Patent Publication Number: US-4730500-A

Title: Vortex generating mass flowmeter

Description:
CROSS REFERENCE TO RLEATED APPLICATIONS 
     This is a continuation-in-part of application Ser. No. 213,843, filed Dec. 8, l980, now U.S. Pat. No. 4,453,542 which is a continuation-in-part of application Ser. No. 40,557, filed May 21, 1979, now U.S. Pat. No. 4,240,293, and Ser. No. 109,839, filed Jan. 7, 1980, now U.S. Pat. No. 4,372,169. The disclosures of these applications are incorporated fully herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to gas flow rate measurement and, more particularly, to a vortex generating mass flowmeter usable over a wide range of flow rates. 
     There are many different types of flowmeters in use today. One type, which is known as a vortex shedding flowmeter, generates intermittent, unstable vortices with a transversely elongated bluff body positioned in the flow stream passing through an unrestricted fluid line. The frequency of the intermittent vortices or perturbations is a measure of the flow rate through the fluid line, and this frequency is sensed to provide a flow rate reading. The devices are generally limited to liquid flow rate measurement due to the effect of compressibility the gas on the vortex shedding process. A typical vortex shedding flowmeter is disclosed on Rodely U.S. Pat. No. 3,572,117, issued Mar. 23, 1971. 
     Another type of flowmeter measures the pressure difference across a calibrated orifice plate. In the case of gas measurement, due to compressibility effects, the mass flow rate is not only dependent upon the pressure difference but also temperature and density variations, and the relationship is nonlinear and highly complex. Thus, the measured pressure difference must be processed further to give a true reading of mass flow rate. These devices generally read gas flow over a limited range due to rapidly increasing pressure difference across the device. 
     My U.S. Pat. Nos. 4,240,293 and 4,372,169 disclose a flowmeter that utilizes the aerodynamic drag resulting from a bluff body to generate a pressure signal related to flow rate. The flowmeter comprises a flow passage in which a restriction is formed, a bluff body, in the form of one or more discs or truncated cones disposed on one side of the restriction, and a pressure sensor. 
     SUMMARY OF THE INVENTION 
     According to the invention, one or more rods are employed in the flow passage of the above-described flowmeter as the drag-producing bluff body. Conveniently, the rods can also serve as probes for sensing the pressure in the flow passage. In the preferred embodiment, one rod is radially oriented upstream of the restriction and another rod is radially oriented at an angle to the first rod within the restriction. The rods have hollow interiors connected to a ΔP transducer. The first rod has a chamfered end facing upstream. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of specific embodiments of the best mode contemplated of carrying out the invention are illustrated in the drawings, in which: 
     FIGS. 1 and 2 are side-sectional and upstream end-sectional views, respectively, of a flowmeter incorporating principles of the invention; 
     FIGS. 3 and 4 are side-sectional and upstream end-sectional views of another embodiment of a flowmeter incorporating principles of the invention; 
     FIGS. 5 and 6 are side-sectional and downstream end-sectional views, respectively, of still another embodiment of a flowmeter incorporating principles of the invention; 
     FIGS. 7 and 8 are side-sectional and downstream end-sectional views, respectively, of still another embodiment of a flowmeter incorporating principles of the invention; and 
     FIGS. 9 and 10 are side-sectional and downstream end-sectional views, respectively, of yet another embodiment of a flowmeter incorporating principles of the invention. 
    
    
     DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS 
     The disclosures of my U.S. Pat. Nos. 4,240,293 and 4,372,169 are incorporated fully herein by reference. These patents describe a number of flowmeters employing frustums as vortex-generating bluff bodies. It has now been discovered that rods extending into the flow passage transverse to the direction of flow can also serve advantageously as vortex-generating bodies in a flowmeter employing the principles of the above-mentioned patents. 
     In FIGS. 1 and 2, fluid, preferably gas, flows through a pipe 18 in the direction of arrows 20. Pipe 18 has a cylindrical upstream chamber 22 and a cylindrical downstream chamber 24 that are connected by a converging section 26, a cylindrical section 28, and a diverging section 30, all smaller in diameter than chambers 22 and 24. The divergence of section 28 is more gradual than the convergence of section 26. Chamber 22 serves as an inlet port and chamber 24 serves as an outlet port. Sections 26, 28, and 30 serve as a restriction in the flow passage. A rod 32 extends radially into cylindrical section 28 beyond the center of the passage. Means for sensing gas pressure in the form of passage 34 through rod 32 is connected to one inlet of a ΔP transducer 36. In the embodiment of FIG. 1, the end of rod 32 in the flow passage is squared off. A rod 38 for producing drag extends radially through chamber 22 at its junction with section 26, to form an acute angle with rod 32 as depicted in FIG. 2. A passage 40 through rod 38 is connected to another inlet of ΔP transducer 36. Rod 38 extends to the center of the flow passage. The end of rod 38 is chamfered to face in an upstream direction. ΔP transducer 36 is connected to an indicator 42 that displays in analog or digital form the pressure difference between the end of rod 34 and the end of rod 38. 
     Considering the small diameter of rods 32 and 38, a large pressure differential signal is generated, which is indicateve of large drag. Typical dimensions for the described flowmeter are as follows: 
     
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Diameter of chambers 22 and 24                                            
                       .612   inch                                        
Diameter of rod 32     .075   inch                                        
Diameter of rod 38     .075   inch                                        
Length of rod 32       .950   inch                                        
Length of rod 38       .950   inch                                        
Chamfer on rod 38      45     degrees                                     
Base diameter of section 26                                               
                       .520   inch                                        
Included angle of section 26                                              
                       45     degrees                                     
Base diameter of section 30                                               
                       .520   inch                                        
Included angle of section 30                                              
                        --21  degrees                                     
Diameter of section 28 .342   inch                                        
Length of section 28   .310   inch                                        
Spacing between rods 32 and 38                                            
                       .400   inch                                        
Angle between rods 32 and 38                                              
                       45     degrees                                     
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     In the embodiments of FIGS. 3 through 10, the same reference numerals are used to identify the components in common with the embodiment of FIGS. 1 and 2. In the embodiment of FIGS. 3 and 4, rod 32 extends to the center of the flow passage, rod 38 extends beyond the center of the flow passage and has a squared off end. A thick, cylindrical rod 44 extends diametrically across the flow passage upstream of rod 38. In the embodiment of FIGS. 5 and 6, rods 32 and 38 are both oriented on different chords. The end of rod 32 is squared off and the end of rod 38 is chamfered to face in an upstream direction. In the embodiment of FIGS. 7 and 8, rod 38 is eliminated and passage 34 is connected to a single inlet pressure sensor to provide an absolute pressure reading. Also, rod 44 for producing drag is located at the junction of chamber 22 and section 26. 
     In the embodiment of FIGS. 9 and 10, first and second rods 32 and 38 are both chamfered to face in the same direction. Rod 32 extends radially through chamber 24 at its junction with section 30 to a point beyond the center of the flow passage. Rod 38 extends radially through chamber 22 at its junction with section 26 to a point beyond the center of the flow passage. Passages 34 and 40 are connected to the respective inlets of a ΔP transducer not shown, which is in turn connected to an indicator. The axes of rods 32 and 38 are aligned. A cylindrical rod 44 extends diametrically across section 28. Its axis is aligned with the axes of rods 32 and 38. The divergence of section 30 is the same as the convergence of section 26, both of which are more gradual than the corresponding sections in the other embodiments. The vortex activity created by rod 44 in this embodiment produces a different signal than the other embodiments because what is being measured is vortex activity within vortex activity. In effect, there is a flowmeter within a flowmeter and the square law governing the signal generated by rods 32 and 38 is offset by the square root relationship of the orifice presented by section 23 and rod 44. The result is a more linear signal as a function of flow rate. Further, this design provides symmetrical, bidirectional flow response--the response is positive at passage 40 with respect to passage 34 for flow in the direction of arrow 20 and positive at passage 34 with respect to passage 40 for flow in the other direction, while the magnitude in both cases is the same for a given flow rate. The flowmeter can be calibrated for different flow rates by changing the diameter of rod 44 or providing as a substitute therefor drag bodies having different shapes, such as a sphere or an aerodynamic foil. Further, this flowmeter appears to have a broader range of operation than the other embodiments. Of importance is the fact that this embodiment can be used to measure either liquid or gas flow with comparable results. The difference in density between liquids and gases can be compensated for by increasing the diameter of rod 44 However, in many cases the same design can be used to measure both liquids and gases. In practice the diameters of rods 32, 38, and 44 can be scaled up or down without any ill effects. The sizes of these rods determines the signal-to-ΔP ratio of the flowmeter. 
     In practice, the embodiment of FIGS. 9 and 10 is preferably fabricated from three injection-molded plastic parts designated 50, 52, and 54. Chamber 22 and rod 38 are formed in part 50. Chamber 24 and rod 32 are formed in part 54. Sections 26, 28, and 30 and rod 44 are formed in part 52. Parts 50 and 54 are standard interchangeably fit together with several different versions of part 52 having a rod 44 with different diameters. As illustrated in FIG. 9, part 52 has annular external shoulders 56 and 58 against which the ends of parts 50 and 54, respectively, abut. Typical dimensions for the described flowmeter are as follows: 
     
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Diameter of chambers 22 and 24                                            
                       .620   inch                                        
Diameter of rods 32 and 38                                                
                       .104   inch                                        
Length of rods 32 and 38                                                  
                       .950   inch                                        
Chamfer on rod 38      .335   degrees                                     
Base diameter of sections 26 and 30                                       
                       .520   inch                                        
Included angle of sections 26 and 30                                      
                        --21  degrees                                     
Diameter of section 28 .342   inch                                        
Length of section 28   .310   inch                                        
Center-to-center spacing between                                          
rods 32 and 44         .451   inch                                        
and 38 and 44           --    inch                                        
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     The described embodiments of the invention are only considered to be preferred and illustrative of the inventive concept; the scope of the invention is not to be restricted to such embodiments. Various and numerous other arrangements may be devised by one skilled in the art without departing from the spirit and scope of this invention. For example, some of the embodiments operate with a flow direction opposite to that illustrated. Further, the sensitivity of a number of the embodiments disclosed herein, particularly FIG. 9, can be increased by employing a bypass arrangement as disclosed in FIG. 2 or FIG. 5 of the above-referenced U.S. Pat. No. 4,372,169.