Patent Grant
10591327
N/A
N/A
To detect steam flow rates, current systems utilize vortex shedding meters, orifice plate flow meters, turbine flow meters, Coriolis mass flow meters, resistance thermometer flow meters, and ultrasonic flow meters, all of which have resulted in a variety of different costs and deficiencies. Some of the problems these flow meters have created include the impedance of the steam flow, the high maintenance costs from moving parts, and low accuracy. Most of these systems require the presence of a physical object in the path of the steam that results in low turndown ratios (the range of flow a flow meter can measure). Additionally, these systems are often susceptible to saturated steam that can condense onto an obtrusion and result in inaccurate mass flow readings. Other problems include their inability to detect sudden fluctuations present in the steam flow rate generated by pressure or temperature variations within these systems.
Laser-based systems generally measure the quality of steam (liquid phase of water as opposed to the vapor phase). Those laser-based systems that attempt to measure mass flow rely on phase change measurements or other more complex methods.
The technical challenge is the accurate measurement of steam mass flow in a conduit where there is variability in the steam flow. The solution is to simultaneously sample transmitted coherent light with light detectors spaced along the longitudinal axis of the conduit. This arrangement allows for the measurement of parameters that result in a measurement of steam mass flow.
The use of the term steam in this application is for convenience. The method and system applies to any two (2) phase system that is translucent. Two (2) phase is defined by state of matter such as gaseous, liquid and solid and is not limited to mixtures of the same species.
A laser-based approach that will result in a flow meter that will be immune to the problems created by saturated steam. The laser-based system will detect the concentration of steam by shining two laser beams through a clear section of pipe and detecting the amount of light that has not been transmitted through the translucent steam. Light will be partially blocked by the microscopic water droplets that make up the saturated steam and will depend on the volumetric concentration of these droplets. Each of the lasers beams will detect precisely the same fluctuations as the inhomogeneous steam flows first past one laser beam and then the other. By identifying identical concentration fluctuations in the steam, the laser system will be able to measure the time the steam is transported from one laser to the other. From this information, the laser steam flow meter will determine the mass flow rate for saturated steam to within ±0.1%.
Fluctuations within the flowing steam will be generated through a variety of different mechanisms, including through turbulence effects from the high Reynolds number flow of the steam, imperfections in the pipe geometry and inner surface roughness, and from inhomogeneous fluctuations inherent from the act of vaporizing water. These will contribute to a variety of density fluctuation patterns along the line of the steam pipe that can be exploited for characterizing the steam mass flow rate.
Basis for Measuring Mass Flow
The net rate of mass flow through a cross sectional control surface of area A through a pipe is given by:
{dot over (m)}=c*v*A
Where {dot over (m)} is mass flow, c is concentration, v is velocity of the steam, and A is the area of the cross section of the pipe carrying steam.
The velocity of the steam is measured as it passes a first light detector and a second light detector spaced along the longitudinal axis of the pipe.
The concentration is related to the absorbance as given by the Beer-Lambert Law and is a simple linear relationship.
Absorbance=a*b*c
c is concentration a is a material coefficient, b is the light path length.
Mass Flow Measurement
First Method and System
Turning to
The light detectors are connected to a control circuit. The control circuit is also connected to the sources of coherent light (not shown). The light detectors are synchronized in time.
A first method an arrangement of coherent light and detectors.
The method records the light detection for a predetermined period 100, tm. The second light detector records for an interval of tm+k, where k is a predetermined number of seconds to allow for capture of the pattern. A graphic representation is show in
In the same interval, absorption is measured, preferably at the first light detector. As previously stated, once the absorbance and light path are measured and knowing the coefficient a for the material (in this case steam), it is possible to measure the concentration. As given by the equation:
Where
The mass flow can then be measured according the previously stated relationship {dot over (m)}=c*v*A.
Preferably after the initial measurement, the time to measure and optionally display the measurement on optional device, preferably an LCD screen is tl. The next step of the process is then triggered. The first light detector records for the predetermined interval and the second light detector is triggered for a period of
This adjusts the interval 130 for the second light detector to account for processing time where j is predetermined constant, x is the distance between light detectors and vprevious is the previously measured velocity. The process continues until completed.
Second Method and System
A second method uses the same arrangement of coherent light and detectors as the first method as shown in
The second method as shown in the flow chart in
The second detector measures both the absorbance 530 and the signal that was previously received by the first detector 520.
The area of the coherent light 330 in
The mass flow is given by:
The parameter Z is a compensation factor that accounts for the fact that the laser beam encompasses a smaller area than the volume of the pipe. The mass flow is measured 540 and preferably reported on a device, preferably such as an LCD screen. Then, the lasers are triggered 500 and the process is repeated until conclusion.
Although specific advantages have been enumerated above, various embodiments may include some, none, or all of the enumerated advantages. Other technical advantages may become readily apparent to one of ordinary skill in the art after review of the following figures and description.
It should be understood at the outset that, although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described below.
Unless otherwise specifically noted, articles depicted in the drawings are not necessarily drawn to scale.
Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the disclosure. For example, the components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses disclosed herein may be performed by more, fewer, or other components and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order.
To aid the Patent Office and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims or claim elements to invoke 35 U.S.C. 112(f) unless the words “means for” or “step for” are explicitly used in the particular claim.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4480483 | McShane | Nov 1984 | A |
| Number | Date | Country | |
|---|---|---|---|
| 20190390988 A1 | Dec 2019 | US |
