Fiber Optic Mass Flow Sensor for Cryogenic Fluids
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Solution Overview
Problem
Cryogenic fluid flow measurement in high-pressure systems is challenging due to turbulence and cavitation, making conventional methods inaccurate or inapplicable, especially in space-related propulsion research where cryogenic fluids like liquid oxygen and hydrogen are used.
Innovation Solution
A noninvasive method using a light beam of multiple wavelengths projected across a pipe to detect the mass flow rate by measuring the relative strengths of the light beam at different positions, employing laser diodes and photodiodes to determine the mass flow rate without direct contact with the fluid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional direct contact measurement techniques (thermocouple, thermoresistor, mechanical flow meters) are used, then measurement capability is provided, but measurement accuracy deteriorates due to turbulence and cavitation in cryogenic flows
Solution Approach 1:
The patent replaces mechanical flow meters and direct contact thermal sensors with a non-contact optical measurement system. Laser beams pass through the cryogenic fluid without mechanical contact, eliminating the harmful interactions between measurement devices and the turbulent, cavitating flow. The system uses optical properties (absorption, scattering) to infer mass flow rate without disturbing the flow field.
Solution Approach 2:
The patent introduces light (electromagnetic radiation) as an intermediary medium to transfer information about the cryogenic flow from one side of the pipe to the other without direct contact. The laser beam serves as a mediator that interacts with the fluid through optical phenomena (absorption, scattering) to provide measurement data while remaining non-invasive.
2Adaptability or versatility
If conventional techniques assume no turbulence and no gaseous medium, then simplified measurement procedures are available, but applicability deteriorates in actual cryogenic systems where turbulence and phase mixing occur
Solution Approach 1:
The patent changes the measurement parameter from mechanical/thermal properties (which are affected by turbulence and phase changes) to optical properties (absorption coefficient, scattering coefficient). These optical parameters can be measured through the turbulent, two-phase cryogenic flow without being disrupted by the flow conditions, thereby increasing adaptability to real-world conditions.
Solution Approach 2:
The patent replaces mechanical assumptions (laminar flow, single phase) with optical measurement capabilities that work regardless of flow regime or phase composition. The optical system naturally adapts to turbulent and two-phase conditions without requiring simplified assumptions about the flow state.
3Measurement precision
If noninvasive optical methods are used, then measurement accuracy improves by avoiding turbulence and cavitation effects, but device complexity increases due to multiple wavelengths and detection positions
Solution Approach 1:
The patent segments the optical measurement into multiple discrete components: multiple laser sources emitting at different wavelengths, multiple detection positions along the pipe, and separate detection for each wavelength at each position. This segmentation allows independent optimization and calibration of each component while maintaining overall measurement accuracy through data fusion.
Solution Approach 2:
The patent utilizes changes in optical parameters (absorption coefficient, scattering coefficient) at different wavelengths to extract multiple flow characteristics. By measuring at multiple wavelengths and positions, the system obtains sufficient data to calculate mass flow rate while compensating for turbulence and phase composition effects through mathematical analysis.
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 and reliable mass flow rate measurements in cryogenic systems, overcoming the limitations of conventional techniques by not assuming turbulence or gaseous absence, suitable for high-flow cryogenic applications.
Implementation Method 1
projecting a light beam of at least two wavelengths from one side of the pipe across the width of the pipe so as to pass through the fluid under test
Implementation Method 2
the light beam passes through the fluid and is dispersed thereby
Data Source
AI summary
A method and apparatus are provided for sensing the mass flow rate of a fluid flowing through a pipe. A light beam containing plural individual wavelengths is projected from one side of the pipe across the width of the pipe so as to pass through the fluid under test. Fiber optic couplers located at least two positions on the opposite side of the pipe are used to detect the light beam. A determination is then made of the relative strengths of the light beam for each wavelength at the at least two positions and based at least in part on these relative strengths, the mass flow rate of the fluid is determined.