APPARATUS FOR AND METHOD OF DRAINING ULTRASONIC TRANSDUCER PORT CAVITIES

Abstract: A self-draining design for an ultrasonic gas meter is disclosed. The self-draining design of the present invention provides either a duct extending generally horizontally between the cavity and the bore to permit gravity to drain liquid therefrom, or extending vertically from the cavity to the outside of the housing to permit accumulated liquid to be drained by gravity and/or the action of a gas blowdown. The self-draining design of the present invention provides that a transducer-port assembly is configured to enhance the movement of fluid by maintaining a distance between the transducer and the surfaces of the port for enhancing the effect of surface tension of the liquid for reducing the surface area of the liquid. By allowing the liquid to assume a smaller surface area, typically spherical, the liquid reduces its friction or drag. The reduction of the surface area/volume ratio of the liquid greatly reduces the friction forces between the liquid and the surfaces of the transducer-port assembly for overcoming inertia and for enhancing the movement of the liquid for draining the meter. The method of draining accumulated liquid from an ultrasonic flowmeter comprises the steps of (a) maintaining a displacement between the transducer and the surfaces of the port which is sufficiently large to enhance the surface tension effect of the liquid for reducing the surface area/volume ratio of the liquid sufficient to reduce the forces between the liquid and the surfaces of the transducer-port assembly, (b) overcoming the inertia associated with the liquid by gravity causing the liquid to move, and (c) enhancing the movement of the liquid from the cavity in the port by gravity providing the force to continue the movement of the liquid such that the liquid is sufficiently removed from the port so that the meter is unfettered by coupling.

Description: .APP.ARATUS FOR AND METHOD OF DRAINING ULTRASONIC TRANSDUCER PORT CAVITIES FIELD OF THE INVENTION The present invention relates generally to draining cavities associated with ultrasonic gas meters. Specifically, the present invention relates to an apparatus for and method of self-draining cavities defined by the transducer-housing assembly of ultrasonic gas meters. The apparatus for and method of draining cavities provides that the ultrasonic gas meter can automatically recover from adverse conditions with respect to liquid build up caused by flooding of the meter, liquid- gas mixtures flowing in the meter, condensation forming in the meter, wet-gas flowing in the meter and the like. BACKGROUND OF THE INVENTION Typically, ultrasonic gas meters provide a gap between the transducer and its confining wall within a housing. Such configurations are prevalent in the art because acoustic waves have greatly enhanced coupling efficiencies through liquid and metal than through gas. Thus, the "coupling" of a transducer to a housing provides a path of "less resistance" for the ultrasonic signal being transmitted from the transducer. As an example, ultrasonic flowmeters for wet-gas systems typically comprise a conduit housing having one or more transducer pairs mounted collinearly in transducer ports formed in the housing. The transducer is isolated from the port by a gap to avoid short circuiting the ultrasonic signal produced by the transducer through the body of the meter. An ultrasonic signal is transmitted from the first transducer through a bore containing the gas being measured to the second transducer, - 1 - and vice versa. .Alternate embodiments include variations of, for example, at least one transducer mounted in a transducer port in a housing. The transducer may be in operative association with a reflector for receiving the radiation from the transducer and reflecting the radiation back to the transducer. A common problem of ultrasonic gas meters is liquid accumulation in the dead or open space between the transducer, the port and the bore containing the gas or material being measured. Typically, the dead space defines an annular space between the transducer and the port, and, if the transducer is recessed, a volume at the remote end of the transducer adjacent the bore containing the material under investigation. Liquid accumulating in the space and volume can act to "couple" a transducer to the housing. Coupling forms an alternate propagation path for the ultrasonic signal through the meter housing. Since the speed of sound is different in different propagation media, such coupling can make the meter inoperative due to erratic signal measurement. Heretofore, erratic signal measurements were used as an indication that the meter was fouled by accumulated liquids. To restore the meter function, the meter had to be removed from service, drained and dried before being returned to service. Removing a meter from service necessitates an expensive maintenance operation and the use of redundant meter stations. For example, a slug of liquid may pass through the bore in a conduit carrying primarily gas. In such a situation, the slug of liquid may completely fill all the gaps and open spaces associated with cavities in and around the transducer and its - 2 - associated ports. Prior known devices do not provide for the drainage of such liquid. U. S. Patent No. 4,823,612 to Ichino describes a socket structure for mounting an ultrasonic gas flow measuring device in a pipe to prevent moisture collection in the socket structure. More particularly, the '612 patent describes the use of two or more grooves in a transducer socket. The grooves are provided so that any condensed moisture that may form a bridge between the transducer and the wall of the socket can escape through at least one of the grooves. The '612 patent describes using a gap between the transducer and the wall of the socket having a sufficient dimension to prevent condensation from forming. The construction of the device described in the '612 patent prevents condensed moisture from forming and thus coupling between the socket and the probe head. If moisture does condense, the device described in the '612 patent provides that the condensation can escape via the grooves. U. S. Patent No. 4,914,959 to Mylvaganam et al. describes an ultrasonic flow meter using obliquely directed transducers. U. S. Patent No. 4,742,717 to Ichino describes a gas flow measuring device having a gas seal mechanism suitable for permitting a probe to be removed from a probe socket. U. S. Patent No. 4,581,942 to Ogura et al. describes a measuring conduit adapted for determining flow rate and concentration of a fluid and to reduce the dead space of the measuring conduit. - 3 - U. S. Patent No. 4,646,575 to O'Hair et al. describes an ultrasonic flowmeter comprising at least four transducer sources arranged in a fluid conduit system. The transducers are adapted to project a beam of ultrasonic sound to corresponding transducers wherein the paths defined by the beams are angularly disposed with regard to both the fluid flow and each other, and are arranged in an intersecting but spaced-apart relationship. Thus, it would be advantageous for ultrasonic gas meters to be maintained dry or to remove liquids to extend operational time between servicing for reduced maintenance and operational costs. It is, therefore, a feature of the present invention to provide an ultrasonic gas meter which in normal use provides self-draining regardless of meter orientation. .Alternately, a feature of the present invention is to provide a method for draining the transducer ports of an ultrasonic gas meter regardless of meter orientation. A feature of the present invention is to provide a method for draining the transducer ports of an ultrasonic gas meter using the gravitational attraction of the liquid to remove the liquid from the meter. A feature of the present invention is to provide an apparatus for draining liquid from cavities associated with ultrasonic gas meter transducer ports such that the gravitational attraction of the liquid to be removed from the apparatus is greater than any other force acting on the liquid such that the liquid will automatically drain from the port. .Another feature of the present invention is to provide an apparatus for draining cavities in ultrasonic transducer ports having a clearance between the transducer and the port sufficient for increasing the surface tension effect of the liquid which effect acts to minimize the surface area of the Uquid for reducing the forces between the Uquid and, either the transducer or, the port such that the Uquid will drain from the cavity. .An additional advantage of the present invention is to provide an apparatus and method of draining ultrasonic transducer cavities which provides that the ultrasonic gas meter can automatically recover from adverse conditions caused by liquid build-up, instrument flooding or the like. A feature of the present invention is to provide an ultrasonic gas meter housing having a duct associated with a transducer port for automatically draining the port. .Another feature of the present invention is to provide an ultrasonic gas meter housing having a duct for automatically draining a transducer port due to the gravitational force being greater than any other force acting on the fluid. Yet another feature of the invention is to provide an ultrasonic gas meter housing having a duct for automatically draining a transducer port due to the force generated by the flow of gas passing through the meter. .Another feature of the present invention is to provide an ultrasonic gas meter housing having a duct for automatically draining a transducer port into the flow path of the meter. - o - Yet still another feature of the present invention is to provide an ultrasonic gas meter housing having a duct for automatically draining a transducer port outside the housing of the meter. Additional features and advantages of the invention will be set forth in part in the description which follows, and in part will become apparent from the description, or may be learned by practice of the invention. The features and advantages of the invention may be realized by means of the combinations and steps particularly pointed out in the appended claims. SUMMARY OF THE INVENTION A self-draining design for an ultrasonic gas meter of the present invention significantly extends the operational time between servicing for enhanced performance and reduced costs. The apparatus of the present invention provides an ultrasonic gas meter that automatically recovers from adverse conditions with respect to liquid build-up. As one embodiment, the present invention provides an improvement for an ultrasonic gas meter having a housing formed in a conduit with an axial bore, and one or more pairs of collinear transducer ports angularly disposed to the bore. Each transducer port defines a cavity in the housing. One or more pairs of cooperating ultrasonic transducers are mounted in the respective transducer ports to define an annular space therein. .An improvement comprises a duct associated with the transducer cavity for draining any accumulated Uquids therefrom. The duct preferably extends from the cavity to an outlet in the bore. A duct can optionally extend from the cavity to an outlet at the housing outside surface rather than an outlet at the axial bore of the housing. The ducts are so oriented as to enhance drainage regardless of the orientation of the meter. For an outlet at the outside surface of the housing, the duct outlet may be piped to a Uquid collection tank and an automatic valve can be used for automatically opening the duct outlet for discharging the liquid. Further, a duct can optionally include a maintenance outlet at the housing outside surface for servicing purposes. In a preferred embodiment, a centerline of the duct can intersect the port at the centerline thereof. .Alternatively, a centerline of the duct can intersect the port tangential to a lower edge of the port. In yet another embodiment, a centerline of the duct can intersect the port at a range of locations between the centerline of the port and the top or bottom extremity of the port. It can be appreciated by those skilled in the art that the location of the duct can be at the position of the port as required by application or choice. In another embodiment, the present invention provides a method of draining accumulated Uquid from an ultrasonic gas meter. The meter comprises a housing having an axial bore through which gas flows and one or more pairs of collinear transducer ports are angularly disposed to the bore. Cooperating pairs of transducers are received in the ports to define a cavity. The method of draining accumulated Uquid from an ultrasonic gas meter comprises the steps of providing ducting having an orientation for propagating the flow of the Uquid, overcoming the inertia of the Uquid by gravity causing the Uquid to move. .And, gravity further enhances the movement of the Uquid from the cavity such that the Uquid is sufficiently drained from the port so as to provide an acoustic path unfettered by coupling. The duct preferably extends from the cavity to an outlet in the bore and the draining step may include the step of circulating gas from the bore through the cavity. A duct can optionally extend from the cavity to an outlet at the housing outside surface and the draining step can include the step of removing the drained Uquid from the flowmeter by opening an automatic valve to a Uquid collection tank. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings which are incorporated in and constitute a part of the specification, illustrate a preferred embodiment of the invention and together with the general description of the invention given above and the detailed description of the preferred embodiment given below, serve to explain the principles of the invention. FIG. 1 is an angled perspective view of the improved ultrasonic gas meter using the present invention formed in a flanged pipe fitting showing four pairs of collinear, angularly disposed transducer ports. FIG. 2 is an elevation view of the meter of FIG. 1 vertically oriented showing the angular orientation of the transducer ports with respect to the meter axis and the central location of the drainage ducts with respect to the circumference of the transducer ports. FIG. 3 is an angled longitudinal cross-sectional view of the meter of FIG. 2 taken along the section lines 3-3 in FIG. 2 showing the general disposition of the transducers and - 8 - generally horizontal drainage ducts intersecting the transducer ports at a central location. FIG. 4 is an angled longitudinal cross-sectional view of the meter of FIG. 2 taken along the section lines 4-4 in FIG. 2 showing the general disposition of the transducers and generally horizontal drainage ducts intersecting the transducer ports at a central location. FIG. 5 is a side view of the meter of FIG. 1 horizontally oriented showing the relative elevation of the transducer ports and optional outlets from the respective boss. FIG. 6 is an upper transverse cross-section of the meter of FIG. 5 taken along the section lines 6-6 in FIG. 5 showing the orientation of the drainage duct and the drain outlet with respect to the meter bore. FIG. 7 is an upper middle transverse cross-section of the meter of FIG. 5 taken along the section lines 7-7 in FIG. 5 showing the orientation of the drainage duct and the drain outlet with respect to the meter bore. FIG. 8 is a lower middle transverse cross-section of the meter of FIG. 5 taken along the section lines 8-8 in FIG. 5 showing the orientation of the drainage duct and the drain outlet with respect to the meter bore. FIG. 9 is a lower transverse cross-section of the meter of FIG. 5 taken along the section lines 9-9 in FIG. 5 showing the orientation of the drainage duct and the drain outlet with respect to the meter bore. FIG. 10 is an offset transverse cross-section of the boss of the meter of FIG. 5 taken along the section lines 10-10 in FIG. 4 showing the enhanced clearance C and the central location of the drainage duct. FIG. 11 is an offset transverse cross-section of the boss of the meter of FIG. 13 taken along the section lines 11-11 in FIG. 13 showing the enhanced clearance C and the tangential location of the drainage duct. FIG. 12 is a top view of the meter of FIG. 1 horizontally oriented showing the angular orientation of the transducer ports with respect to the meter axis and the drainage ducts with respect to the circumference of the transducer ports. FIG. 13 is an angled longitudinal cross-sectional view of the meter of FIG. 12 taken along the section lines 13-13 in FIG. 12 showing the general disposition of the transducers and generally tangent drainage ducts intersecting the transducer ports at a lower edge thereof. FIG. 14 is an angled longitudinal cross-sectional view of the meter of FIG. 12 taken along the section lines 14-14 in FIG. 12 showing the general disposition of the transducers and generally tangent drainage ducts intersecting the upper transducer ports at a lower edge thereof and vertical drainage ducts at the lowest transducer ports. FIG. 15 is a side view of the meter of FIG. 12 showing the relative elevation of the transducer ports and optional outlets from the respective boss. FIG. 16 is an upper transverse cross-section of the meter of FIG. 15 taken along the section lines 16-16 in FIG. 15 showing the orientation of the drainage duct and the drain outlet with respect to the meter bore. - 10 - FIG. 17 is an upper middle transverse cross-section of the meter of FIG. 15 taken along the section Unes 17-17 in FIG. 15 showing the orientation of the drainage duct and the drain outlet with respect to the meter bore. FIG. 18 is a lower middle transverse cross-section of the meter of FIG. 15 taken along the section Unes 18-18 in FIG. 15 showing the orientation of the drainage duct and the drain outlet with respect to the meter bore. FIG. 19 is a lower transverse cross-section of the meter of FIG. 15 taken along the section lines 19-19 in FIG. 15 showing the relative placement of the vertical drainage duct. FIGS. 20-22 are cross-sections illustrating the relationship between the transducer and its associated port and Uquid therebetween. FIG. 23 is a flow diagram illustrating a preferred method of the present invention. The above general description and the following detailed description are merely illustrative of the generic invention, and additional modes, advantages, and particulars of this invention will be readily suggested to those skilled in the art without departing from the spirit and scope of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides an apparatus for and method of draining ultrasonic transducer port cavities associated with gas meters or the like. The invention is distinct from prior art devices which are limited to small amounts of Uquid or condensation associated with a transducer and its socket. The present invention provides that the combination of the port, the transducer and the housing of the meter define a combination of elements which results in drainage of any amount of Uquid which may become engaged with the apparatus of the present invention for draining an ultrasonic transducer cavity. For example, it is not unusual for a slug of Uquid to pass through the axial bore in a conduit carrying primarily natural gas. In such a situation, the slug of Uquid may completely engulf all the gaps and open spaces associated with cavities in and around the transducer and its associated ports. Prior known devices do not provide for the drainage of such Uquid as does the present invention. Using the present invention, the slug deposited liquid will readily drain. Although, it is primarily the gravitational force that provides the energy for draining the port using the present invention, it is the enhanced surface tension effect that enables the force of gravity to be effective. Thus, the present invention provides that drainage occurs automatically as long as the apparatus is maintained in a gravitational field, the Uquid characteristics are sufficiently known and the meter is configured to enhance the surface tension effect of the Uquid. In most gas meter applications, the surface tension effect of water is the controlling parameter. For the purpose of the present invention, surface tension is defined as a property of Uquids arising from unbalanced molecular cohesive forces at or near the surface. As a result of the unbalanced surface forces the surface of the Uquid tends to contract. The surface contraction creates properties resembling those of a stretched elastic membrane. - 12 - In the interior of a Uquid, a molecule is surrounded uniformly by its fellow molecules. Hence, the forces of attraction on an interior molecule are the same from all directions and cancel one another out. Such an interior molecule is free to move as though forces of attraction did not exist. However, a molecule in the surface of a Uquid experiences a pull to the interior which is not balanced by an outward pull. The result is that as few molecules as possible remain on the surface of the Uquid. The surface of the Uquid acts as if it were under a tension that tends to minimize its area. Hence, a drop of a Uquid tends to assume a spherical shape, since the surface area of a sphere as compared with its volume is smaller than the surface area of a volume of any other shape. A basis for the efficacy of the present invention is to adapt a gas meter for enhancing the effect of the surface tension of undesirable Uquids. Enhancing the surface tension effect changes the physical shape of the Uquid to sufficiently reduce the forces between the Uquid and any contacting surface such that the force of gravity acting on the Uquid causes the Uquid to drain from the meter. Reference will now be made in detail to the present preferred embodiments of the invention as described in the accompanying drawings. The present invention provides a housing for an ultrasonic gas meter commonly used for making accurate flowrate measurements of wet gases such as natural gas. The housing has a drainage duct associated with dead space where undesirable Uquids can accumulate in the transducer port. .An improved flowmeter and associated housing with a self-draining feature provides for extended operational time between servicing cycles. Enhanced operation time is highly desirable to avoid the costly and time consuming need to remove the meter from service to drain accumulated Uquids. Referring to FIGS. 1-19, a wet gas ultrasonic flowmeter of the present invention having a self-draining design comprises one or more pairs of collinear transducers disposed at an angle to the flow of gas through the meter. The flowmeters 10, 100 are made up of, for example, four collinear pairs of transducers as described in U. S. Patent No. 4,646,575 to OΗair et al.. the disclosure of which is hereby incorporated herein by reference, is preferred and shown in FIG. 1. FIG. 1 is an angled perspective view of the improved ultrasonic gas meter of the present invention formed in a flanged pipe fitting showing four pairs of collinear, angularly disposed transducer ports. In the illustrated embodiment, the flowmeter 10 of the present invention comprises a housing 12 formed in a conduit 14 having an axial bore 16 and flanged pipe connectors 18. FIG. 2 is an elevation view of the meter of FIG. 1 vertically oriented showing the angular orientation of the transducer ports 20 with respect to the meter axis 17 or the bore 16 and the location of the drainage ducts 38 with respect to the circumference of the transducer ports 20. FIG. 3 is an angled longitudinal cross-sectional view of the meter of FIG. 2 taken along the section lines 3-3 in FIG. 2 showing the general disposition of the transducers 24, 26 and generally horizontal drainage ducts 38 intersecting the transducer ports 20 at a central location. FIG. 4 is an angled longitudinal cross-sectional view of the meter of FIG. 2 taken along the section Unes 4-4 in FIG. 2 showing the general disposition of the transducers 24, 26 and generally horizontal drainage ducts 38 intersecting the transducer ports 20 at a central location. As illustrated in FIGS. 1-4, the housing 12 has four pairs of transducer ports 20 disposed therein so that each port pair is collinearly angled to the bore 16 and positioned in an angular relationship with respect to the diameter of the bore 16 (see particularly FIGS. 3-5 and 13-15). As illustrated in FIGS. 3-4, each pair of transducer ports 20a, 20'a; 20b, 20'b; 20c, 20 , c; 20d, 20'd creates a specific path A, B, C, D, respectively. The measurements from each transducer pair thus obtained over a greater area of the conduit cross-section can then be averaged for enhanced accuracy as known in the art. To achieve a compact layout of the transducer pairs given the limitations of the geometry involved, the housing 12 has conventionally been fitted with bosses 22 each having a transducer port. The bosses 22a, 22'a; 22b, 22'b; 22c, 22'c; 22d, 22'd preferably have a connection means 25 for securing the transducer elements in the ports 20a, 20'a; 20b, 20'b; 20c, 20'c; 20d, 20'd, respectively. The connection means can be any conventional connector, and two examples are illustrated in the figures. FIG. 1 illustrates the connection means to be holes for accepting bolts, screws or the like to secure a flanged transducer. FIGS. 3-4 illustrate the connection means to be a threaded connection to secure a threaded transducer. Any known connector, or any combination of connectors, is possible for use with the present invention, e.g., a threaded connection further secured by bolts. Four pairs of cooperating ultrasonic transmitter/receiver transducers 24, 26 are received in the transducer ports 20a, 20'a; 20b, 20'b; 20c, 20'c; 20d, 20'd formed in the bosses 22a, 22'a; 22b, 22'b; 22c, 22'c; 22d, 22'd wherein each ultrasonic transducer 24 is collinear to an ultrasonic transducer 26 and angled to the bore 16. The transducers 24, 26 are acoustically isolated from the meter ports 20a, 20'a; 20b, 20'b; 20c, 20'c; 20d, 20'd to avoid an acoustic path to the meter housing. Also, the transducers 24, 26 may be recessed from the meter bore 16 to avoid possible interference with the flow of gas through the meter 10. The recess distance 36 is illustrated in FIGS. 3, 4, 13, and 14. A recess volume or void 37 is defined by the respective transducer 24, 26, port 20 and bore 16. The transducers 24, 26 are typically cantilevered within the respective port 20 forming an annular air gap 28 between the walls of the port 20 and the transducer 24, 26 to define a cavity 30. .Also, the transducers 24, 26 may be recessed from the bore 16 to define a volume 37 in each of the respective ports 20. The volume 37, as well as the cavity 30, allows for the accumulation of Uquid. A dead space 39 is defined as the total of the volume 37 and the cavity 30. Each transducer 24, 26 is preferably secured to the respective port 20 by a boss 22 and associated connection means 25 as previously discussed. The transducers 24, 26 are acoustically isolated from the meter housing 12 near the connection means 25 by frequency barriers (not shown) as known in the art. It can be seen that the cavity 30 including the annular gap 28 and a recess 36 adjacent the bore 16 forms the dead space 39 in which undesired Uquid accumulations can occur. In accordance with the present invention, the transducer ports 20a, 20'a; 20b, 20'b; 20c, 20'c; 20d, 20'd include one or more drainage ducts 38 for permitting Uquid accumulating in the dead space 39 to be drained. The duct 38 preferably extends from the port 20 to an outlet 40 in the meter bore 16 so that the Uquid can be drained to the bore 16. Both the actions of gravity and process gas circulating from the bore 16 can influence the draining action of the duct 38. The dominate force used for draining the ports by the present invention is the force of gravity. Therefore, the properties of the Uquid and the configuration of the meter with respect to those properties are critical in practicing the present invention. Ml forces on the liquid caused by the configuration of the meter must be sufficiently reduced to allow the force of gravity to drain the ports. It can be appreciated that when the meter 10 is oriented vertical to the horizon, as illustrated in FIG. 2, each lower port 20 requires the associated lower duct 38 to drain Uquid from the port 20 for avoiding acoustic coupling. Each lower duct 38 preferably extends from its respective port 20 to its outlet 40 in the meter bore 16. The liquid is drained from the port 20, to the outlet 40 and into the bore 16. Further in the configuration oriented vertical to the horizon, each upper port 20 drains directly into the bore 16. FIGS. 2-9 illustrate an embodiment of the present invention oriented with the centerline 17 of the bore 16 vertical to the horizon. The ducts 38 intersect the ports 20 at a point of intermediate location. Since the meter 10 is installed at a vertical attitude, the ducts 38 also have a vertical component to their orientation, but angled with respect to the bore axis as seen in FIGS. 2 and 6-9. Therefore, the centerline of each duct 38 preferably intersects the centerline of the respective port 20 at an edge 48 of the port 20 as seen in FIGS. 2-9. The centerline-centerline alignment of each duct 38 with its respective port 20 assists the action of gravity to drain the dead space 39. The points of intersection by the ducts 38 with the ports 20 are preferably at the end of each port 20 furthest from the bore 16 to minimize Uquid accumulation in the end area. The actual machined design of the ducts 38 at each of the ports 20 is a matter of practitioner preference and numerous different duct combinations and geometries can be contemplated depending on the design and utiUty of the meter and associated process conditions including rate of flow, pressure rating, properties of the gas, material of construction, and the like. Use of the meter 10 having port draining ducts 38 is inherently self-draining due to the ongoing drainage effect of gravity on the liquid after minimizing any inhibiting forces. In some configurations, e.g., parallel to the horizon, draining is assisted by the effect of the gas flow while the meter is on-line. However, the present invention will operate to drain the ports 20 even when the meter 10 is off-line and no flow is moving through the bore 16. A self-draining flowmeter of the present invention can be conveniently made by machining the drainage ducts 38 on an existing flowmeter from the outside of the bosses 22 to form an opening. Further, the opening can be secured. The opening of the duct 38 can be permanently closed, as illustrated in FIG. 7, or can be tapped and fitted with a plug so that the duct 38 can be easily accessed for maintenance purposes, as illustrated in FIG. 8. Alternatively, the present meter can be conventionally made from a piece of metal pipe stock welded with sockets and flange fittings, and suitably machined to form the meter bore, transducer ports and drainage ducts. FIGS. 12-19 illustrate the meter 100 horizontally oriented such that the bore 116 and the centerline 117 of meter 100 are parallel to the horizon. FIG. 12 is a top view of the meter 100 of FIG. 1 horizontally oriented. FIG. 12 illustrates the angular orientation of the transducer ports 120 with respect to the meter axis and the location of the drainage ducts 138 with respect to the circumference of the transducer ports 120. FIG. 13 is an angled longitudinal cross-sectional view of the meter 100 of FIG. 12 taken along the section Unes 13-13 in FIG. 12 showing the general disposition of the transducers and generally tangent drainage ducts 138 intersecting the transducer ports 120 at a lower edge thereof. FIG. 14 is an angled longitudinal cross-sectional view of the meter 100 of FIG. 12 taken along the section Unes 14-14 in FIG. 12 showing the general disposition of the transducers and generally tangent drainage ducts 138 intersecting the upper transducer ports 120 at a lower edge thereof and vertical drainage ducts 142 at the lowest transducer ports 120. - 19 - The ducts 138, 142 are preferably made to intersect the respective port 120 at a point of lowest elevation of the port 120. Since the meter 100 must generally be installed at a horizontal attitude with the central axis of the bore 116 parallel to the ground, the duct 138 also has a generally horizontal attitude with respect to the ground but angled with respect to the bore axis as seen in FIGS. 16-19. Therefore, a centerline 146 of the duct 138 preferably intersects the port 120 at a lower edge 148 as seen in FIGS. 13-14 to assist the action of gravity to drain the cavity 130. In addition, the intersection point in the port 120 is preferably at an end furthest from the bore 116 to minimize Uquid accumulation. .Also, the circulation of gas from the bore 116 through the duct 138 may provide a drainage force. In such a case, the duct 138 can be made to intersect the cavity of the lower edge 148 of the port 120, and preferably between the lower edge of the ports 120a, 120'a; 120b, 120T>; 120c, 120'c; 120d, 120'd and the port centerline 138. The duct 142 preferably has a generally vertical attitude with respect to an installed meter 100 having a horizontal central axis to gain the advantage of gravity for drawing away accumulated Uquids from the cavity 130 to a blow down system (not shown). A drainage means employing a blow down system for draining outside the pipeline is generally less preferred since such equipment can be eliminated by draining the accumulated Uquids back into the pipeline as is the case using the duct 138. The present flowmeter 100 illustrated by the FIGS. 12-19 combines both the meter bore draining ducts 138 and the outside draining ducts 142 for ease of machining and manufacture. It can be seen that in some embodiments the lowest ports 120d have a bottom edge abutting the lowest point of the bore 116 thus a vertical outside draining duct 142 is more advantageous than a horizontal bore draining duct 138 for the ports 120d since the bore draining duct 138 cannot be easily made at the lowest elevation point but must be moved closer to the centerline. However, the actual machine design of the ducts at each of the ports 120a, 120'a; 120b, 120T>; 120c, 120O; 120d, 120'd is a matter of practitioner preference and numerous different duct combinations and geometries can be contemplated depending on the design of the meter and associated process conditions including rate of flow, pressure rating, properties of the gas, material of construction, and the like. FIG. 15 is a side view of the meter 100 of FIG. 12 showing the relative elevation of the transducer ports 120 and drainage ducts 138 with respect to the meter bore 116. FIG. 16 is an upper transverse cross-section of the meter 100 of FIG. 15 taken along the section lines 16-16 in FIG. 15 showing the horizontal orientation of the drainage ducts 138 and the drain outlet 140 in the meter bore 116. FIG. 17 is an upper middle transverse cross-section of the meter 100 of FIG. 15 taken along the section lines 17-17 in FIG. 15 showing the horizontal orientation of the drainage duct 138 and the drain outlet 140 in the meter bore 116. FIG. 18 is a lower middle transverse cross- section of the meter 100 of FIG. 15 taken along the section Unes 18-18 in FIG. 15 showing the horizontal orientation of the drainage duct 138 and the drain outlet 140 in the meter bore 116. FIG. 19 is a lower transverse cross-section of the meter 100 of FIG. 15 taken along the section lines 19-19 in FIG. 15 showing the relative placement of the vertical drainage duct 142. Use of the meter 100 having bore draining ducts 138 is inherently self-draining due to the ongoing drainage effect of gravity and the sweep gas while the meter is on-line. Use of the outside draining ducts 142, on the other hand, have the inherent self-draining effect of gravity but also depends on a periodical blowdown procedure to permit drainage by the sweep of blowdown gas from the process. Thus, the outlet 144 of the duct 142 is preferably piped to an automatic valve (not shown) and a Uquid collection tank (not shown) having a lower pressure than the meter 100. During blowdown, a pressure differential between the process gas and the collection tank causes process gas from the bore 116 to sweep Uquids from the cavity 130, duct 142 and associated piping into the collection tank when the automatic valve is opened. A self-draining flowmeter of the present invention can be conveniently made by machining the drainage ducts 138, 142 on an existing flowmeter from the outside of the bosses 122 and in the case of the ducts 138, plugging a duct outlet opening formed on the outside surface of the respective boss 122. The outlet opening of the duct 138 can be permanently closed or can be tapped and fitted with a plug so that the duct 138 can be easily accessed for inspection, maintenance or other purposes. Alternatively, the present flowmeter can be conventionally made from a piece of metal pipe stock welded with sockets and flange fittings, and suitably machined to form the meter bore, transducer ports and drainage ducts. FIG. 20 is a cross-section illustrating the relationship between the transducer and its associated port. The transducer 24 is located along the central axis of the port 20. The difference between the outside diameter of the transducer 24 and the inside diameter of the port 20 creates a gap 28A. In the space within the gap 28A is a portion of liquid L. The Uquid L is iUustrated having a concaved meniscus. The concaved meniscus is illustrated since the primary inhibitor would be aqueous solutions. Aqueous solutions tend to wet the walls of the port 20 and the transducer 24. FIG. 21 is an illustration similar to Fig. 20, but with a wider gap 28B between the transducer 24 and the inside diameter of the port 20. The Uquid L is illustrated having a shorter surface area along the surfaces of the transducer 24 and walls of the port 20. FIG. 22 is an illustration practicing the present invention wherein the surface tension effect of the Uquid L has been enhanced by providing a gap 28 between the transducer 24 and the walls of the port 20 sufficient to create a smaller surface area for the liquid L. Another embodiment of the present invention is a method of draining accumulated Uquid from an ultrasonic flowmeter. FIG 23 is a flow diagram illustrating a preferred method of the present invention. The method is adapted for use with a housing having an axial bore through which gas flows and one or more pairs of collinear transducer ports angularly disposed to the bore for providing transmission paths, and corresponding pairs of transducers received in the ports. The transducer defines a cavity in the port in which Uquid can accumulate. The method of draining accumulated Uquid from an ultrasonic flowmeter provides the steps of providing ducting having an orientation for propagating the flow of the Uquid, overcoming the inertia associated with the Uquid by gravity causing the liquid to move, and enhancing the movement of the Uquid from the cavity in the port by gravity providing the force to continue the movement of the Uquid through the ducting such that the Uquid is sufficiently removed from the port so as to provide a transducer path unfettered by the Uquid. The present improvement to a wet gas ultrasonic flowmeter is illustrated by way of the foregoing description. The foregoing description is intended as a non-limiting illustration, since many variations will become apparent to those skilled in the art in view thereof. It is intended that all such variations within the scope and spirit of the appended claims be embraced thereby.

Claims: WHAT IS CLAIMED IS: 1. In an ultrasonic gas meter having a housing with an axial bore through which a fluid flows, the housing having one or more transducer ports disposed to the bore, and one or more cooperating ultrasonic transducers mounted in the respective transducer ports, wherein the transducer-housing assembly defines a cavity in the port in which Uquid can accumulate, the improvement comprising enhancing the movement and ultimate drainage of the fluid by maintaining a distance between the transducer and the surfaces of the port for enhancing the effect of surface tension of the Uquid for reducing the surface area/volume ratio of the Uquid sufficient to reduce the forces between the Uquid and the surfaces of the transducer-port assembly for overcoming inertia and for enhancing the movement of the Uquid for draining the meter. 2. In an ultrasonic gas meter having a housing with an outside surface and an axial bore through which a fluid flows, the housing having one or more transducer ports disposed to the bore, and one or more cooperating ultrasonic transducers mounted in the respective transducer ports, wherein the transducer-housing assembly defines a cavity in the port in which Uquid can accumulate, the improvement comprising a duct connecting the port for draining accumulated Uquids from the cavity. 3. The improvement as defined in claim 2, wherein the duct extends from the cavity to the bore. - 25 - 4. The improvement as defined in claim 3, wherein a centerline of the duct is tangential to a lower edge of the port. 5. The improvement as defined in claim 3, wherein a centerline of the duct intersects the port at a centerline thereof. 6. The improvement as defined in claim 3, wherein a centerline of the duct intersects the port at a point between the centerline of the port and a lower edge of the port. 7. The improvement as defined in claim 3, wherein a centerline of the duct intersects the port at a point between the centerline of the port and an upper edge of the port. 8. The improvement as defined in claim 2, wherein the duct extends from the cavity to an outlet at the housing outside surface. 9. The improvement as defined in claim 8, wherein the duct outlet is piped to a liquid collection tank. 10. The improvement as defined in claim 8, including an automatic valve for automatically opening the duct outlet. 11. The improvement as defined in claim 8, wherein a centerline of the duct is tangential to a lower edge of the port. 12. The improvement as defined in claim 8, wherein a centerline of the duct intersects the port at a centerline thereof. 13. The improvement as defined in claim 8, wherein a centerline of the duct intersects the port at a point between the centerline of the port and a lower edge of the port. - 26 - LE 2 14. The improvement as defined in claim 8, wherein a centerline of the duct intersects the port at a point between the centerline of the port and an upper edge of the port. 15. A method of draining accumulated Uquid from an ultrasonic gas meter comprising a housing having an axial bore through which fluid flows and one or more pairs of collinear transducer ports angularly disposed to the bore for providing transducer paths, and corresponding pairs of transducers received in the ports, wherein the transducer defines a cavity in the port in which undesirable Uquid having a mass can accumulate, the method of draining accumulated Uquid from an ultrasonic gas meter comprising the steps of: (a) maintaining a displacement between the transducer and the surfaces of the port which is sufficiently wide to enhance the surface tension effect of the Uquid such that the liquid assumes a more spherical shape for reducing the surface area/volume ratio of the Uquid sufficient to reduce the forces between the Uquid and the surfaces of the transducer- port assembly, (b) overcoming the inertia associated with the Uquid by gravity causing the Uquid to move, and (c) enhancing further the movement of the Uquid from the cavity in the port by gravity providing the force to continue the movement of the Uquid such that the Uquid is sufficiently removed from the port so that the meter is unfettered by coupling.

Inventors: ALLEN CHARLES R, FREUND WILLIAM JR, ALLEN, CHARLES, R., FREUND, WILLIAM, JR.
Applicants: DANIEL IND INC, DANIEL INDUSTRIES, INC.
Application year: 1995
Main classification: G01F1
IPC codes: G01F1, G01F15