Apparatus and methods for measuring fluid flow parameters

• US 4,596,133 A
• Filed: 07/29/1983
• Issued: 06/24/1986
• Est. Priority Date: 07/29/1983
• Status: Expired due to Term

• Current Assignee: Panametrics, Inc. (General Electric Company)
• Original Assignee: Exxon Research and Engineering Company (Exxon Mobil Corporation), Panametrics, Inc. (General Electric Company)
• Inventors: Lynnworth, Lawrence C., Smalling, Jack W., Braswell, Leonard D.
• Primary Examiner(s): Kreitman, Stephen A.
• Application Number:
  US06/518,444
• Time in Patent Office: 1,061 Days
• Field of Search: 73/24, 73/30, 73/32 A, 73/597
• US Class Current: 73/24.01
• CPC Class Codes: G01F 1/662 Constructional details
• CPC Class Codes: G01F 1/667 Arrangements of transducers for ultrasonic flowmeters; Circuits for operating ultrasonic flowmeters
• CPC Class Codes: G01M 3/24 using infrasonic, sonic, or ultrasonic vibrations
• CPC Class Codes: G01N 2291/0258 Structural degradation, e.g. fatigue of composites, ageing of oils
• CPC Class Codes: G01N 2291/02818 Density, viscosity
• CPC Class Codes: G01N 2291/02836 Flow rate, liquid level
• CPC Class Codes: G01N 2291/02881 Temperature
• CPC Class Codes: G01N 2291/0289 Internal structure, e.g. defects, grain size, texture
• CPC Class Codes: G01N 29/024 by measuring propagation velocity or propagation time of acoustic waves
• CPC Class Codes: G01N 29/4454 Signal recognition, e.g. specific values or portions, signal events, signatures
• CPC Class Codes: G01P 5/245 by measuring transit time of acoustical waves measuring propagation velocity of acoustical waves per se G01H5/00

Abstract

An apparatus and method for measuring fluid flow parameters operate under conditions wherein the composition of the fluid flow can change rapidly thereby changing the speed of sound within the fluid and wherein the actual flow rate can change rapidly thereby further changing the transit time of acoustic energy traversing an interrogation path within the fluid. The apparatus determines the speed of sound in the fluid and the fluid flow velocity by measuring an upstream and a downstream transit time of acoustic energy within the fluid. The fluid is typically flowing within a conduit, and the transducers for transmitting and receiving the acoustic energy are precisely and carefully installed in the conduit. The measurements also allow an estimate to be made of the average molecular weight of gases passing through the conduit and hence of the mass flow rate of a gas. The measurements are taken at a frequency sufficient to satisfy the Nyquist criterion with regard to the maximum frequencies of interest for the fluid flow parameters being measured. Special techniques are developed for enabling transducer placement in preexisting conduit arrangements wherein access to the conduit is limited.

Claims

1. An apparatus for determining average molecular weight of a gas flowing through a conduit comprising

transit time measuring means for measuring the transit time of acoustic energy traversing a path across said conduit, and

means for accurately determining in response to said transit time, the average molecular weight of the gas flowing through the conduit at the time of said transit time measurement, said gas having an unknown specific heat ratio.

2. The apparatus of claim 1 further wherein said determining means employs an empirical relationship between molecular weight and the specific heat ratio of the gas for determining said average molecular weight.

3. The apparatus of claim 2 further wherein said relationship can be approximated by a straight line.

4. The apparatus of claim 1 further comprising

means for alternately and repetitively measuring said transit time in an upstream and a downstream direction, and

said determining means being responsive to said transit time measurements for averaging said measurements.

5. The apparatus of claim 4 further wherein said determining means comprises

means for temporally filtering said transit time measurements for responding to recent measurements and for ignoring past measurements.

6. The apparatus of claim 5 wherein said filtering means includes means for effecting a truncated binary weighting of said transit time measurements.

7. A method for determining average molecular weight of a gas flowing through a conduit comprising

measuring the transit time of acoustic energy traversing a path across said conduit, and

accurately determining, in response to said transit time, the average molecular weight of the gas flowing through the conduit at the time of said transit time measurement, said gas having an unknown specific heat ratio.

8. The method of claim 7 further comprising the step of

employing an empirical relationship between molecular weight and specific heat ratio of the gas for determining said average molecular weight.

9. The molecular weight determining method of claim 8 further comprising the steps of

employing received acoustic measurement data for determining the temperature and pressure of said fluid

whereby mass flow rate can be determined using solely acoustic transducer derived data.

10. The method of claim 7 further comprising the steps of alternately and repetitively measuring said transit time in upstream and downstream directions, and

responding to said transit time measurements for averaging said measurements to thereby smooth the transit time

11. The method of claim 10 further wherein said averaging step comprises

employing a truncated binary weighting of said transit time data.