System and method for determining thermodynamic properties

• US 6,209,387 B1
• Filed: 06/29/1999
• Issued: 04/03/2001
• Est. Priority Date: 07/30/1997
• Status: Expired due to Term

• Current Assignee: Gas Technology Institute
• Original Assignee: Gas Research Institute (GTI Energy)
• Inventors: Savidge, Jeffrey L.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): WIGGINS, JOHN DAVID
• Application Number:
  US09/342,383
• Time in Patent Office: 644 Days
• Field of Search: 73/24.05, 73/23.2, 73/23.29, 73/25.01, 73/589, 73/597, 73/646, 73/861.28, 73/1 G
• US Class Current: 73/24.05
• CPC Class Codes: G01F 1/66 by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
• CPC Class Codes: G01N 2291/0215 Mixtures of three or more gases, e.g. air
• CPC Class Codes: G01N 2291/02818 Density, viscosity
• CPC Class Codes: G01N 2291/02836 Flow rate, liquid level
• CPC Class Codes: G01N 2291/02872 Pressure
• CPC Class Codes: G01N 2291/02881 Temperature
• CPC Class Codes: G01N 29/024 by measuring propagation velocity or propagation time of acoustic waves
• CPC Class Codes: G01N 29/323 compensating for pressure or tension variations
• CPC Class Codes: G01N 29/326 compensating for temperature variations
• CPC Class Codes: G01N 9/24 by observing the transmission of wave or particle radiation through the material

Abstract

Disclosed is a system and method for determining the thermodynamic properties and percentage of each component of a multi-component gas medium by using speed of sound in conjunction with other data. The present system comprises a computer system with means for obtaining the temperature, pressure, and speed of sound of a gas medium. The computer system operates according to operating logic stored in memory. According to the operating logic, measurements of the temperature, pressure, speed of sound and acoustic impedance are recorded in a gas pipe or other transport device to determine a convergent temperature range. Next a convergent series is extrapolated from the convergent temperature range and a convergent series calculation using isochoric convergence iterations is performed to obtain estimates of the thermo-physical properties of the gas medium. Thereafter, the percentage of the gas medium which comprises each known gas components is determined using state equations and the estimated thermo-physical properties.

Claims

1. A system for determining the thermodynamic properties of a gas medium, comprising:

a transducer disposed in the gas medium to emit a sound pulse based on an excitation signal having a voltage V and frequency f into the gas medium and detecting the return pulse therefrom;

a temperature sensor disposed in the gas medium to measure the temperature of the gas medium;

a pressure sensor disposed in the gas medium to measure the pressure of the gas medium;

means for acquiring and storing measurements of the speed of sound in the gas medium, the acoustic impedance of the gas medium, the pressure and temperature of the gas medium;

means for determining the thermodynamic properties of the gas medium based on the stored measurements;

means for detecting the existence of a temperature gradient of a predetermined range among the stored measurements; and

means for determining the percentage of a plurality of gas components making up the gas medium.

2. The system of claim 1, further comprising means for calibrating the frequency and voltage of the excitation signal to achieve maximum power transfer into the medium.

3. The system of claim 2, wherein the means for acquiring and storing measurements of the acoustic impedance of the gas medium further comprises calculating the acoustic impedance based on the excitation signal, wherein the acoustic impedance is proportional to the calibrated voltage of the excitation signal at maximum power transfer.

4. The system of claim 3, wherein the means for determining the thermodynamic properties of the gas medium further comprises the calculation of the density of the gas medium based upon the acoustic impedance and the speed of sound through the gas medium, where $\rho$



 

=β

ν

2,

where ρ

is the density, β

is the acoustic impedance, and ν

is the speed of sound through the gas medium.

5. A system for determining the thermodynamic properties of a gas medium comprising:

a transducer disposed in the gas medium to emit a sound pulse based on an excitation signal having a voltage V and frequency f into the gas medium and detecting a return pulse therefrom, the transducer being in electrical communication with a transducer interface, the transducer interface being electrically coupled to a data bus;

a temperature sensor disposed in the gas medium to measure the temperature of the gas medium, the temperature sensor being in electrical communication with a temperature probe interface, the temperature probe interface being electrically coupled to the data bus;

a pressure sensor disposed in the gas medium to measure the pressure of the gas medium, the pressure sensor being in electrical communication with a pressure transducer interface, the pressure transducer interface being electrically coupled to the data bus;

a microprocessor electrically coupled to the data bus;

a memory electrically coupled to the data bus; and

operating logic stored in the memory, the operating logic directing the acquisition and storage in memory of measurements of the speed of sound and the acoustic impedance of the gas medium using the transducer, measurements of the pressure of the gas medium using the temperature sensor and detection of the existence of a temperature gradient of a predetermined range among stored temperature measurements, the operating logic further calculating the thermodynamic properties of the gas medium based on the stored measurements.

6. The system of claim 5, wherein the operating logic further comprises the calibration of the frequency and voltage of the excitation signal to achieve maximum power transfer into the gas medium.

7. The system of claim 6, wherein the operating logic further comprises the calculation of the acoustic impedance based on the excitation signal, wherein the acoustic impedance is proportional to the calibrated voltage of the excitation signal at maximum power transfer.

8. The system of claim 7, wherein the operating logic further comprises the calculation of the density of the gas medium based upon the acoustic impedance and the speed of sound though the gas medium, where $\rho$



 

=β

ν

2,

where ρ

is the density, β

is the acoustic impedance, and ν

is the speed of sound through the gas medium.

9. A method for determining the thermodynamic properties of a gas medium, comprising the steps of:

establishing and applying an excitation signal having a voltage V and frequency f to an acoustic transducer;

measuring the speed of sound through the gas medium;

measuring the acoustic impedance of the gas medium;

measuring the pressure of the gas medium;

measuring the temperature of the gas medium;

storing the measurements of the speed of sound, acoustic impedance, pressure, and temperature;

calculating the thermodynamic properties of the gas medium based on the stored measurements;

detecting the existence of a temperature gradient of a predetermined range among stored temperature measurements; and

means for determining the percentage of a plurality of gas components making up the gas medium.

10. The method of claim 9, further comprising the step of calibrating the frequency and voltage of the excitation signal to achieve maximum power transfer into the gas medium.

11. The method of claim 10, further comprising the step of calculating the acoustic impedance based on the excitation signal, wherein the acoustic impedance is proportional to the calibrated voltage of the excitation signal at maximum power transfer.

12. The method of claim 11, further comprising the step of calculating the density of the gas medium based upon the acoustic impedance and the speed of sound through the gas medium, where $\rho$



 

=β

ν

2,

and where ρ

is the density, β

is the acoustic impedance, and ν

is the speed of sound through the gas medium.