GAS PROBES

Abstract

A fluid sampling probe is provided. The probe comprises an elongate main tube having: an inlet end, an outlet end, and a fluid-sampling bore disposed within the elongate main tube and extending from the inlet end and to the outlet end; at least three elongate helical fins which are adapted to prevent or reduce probe damage caused by vortex-induced vibration. The elongate helical fins overlap along a length of the elongate main tube; and the fluid-sampling bore is open at or adjacent to the inlet end, and is adapted to receive a fluid-sample extracted from a fluid flowing past the fluid sampling probe. Numerous other aspects are provided.

Claims

1. A fluid sampling probe comprising: an elongate main tube having: an inlet end, an outlet end, and a fluid-sampling bore disposed within the elongate main tube and extending from the inlet end and to the outlet end; at least three elongate helical fins which are adapted to prevent or reduce probe damage caused by vortex-induced vibration, wherein the elongate helical fins overlap along a length of the elongate main tube; and wherein the fluid-sampling bore is open at or adjacent to the inlet end, and is adapted to receive a fluid-sample extracted from a fluid flowing past the fluid sampling probe.

2. The fluid sampling probe of claim 1, wherein the elongate main tube is substantially circular in cross-section.

3. The fluid sampling probe of claim 1, wherein each elongate helical fin includes a radially outermost surface which is flat.

4. The fluid sampling probe of claim 1, wherein circumferentially-spaced helical flow channels are defined by respective neighboring elongate helical fins.

5. The fluid sampling probe of claim 4, wherein the elongate helical fins form edges of the associated helical flow channels.

6. The fluid sampling probe of claim 4, wherein an end of each circumferentially-spaced helical flow channel is substantially flush with the outlet end.

7. The fluid sampling probe of claim 4, wherein the circumferentially-spaced helical flow channels terminate at or adjacent to the outlet end and at separate locations.

8. The fluid sampling probe of claim 1, wherein the elongate helical fins have a constant depth which is in the range 0.05 D to 0.5 D, where D is an external diameter or width of the outlet end.

9. The fluid sampling probe of claim 1, wherein a pitch of each of the plurality of elongate helical fins is in the range D to 20D, where D is an external diameter or width of the inlet end.

10. The fluid sampling probe of claim 1, wherein the elongate helical fins overlap each other in an axial direction of the elongate main tube.

11. The fluid sampling probe of claim 1, wherein a or more of a portion of the probe that lies within a flowing fluid has said elongate helical fins.

12. The fluid sampling probe of claim 1, wherein the elongate helical fins originate adjacent to the inlet end at separate locations.

13. The fluid sampling probe of claim 1, wherein a number of elongate helical fins is in a range of three to nine.

14. The fluid sampling probe of claim 1, wherein the elongate helical fins are integrally formed on the elongate main tube.

15. A fluid sampling probe comprising: an elongate main tube having: an inlet end, an outlet end; a fluid-sampling bore disposed within the elongate main tube, the fluid-sampling bore extending from the inlet end to the outlet end; the fluid-sampling bore being open at or adjacent to the inlet end and adapted to receive a fluid sample extracted from a fluid flowing past the fluid-sampling probe; a plurality of elongate helical fins which are adapted to prevent or reduce probe damage caused by vortex-induced vibration, a number of said elongate helical fins being in a range of three to nine, the helical fins winding along and around an outer surface of at least a portion of the elongate main tube so as to overlap each other.

16. A fluid sampling probe comprising: an elongate main tube having: an inlet end, an outlet end, and a fluid-sampling bore disposed within the elongate main tube and extending from the inlet end and to the outlet end; at least three elongate helical fins which are adapted to prevent or reduce probe damage caused by vortex-induced vibration, wherein the elongate helical fins wind along and around at least a portion of the length of the elongate main tube so as to overlap each other; and wherein the fluid-sampling bore is open at or adjacent to the inlet end, and is adapted to receive a fluid-sample extracted from a fluid flowing past the fluid sampling probe.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Features of the present invention can be more clearly understood from the following detailed description considered in conjunction with the following drawings, in which the same reference numerals denote the same elements throughout, and in which:

[0042] FIG. 1 shows a side view of a gas sampling probe according to a first embodiment of the invention;

[0043] FIG. 2 shows a diametric sectioned view corresponding to FIG. 1;

[0044] FIG. 3 is a more detailed section of the hemispherical inlet end shown in FIG. 2;

[0045] FIG. 4 shows a section of an example of a retractable gas sampling probe, according to a second embodiment of the invention;

[0046] FIG. 5 shows a side view of a thermowell according to a third embodiment of the invention;

[0047] FIG. 6 shows a side view of a thermowell according to a fourth embodiment of the invention;

[0048] FIG. 7 shows a side view in cross section of a thermowell according to a fifth embodiment of the invention; and

[0049] FIG. 8 shows a side view of a thermowell according to a sixth embodiment of the invention.

DETAILED DESCRIPTION

[0050] FIG. 1 shows a side view of a gas sampling probe according to a first embodiment of the invention. The gas sampling probe 10 comprises an elongate main tubular body 12 with an inlet end 14 and an outlet end 16. A flange 18 is attached to the main body 12 near the outlet end 16. This is a conventional flange that in use allows the probe to be attached in a fluid tight manner to the system being sampled. Main body 12 comprises an upper tubular portion 20 that is integral with a slightly smaller diameter lower portion 22. The difference in diameter between the upper portion 20 and lower portion 22 may be such as to allow several helical fins 24 to be attached in a streamline fashion; that is such that the radial extension of the lower portion 22 plus fin 24 fairly closely corresponds to the external radius of the upper tube portion 20. It should be noted that while a plurality of fins is preferred it is not essential to have three fins; for example two or four fins may be used.

[0051] FIG. 2 shows a diametric sectioned view corresponding to FIG. 1. It can be seen that main body 10 has a constant diameter bore 30. The main body member 10 has a wall thickness selected to provide the structural strength required of the probe in use. A sampling tube 32 is positioned within bore 30, preferably along the central axis of bore 30. Sampling tube 32 is held in place by an end member 34. The sampling tube is preferably constructed from stainless steel, and preferably has an internal diameter of 0.05 to 5 mm; and more preferably a diameter in the range 2 to 4 mm. The sampling tube 32 has a wall thickness selected to provide the structural strength required of the probe in use. Preferably the sampling tube has a wall thickness in the range 0.2 to 2 mm.

[0052] FIG. 3 is a more detailed section of the hemispherical inlet end shown in FIG. 2. Preferably, end member 34 takes the form of a hemispherical insert and is sealed within the lower portion 22 by a circumferential weld 38. The surface finish 40 of the hemispherical insert 34 is machined to give a surface roughness of less than 0.4 RA; this reduces local turbulence and help prevent the buildup of particulates and contaminants from the process on surface 40. Preferably, the surface finish 40 is further smoothed by the application of the Silcosteel-AC surface coating or the like. The inlet end of sampling tube 32 is sealed into the hemispherical insert 34 by means of a circumferential weld 41. The internal surface of the sampling tube 32 is preferably treated, with an electro-polishing treatment, to reduce surface roughness; and for critical analysis conditions may be further treated with either the Silcosteel or Sulfinert surface coating or the like. Sampling tube 32 may comprise PTFE or a similar inert material; such as PVDF, in which case weld 41 would be replaced by an appropriate adhesive bond.

[0053] FIG. 4 shows a section of an example of a retractable gas sampling probe, according to a second embodiment of the invention. In this embodiment main body 12 is not directly fixed to a flange 50 but rather is fixed to a flange by an adjustment/retraction means 52. This adjustment means can be any of several known to the skilled artisan; for example it may comprise a threaded tube 54 fixed at one end to flange 50 through which the main body 12 passes; tube 54 having fluid sealing means 56; for example an O-ring seal. Adjustment means 52 further comprises an arm member that comprises cylindrical portion 6o and arm portions 62. Cylindrical portion 60 has a threaded bore that in use co-operates with the outer thread of tube 54 to allow the position of the probe 10 to be adjusted in an axial direction.

[0054] The use of the helical fins 24 and small bore lining tube 32 to such retractable probes is generally more beneficial than to fixed probes because they generally have longer unsupported probe lengths making it more susceptible to the effects of vortex shedding and the probe itself is much longer making the internal volume that much greater.

[0055] FIG. 5 shows a thermowell according to a third embodiment of the invention. The thermowell 110 comprises an elongated tube 112 with an internal bore (not shown) and sealed with a hemispherically shaped cap 118 at one end. The other end of tube 112 is connected via a flange 114 to temperature probe inlet 116. Inlet 116 comprises a short tube through which a temperature probe such as a thermocouple or thermistor may be inserted into the internal bore of tube 112 such that the sensing element of the probe is near the bottom of the internal bore and so in close thermal proximity to end cap 118.

[0056] Tube 112 further comprises three helically arranged fins 120a, 120b, 120c each fin being of width W and depth d. In this case the fins trace a three dimensional curve round and simultaneously advancing along a cylinder. However, tube 112 may have a shape other than a cylinder; for example it may have a somewhat conical portion. The fins are shown extending along the entire length of elongated tube 112; however; the fins may alternatively extend only part way along the length of tube 112. The fins 120 may be integrally formed with or attached to tube 112.

[0057] It has been found that in use such fins may reduce or eliminate vortex shedding from the thermowell; this is a significant benefit as such vortex shedding can result in cyclic forces that will damage the thermowell, or even the temperature sensor itself: especially if the period of such cycles is at or near the resonant frequency of the thermowell. While the fin preferably has a cross section with a sharp edge; for example a rectangular cross section other shaped cross sections are possible; for example the cross section may have a semicircular outer portion. Preferably the width (W) of the fin is in the range 0.005 D to 0.2 D, where D is the external diameter or width of the tube. Preferably, the depth of the fin (d) is in the range 0.05 D to 0.5 D. The pitch of each helical fin is preferably in the range D to 20 D, more preferably 2 D to 10 D and most preferably 3 D to 7 D. It has been found that fins having dimensions within these ranges are particularly effective in reducing or eliminating such vortex shedding.

[0058] FIG. 6 shows a fourth embodiment of the invention. In this embodiment the thermowell 210 comprises a cylindrical tube 212 with a flat closed end 218 at one end of the tube and a threaded 214 hexagonal connector 216 at the other. Again, connector 216, threaded portion 214 and tube 212 have an internal bore (not shown) that in use accommodates a temperature sensor. In this embodiment three helical fins 220a, 220b and 220c are attached or formed to the outer surface of tube 212.

[0059] FIG. 7 shows a thermowell where the tip 310 of the thermowell, which is the active portion in providing the measurement/thermometry requirements, is made of a higher conductivity material than the main body 320. Further tip 310 may be made of a thinner section material than the main body 320. Ideally tip 310 is thermally separated or partially thermally separated from main body 320 by a thermal barrier 330. Tip 310 is attached to main body 320 by means such as screwing, gluing, soldering, welding or any appropriate method suitable for the application.

[0060] FIG. 8 shows a thermowell were the measurement/thermometry requirements are provided by a capsule 410, containing the primary temperature measuring device (not shown) which is held, supported and attached, to the containment means, by main body 420. In this case the main body 420 is of an open lattice structure allowing the medium whose temperature is to be measured to be in thermal contact with the capsule 410. Preferably, thermal capsule 410 is thermally separated or partially thermally separated from main body 420 by a thermal barrier 430. In this embodiment the means of transmitting the measured temperature from the primary measuring device contained in capsule 410 may be a conduit or cable 440 which is sealed/connected to main body 420 at a distance from capsule 410 thereby reducing conductivity loss.

[0061] The foregoing merely illustrates the principles of this invention, and various modifications can be made by persons of ordinary skill in the art without departing from the scope and spirit of this invention.