Optical Fluid Flow Velocity Measurement via Scattering
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Solution Overview
Problem
Existing optical fluid flow measurement systems face challenges in accurately measuring liquid flows due to significant Rayleigh scattering from fluid molecules, which deteriorates the accuracy of cross-correlation or time-of-flight methods.
Innovation Solution
A compact optical system using a single continuous wave light source outside the pipe, emitting a narrow beam or light sheet, and a two-dimensional CCD or CMOS detector array positioned outside the pipe to collect scattered light without direct optical communication with the light source, maximizing Mie scattering and minimizing Rayleigh scattering detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cross-correlation or time-of-flight optical methods are used to measure liquid flow, then measurement capability is provided, but accuracy deteriorates due to significant Rayleigh scattering from fluid molecules
Solution Approach 1:
The patent applies local quality by using a specific wavelength range (400-700 nm) for the light source to optimize the scattering characteristics. This wavelength selection creates a local quality difference in the optical interaction, enhancing Mie scattering from particles while minimizing Rayleigh scattering from liquid molecules, thereby improving measurement accuracy in the presence of harmful scattering effects
Solution Approach 2:
The patent introduces an intermediary approach by using particles suspended in the liquid flow as mediators for the measurement. Instead of directly measuring the liquid molecules (which cause Rayleigh scattering), the system measures the scattering from suspended particles (Mie scattering), which are less affected by molecular density variations. This intermediary approach allows accurate flow velocity measurement while avoiding the harmful Rayleigh scattering interference
2Measurement precision
If multiple light beams and pulsed mode operation are used in optical flow measurement, then measurement capability is provided, but system complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates unnecessary components from complex optical flow measurement systems. Instead of using multiple light beams and pulsed mode operation with fast electronics, the invention uses a single continuous wave light source and simplified detection architecture. This extraction of essential functions reduces system complexity and cost while maintaining measurement capability through the optimized single-beam cross-correlation method
Solution Approach 2:
The patent applies segmentation by dividing the detection function into spatially separated photodetectors arranged in a linear array. Each photodetector detects light intensity at a specific position, and the temporal cross-correlation is computed from these spatially segmented measurements. This segmentation approach simplifies the electronics requirements compared to pulsed mode systems, as continuous wave detection with simpler timing electronics suffices
3Measurement precision
If optical sensors are positioned to detect scattered light, then measurement capability is provided, but direct optical communication with light source creates noise and interference
Solution Approach 1:
The patent applies asymmetry in the optical geometry by positioning the light source and photodetector array at asymmetric locations relative to the flow path. The light source is positioned to illuminate the flow, while the photodetectors are positioned to detect scattered light at a specific angle. This asymmetric arrangement creates geometric separation that prevents direct optical communication between source and detectors, eliminating direct light interference while maintaining measurement capability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides accurate fluid flow velocity measurements across a wide range of flow values, reduces system complexity and cost, and allows for simultaneous density determination and real-time video visualization of the flow.
Implementation Method 1
detect light caused by scattering of the beam with particles found in the fluid
Implementation Method 2
Rayleigh scattering from fluid molecules, which deteriorates the accuracy of cross-correlation or time-of-flight methods
Implementation Method 3
maximizing Mie scattering and minimizing Rayleigh scattering detection
Data Source
AI summary
A method of fluid flow velocity measurement includes emitting a beam from a light source via a first window into a pipe through which a fluid flows, the beam illuminating the fluid flowing in the pipe, using a light detector array, which is coupled via a second window to the pipe and which is outside a field of view of the light detector, to detect light caused by scattering of the beam with particles found in the fluid, and determining a velocity of the fluid flowing in the pipe as a function of signals from the light detector array.