Drain tube for gas-liquid separation systems

1. A drain tube for an air-oil separator system, the tube being configured substantially vertically in the system, the tube having an upper opening for receiving oil separated from air in the system on a collection-side of the system, and a lower opening for releasing oil separated from air in the system to a drainage-side of the system, wherein the upper opening has a horizontal cross-sectional area A 1 that is greater than a horizontal cross-sectional area of the lower opening A 2 , pressure in the drainage-side P 1 is greater than pressure in the collection-side P 2 , the tube has a height H 1 , the oil forms a film at the lower opening by surface tension and collects in the tube to a height H 2 prior to the film rupturing and the oil draining out of the lower opening, and P 3 is surface tension pressure associated with rupturing the oil film at the lower opening.

2. The drain tube of claim 1 , wherein 4≦(A 1 /A 2 )≦25.

3. The drain tube of claim 2 , wherein the upper opening is circular in cross-section and has a diameter D 1 and the lower opening is circular in cross-section and has a diameter D 2 .

4. The drain tube of claim 1 , wherein the tube comprises an upper tube portion and a lower tube portion, the upper tube portion extending from the upper opening and the lower tube portion extending from the lower opening, and the upper tube portion having a height defined by H 1 and the oil collects in the upper tube portion to a height H 2 prior to the film rupturing and the oil draining out of the lower opening and through the lower tube portion.

5. The drain tube of claim 1 , wherein the upper opening and lower opening are substantially aligned.

6. The drain tube of claim 1 , wherein the upper opening and lower opening are substantially offset.

7. The drain tube of claim 1 , wherein the lower opening is oriented substantially horizontally.

8. The drain tube of claim 1 , wherein the lower opening is oriented substantially vertically.

9. A multi-stage impactor comprising the drain tube of claim 1 .

10. A drain tube for an air-oil separator system, the tube being configured substantially vertically in the system, the tube having an upper opening for receiving oil separated from air in the system on a collection-side of the system, and a lower opening for releasing oil separated from air in the system to a drainage-side of the system, wherein the upper opening has a horizontal cross-sectional area A 1 that is greater than a horizontal cross-sectional area of the lower opening A 2 , the tube is cylindrical in shape and the upper opening has a diameter D 1 that is greater than the diameter of the lower opening D 2 , pressure in the drainage-side P 1 is greater than pressure in the collection-side P 2 , the tube has a height H 1 , the oil forms a film at the lower opening by surface tension and collects in the tube to a height H 2 prior to the film rupturing and the oil draining out of the lower opening, and P 3 is surface tension pressure associated with rupturing the oil film at the lower opening.

11. The drain tube of claim 10 , wherein 2≦(D 1 /D 2 )≦5.

12. The drain tube of claim 10 , wherein the tube comprises an upper tube portion and a lower tube portion, the upper tube portion extending from the upper opening and the lower tube portion extending from the lower opening, and the upper tube portion having a height defined by H 1 and the oil collects in the upper tube portion to a height H 2 prior to the film rupturing and the oil draining out of the lower opening and through the lower tube portion.

13. The drain tube of claim 10 , wherein the upper opening and lower opening are substantially aligned.

14. The drain tube of claim 10 , wherein the upper opening and lower opening are substantially offset.

15. The drain tube of claim 10 , wherein the lower opening is oriented substantially horizontally.

16. The drain tube of claim 10 , wherein the lower opening is oriented substantially vertically.

17. A multi-stage impactor comprising the drain tube of claim 10 .

18. A drain tube for an air-oil separator system, the tube being configured substantially vertically in the system, the tube having an upper opening for receiving oil separated from air in the system on a collection-side of the system, and a lower opening for releasing oil separated from air in the system to a drainage-side of the system, wherein the upper opening has a horizontal cross-sectional area A 1 that is greater than a horizontal cross-sectional area of the lower opening A 2 , pressure in the drainage-side P 1 is greater than pressure in the collection-side P 2 , the tube has a height H 1 , the separated oil forms a film at the lower opening by surface tension and is not released from the tube until oil collects in the tube and reaches a sufficient height H 2 to overcome sum of surface tension at the lower opening P 3 and differential air pressure across the drain port (P 1 −P 2 ).

19. The drain tube of claim 18 , wherein the upper opening is circular in cross-section and has a diameter D 1 and the lower opening is circular in cross-section and has a diameter D 2 , and 2≦(D 1 /D 2 )≦5.

20. The drain tube of claim 18 , wherein the tube comprises an upper tube portion and a lower tube portion, the upper tube portion extending from the upper opening and the lower tube portion extending from the lower opening, and the upper tube portion having a height defined by H 1 and the oil collects in the upper tube portion to a height H 2 prior to the film rupturing and the oil draining out of the lower opening and through the lower tube portion.

21. The drain tube of claim 18 , wherein the upper opening and lower opening are substantially aligned.

22. The drain tube of claim 18 , wherein the upper opening and lower opening are substantially offset.

23. The drain tube of claim 18 , wherein the lower opening is oriented substantially horizontally.

24. The drain tube of claim 18 , wherein the lower opening is oriented substantially vertically.

25. A multi-stage impactor comprising the drain tube of claim 18 .