US2704555A - Low loss venturi tube - Google Patents

Description

Match 22, 1955 5, BALL 2,704,555

LOW LOSS VENTURI TUBE Filed June 11, 1951 2 Shets-Sheet 1 FIG-2'.

United States Patent Low Loss VENTURI TUBE Horace Edward Dall, Luton, England, assignor to George llxient Limited, London, England, a company of Great ritain Application June 11, 1951, Serial No. 230,997 Claims priority, application Great Britain June 23, 1950 9 Claims. (Cl. 138-44) This invention is an improved Venturi tube of the compact steep-angled type for insertion between an inlet and outlet pipe to produce a diflerential pressure for measurement of fluid flow.

In previously known Venturi tubes of this type such as that described in British specification No. 473,562 (Nathan), the inlet and outlet angles were made steeper and the throat joining them was made shorter than with the orthodox type of Venturi, and as a result there was obtained a lower overall pressure loss and a simpler and more compact device.

We have found that, if a particular relationship is made between the inlet pipe size, the mouth diameter of the inlet cone and the throat length, and if the inlet and outlet angles are within a certain range of values, the discharge coefficient instability which was experienced with the previous device is largely eliminated, and a stable coeflicient obtained over the usual range of Reynolds fiumbers, together with an even lower overall pressure oss.

The Venturi tube according to the invention comprises two truncated cones with smaller ends adjacent which are separated by a throat of length between 0.03d and 0.1a where d is the diameter of the throat, the inlet cone having an included angle between 40 and 50, the outlet cone having an included angle between 12 and 17, the arrangement being that the area of flow abruptly changes between the inlet pipe and the inlet cone, and the mouth diameter Dm of the inlet cone being related to the diameter D of the inlet pipe and the diameter d of the throat in accordance with the equation where k is 0.5-0.75. The preferred cone angles are substantially 45 and 15 respectively, and the preferred length of the throat is 0.0611. The abrupt change of area of flow may be efiected by locating between the mouth of the inlet cone and the inner periphery of the inlet pipe a wall which is substantially radial.

It has been found advantageous to connect the mouth of the outlet cone to the smaller end of a further truncated cone having an included angle less than that of the outlet cone. Alternatively, the outlet cone can be connected in the same way with two or more outwardly diverging truncated cones in series, having included angles progressively decreasing from that of the outlet cone. By these means the fluid is brought by gradually by progressively decreasing inclines from the throat to the outlet pipe.

If one considers the hypothetical provision of an infinitely large number of outlet cones in series each of infinitely small length, a concave curve is achieved. Thus, in a modification of the invention, the outlet cone is concave from the smaller end to the larger end, the tangents to the curved wall at the smaller end having an included angle between 12 and 17.

In the preferred form of the device, the higher pressure ofltake is located in the wall of the inlet pipe immediately adjacent to the position of the said abrupt change in area of fluid flow and the lower pressure offtake is located entirely within the said throat. These ofitakes may be in the form of slots, holes or annular recesses. Especially at extremely low values of the throat length it may be necessary to utilise for the low pressure oiftake an annular recess surrounding the throat.

In one embodiment of the invention the lower pressure offtake may be connected to an annular space surice rounding the throat, e. g. between the backs of the cones and a casing enclosing the cones. A pipe may then be provided to connect this annular space to a difierential gauge. The backs of the cones may be connected and strengthened by struts or ribs inside the said annular space.

The invention is illustrated diagrammatically in the accompanying drawing, in which:

Figure 1 is a section of one form of a Venturi tube attachment adapted for difierential pressure measurement of fluid flow; and

Figures 2, 3 and 4 are respectively a first, second and third modification of the same.

In Figure 1, a Venturi attachment 1 is adapted to be inserted between an inlet pipe 2 and an outlet pipe (not shown in Figure 1). At the inlet end of the attachment 1 is a cylindrical chamber 3 of the same diameter as that of the inlet pipe 2 and forms an extension thereof. In this chamber 3 is a higher pressure ofltake consisting of a comparatively narrow bore 4 and a comparatively wide tapping 5. An inlet cone 6 has a mouth 7, located in an obstructing end wall 8 of the chamber 3, and terminates in a throat 9. An annular space 10 is formed in the main casing round the throat 9 and is connected to the space enclosed by the throat by an annular recess 11 formed in the throat wall leaving small lands 12 in said wall on either side of the recess 11 in order to avoid a sharp angle. These lands are accentuated in the drawing for clarity. A lower pressure otftake 13 is located in the space 10. An outlet cone 14 extends from the throat 9 on the side remote from the inlet cone 6.

In Figure 2, a further outlet cone 15 is connected to the downstream end of the outlet cone 14. The outlet cone 15 has a smaller included angle than that of the outlet cone 14. An outlet pipe 16 is shown secured to the outlet cone 15.

In Figure 3, three further outlet cones 17, 18, 19 are connected in series to the downstream end of the outlet cone 14, the cones 17, 18, 19 having included angles progressively decreasing from that of the outlet cone 14.

In Figure 4, the outlet cone 14 is concave from the smaller end to the larger end, the tangents to the curved wall at the smaller end having an included angle of 15.

Besides obtaining a stable discharge coefficient, the improved Venturi tube has an extremely low overall pressure loss averaging only 5 or 6% of the differential pressure for tubes of medium proportion, which loss is between 2 and 3 times less than for an orthodox type of venturi tube.

I claim:

1. A Venturi tube for insertion between an inlet pipe and an outlet pipe for the diflerential pressure measurement of fluid flow, comprising two truncated cones with smaller ends adjacent which are separated by a throat of length between 0.03d and 01d where d is the diameter of the throat, the inlet cone having an included angle between 40 and 50, the outlet cone having an included angle between 12 and 17, the mouth diameter Dm of the inlet cone being related to the diameter D of the inlet pipe and the diameter d of the throat in accordance with the equation Dm d =k(D d where k is 05-075, and a Wall disposed between and joining the mouth of the inlet cone and the inner periphery of the inlet pipe, said wall forming an abrupt obstruction to the fluid flow.

2. A Venturi tube as claimed in claim 1 in which the inlet cone has an included angle of about 45.

3. A Venturi tube as claimed in claim 1 in which the outlet cone has an included angle of about 15.

4. A Venturi tube as claimed in claim 1 in which the length of the throat is about 0.06.

5. A Venturi tube for insertion between an inlet pipe and an outlet pipe for the difierential pressure measurement of fluid flow, comprising two truncated cones with smaller ends adjacent which are separated by a throat of length between 0.03a' and 0.1d Where d is the diameter of the throat, the inlet cone having an included angle between 40 and 50, the outlet cone having an included angle between 12 and 17, the mouth diameter Dm of the inlet cone being related to the diameter D of the inlet pipe and the diameter d of the throat in accordance with the equation Dm -d =k(D -d-), where k is 0.5-0.75, and a substantially radial wall joining the mouth of the inlet cone and the inner periphery of the inlet pipe.

6. A Venturi tube for insertion between an inlet pipe and an outlet pipe for the differential pressure measurement of fluid flow, comprising two truncated cones with smaller ends adjacent which are separated by a throat of length between 0.03d and 0.141 Where d is the diameter of the throat, the inlet cone having an included angle between 40 and 50, the outlet cone having an included angle between 12 and 17, the mouth diameter Dm of the inlet cone being related to the diameter D of the inlet pipe and the diameter d of the throat in accordance with the equation Dm -d =k(D d where k is 0.50.75, a wall disposed between and joining the mouth of the inlet cone and the inner periphery of the inlet pipe, said wall forming an abrupt obstruction to the fluid flow, and a further truncated cone having an included angle less than that of the outlet cone, the mouth of the outlet cone being connected to the smaller end of the said further truncated cone.

7. A Venturi tube for insertion between an inlet pipe and an outlet pipe for the differential pressure measurement of fluid flow, comprising two truncated cones with smaller ends adjacent which are separated by a throat of length between 0.0311 and 0.10 where d is the diameter of the throat, the inlet cone having an included angle between 40 and 50, the outlet cone having an included angle between 12 and 17, the mouth diameter Dm of the inlet cone being related to the diameter D of the inlet pipe and the diameter d of the throat in accordance with the equation Dm -d =k(D d where k is 0.5-0.75, a wall disposed between and joining the mouth of the inlet cone and the inner periphery of the inlet pipe, said wall forming an abrupt obstruction to the fluid flow, and a plurality of outwardly diverging truncated cones in series connected to the outlet cone, the said outwardly diverging truncated cones having included angles progressively decreasing from that of the outlet cone.

8. A Venturi tube for insertion between an inlet pipe and an outlet pipe for the differential pressure measurement of fluid flow, comprising two truncated cones with smaller, ends adjacent which are separated by a throat of length between 0.03d and 01:1 where d is the diameter of the throat, the inlet cone having an included angle between 40 and the inner wall of the outlet cone being concave from the smaller end to the larger end, the tangents to the curved wall at the smaller end of the outlet cone having an included angle between 12 and 17, the mouth diameter Dm of the inlet cone being related to the diameter D of the inlet pipe and the diameter d of the throat in accordance with the equation where k is 0.5-0.75, and a wall disposed between and joining the mouth of the inlet cone and the inner periphery of the inlet pipe, said wall forming an abrupt obstruction to the fluid flow.

9. A Venturi tube for insertion between an inlet pipe and an outlet pipe for the differential pressure measurement of fluid flow, comprising two truncated cones with smaller ends adjacent which are separated by a throat of length between 0.03d and 0.1:! where d is the diameter of the throat, the inlet cone having an included angle between 40" and 50, the inner wall of the outlet cone being concave from the smaller end to the larger end, the tangents to the curved wall at the smaller end of the outlet cone having an included angle between 12 and 17, the mouth diameter Dm of the inlet cone being related to the diameter D of the inlet pipe and the diameter d of the throat in accordance with the equation Dm -d =k(D -d where k is 0.5-0.75, and a substantially radial wall joining the mouth of the inlet cone and the inner periphery of the inlet pipe.

References Cited in the file of this patent UNITED STATES PATENTS 1,802,766 Kerr Apr. 28, 1931 FOREIGN PATENTS 418,349 Germany Sept. 5, 1925 473,562 Great Britain Oct. 15, 1937

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