Thermocouple with out-of-line aspiration holes

Abstract

The response time of a thermocouple is improved by offsetting the outlet aspiration opening or openings in the thermocouple protective housing from the gas flow axis and the inlet opening. The outlet aspiration opening is located substantially at the gas separation point which is a point of minimum gas pressure. The degree of offset is thus chosen to maximize the pressure differential, ΔP, between the inlet and the outlet openings. This increases the gas flow rate through the housing and past the thermocouple junction thereby substantially improving the thermocouple response time.

What is claimed as new and desired to be secured by Letters Patent of the United States is: 
     
       1. A thermocouple assembly for measuring the temperature of a fluid stream comprising: (a) a casing,   (b) at least one pair of dissimilar wires disposed in said casing and forming a thermocouple junction,   (c) insulation dispersed in said casing and separating said dissimilar wires from said casing and from each other,   (d) a protective housing spaced apart from and surrounding at least a portion of said casing containing a thermocouple junction,   (e) means to allow a part of the heated stream to flow through said protective housing and past said casing in the area of the thermocouple junction, including: (1) an inlet opening in said housing positioned essentially along the flow axis of the stream, .Iadd.said inlet opening in axial alignment with said thermocouple junction, and .Iaddend.   (2) at least one outlet opening in said housing downstream from the inlet opening to establish a flow path through said housing, .Iadd.and .Iaddend.     (f) means for increasing the flow rate of the fluid through said housing by locating the outlet opening at a minimum fluid pressure point, thereby maximizing the pressure difference between inlet and outlet openings to provide rapid response of the thermocouple to changes in fluid stream temperature.   
     
     
       2. The thermocouple assembly according to claim 1 wherein said outlet opening is radially offset from the axis of said inlet opening. 
     
     
       3. The thermocouple according to claim 2 wherein an outlet opening in the housing is located either 75° or 285° from the downstream side of the fluid stream flow axis. 
     
     
       4. The thermocouple according to claim 2 wherein an outlet opening in the housing is located within a band extending either from 45°-85° or 275°-315° from the downstream side of the fluid stream flow axis. 
     
     
       5. The thermocouple according to claim 2 wherein offset outlet openings are located on both sides of said axis. 
     
     
       6. The thermocouple according to claim 5 wherein the offset outlet openings are respectively located 75° and 285° from the downstream side of the fluid stream flow axis. 
     
     
       7. The thermocouple according to claim 5 wherein the offset openings are respectively located within bands extending from 45°-85° and from 275°-315° from the downstream side of the fluid stream flow axis. 
     
     
       8. The thermocouple according to claim 5 wherein the outlet openings are axially offset from the plane of the inlet opening. 
     
     
       9. The thermocouple according to claim 8 wherein the outlet openings are respectively located above and below the plane of the inlet openings. 
     
     
       10. The thermocouple according to claim 6 wherein the outlet openings are axially offset from the plane of the inlet opening. 
     
     
       11. The thermocouple according to claim 6 wherein the outlet openings are respectively located above and below the plane of the inlet opening. 
     
     
       12. The thermocouple according to claim 7 wherein the outlet openings are axially offset from the plane of the inlet opening. 
     
     
       13. The thermocouple according to claim 7 wherein the outlet openings are respectively located above and below the plane of the inlet opening. 
     
     
       14. A thermocouple assembly for measuring the temperature of a gaseous stream including at least one thermocouple junction positioned in a casing surrounded by a protective housing spaced from said casing, (a) means to expose the thermocouple junction in said housing to a gaseous stream including an inlet opening and at least one outlet opening in said housing, .Iadd.the inlet opening and thermocouple junction being axially aligned,.Iaddend.   (b) said outlet opening being .Iadd.radially .Iaddend.offset from the inlet opening, the degree of off-set being chosen to locate the outlet opening in a minimal pressure area on the outside of the housing to maximize the pressure difference across said openings and the gas flow rate through said housing.   
     
     
       15. A thermocouple assembly for measuring the temperature of a gaseous stream including at least one protected thermocouple junction surrounded by a housing spaced from said thermocouple, the space between said protected thermocouple and said housing being accessible to the gaseous stream, (a) an inlet and at least one outlet opening in said housing to produce gas flow through the space between said thermocouple and . .the.!. .Iadd.said .Iaddend.housing, .Iadd.the inlet opening and thermocouple junction being axially aligned,.Iaddend.   (b) means to maximize the gas flow rate . .throught.!. .Iadd.through .Iaddend.said space comprising locating the outlet opening in said housing substantially at the gas separation point for the gaseous boundary layer on the exterior of the housing whereby the gas pressure at the outlet opening is minimized and the pressure differential between inlet and outlet openings is maximized. .Iadd.16. A thermocouple assembly for measuring the temperature of a fluid stream comprising:   (a) a casing;   (b) a first pair of dissimilar wires disposed in said casing and forming a first thermocouple junction;   (c) a second pair of dissimilar wires disposed in said casing and forming a second thermocouple junction axially spaced from said first thermocouple junction;   (d) insulation dispersed in said casing and separating said dissimilar wires from said casing and from each other;   (e) a protective housing spaced apart from and surrounding at least a portion of said casing containing a first thermocouple junction;   (f) means to allow a part of the heated stream to flow through said protective housing and past said casing in the area of the thermocouple junctions, including: (1) an inlet opening in said housing positioned essentially along the flow axis of the stream, and   (2) at least one outlet opening in said housing downstream from the inlet opening to establish a flow path through said housing; and     (g) means for increasing the flow rate of the fluid through said housing by locating the outlet opening at a minimum fluid pressure point, thereby maximizing the pressure difference between inlet and outlet openings to provide rapid response of the thermocouple to changes in fluid stream   
     
     
        temperature..Iaddend..Iadd.17.  The thermocouple assembly according to claim 16 wherein said housing has one open end, and one of said thermocouple junctions extends beyond said open end of said housing..Iaddend..Iadd.18. The thermocouple assembly according to claim 16 further including a second outlet opening, wherein the outlet openings are respectively located above and below the plane of the inlet opening..Iaddend..Iadd.19. The thermocouple assembly according to claim 17 wherein said outlet opening is radially offset from said inlet opening..Iaddend..Iadd.20. The thermocouple assembly according to claim 19 wherein an outlet opening in the housing is located within a range of from 45° to 85° on either side of the downstream side of the 
     
     
        fluid stream flow axis..Iaddend..Iadd.21.  The thermocouple assembly of claim 20 including two outlet openings, one located 45° to 85° on one side and one located 45° to 85° on the other side of the downstream side of the fluid flow stream 
     
     
        axis..Iaddend..Iadd.22.  The thermocouple assembly of claim 21 wherein the outlet openings are respectively located above and below the plane of the inlet opening..Iaddend..Iadd.23. The thermocouple assembly according to claim 17 further including a second outlet opening, wherein the outlet openings are respectively located above and below the plane of the inlet opening..Iaddend..Iadd.24. The thermocouple assembly according to claim 19 wherein offset outlet openings are located on both sides of the fluid stream flow axis..Iaddend..Iadd.25. The thermocouple assembly according to claim 24 wherein the offset outlet openings are respectively located within bands extending from 45°-85° and from 275°-315° from the downstream side of the fluid stream flow axis..Iaddend..Iadd.26. The thermocouple assembly according to claim 24 wherein the outlet openings are respectively located above and below the plane of the inlet opening..Iaddend..Iadd.27. The thermocouple assembly of claim 1 further including a second pair of dissimilar wires disposed in said casing and forming a second thermocouple junction axially spaced from said first thermocouple junction, wherein said protective housing has one open end, and one of said thermocouple   
     
     
        junctions extends beyond said open end of said housing..Iaddend..Iadd.28. The thermocouple assembly according to claim 27 wherein an outlet opening in the housing is located within a range of from 45° to 85° on either side of the downstream side of the fluid stream flow axis..Iaddend..Iadd.29. The thermocouple assembly of claim 28 including two outlet openings, one located 45° to 85° on one side and one located 45° to 85° on the other side of the downstream side of the fluid flow stream axis..Iaddend..Iadd.30. The thermocouple assembly of claim 29 wherein the outlet openings are respectively located above and below the plane of the inlet opening..Iaddend..Iadd.31. The thermocouple assembly according to claim 1 wherein an outlet opening in the housing is located within a range of from 45° to 85° on either side of the downstream side of the fluid stream flow axis..Iaddend..Iadd.32. The thermocouple assembly of claim 31 including two outlet openings, one located 45° to 85° on one side and one located 45° to 85° on the other side of the downstream side of the fluid flow stream axis..Iaddend..Iadd.33. The thermocouple assembly of claim 32 wherein the outlet openings are respectively located above and below the plane of the inlet opening..Iaddend.