WO1994025842A1

WO1994025842A1 - Temperature sensor with integral debris guard

Info

Publication number: WO1994025842A1
Application number: PCT/US1994/004510
Authority: WO
Inventors: Pennelle J. Trongard; James T. Soukup
Original assignee: Rosemount Aerospace Inc.
Priority date: 1993-04-29
Filing date: 1994-04-25
Publication date: 1994-11-10
Also published as: IL109388A0

Abstract

A sensor measures a temperature of a fluid flowing through a passage (20) in a strut (12), and a debris guard (26) disposed at least partially in the passage (20) splits the flow into two flow portions within the passage (20). A sensing element (32) is disposed in the passage (20) at least partially between the two flow portions. The sensing element (32) has a width (40) which is greater than a width (38) of the debris guard (26). A leading surface (26a) of the debris guard, and a portion of an inner strut wall extending from a point adjacent the leading surface to a point adjacent the sensing element, slant away from an axis of the strut (12). The strut is a cylindrical housing, and a leading edge (42) of the housing is disposed forward of a leading edge (26a) of the debris guard.

Description

TEMPERATURE SENSOR WITH INTEGRAL DEBRIS GUARD

BACKGROUND OF THE INVENTION The present invention relates to a sensor for measuring a temperature of a fluid which is in relative motion with respect to the sensor. In particular, the present invention relates to temperature sensors useable in gas turbine engine applications and other applications for air vehicles. In this field, numerous sensors have been disclosed in the past. U.S. Patent No. 2,970,475 by Werner, for example, teaches a gas temperature probe comprising a hollow elongated conduit connected to a base by a streamlined hollow post. U.S. Patent No. 3,512,414 by Rees teaches a slotted airfoil sensor housing for a temperature sensing element.

SUMMARY OF THE INVENTION The present invention uses a unique configuration to achieve a fast response time of the sensor and good protection of the sensing element from debris which may be entrained in the fluid, while keeping the mass of the sensor housing low and keeping the design of the sensor housing simple, for ruggedness and ease of manufacture. The invention relates to a sensor for measuring a temperature of a fluid flowing relative to the sensor. In one aspect of the invention, the fluid flows through a passage in a strut, and a flow splitter disposed at least partially in the passage splits the flow into two flow portions within the passage. The sensor further includes a sensing element disposed in the passage -at least partially between the two flow portions. According to this aspect of the invention, the sensing element has a width which is greater than a width of the flow splitter.

In a second aspect of the invention a leading surface of the flow splitter, and a portion of an inner strut wall extending from a point adjacent the leading surface to a point adjacent the sensing element, slant away from an axis of the strut. In a third aspect of the invention, the strut is a cylindrical housing, and a leading edge of the housing is disposed forward of a leading edge of the flow splitter.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an oblique view of a temperature sensor according to the invention;

FIG. 2a is a sectional view of the temperature sensor of FIG. 1 along line 2-2;

FIG. 2b is another view of the temperature sensor along line 2-2;

FIG. 3 is a sectional view of the temperature sensor along line 3-3 in FIG. 2a; FIG. 4 is a side elevational view of the temperature sensor of FIG. 1; and

FIG. 5 is a rear elevational view of the temperature sensor of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The terms thermal response time and recovery error are used herein as measures of performance of the sensor. Thermal response time refers to the time required after a step change in fluid temperature for the sensor output to come within a predetermined amount of a final output value, where the predetermined amount is typically 1/e of the difference between the initial and final output values and where e is the base of natural logarithms. Recovery error refers to the quantity

T ¹ t - T ¹ m

T

where T_m is a measured temperature of the fluid from the sensor output and T_c is a total temperature of the fluid. Generally, the more a moving parcel of fluid is slowed down at the sensing location the more kinetic energy is converted to heat within the fluid parcel, and the better (lower) the recovery error will be. Such heating is herein called "adiabatic heating" .

In FIG; 1, temperature sensor 10 comprises a strut 12 mounted on a base 14. Strut 12 contacts a surrounding fluid 16, which moves relative to sensor 10 in the general direction of arrow 18. In a preferred embodiment, base 14 attaches to a wall of a gas turbine engine (not shown) such that strut 12 protrudes into a duct through which fluid 16 passes. Fluid 16 flows through a slot or passage 20 extending from a front face 22 of strut 12 to a rear face 24 of strut 12. Partly visible in FIG. 1 is a debris guard (flow splitter) 26 disposed in passage 20. Strut 12 has a strut axis 28 which as shown is generally perpendicular to flow direction 18. Alternately, strut 12 can be tilted relative to base 14 so that strut axis 28 makes an acute or obtuse angle with flow direction 18. A temperature output 30 issues from a temperature sensing element disposed in passage 20.

FIG. 2a shows a sectional view of temperature sensor 10 along line 2-2 in FIG. 1, with base 14 partially broken away. In this and in other figures, components with reference numbers corresponding to previously described components perform the same functions. Strut 12, shown to be a cylinder, has a streamlined cross-sectional shape elongated along a longitudinal axis 9, substantially parallel to flow direction 18, to reduce drag. A sensing element 32 is positioned in passage 20 downstream of debris guard 26 and between inner walls 34,36 of strut 12, which border passage 20. Sensing element 32 is preferably a platinum resistance thermometer of open-ended hollow tube construction, similar to embodiments taught in U.S. Patent Nos. 3,513,541 and 3,237,139, both of which are incorporated herein by reference. In such construction, a length of platinum wire winds around a hollow tube inside a thin protective metal skin. Hollow tube construction allows sensing element 32 to have less mass, and therefore a faster thermal response time, than a similar element utilizing solid tube construction. However, hollow tube construction generally requires a larger diameter tube than that required in solid tube construction.

It is desirable to protect sensing element 32 at least partially from particles entrained in fluid 16. Debris guard 26 upstream of sensing element 32 deflects debris away from element 32 by simple geometric shielding of a portion of element 32 and also by diverting fluid flow, and thereby also entrained particles, away from a portion of element 32. The desire to keep the weight of temperature sensor 10 low favors a small overall dimension of strut 12. Because of this, debris guard 26 is recessed in passage 20 and has a width 38 which is less than a width 40 of sensing element 32. Strut leading edge 42 is therefore preferably forward of debris guard leading edge 26a, and strut leading edge 42 is also forward of inner wall leading edges 34a and 36a. For a given desired fluid inlet area, making debris guard width 38 smaller than sensing element width 40 permits a narrowing of a portion of passage 20 proximate debris guard 26, thereby permitting a reduced transverse dimension of strut 12 and hence lower weight. Recessing debris guard 26 in passage 20 also helps prevent damage to leading edge 26a of debris guard which may occur during handling. Debris guard 26 has leading surfaces 44,46 forming a wedge to help divert oncoming fluid from sensing element 32. Where the fluid is air, entrained particles having a size of up to about 50 micrometers are thus diverted from striking sensing element 32. Flow splitter leading surfaces 44,46 have flattened portions oriented such that tangent lines 44a,46a (respectively) extending therefrom are also substantially tangent to outer portions of sensing element 32. Preferably, tangent lines 44a, 46a fall within a predetermined distance of an outer surface of element 32, the predetermined distance being approximately 30% of element width 40. Shaping the leading surfaces 44,46 in this way promotes diversion of entrained particles away from sensing element 32 by a gradual turning of the flow so that the particles follow streamlines of the flow. For purposes of ruggedness and ease of manufacture, debris guard 26 in a preferred embodiment is made of stainless steel type 304L and is of unitary construction with neighboring parts of strut 12, which are also made of stainless steel type 304L. Other metals, and nonmetals, can also be used.

Sensing element 32 is sized and positioned relative to neighboring parts of sensor 10 so as to expose portions of element 32 to relatively rapid fluid flow to enhance response time of sensor 10, and to expose other portions of element 32 to relatively stagnant fluid to help reduce recovery error of sensor 10. Sensing element 32 includes thermally responsive zones 32a,32b,32c, 32d as shown in FIG. 2a. The temperature of fluid portions proximate each of these zones influences temperature output 30 because heating or cooling of one zone influences other zones via thermal conduction through sensing element 32, and also because a portion of a transducer wire (discussed below) is embedded proximate each zone. Debris guard 26, sensing element 32, and inner housing walls 34,36 cooperate to direct primary fluid flow between sensing element 32 and inner walls 34,36 to expose zones 32b, 32d to regions of relatively high speed fluid flow and to expose zone 32a to relatively stagnant fluid flow. Thus, debris guard leading surfaces 44,46, and portions of inner walls 34,36 extending from a point adjacent leading surfaces 44,46 (respectively) to a point adjacent sensing element 32, slant away from longitudinal axis 9 to direct fluid toward zones 32b,32d, while debris guard 26 and zone 32a are substantially centered on longitudinal axis 9. For a flow speed far upstream of sensor 10 (hereinafter "external flow speed") of Mach 0.5, a maximum speed of fluid flow proximate zones 32b,32d is calculated to be more than four times a maximum speed of fluid flow- proximate zone 32a. The fast flowing fluid proximate zones 32b,32d undergoes relatively little adiabatic heating, degrading somewhat the recovery error of sensor 10 but enhancing response time by providing fast fluid circulation proximate sensing element 32. Relatively stagnant fluid proximate zone 32a undergoes more adiabatic heating, enhancing recovery error but degrading somewhat thermal response time. Strut 12 further includes obstruction 50 downstream of sensing element 32 and centered on axis 9 to promote a second relatively stagnant fluid parcel proximate zone 32c. Obstruction width 54 is approximately equal to debris guard width 38 and less than sensing element width 40. The invention balances recovery error considerations with thermal response time considerations by exposing zones 32b, 32d to relatively fast flowing fluid and zones 32a, 32c to relatively stagnant fluid, while also partially shielding the sensing element from entrained particles and providing a compact and rugged sensor design.

FIG. 2b shows the same view of sensor 10 as shown in FIG. 2a, but with lines of fluid flow superimposed thereon. The lines of flow are representative of fluid flow for external flow speeds up to approximately Mach 1.0. At such speeds, most of the fluid 16 entering passage 20 flows generally along streamlines 56a, 56b. Debris guard 26 splits the fluid into a first and second flow portion within passage 20, corresponding generally to streamlines 56a and 56b (respectively) . The first flow portion achieves its highest speed at region 58, where it experiences a minimum in an unobstructed transverse dimension of passage 20. At region 58 a portion of inner wall 34 and an outer portion of sensing element 32 form substantially concentric circular arcs. Likewise, the second flow portion achieves its highest speed, approximately equal to the highest speed of the first flow portion, at region 60. Region 60 is substantially congruent to region 58.

As stated earlier, the relative size and position of the parts promotes relatively stagnant fluid in regions 62 and 64. Arrows 66a, 66b and 68a, 68b depict swirling or churning fluid at relatively low speed in those regions. Preferably, outer boundaries of regions 58,60,62,64 delineate a circular cylindrical bore in which sensing element 32 is disposed.

FIG. 3 depicts sensor 10 in cross-section along line 3-3 of FIG. 2a. Both debris guard 26 and obstruction 50 are seen to be unitary members of strut 12. Strut 12 and sensing element 32 are elongated along axis 28, and debris guard 26 is elongated along axis 73 which is parallel to axis 28 and generally perpendicular to flow direction 18.

Sensing element 32 comprises a transducer wire 31 embedded therein and galvanically isolated from outwardly- and inwardly-facing walls of sensing element 32, but in close thermal contact with such walls. Transducer wire 31 is made of platinum, has an approximate diameter of 0.0007 inches (17.78 micrometers) , and has a length sufficient to provide a resistance at zero degrees Celsius of approximately 200Ω. In a preferred embodiment, sensing element 32 has two distinct bifilar transducer wires, coextensive with each other over a sensing length L_τ, to provide two independent temperature outputs corresponding to two measurement channels. Such preferred sensing element combines known subassembly structure of sensor model 153BR3 (which uses a single channel sensing element) with known dual transducer winding construction of sensor model 102CA2W, both models sold by Rosemount Aerospace Inc. of Eagan, Minnesota, U.S.A. Hereafter, only single channel sensing elements will be described for ease of discussion.

Sensing element 32 is disposed within circular cylindrical bore 70 and held in place by stem 72 and bracket 74. A braze joint (not shown) rigidly attaches one end of sensing element 32 to stem 72, while a downward extending sleeve of bracket 74 slidingly engages an inwardly-facing wall at another end of sensing element 32 to provide support yet allow for relative longitudinal movement of parts caused by a thermal expansion mismatch. A weld joint bonds bracket finger 75, and the other two fingers of bracket 74 (see FIG. 1) , to strut 12. Weld joint 81 connects stem 72 to base 14. Transducer wire 31 connects to low impedance wires 33 which exit through base 14 to provide output 30. Low impedance wires 33 comprise platinum alloy wire of approximate diameter 0.012 inches (0.3048 milli¬ meters) . Wires 33 also feed through a barrier 77 of stem 72, which barrier 77 operates to prevent buildup of contaminants from fluid 16 in base 14. Known circuit means for measuring a resistance of transducer wire 31 couples to low impedance wires 33 and provides an indication of measured temperature. Coiled transducer wire 31 extends over a length L_τ less than a length L_p of passage 20, and¹ is displaced in passage 20 away from base 14 to reduce errors due to heat conduction through base 14 and strut 12 from hot bodies proximate base 14. Stem 72 can have a small hole 76 in a leading face thereof to permit fluid to flow relatively slowly from region 62 into a center bore 78 of sensing element 32 and along flow line 79 out the top of strut 12. This lowers recovery error by exposing inner walls of element 32 to relatively stagnant fluid, but also enhances somewhat thermal response time of sensor 10 by providing some fluid circulation along element 32. Debris guard 26 can also have a hole aligned with hole 76 to promote greater fluid flow in bore 78, but such a debris guard hole is not preferred because it structurally weakens debris guard 26.

FIG. 4 shows a side elevational view of temperature sensor 10. Strut 12 and base 14 preferably constitute a unitary, integrally cast or machined body for ease of manufacture. FIG. 5 shows a rear elevational view of temperature sensor 10.

Many variations are permissible within the scope of the invention. For example, rather than having the preferred hollow circular cylindrical shape, the sensing element can have other shapes such as a solid circular cylinder or a hollow polygonal cylinder, or the sensing element can comprise a thick resistive film deposited on a flat substrate which faces in a direction antiparallel to flow direction 18. The sensing element can use other known sensing techniques such as fluorescent time-rate-of-decay or other optical techniques. The sensor can include means for heating the strut for deicing purposes, in which case the strut is preferably made of beryllium-copper alloy. Thermocouples or multiple sensing elements can be used to advantage in some aspects of the invention.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. A sensor for measuring a temperature of a fluid flowing relative to the sensor, comprising: a strut adapted to contact the fluid and having a passage to permit fluid flow through the strut; a wedge-shaped flow splitter having a splitter width and disposed at least partially in the passage, the flow splitter operable to split the flow into two flow portions within the passage; and a sensing element having an element width and being disposed in the passage at least partially between the two flow portions; wherein the splitter width is less than the element width.

2. The sensor of claim 1, wherein the strut, the flow splitter, and the sensing element are elongated along a strut axis, a splitter axis, and an element axis, respectively, and wherein the strut axis, splitter axis, and element axis are generally parallel to each other and generally perpendicular to the fluid flow.

3. The sensor of claim 1, wherein the flow splitter has a first and second leading surface forming a wedge which faces upstream of the fluid flow.

4. The sensor of claim 3, wherein the first leading surface has a substantially flat portion, and wherein a line which is tangent to the flat portion passes within a predetermined distance of an outer surface of the sensing element, wherein the predetermined distance is 30% of the element width.

5. A sensor for measuring a temperature of a fluid flowing relative to the sensor, comprising: a strut having a passage therethrough along an axis to permit fluid flow through the strut, the strut further having an inner wall flanking the passage; a deflector disposed at least partially in the passage and having a leading surface adjacent the inner wall; and a sensing element disposed in the passage; wherein the inner wall has a wall portion extending from a point adjacent the leading surface to a point adjacent the sensing element; and wherein the wall portion and the leading surface slant away from the axis.

6. The sensor of claim 5, wherein the sensing element has a first and second thermally responsive zone, wherein the deflector has a deflector width, and wherein the sensing element is disposed such that the first thermally responsive zone lies within one-half of the deflector width from the axis, and wherein the second thermally responsive zone lies further than one- half of the deflector width from the axis.

7. The sensor of claim 5, wherein the sensing element and the deflector are substantially centered on the axis, the sensor further including an obstruction disposed in the passage such that the sensing element lies between the obstruction and the deflector.

8. The sensor of claim 5, wherein the strut has a cross-sectional shape which is substantially symmetrical about the axis.

9. A temperature sensor, comprising: a cylindrical housing having a slot extending from a front face of the housing to a rear face of the housing, the front face including a leading edge of the housing, the slot being flanked by a first and second inner housing wall which have respectively a first and second leading wall edge, the housing further including a flow splitter integral with the housing and positioned between the first and second inner housing walls, the flow splitter having a leading splitter edge; and a sensing element disposed in the slot; wherein the leading housing edge is forward of the leading splitter edge.

10. The sensor of claim 9, wherein the leading housing edge is forward of the first and second leading wall edge, and wherein the flow splitter has a splitter width and the sensing element has an element width greater than the splitter width.

11. The sensor of claim 9, wherein the slot is disposed along a strut axis, wherein the flow splitter has a leading surface, wherein the first inner housing wall has a wall portion extending from a point adjacent the flow splitter to a point adjacent the sensing element, and wherein the wall portion and leading surface slant away from the strut axis.