Abstract:
A flow meter system is disclosed that includes a first flow sensor and first and second fluid flow conduits extending from the first flow sensor. The second fluid flow conduit may be disposed inside the first fluid flow conduit thereby forming a fluid annulus between the first and second fluid flow conduits. The first fluid flow conduit may be metal to resist a fluid pressure differential and the second fluid flow conduit may be non-metal to balance a fluid pressure across the second fluid flow conduit and attenuate noise therein. The fluid annulus may be configured to receive a fluid to balance the fluid pressure across the second fluid flow conduit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. provisional patent application Ser. No. 62/218,562 filed Sep. 14, 2015, entitled “Flow Meter System,” which is hereby incorporated herein by reference in its entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND 
       [0003]    Flow meters are used in various industries to measure flow rates of moving fluids. For example, flow meters are used in the hydrocarbon exploration and production industry to measure various fluids moving in pipelines or other conduits during the process of drilling and producing an oil and gas well. A well is drilled to below the surface of the earth such that oil, natural gas, and water can be extracted via the well. Some wells are used to inject materials below the surface of the earth. For example, materials or fluids can be injected below the surface of the earth to sequester carbon dioxide, store natural gas for later use, or to inject steam or other substances near an oil well to enhance recovery. In some cases, a well can be maintained or enhanced using a chemical injection management system. A chemical injection management system may inject corrosion-inhibiting materials, foam-inhibiting materials, wax-inhibiting materials, antifreeze, and/or other similar chemicals to extend the life of a well or increase the rate at which resources are extracted from a well. Such materials may be injected into the well in a controlled manner over a period of time. The chemical injection management system may include a flow meter to measure and help regulate the injected material flow rate. 
       SUMMARY 
       [0004]    In some embodiments, a flow meter system includes a first flow sensor and first and second fluid flow conduits extending from the first flow sensor. The second fluid flow conduit may be disposed inside the first fluid flow conduit thereby forming a fluid annulus between the first and second fluid flow conduits. The first fluid flow conduit may be metal to resist a fluid pressure differential and the second fluid flow conduit may be non-metal to balance a fluid pressure across the second fluid flow conduit and attenuate noise therein. The second fluid flow conduit is attenuative to absorb ultrasound along non-fluid paths. The fluid annulus may be configured to receive a fluid to balance the fluid pressure across the second fluid flow conduit. The second fluid flow conduit may include an internal bore to receive a process fluid that is also the received fluid of the fluid annulus. The flow meter system may further include a second flow sensor, wherein the first and second fluid flow conduits extend between the first and second flow sensors. 
         [0005]    In some embodiments, the flow meter system may further include a housing surrounding the first flow sensor and an axial distance between an end face of the first and second fluid flow conduits and the first flow sensor in the first flow sensor housing. The axial distance forms a fluid chamber, and in some embodiments, the fluid chamber disposed between the fluid flow conduits and the sensor is operable to reduce fluid cavitation. The axial distance may be a pre-determined focal length for the first flow sensor. The first flow sensor may include a pre-determined window thickness. 
         [0006]    In some embodiments, the flow meter system further includes a housing surrounding the first flow sensor and a fluid inlet in the first flow sensor housing having an angled junction. In some embodiments, the angled junction serves to reduce fluid cavitation. The angled inlet may serve as a flow passage directing fluid into a fluid chamber of the sensor housing. 
         [0007]    In some embodiments, the noise attenuation of the second fluid flow conduit allows the first flow sensor to measure a laminar flow rate at high pressure. In some embodiments, the first flow sensor is configured to measure a fluid viscosity. In some embodiments, an internal bore of the second fluid flow conduit is adjustable. In further embodiments, the internal bore is configured to flow a fluid in a viscosity range of 0.1 cP to 500 cP. In some embodiments, a seal is disposed between the first and second fluid flow conduits to stagnate the received fluid in the fluid annulus. 
         [0008]    In some embodiments, a flow meter system includes metal seals axially offset from an ultrasonic piezoelectric crystal. The flow meter system may include a housing surrounding the first flow sensor and having a first metal seal between the housing and the first flow sensor, and a second metal seal between the housing and the first fluid flow conduit, wherein the first and second metal seals are axially offset relative to a crystal of the first flow sensor. In some embodiments, the flow meter system includes a first housing surrounding the first flow sensor and having a first metal seal between the first housing and the first flow sensor, a second metal seal between the first housing and the first fluid flow conduit, wherein the first and second metal seals are axially offset relative to a crystal of the first flow sensor, a second housing surrounding the second flow sensor and having a third metal seal between the second housing and the second flow sensor, a fourth metal seal between the second housing and the second fluid flow conduit, wherein the third and fourth metal seals are axially offset relative to a crystal of the second flow sensor. In some embodiments, the flow meter system is coupled to a chemical injection management system 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    For a detailed description of exemplary embodiments, reference will now be made to the accompanying drawings in which: 
           [0010]      FIG. 1  is a schematic view of an embodiment of a well system; 
           [0011]      FIG. 2  is a schematic view of an embodiment of wellhead and chemical injection management system of the well system of  FIG. 1 ; 
           [0012]      FIG. 3  is a perspective, partial phantom view of a flow meter and valve or regulator assembly of  FIG. 2 ; 
           [0013]      FIG. 4  is a schematic of the architecture of the flow meter and valve or regulator assembly of  FIG. 3 ; 
           [0014]      FIG. 5  is a side and end views of an embodiment of a flow meter system in accordance with principles disclosed herein; 
           [0015]      FIG. 6  is an enlarged, cross-section view of an inlet sensor body of the flow meter system of  FIG. 5 ; 
           [0016]      FIG. 7  is an enlarged, cross-section view of an outlet sensor body of the flow meter system of  FIG. 5 ; 
           [0017]      FIG. 8  is a cross-section view of an alternative embodiment of an inlet sensor body; 
           [0018]      FIG. 9  is a cross-section view of another alternative embodiment of an inlet sensor body and an outlet sensor body of a flow meter system; 
           [0019]      FIG. 10  is a cross-section view of a further alternative embodiment of an inlet sensor body and an outlet sensor body of a flow meter system; and 
           [0020]      FIG. 11  is a perspective view of an alternative embodiment of a flow meter and valve assembly including a plurality of flow meter assemblies or cores. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    In the drawings and description that follow, like parts are typically marked throughout the specification and drawings with the same reference numerals. The drawing figures are not necessarily to scale. Certain features of the disclosed embodiments may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. The present disclosure includes embodiments of different forms. Specific embodiments are described in detail and are shown in the drawings, with the understanding that the present disclosure is to be considered an exemplification of the principles of the disclosure, and is not intended to limit the disclosure to that illustrated and described herein. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results. 
         [0022]    Unless otherwise specified, in the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ”. Any use of any form of the terms “connect”, “engage”, “couple”, “attach”, or any other term describing an interaction between elements is not meant to limit the interaction to direct interaction between the elements and may also include indirect interaction between the elements described. The various characteristics mentioned above, as well as other features and characteristics described in more detail below, will be readily apparent to those skilled in the art upon reading the following detailed description of the embodiments, and by referring to the accompanying drawings. 
         [0023]      FIG. 1  is a schematic diagram showing an embodiment of a well system  100 . The well system  100  can be configured to extract various minerals and natural resources, including hydrocarbons (e.g., oil and/or natural gas), or configured to inject substances into an earthen surface  110  and an earthen formation  112  via a well or wellbore  114 . In some embodiments, the well system  100  is land-based, such that the surface  110  is land surface, or subsea, such that the surface  110  is the sea floor. The system  100  includes a wellhead  115  disposed over the wellbore  114 . The system  100  may be used to extract oil, natural gas, and other related resources from the wellbore  114  and the wellhead  115 , through a conduit  106 , and to an extraction point  104  at a surface location  102 . The extraction point  104  may be an on-shore processing facility, an off-shore rig, or any other extraction point. The system  100  may also be used to inject fluids, such as the materials noted above, into the wellbore  114 . The injected fluids may be supplied to the subsea equipment using the conduit  106 , which may include flexible jumper or umbilical lines. The conduit may comprise reinforced polymer and small diameter steel supply lines, which are interstitially spaced into a larger reinforced polymer liner. As the working pressure of the subsea equipment increases, the supply pressures and injection pressures also increase. 
         [0024]    Referring now to  FIG. 2 , the wellhead  115  includes a Christmas tree or tree  108 . The tree  108  includes a valve receptacle  116  and a chemical injection management system (CIMS)  118 . When assembled, the tree  108  may couple to the well  114  and include a variety of valves, fittings, and controls for operating the well  114 . The chemical injection management system  118  is coupled to the tree  108  via the valve receptacle  116 . The tree  108  provides fluid communication between the chemical injection management system  118  and the well  114 . The chemical injection management system  118  further includes a flow valve or flow regulator assembly  120 , and as explained below, the chemical injection management system  118  may be configured to regulate the flow of a fluid through the tree  108  and into the well  114  using the flow valve assembly  120 . 
         [0025]    Referring now to  FIG. 3 , a perspective and partial phantom view of the flow meter and valve assembly  120  is shown. The flow valve assembly  120  includes a housing  112  with a handle  124 , a first coupling interface  126 , and a second coupling interface  128 . In some embodiments, the coupling interfaces  126 ,  128  are used to couple to the chemical injection management system  118 , the tree  108 , an ROV (remotely operated vehicle), or other portions of the wellhead  115  equipment. The housing  122  contains a flow meter  130 , a valve actuator assembly  132 , and a conduit or flowline  134  fluidly coupling an inlet  150  of the valve actuator assembly  132  to an outlet  138  of the flow meter  130 . The housing  122  may also contain other mechanical, electrical, and hydraulic components of the flow meter and valve assembly  120 . For example, and referring to  FIG. 4 , the flow meter and valve assembly  120  includes an inlet or hydraulic coupler  136  fluidly coupled to the flow meter  130 . A control module  146  and a first pressure sensor  142  are electrically coupled to the flow meter  130 . In some embodiments, the flow meter  130  is an ultrasonic flow meter, and thus the control module  146  is an ultrasonic control module. An electronic control module  148  and a second pressure sensor  144  are also electrically coupled to the flow meter  130 . Fluid directed through the flow meter  130  exits the flow meter  130  at the outlet  138 , travels through the flowline  134 , and enters the valve actuator assembly  132  at the inlet  150 . In some embodiments, the valve actuator assembly  132  is a motor actuated control valve with position feedback. The valve actuator assembly  132  is fluidly coupled to an outlet or hydraulic coupler  152  of the flow valve assembly  120 . The ultrasonic control module  146 , the electronic control module  148 , and the pressure sensors  142 ,  144  are used to operate the flow valve assembly  120 , and are electrically coupled to an electrical connector  140  for signal and power communication to and from the flow valve assembly  120 . 
         [0026]    Referring next to  FIG. 5 , a side and end views of an embodiment of a flow meter system  200  is shown in accordance with principles of the present disclosure. In some embodiments, the flow meter system  200  is an ultrasonic flow meter system. In some embodiments, the flow meter system  200  can be used to replace the flow meter  130  of the above-described flow valve assembly  120 . The flow meter system  200  includes a first sensor or transducer end  202  and a second sensor or transducer end  204 . Coupled between the sensor ends  202 ,  204  is a fluid pipe or conduit  210 . The first sensor end  202 , which may also be referred to as an inlet or upstream sensor body, includes an inlet interface  206  having a fluid inlet  220 . The second sensor end  204 , which may also be referred to as an outlet or downstream sensor body, includes an outlet interface  208  having a fluid outlet  218  and other interface mechanisms  217 ,  219 . A control module canister  212  is mounted on the flow meter system  200  using clamps  214  and retainers  216 . In some embodiments, the canister  212  includes an ultrasonic control module. In some embodiments, the canister  212  is retained on the pipe  210 . 
         [0027]    Referring now to  FIG. 6 , an enlarged, cross-section view of the inlet sensor body  202  is shown. The inlet sensor body  202  includes a housing  222 , a retainer plate  224 , a retainer or screw  226 , and a retainer ring  236 , which help to couple the pipe  210  to the housing  222 . The pipe  210  may be sealed against the housing  222  by a first seal ring  264 , a seal ring  265 , and a backup ring  267 . The pipe  210  includes an outer pipe or tube  228  and an inner pipe or tube  230 . Disposed between the outer pipe  228  and the inner pipe  230  is an annular gap or flow passage  232 . The inner pipe  230  includes an inner bore or flow passage  234  having an axis  235 . In some embodiments, the outer pipe  228  comprises metal. In some embodiments, the metal is steel. In certain embodiments, the metal is stainless steel. In some embodiments, the inner pipe  230  comprises a non-metal material. In some embodiments, the non-metal material is an attenuative material. In some embodiments, the non-metal material is a polymer. In certain embodiments, the non-metal material is a thermoplastic polymer. In certain embodiments, the inner pipe  230  is made from polyether ether ketone (PEEK), or glass filled PEEK. 
         [0028]    The housing  222  includes an internal bore  238 , and a sensor or transducer assembly  250  is mounted in the bore  238 . The sensor assembly  250  includes a sensor housing  252 , a piezoelectric crystal  254 , an inner support member  256 , and a biasing or retention member  258  which can be, for example, a Bellville spring. The sensor housing  252  may be sealed against the housing  222  by a second seal ring  266 , a seal ring  269 , and a backup ring  271 . In some embodiments, a threaded connection couples the sensor housing  252  to the housing  222 . The sensor housing  252 , the pipe  210 , and the housing bore  238  form a fluid chamber or cavity  240  in the sensor body housing  222 . A first dimension of the fluid chamber  240  is an axial distance D 1  between an end face  260  of the sensor housing  252  and an end face  262  of the pipe  210 . A second dimension of the fluid chamber  240  is an axial distance D 2  between the first seal ring  264  and the piezoelectric crystal  254 . In some embodiments, the first seal ring  264  is disposed adjacent the pipe end face  262 . A third dimension of the fluid chamber  240  is an axial distance D 3  between the second seal ring  266  and the piezoelectric crystal  254 . In some embodiments, the second seal ring  266  is disposed adjacent an intermediate portion of the sensor housing  252  and axially offset from the housing end face  262  and the piezoelectric crystal  254 . In some embodiments, the second seal ring  266  is axially offset upstream of or backed away from the piezoelectric crystal  254 . In some embodiments, the seal rings  264 ,  266  are made from metal. The fluid chamber  240  and the sensor assembly  250  are sealed inside the sensor body housing  222  by a wired connector  270  sealed against a radial bore  272 . The wired connector  270  provides power and communications to and from the sensor assembly  250 . In some embodiments, the wired connector  270  also seals the sensor assembly  250  from the external environment. 
         [0029]    The fluid inlet  220  and the fluid chamber  240  are in fluid communication via the flow bore or passage  274  and the flow bore or passage  276  that come together at an angled junction  278 . In some embodiments, the fluid inlet  220  includes an enlarged diameter as compared to the reduced diameters of the flow passages  274 ,  276 . 
         [0030]    Referring next to  FIG. 7 , the second or outlet sensor end  204  is shown enlarged and in cross-section. The outlet sensor end  204  shares many of the same components as the inlet sensor end  202 , with some differences. In the interest of clarity, similar components will not be described in detail while others will be focused on. For example, the outlet sensor end  204 , like the inlet sensor end  202 , includes a housing  322 , a retainer plate  324 , a retainer or screw  326 , and a retainer ring  336 , which help to couple the pipe  210  to the housing  322 . The pipe  210  connection may further comprise an additional connection member  337 . The pipe  210  may be sealed against the housing  322  by a first seal ring  364 , a seal ring  365 , and a backup ring  367 . Furthermore, a seal ring  373  may be disposed in the fluid annulus  232  to provide a seal between the outer pipe  228  and the inner pipe  230 . 
         [0031]    The housing  322  includes an internal bore  338 , and a sensor or transducer assembly  350  is mounted in the bore  338 . The sensor assembly  350  includes a sensor housing  352 , a piezoelectric crystal  354 , an inner support member  356 , and a biasing or retention member  358  which can be, for example, a Bellville spring. The sensor housing  352  may be sealed against the housing  322  by a second seal ring  366 , a seal ring  369 , and a backup ring  371 . In some embodiments, a threaded connection couples the sensor housing  352  to the housing  322 . The sensor housing  352 , the pipe  210 , and the housing bore  338  form a fluid chamber or cavity  340  in the sensor body housing  322 . A first dimension of the fluid chamber  340  is an axial distance D 4  between an end face  360  of the sensor housing  352  and an end face  362  of the pipe  210 . A second dimension of the fluid chamber  340  is an axial distance D 5  between the first seal ring  364  and the piezoelectric crystal  354 . In some embodiments, the first seal ring  364  is disposed adjacent the pipe end face  362 . A third dimension of the fluid chamber  340  is an axial distance D 6  between the second seal ring  366  and the piezoelectric crystal  354 . In some embodiments, the second seal ring  366  is disposed adjacent an intermediate portion of the sensor housing  352  and axially offset from the housing end face  362  and the piezoelectric crystal  354 . In some embodiments, the second seal ring  366  is axially offset downstream of or backed away from the piezoelectric crystal  354 . In some embodiments, the seal rings  364 ,  366  are made from metal. The fluid chamber  340  and the sensor assembly  350  are sealed inside the sensor body housing  322  by a wired connector  370  sealed against a radial bore  372 . The wired connector  370  provides power and communications to and from the sensor assembly  350 . In some embodiments, the wired connector  370  also seals the sensor assembly  350  from the external environment 
         [0032]    The fluid chamber  340  is in fluid communication with a fluid outlet  320  of the sensor body housing  322 . 
         [0033]    In operation, a fluid, such as a chemical injection or other process fluid, is directed to the fluid inlet  220  of the inlet sensor end  202 . The fluid then flows through the passage  274 , through the angled junction  278 , through the passage  276 , and into the fluid chamber  240 . In some embodiments, the angled junction  278  is designed to reduce cavitation in the fluid flowing therethrough and that is entering the fluid chamber  240 . In some embodiments, one or more of the fluid passages  274 ,  276  are adjustable in diameter. For example, the diameters are adjustable between 5 mm, 6 mm, 7 mm, 8 mm, and other desirable diameters. In some embodiments, the fluid chamber  240  provides a volume in which the flowing fluid is allowed to slow down. In some embodiments, the reduction in velocity of the flowing fluid reduces cavitation in the fluid. In some embodiments, the velocity reduction causes the fluid to reach a steady state just prior to entering the tube flow bore  234 . Consequently, in some embodiments, the fluid chamber  240  is an anti-cavitation, pro-steady state fluid chamber providing a more stable fluid flow to the internal bore  234  of the pipe  210 . The angled flow passage just prior to the fluid chamber  240  can aid in the anti-cavitation effects in the fluid. The volume of the fluid chamber is determined by the diameter of the internal bore  238  and the axial distance D 1 . In some embodiments, the axial distance D 1  is 0.5 in., but can also be other distances. 
         [0034]    Fluid then flows from the fluid chamber  240  and into the pipe flow bore  234  as well as the fluid annulus  232  between the outer pipe  228  and the inner pipe  230 . In some embodiments, the process fluid directed into the annulus  232  is allowed to stagnate therein because of the sealing of the seal ring  373  at the outlet sensor end  204 . In some embodiments, the seal  373  prevents an unmetered flow of fluid through the annulus  232 . Thus, the process fluid in the annulus  232  is at the same or substantially the same pressure as the process fluid flowing in the bore  234 . Consequently, there is little or no pressure differential across the inner pipe  230 , i.e., the inner pipe  230  is pressure-balanced. Because the inner pipe  230  is preferably made from an attenuative material, it absorbs ultrasound waves such that non-fluid paths of sound are absorbed while the inner pipe  230  is not subjected to high stress. Instead, because the annulus  232  fluid is at the process fluid pressure, the outer metal pipe  228  withstands the high stresses generated by the process fluid pressure differential. Thus, in one aspect, the outer pipe  228  is a pressure backup pipe to the inner attenuative pipe  230 . In some embodiments, the process fluid pressures are 30,000 psi or above. In some embodiments, the internal flow bore  234  is adjustable in diameter. For example, the diameter is adjustable between 5 mm, 6 mm, 7 mm, 8 mm, and other desirable diameters. 
         [0035]    As shown by the distances axial D 2 , D 3 , D 5 , and D 6 , the metal seals are axially offset from the piezoelectric crystals. Distancing the metal seals form the piezoelectric crystals helps to increase acoustic isolation of the piezoelectric crystals. 
         [0036]    The flow meter system embodiments described above can be used to measure laminar fluid flow in high pressure systems with ultrasound. In some embodiments, the process fluid being measured ranges in viscosity from 0.1 cP to 500 cP, and such viscosities can be measured by the flow meter systems described herein. At laminar, and super laminar, flow rates the fluid velocity is low. Consequently, the time difference between pulses of ultrasound travelling upstream and downstream can be small (for example, nanoseconds) which makes repeatable measurement of the time difference (and thus velocity) challenging due to the noise that transmits between the two ultrasonic transducers via non-fluid paths. Such noise can affect processing of the ultrasonic signals. Further, high fluid pressure (such as 30,000 psi) will affect the materials of the pipes and transducers, which must be able to withstand high stresses generated by such high pressures. As described above, the inner pipe is made of an attenuative material that will absorb the non-fluid path noise, such as the sounds transmitted by solid components. The attenuative, non-metal inner pipe is surrounded by process fluid such that it is pressure-balanced, and the high pressure of the process fluid is transferred to the more robust outer metal pipe. The pressure-balancing annulus is disposed between the inner and outer pipes, thus it extends along the pipe  210 . In some embodiments, the pressure-balancing is along the pipe  210  only, meaning the pressure-balancing is limited to the metering run only. 
         [0037]    In the embodiments described above, the distances D 1  and D 2  can be pre-determined or chosen for optimum focal lengths between the transducer face and the pipe face. In some embodiments, the pre-determined optimum focal length is 0.5 in., though other focal lengths are chosen for desired results in other embodiments. In some embodiments, one or more of the transducers may include a pre-determined window thickness, for example, of 0.375 in. In some embodiments, a window thickness is the portion of the sensor housing  252  having an axial length of D 2  minus D 1  in  FIG. 6 . In some embodiments, a window thickness is the portion of the sensor housing  352  having an axial length of D 5  minus D 4  in  FIG. 7 . 
         [0038]    Referring to  FIG. 8 , an alternative embodiment of an inlet sensor body  400  is shown in cross-section. In certain embodiments, features of the sensor assembly are adjusted as compared to embodiments described above. For example, the size and shape of a sensor housing  452  of a sensor assembly  450  can vary at such locations as an end face  460  and a threaded connection  455 . Other features are similar or vary only slightly from other embodiments described herein. For example, a fluid chamber  440  separates the sensor assembly  450  from an end face  462  of the pipe  210 . The pipe  210  includes the fluid annulus  232  which can receive and stagnate process fluid for pressure balancing. An angled fluid inlet  478  carries fluid to the fluid chamber  440 . 
         [0039]    Referring to  FIG. 9 , a cross-section view of another alternative embodiment of an inlet sensor body  502  and an outlet sensor body  504  of a flow meter system  500  is shown. Certain features are adjusted as compared to embodiments described above. For example, the physical configurations of the sensor assemblies and adjacent structure are adjusted. A sensor assembly  550  next to an angled fluid inlet  578  includes an end face  560  that is in close proximity to an end face  562  of a flow conduit or metering pipe  510 . In the outlet sensor body  504 , a sensor assembly  552  includes an end face  554  that is in close proximity to an end face  556  of the metering pipe  510 . Further, the piezoelectric crystals of the sensor assemblies  550 ,  552  are in-line and are not loaded or are uncompressed. Additionally, the angled fluid inlet  578  is directly coupled into the metering pipe  510  at a fluid connection  515 . 
         [0040]    Referring next to  FIG. 10 , a cross-section view of a further alternative embodiment of an inlet sensor body  602  and an outlet sensor body  604  of a flow meter system  600  is shown. Certain features are adjusted as compared to embodiments described above. For example, the physical configurations of the sensor assemblies and adjacent structure are adjusted. A sensor assembly  650  next to an angled fluid inlet  678  includes an end face  660  that is in close proximity to an end face  662  of a flow conduit or metering pipe  610 . In the outlet sensor body  604 , a sensor assembly  652  includes an end face  654  that is in close proximity to an end face  656  of the metering pipe  610 . Further, the piezoelectric crystals of the sensor assemblies  650 ,  652  are not in-line but at right angles, and are loaded or are compressed. Additionally, the angled fluid inlet  678  is directly coupled into the metering pipe  610  at a fluid connection  615 . 
         [0041]    Referring to  FIG. 11 , a perspective view of an alternative flow meter system  700  is shown, having a plurality of flow meter assemblies or cores  702 ,  704  in a single assembly. 
         [0042]    According to various embodiments disclosed herein, a flow meter system is presented which can accurately measure low or very low flow rate or velocity of the process fluid using ultrasonic transducers. Further, various embodiments of the flow meter system can accurately measure viscous fluids with ultrasonic transducers. The flow meter system embodiments are configurable to variously measure fluid velocity, fluid flow rate, fluid viscosity, fluid pressure, and other fluid characteristics, or a combination thereof. 
         [0043]    The above discussion is meant to be illustrative of the principles and various embodiments of the present disclosure. While certain embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the disclosure. The embodiments described herein are exemplary only, and are not limiting. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims.