Apparatus and technique for metering liquid flow

Abstract

The gravity flow of a liquid in an open pipe is metered during open channel flow, during surcharged flow, and during the transition between the two. A tubular venturi metering device is employed, and when during open channel flow, the liquid depth rises in the section of the pipe upstream from the device, the throat of the device fills with liquid substantially simultaneously with the upstream section of the pipe, so that during the transition, the device continues to provide a flow determination.

Description

The present application is a continuation in part of copending application Ser. No. 846,516 filed Mar. 31, 1986, and entitled Portable Wasterwater Device necessary preferred to provide an axially inwardly tapered entrance section 22 to the throat, as shown in FIGS. 1-4, and in which the entrance section must converge converges toward the axis of the bore in vertical planes paralleling the axis and in that axial direction relatively toward the downstream end 28 of the bore. Only when When the entrance section converges in this fashion can the cross-section of the throat can be dimensioned so that the "necking down" effect abates to zero when the upstream section of the pipe fills with liquid. One may constrict the sides of the entrance section, or one side, but he must also constrict the entrance section in vertical planes parallel to the axis of the bore.

Given the diameter of the sewer pipe and the range of flow rates in the same, the cross-section of the throat can be determined empirically using the following equations: ##EQU1##

In the above equations, "Q_c " is the flow rate in the throat under open channel flow conditions; "a" is the cross-sectional area of flow in the throat and thus the cross-sectional area of the throat itself when the throat is filled with liquid; "T" is the width of the top of the flow in the throat and thus the width of the throat at the top of the same when the throat is filled with liquid; and "g" is acceleration due to gravity. "D₁ " is the depth of flow in the upstream section of the pipe; V₁ is the average velocity of flow in the upstream section of the pipe; "V₂ " is the average velocity of flow in the throat; "Z" is the height to which the bottom of the throat is raised above the bottom of the pipe (i.e., the "sill height"); "D_c " is the depth of flow in the throat; "h_L " is the head loss between the upstream section of the pipe and the throat.

Typically, the had loss can be expected to be 5-10 percent of the difference in kinetic energy (velocity head) between the upstream section of the pipe and the throat. This is a very small number for practical purposes, and therefore, for simplicity, is ignored in the example following.

To illustrate the application of the equations, assume that the pipe diameter is 8 inches, that the device itself has a 1/4 inch wall thickness and that because of its wall thickness the pipe diameter at the mouth of the device is effectively 71/2 inches. Assume, moreover, that a device with a rectangular throat is to be used, and that the throat has a width of 4 inches and a sill height of 13/4 inches. For such an rectangular throat, ##EQU2##

Using conventional empirical practice, D_c is 4 inches or 0.333 feet. ##EQU3##

Following the same practice, D₁ is the effective pipe diameter of 0.625 foot.

0.625=0.333+0.146+0.167-0.022=0.624

Thus, when a device with 1/4 inch thick walls is inserted into an 8 inch pipe, a throat that is 4 inch square and centered in the device will cause the throat to fill with liquid substantially simultaneously with the upstream section of the pipe when the liquid depth rises therein.

The equations are equally applicable to other throat configurations. In the case of a rectangular configuration, the cross-section can be vertically rectangular, but with a risk of clogging in small diameter sewers. On the other hand, with large diameter sewers, a vertically rectangular cross-section may in fact be the most desirable to accomplish the simultaneous fill function.

The throat need not be orthogonal, nor even polygonal. It may, for example, have convexly bowed sides, and in fact, sides formed by the pipe itself, as in FIGS. 8-10.

Similarly, the body 4 of the device need not be solid. It may be hollow between the outer cylindrical wall and the bore 18 thereof; and if desired, when hollow, the cylindrical wall of the same may be perforated (not shown) to allow air and liquid to escape from within the device.

Claims

1. A method of metering the flow of liquid which is flowing by gravity in an elongated pipe that is open to atmosphere, comprising:

installing in the pipe a tubular venturi metering device which has an open-ended bore therethrough having an axis extending end-to-end thereof,

arranging the device in the pipe so that the axis of the bore is disposed substantially parallel to the longitudinal axis of the pipe and the bore thus has an end which is normally oriented upstream of the liquid flow in the pipe and an end which is normally oriented downstream of the liquid flow of the pipe,

the bore having an axially inwardly tapered entrance section adjacent the upstream end thereof which converges toward the axis of the bore in vertical planes paralleling the axis of the bore relatively toward the downstream end of the bore but terminates short of the axis of the bore so that a throat is formed in the bore which opens to the downstream end thereof,

forming a liquid seal between the device and the pipe at the outer periphery of the device so that the liquid in that section of the pipe disposed upstream from the upstream end of the bore of the device, is constrained to flow through the bore of the device, relatively toward the downstream end thereof,

determining the static pressure of the liquid in the aforesaid upstream section of the pipe when the liquid is flowing in the pipe at a depth less than that adapted to fill the upstream section of the pipe, to meter the flow in the pipe for the less-than-full condition thereof,

configuring the cross-sectional area of the throat, relative to that of the upstream section of the pipe, transverse the respective axes thereof, so that the throat will fill with liquid substantially simultaneously with the upstream section of the pipe, when the liquid depth rises therein, and

providing means whereby the static pressure of the liquid in the throat of the device and the upstream section of the pipe can be determined when both the upstream section of the pipe and the throat are filled, so that the difference between the latter two pressures can be determined to meter the flow in the pipe for the full condition thereof, and thereby enable the flow in the pipe to be metered for the full condition thereof as well as the less-than-full condition thereof and the transition therebetween.

2. The method according to claim 1, further comprising leveling the bottom of the throat of the device before the respective determinations are made.

3. The method according to claim 1, wherein the throat has a polygonal cross-section, transverse the longitudinal axis of the bore of the device.

4. In combination,

an elongated pipe which is open to atmosphere and adapted for the flow of liquid by gravity therein,

a tubular venturi metering device installed in the pipe and having an open-ended bore therethrough which has an axis extending end-to-end thereof,

the device being arranged in the pipe so that the axis of the bore is disposed substantially parallel to the longitudinal axis of the pipe and the bore thus has an end which is normally oriented upstream of the liquid flow in the pipe and an end which is normally oriented downstream of the liquid flow in the pipe,

the bore having an axially inwardly tapered entrance section adjacent the upstream end thereof, which converges toward the axis of the bore in vertical planes paralleling the axis of the bore and in that axial direction of the bore relatively toward the downstream end of the bore, but terminates short of the axis of the bore so that a throat is formed in the bore which opens to the downstream end thereof,

means for forming n liquid seal between the device and the pipe at the outer periphery of the device so that the liquid in that section of the pipe disposed upstream from the upstream end of the bore of the device, is constrained to flow through the bore of the device, relatively toward the downstream end thereof, and

first means for determining the static pressure of the liquid in the aforesaid upstream section of the pipe when the liquid is flowing in the pipe at a depth less than that adapted to fill the upstream section of the pipe, to meter the flow in the pipe for the less-than-full condition thereof,

the cross-sectional area of the throat being configured relative to that of the upstream section of the pipe, transverse the respective axes thereof, so that the throat will fill with liquid substantially simultaneously with the upstream section of the pipe, when the liquid depth rises therein, and

there being second means for determining the static pressure of the liquid in the throat of the device and the upstream section of the pipe when both the upstream section of the pipe and the throat are filled, so that the difference between the latter two pressures can be determined to meter the flow in the pipe for the full condition thereof, and thereby enable the flow in the pipe to be metered for the full condition thereof, as well as the less-than-full condition thereof and the transition therebetween.

5. The combination according to claim 4 wherein the axially inwardly tapered entrance section of the bore of the device has a top, bottom and sides which taper axially inwardly of the axis of the bore in the aforesaid downstream axial direction thereof.

6. The combination according to claim 4 wherein the wall of the axially inwardly tapered entrance section of the bore has a trapezoidal cross-section in that vertical plane coinciding with the axis of the bore.

7. The combination according to claim 4 wherein the bore also has an axially outwardly tapered exit section adjacent the downstream end thereof, which diverges from the axis of the bore in the aforesaid downstream axial direction thereof.

8. The combination according to claim 7 wherein the wall of the axially outwardly tapered exit section of the bore has a trapezoidal cross-section in that vertical plane coinciding with the axis of the bore.

9. The combination according to claim 4 wherein the first pressure determination means include a first pressure sensor which is disposed on the device adjacent the upstream end of the bore.

10. The combination according to claim 9 wherein the first pressure sensor is disposed adjacent the bottom of the upstream end of the bore.

11. The combination according to claim 4 wherein the second pressure determination means include a second pressure sensor which is disposed on the device adjacent the throat of the bore therein.

12. The combination according to claim 11 wherein the second pressure sensor is disposed adjacent the top of the throat.

13. The combination according to claim 4 further comprising means for leveling one side of the device in the pipe.

14. The combination according to claim 13 wherein the leveling means are operable to level the bottom of the throat in the bore of the device.

15. The combination according to claim 4 wherein the throat has a polygonal cross section, transverse the longitudinal axis of the bore.

16. The combination according to claim 4 wherein the pipe and the device have cylindrical cross-sections transverse the respective longitudinal axes thereof, and the seal forming means include an inflatable tube which is circumposed about the device between it and the pipe.

17. The combination according to claim 16 wherein the inflatable tube is seated in an annular groove formed about the outer periphery of the device.

18. The combination according to claim 4 wherein there is a manhole to the sewer pipe, and the metering device is inserted in that portion of the pipe through which the flow enters the manhole.

19. The combination according to claim 4 further comprising means for determining the flow in the pipe under the full and less-than-full conditions thereof, from the pressure of the liquid in the throat and the upstream section of the pipe.

20. Apparatus for metering the flow of liquid which is flowing by gravity in an elongated pipe that is open to atmosphere, both for the condition wherein the pipe is less than filled with the liquid, and the condition wherein the pipe is filled with the liquid, comprising, in combination,

a cylindrical member having end portions disposed at substantially the same elevation and an inner surface face forming a tubular venturi-type device which in turn has an entrance section and a throat section,

means circumposed about the cylindrical member and operable to form a fluid fight connection between the member and the internal wall of the pipe when the member is substantially coaxially inserted therein, whereby the liquid in that section of the pipe upstream from the member is constrained to flow through the entrance and throat sections of the venturi-type device,

means for sensing the pressure of the liquid at the crest of the throat section of said tubular venturi-type device, and

means for sensing the pressure of the liquid at the invert of the entrance section of said tubular venturi-type device.

21. The apparatus according to claim 20 wherein the fluid-tight connection forming means include an inflatable tube seated in an annular groove about the circumference of the cylindrical member.

22. A device for metering fluid flow comprising a cylindrical member having open ends, at least a portion of the outer surface of said cylindrical member configured substantially to fit inside the contour of an entrance pipe to a sewer manhole, a single tubular venturi-type member having an entrance section a throat section and an exit section mounted in said cylindrical member in such a manner that all of the liquid that flows through the open ends of said cylindrical member must pass through said tubular venturi-type member, means for securing said cylindrical member in said entrance pipe attached to said cylindrical member whereby a seal is established between the inside contour of said entrance pipe and an annular portion of the outer surface of said cylindrical member, means attached to the invert of the entrance section of said tubular venturi-type member to sense the pressure of the liquid therein, means attached to the crest of said throat section to sense the pressure of the liquid therein, conductor means attached to each of said pressure sensor means to conduct pressure signals therefrom, and means attached to said conductor means to convert said pressure signals into flow rates and store in said flow rate data.

23. A device for metering liquid flow in a substantially cylindrical entrance pipe to a sewer manhole, said entrance pipe flowing either partially filled or filled with liquid, said device comprising, in combination, a cylindrical member, the inner surface of which forms a tubular venturi-type member having an entrance section and a throat section therein, the outer surface of which member is dimensioned substantially to fit the inside contour of said substantially cylindrical entrance pipe, means for securing said cylindrical member in said entrance pipe and for forming a closed connection between the outer surface of said cylindrical member and the inner surface of said substantially cylindrical entrance pipe, means attached to the invert of the entrance section of said tubular venturi-type member to sense the pressure of the liquid therein, means attached to the crest of the throat section of said venturi-type member to sense the pressure of the liquid therein, conductor means attached to each of said pressure sensor means to conduct pressure signals therefrom, and means attached to said conductor means to convert said pressure signals into flow rates and store said flow rate data.

24. An apparatus for measuring flow in a closed conduit, comprising:

a venturi metering member for disposition in said closed conduit in a manner as to accept the flowing material in a flowpath therethrough and otherwise substantially block the conduit;

said venturi metering member formed having an axially inward tapered constricting inlet section in the direction of flow, terminating within said member in a throat section, said throat section defined as a passage continuing from said constricting inlet section;

access means to permit sensing of the pressure in the region of said constricting inlet section and in said throat in less than full and in full closed conduit flow conditions;

said throat dimensioned relative to said constricting inlet section transverse the respective longitudinal axes thereof so that said throat will fill with liquid substantially simultaneously with said constricting inlet section upon increasing flow in the closed conduit.

25. The apparatus of claim 24, wherein said access means further comprises:

a first pressure-sensing point in said constricting inlet section and a second pressure-sensing point in said throat, said first sensing point located adjacent the end of and the bottom of said constricting inlet section opposite from said throat and said second sensing point located adjacent the upper portion of said throat.

26. An apparatus for measuring flow in a closed conduit, comprising:

a tubular venturi metering member for disposition in said closed conduit in a manner as to accept the flowing material in a flowpath therethrough and otherwise substantially block said conduit;

said tubular venturi metering member formed having an axially inward tapered constricting inlet section in the direction of flow, terminating within said member in a throat section;

access means to permit sensing of the pressure in said constricting inlet section and in said throat in less than full and in full closed conduit flow conditions;

said throat dimensioned relative to said constricting inlet section transverse to the respective longitudinal axes thereof so that said throat will fill with liquid substantially simultaneously with said constricting inlet section upon increasing flow in the closed conduit.

27. The apparatus of claim 26, wherein said access means further comprises:

a first pressure-sensing point in said constricting inlet section and a second pressure-sensing point in said throat, said first sensing point located adjacent the end of and the bottom of said constricting inlet section opposite from said throat and said second sensing point located adjacent the upper portion of said throat. 28. The apparatus of claim 26, wherein:

said constricting inlet section has a trapezoidal longitudinal section is a plane parallel to the axis of said flowpath;

said throat has a substantially constant longitudinal section; and further comprising

an outlet section extending from the opposite end of said throat from said constricting inlet section, said outlet section expanding from the flowpath axis as said outlet section extends from said throat, said outlet section having a trapezoidal longitudinal section in a plane parallel to said axis of said flowpath. 29. The apparatus of claim 28, wherein said access means further comprises:

pressure-sensing means connected to said first and second sensing points to allow the apparatus to measure flow in less than full and in full closed conduit flow conditions. 30. The apparatus of claim 29, further comprising:

sealing means disposed on the exterior of said tubular member selectively

engageable to the closed conduit. 31. The apparatus of claim 30, further comprising:

leveling means on said member to level it in said closed conduit;

said sealing means disposed in a recess on the outer periphery of said tubular member and selectively inflatable to engage a pipe for sealing therewith. 32. The apparatus of claim 31, further comprising:

pressure-transmission means connected to said first and second pressure-sensing means to transmit pressure readings to a location remote from said member;

calculation means to accept input from said pressure-transmission means and

to calculate flow through said member. 33. A method for measuring flow in a closed conduit, comprising the steps of:

placing in the closed conduit a closed conduit venturi metering member with an axially inwardly tapered constricting inlet section leading to a throat section so that the flow in the closed conduit passes therethrough;

configuring said throat section dimensionally relative to said constricting inlet section in a direction transverse to the respective longitudinal axes thereof so that said throat will fill with liquid substantially simultaneously with said constricting inlet section upon increasing flow in the closed conduit;

measuring the static pressure in said throat and/or said constricting inlet; and

determining the flow in said flowpath for less than full and full closed conduit flow conditions. 34. An apparatus for permitting measuring flow in a closed conduit in which a liquid is flowing generally parallel to the longitudinal axis of said closed conduit due to gravity, comprising;

a closed conduit;

at least two different cross-sectional shapes along said conduit's axis, the smaller of the two said shapes forming a throat resulting from a transition from said larger shape, said throat and said larger cross-sectional shape dimensioned relative to one another transverse to the respective longitudinal axes thereof such that they fill with liquid, substantially simultaneously as the flowrate of liquid in said closed conduit increases;

means for sensing pressure adjacent said cross-sectional shapes. 35. The conduit of claim 33, wherein the highest of each cross-sectional point of each section is different from the other top elevation. 36. An apparatus for use in a flow meter for a closed conduit, comprising:

a closed conduit having an upstream section:

a throat formed by a transition from said closed conduit;

the cross-section of said throat dimensioned relative to that of the upstream section of the conduit transversely respective longitudinal axes thereof so as to dictate that said throat will fill with liquid substantially simultaneously with the upstream section of said conduit; and

means operatively associated therewith for determining flowrate in less

than full and full flow through said closed conduit. 37. The meter of claim 36, wherein:

said throat section is constricted in at least one vertical plane parallel to the direction of flow. 38. The meter of claim 36, wherein:

said throat section has a finite length in the direction of flow. 39. A flow measuring apparatus for closed conduits, comprising:

a closed conduit having an upstream section;

a flow restriction in said closed conduit comprising a throat, said throat formed having a transition from said closed conduit;

said throat having a cross-section so dimensioned relative to the upstream section of the closed conduit transverse the respective longitudinal axes thereof so as to dictate that said throat will fill with liquid substantially simultaneously with the upstream section of said conduit;

static pressure measurement means to allow sensing the static pressure in less than full and full flow through said closed conduit. 40. A method of measuring flow in a closed conduit, comprising:

placing a restriction within the closed conduit which by virtue of a transition forms a throat therein;

sizing the cross-section of the throat relative to that of the upstream section of the conduit in a direction transverse respective to the longitudinal axes thereof so as to dictate that the throat will fill with liquid substantially simultaneously with the upstream section of the conduit;

measuring the static pressure upstream of said throat and in at least said throat for use in computing the flowrate at less than full and full flow

through said closed conduit. 41. A process of metering the flow of liquid which is flowing in a pipe, wherein a closed conduit venturi metering device is installed in the pipe, which device has an open-ended bore about an axis therethrough extending end-to-end thereof, the bore having an entrance section adjacent a first end thereof, an exit section adjacent the second end thereof, and between the entrance and exit sections, a throat having a top and bottom and a smaller cross-sectional area than the entrance and exit sections, comprising the steps of:

arranging the device in the pipe to accept flow into the entrance from the pipe and otherwise to substantially block the pipe,

configuring the throat with at least a portion of the top or bottom thereof or both in a separate horizontal plane parallel to the throat axis, and with a distance between the throat top and bottom, so that the throat will fill with liquid substantially simultaneously with the entrance section, when liquid depth rises in the entrance section, and

determining flow through said pipe in less than full and in full flow. 42. A process of metering the flow of liquid which is flowing by gravity in an elongated pipe that is open to the atmosphere, wherein a tubular venturi metering device is installed in the pipe, which device has an open-ended bore therethrough having an axis extending end-to-end thereof, the bore having an entrance section adjacent a first end thereof which converges toward the second end of the bore but terminates short of the axis of the bore so that a throat is formed in the bore which opens to said second end, the bore having an exit section adjacent said second end which diverges from the bore toward said second end, comprising the steps of:

arranging the device in the pipe to accept flow into said entrance and otherwise to substantially block the pipe,

configuring the throat with a smaller cross sectional area than said entrance section, with at least a portion of the top or bottom thereof or both in a separate horizontal plane parallel to the throat axis, and with a distance between the throat top and bottom, so that the throat will fill with liquid substantially simultaneously with the entrance section, when the liquid depth rises in the entrance section, and

determining flow through said pipe in less than full and in full flow. 43. Apparatus for metering flow of liquid which is flowing in a closed conduit, comprising:

a closed conduit venturi metering member having an open-ended bore about an axis therethrough extending end-to-end thereof, said bore having an entrance section adjacent a first end thereof, an exit section adjacent the second end thereof, and between the entrance and exit sections, a throat having a top and bottom and a smaller cross-sectional area than the entrance and exit sections,

said member having means for arrangement of the member in a closed conduit to accept flow into said entrance from the closed conduit and otherwise to substantially block the closed conduit,

said throat being configured with at least a portion of the top or bottom thereof or both in a separate horizontal plane parallel to the throat axis, and with a distance between the throat top and bottom, such that the throat will fill with liquid substantially simultaneously with the entrance section, when liquid depth rises in the entrance section, and

means for measuring flow through said closed conduit in less than full and

in full flow conditions. 44. Apparatus for metering the flow of liquid which is flowing in an elongated pipe, comprising,

a tubular venturi metering device having an open ended bore therethrough about having an axis extending end-to-end thereof, said bore having an entrance section adjacent a first end thereof which converges toward the second end of the bore but terminates short of the axis of the bore so that the throat is formed in the bore which opens to said second end, such bore having an exit section adjacent said second end which diverges from the bore toward that second end,

said device having means for arrangement in the pipe to accept flow into said entrance from the pipe and otherwise to substantially block the pipe,

the throat being configured with a smaller cross sectional area than said entrance section, with at least a portion of the top or bottom thereof or both in a separate horizontal plane parallel to the throat axis, and with a distance between the throat top and bottom, so that the throat will fill with liquid substantially simultaneously with the entrance section, when the liquid depth rises in the entrance section, and

means for determining the head of liquid in said entrance section and in said throat to determine flow in less than full and full flow through said device.