Abstract:
A tube holder for use in turbomachinery includes a housing having a passage for receiving a tube, the housing adapted for attachment to a turbomachinery component; and a metal foam component located within the housing and arranged to engage a length portion of the tube to thereby hold the tube within the housing and reduce undesirable vibrations in the tube during operation of the turbomachinery.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to gas turbine technology generally, and more specifically, to a method and system for protecting sensitive instrumentation subject to thermal stress vibration and stress concentrators in, for example, an exhaust gas duct of the gas turbine. 
         [0002]    In certain gas turbine applications, a tubing system is housed in an exhaust duct of a gas turbine and is used to contain one or more sensors, for example, thermal Bragg sensors. During testing, however, the flexible tube and/or sensors have been known to fail due to a combination of thermal stress, vibration and stress concentrators introduced by the support mechanisms used to hold and/or clamp the sensor tube to an array of circumferentially-spaced holders (or tube supports). 
         [0003]    Various clamping schemes have been tried with only limited success. In addition, more exotic sensor holding materials have been tested but the materials of choice can have a significant negative impact on cost. Accordingly, there remains a need for a relatively simple and inexpensive mechanism by which the sensor tube and the sensors within the tube can be better protected in the harsh thermal environment of a gas turbine exhaust duct. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    In accordance with an exemplary but nonlimiting embodiment, there is provided a tube holder for use in turbomachinery comprising a housing having a passage for receiving a tube, said housing adapted for attachment to a turbomachine component; and a metal foam component located within the housing and shaped and arranged to engage and hold a length portion of the tube within the housing. 
         [0005]    In another aspect, there is provided a tube holder for a sensor tube adapted to be supported within a duct of a turbine engine, the tube holder comprising a housing adapted for mounting on a support post extending into the duct; the housing having a passage for receiving the sensor tube; and a metal foam component located within the housing and arranged to engage a length portion of the sensor tube. 
         [0006]    In still another aspect, the invention provides a method of supporting a flexible sensor tube in a tube holder comprising providing a housing formed with a passage therethrough; and locating a metal foam sleeve within the passage and supporting the sensor tube within the metal foam sleeve. 
         [0007]    The invention will now be described in greater detail in conjunction with the drawings identified below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a simplified partial end elevation showing a sensor tube supported within a duct by a plurality of supports; 
           [0009]      FIG. 2  is an enlarged detail of an installation as shown in  FIG. 1 ; 
           [0010]      FIG. 3  is a side elevation, partly in section, showing a tube holder for use in a support as shown in  FIGS. 1 and 2  in accordance with a first exemplary but nonlimiting embodiment; 
           [0011]      FIG. 4  is a side elevation, partly in section, showing another tube holder for use in a support as shown in  FIGS. 1 and 2  in accordance with another exemplary but nonlimiting embodiment; and 
           [0012]      FIG. 5  is a perspective view, partly in section, of a third tube holder for use in a support as shown in  FIGS. 1 and 2  accordance with still another exemplary but nonlimiting embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]      FIGS. 1 and 2  partially illustrate in simplified form a cylindrical duct or housing  10  which may be, in the illustrated example, a turbine exhaust duct. The duct  10  is comprised of an annular wall  12 , only partially shown. A flexible sensor tube  14  extends about the duct wall  12 , supported by radially inwardly directed posts or tubing supports  16 . The sensor tube  14  encloses and supports one or more sensors (for example, thermal Bragg sensors, not shown) that may be spaced circumferentially about the duct wall. As shown in  FIG. 1 , the flexible tube enters the duct wall at  18  and may exit the duct wall at a location proximate the entry location. As shown on the right-hand side of the  FIG. 1 , the flexible tube  14  may sag between posts  16  due to differential thermal growth, high stresses and other factors. Typically, the tube  14  is clamped to the posts  16  by various known tube holders or supports  20  as best seen In  FIG. 2 . It has been observed that where the tube is tightly clamped within the holder  20 , the sagging of the tube tends to produce crimps in the tube where it enters and exits the holder, giving rise to stress concentrators leading to eventual failure of the tube. 
         [0014]    In other prior arrangements, the tube passes through a tube holder or support (similar to the device  20 ) on the support post  16 , but without an internal clamping mechanism, so as to enable the tube to slide relative to the holder and thus avoid sagging and bending stresses. On the other hand, the non-clamped arrangement promotes undesirable vibrations in the tube, possibly leading to fatigue cycle failures. 
         [0015]      FIG. 3  illustrates a first exemplary but nonlimiting embodiment of a tube clamp that may be mounted within an axial passage through the holder  20  that does not result in crimping of the tube  14 , and that allows some limited sliding movement but without vibrations attendant the known, non-clamped tube holders. 
         [0016]    More specifically, the opening in the end plate or wall  22  (see  FIG. 2 ) of a tube holder  20  is fitted with a nut body  24  by any suitable fastening arrangement. The nut body includes a projecting, exteriorly threaded inner nut component  26  formed with a tapered or conical inside wall  28 . An open-ended metal foam ferrule or sleeve  30  has a smooth interior diameter defined by wall  32 , and a conical exterior wall  34  adapted to mate with the inside wall  28  of the nut component  26 . An internally threaded outer nut component (or lock nut)  36  is threaded onto the inner nut component  26 , such that an end face  38  urges the ferrule  30  axially into the nut component  26 , thereby wedging the metal foam ferrule  30  against a length portion of the tube  14 . The nut component is formed with a center aperture  40  permitting passage of the tube. It will be understood that the lock nut  36  will be tightened to the prescribed torque that results in optimum clamping of the tube  14  but allows some limited axial movement. The tube  14  is fully engaged by the ferrule  30 , however, thereby reducing if not eliminating any undesired vibration of the tube  14  within the holder  20 . It will be appreciated that the clamping device described above is not limited to use with the illustrated holders  20 , but may be used in other holder designs as well. 
         [0017]    The metal foam ferrule  30  may be formed from any of a variety of high temperature alloys typically used in gas turbine applications, e.g. iron-chrome alloys (e.g. FeCrAlY), nickel-iron alloys (e.g., Inconel), aluminum alloys (for low temperature applications), etc. The density of the foam will be chosen so as to provide the required holding power without, however, also resulting in crimping of the tube. The metal foam ferrule may be of one- or two-piece construction. 
         [0018]      FIG. 4  illustrates another exemplary but nonlimiting embodiment where a tubing holder  42  is composed of two substantially identical housing portions  44 ,  46  joined together by, for example, bolts  48  and formed so as to provide a center cavity  50  of spherical shape. A metal sphere  52 , comprised of hemispheres  54 ,  56  is seated with in the cavity  50 , with center bores  58 ,  60  axially aligned to provide a through passage for the tube  14 . The bores  58 ,  60  have diameters sufficiently large to accommodate a metal foam sleeve  62  that fits over the tube  14 . Tightening of the bolts  48  applies a light clamping force on the tube  14  through the foam sleeve  62 . Note that the space surrounding the tubing  14  at either end of the housing (beyond the edges of the sleeve  62 ) will allow for some relative angular movement between the tube and the housing portions  44 ,  46  without wearing on the tube. In addition, the sphere  52  is permitted some limited degree of rotation within the cavity  50 , again permitting movement of the tube without damaging the tube and without affecting the clamping of the tube via the foam sleeve  62 . 
         [0019]      FIG. 5  illustrates another exemplary but nonlimiting embodiment of a tube holder. In this variant, back-to-back tube holders  64 ,  66  are mounted on the post  16  so as to support a pair of adjacent sensor tubes  14 . Each holder is composed of split housing sections  68 ,  70 , noting that the housing section  68  for the holder  66  has been removed to facilitate an understanding of the construction. The holders  64 ,  66  may be fastened together by bolts (not shown) passing through aligned sets of bolt holes  72 . A generally semi-cylindrical cavity  74  is formed in each housing section, with larger-diameter annular grooves  76 ,  78  formed at opposite ends of the cavity. These grooves receive oversized tube guides or disks  80 ,  82  with center apertures (one shown at  84 ) that receive the tube. The disks  80 ,  82  may be formed with tabs or keys  86  that fit into notches formed in the grooves  76 ,  78  to lock the disks against rotation when secured between the housing sections. 
         [0020]    Between the tube guides or disks  80 ,  82 , the cavity  74  is filled with a metal foam sleeve  88  having a metal foam composition as described above. The foam sleeve  88  encloses and engages the tube  14 , but the tube is able to slide axially relative to the sleeve and the holder  66 . This arrangement provides support while preventing vibration “chatter” and thus wear on the tube. Note that clamping forces generated by the assembly of housing sections  68 ,  70  are absorbed by the disks  80 ,  82 , insuring that the sleeve  88  is not subject to excessive clamping forces. 
         [0021]    In each of the described embodiments, the metal foam sleeve is used to either clamp the sensor tube without damage to the tube, and/or to support the sensor tube in a manner that prevents unwanted vibrations. 
         [0022]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.