly;

#Referring to the drawings in which reference numbers are used to refer to the same or functionally similar elements, FIG. 3 shows a portion of an improved tube support bar 260 according to the present invention.

#The detailed features of the pocketed tube support bar 260 are shown in FIGS. 3-5. FIGS. 3 and 5 both show that the general shape of the cross section of the pocketed tube support bar 260 resembles the letter “Z.” In the following description the central and extremity portions of the Z-shape will be referred to as the body and the shoulders, respectively. The body is roughly in the shape of a parallelogram having a long diagonal and a short diagonal, shorter than the long diagonal, wherein the diagonals meet at the center of tube support bar 260.

#As shown in FIG. 5 the cross sectional shape of the pocketed tube support bar 260 is defined primarily by two axes passing through the center of the pocketed tube support bar 260; a first axis 20, shown in, but not limited to, the vertical orientation, and a second, diagonal axis 30 at an angle to axis 20.