Sample fluid stream probe gas sheet nozzle

1. A method comprising:

receiving a sample fluid stream from a main fluid stream through a nozzle of a probe located at least partially in the main fluid stream, wherein the sample fluid stream flows into the nozzle and a portion of the main fluid stream adjacent to the sample fluid stream flows past the probe without entering the probe, the sample fluid stream flowing downstream within the probe, and a portion of the main fluid stream flowing downstream outside the probe; and

while receiving the sample fluid stream, directing a gas sheet away from the probe, with the gas sheet flowing upstream against the main fluid stream and separating the sample fluid stream from the main fluid stream.

2. The method of claim 1 , wherein gas from the gas sheet forms a layer of gas along an inner surface of the probe that faces the sample fluid stream flowing downstream within the probe.

3. The method of claim 1 , wherein gas from the gas sheet forms a layer of gas along an outer surface of the probe that faces the portion of the main fluid stream flowing downstream outside the probe.

4. The method of claim 1 , wherein gas from the gas sheet inhibits collection of material from the main fluid stream on one or more outer surfaces of the probe, the one or more outer surfaces facing the portion of the main fluid stream flowing around the probe.

5. The method of claim 1 , wherein gas from the gas sheet inhibits collection of material from the main fluid stream on one or more inner surfaces of the probe, the one or more inner surfaces facing the sample fluid stream within the probe.

6. The method of claim 1 , wherein gas from the gas sheet inhibits collection of material from the main fluid stream on a leading edge of the probe.

7. The method of claim 1 , wherein the main fluid stream includes droplets and wherein the gas sheet sheers and splits droplets from the main fluid stream.

8. The method of claim 1 , wherein the gas sheet focuses the sample fluid stream within a central portion of a conduit extending through the nozzle and into the probe.

9. The method of claim 1 , wherein the gas sheet passes through an annular opening in the nozzle between an inner surface and an outer surface.

10. The method of claim 9 , wherein the inner surface extends farther upstream from a terminus of the outer surface.

11. The method of claim 1 , wherein the gas sheet flows from the probe in a direction that is within three degrees of a direction that is directly opposite to a direction of flow of the main fluid stream.

12. The method of claim 1 , wherein the gas sheet is an annular gas sheet.

13. The method of claim 1 , further comprising passing the sample fluid stream through a shroud before receiving the sample fluid stream through the nozzle of the probe.

14. The method of claim 1 , wherein the gas sheet has a velocity of at least 100 miles per hour relative to the probe as the gas sheet leaves an opening in the probe.

15. The method of claim 1 , wherein the gas sheet has a velocity of at least 150 miles per hour relative to the probe as the gas sheet leaves an opening in the probe.

16. A probe apparatus comprising:

a nozzle inlet configured to receive a sample fluid stream from a main fluid stream, with the sample fluid stream flowing downstream into the nozzle inlet while a portion of the main fluid stream flows downstream outside the nozzle inlet; and

a pressurized gas source connected to a gas sheet outlet, the gas source and the gas sheet outlet being in fluid communication with each other and configured to direct gas from the gas source through the gas sheet outlet, with the probe apparatus being configured such that the gas passing through the gas sheet outlet forms a gas sheet flowing upstream from a leading portion of the nozzle inlet against the flow of the main fluid stream, and with the probe apparatus being configured such that the gas sheet separates the sample fluid stream from the portion of the main fluid stream prior to the sample fluid stream reaching the nozzle inlet.

17. The probe apparatus of claim 16 , wherein the gas sheet outlet extends around a perimeter of the nozzle inlet.

18. The probe apparatus of claim 16 , wherein the gas sheet outlet is defined by an outer surface and an inner surface, wherein the outer surface faces inwardly toward the inner surface, and wherein the inner surface extends farther upstream relative to the flow of the main fluid stream than the outer surface.

19. The probe apparatus of claim 18 , wherein the gas sheet outlet has an opening slit width of less than 0.01 inch.

20. The probe apparatus of claim 18 , wherein the gas sheet outlet has an opening slit width of less than 0.005 inch.

21. A method comprising:

receiving a sample fluid stream from a main fluid stream through a nozzle of a probe located at least partially in the main fluid stream, the sample fluid stream traveling into the nozzle and a portion of the main fluid stream adjacent to the sample fluid stream flowing past the probe without entering the probe, the sample fluid stream flowing downstream within the probe, and a portion of the main fluid stream flowing downstream outside the probe; and

while receiving the sample fluid stream, directing a gas sheet away from the probe, with the gas sheet flowing upstream against the main fluid stream;

wherein gas from the gas sheet forms a layer of gas along an inner surface of the probe that faces the sample fluid stream flowing downstream with the probe, the layer of gas along the inner surface inhibiting collection of material from the sample fluid stream on the inner surface;

wherein gas from the gas sheet forms a layer of gas along an outer surface of the probe that faces the portion of the main fluid stream flowing downstream outside the probe, the layer of gas along the outer surface inhibiting collection of material from the main fluid stream on the outer surface; and

wherein gas from the gas sheet inhibits collection of material from the main fluid stream on a leading edge of the probe.