Optical Waveguide Sensor for Cryogenic Liquefied Gas Level Measurement
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Solution Overview
Problem
Conventional methods for determining state variables in liquefied gas containers, such as hydrogen storage in motor vehicles, are inaccurate and unreliable due to inhomogeneous temperature and mass density distributions, and pose safety risks with electrical measurements and mechanical failures at low temperatures.
Innovation Solution
A method using a bundle of optical waveguides distributed within the container to measure light intensity and refractive index at specific points, allowing for precise determination of state variables like phase state, mass density, and temperature distribution, without extended contact with the container content, using a lighting unit, beam splitter, and evaluation unit with an image sensor and computer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an optical waveguide touches the container content by means of a sensor surface extended in its longitudinal direction, then the liquid level height can be measured, but the measurement accuracy is insufficient due to poor dependency of liquid level on scattering losses
Solution Approach 1:
The patent divides the optical waveguide into multiple discrete sensor elements along its length, each providing independent measurement data. This segmentation allows for more precise localization of the liquid level by identifying which specific segments are in contact with the liquid, rather than relying on cumulative scattering losses from an extended continuous surface.
2Measurement precision
If electrical measurement methods are used, then state variables can be measured, but heat bridges are introduced and explosion risk increases
Solution Approach 1:
The patent replaces electrical measurement systems with an optical measurement system using waveguides. Light is transmitted through the optical waveguide to sense the liquid level and state variables without requiring electrical contacts inside the cryogenic container, thereby eliminating heat bridges and explosion risks associated with electrical lines.
3Measurement precision
If mechanical systems with moving parts are used, then measurement can be performed, but they are completely impracticable in the low-temperature range
Solution Approach 1:
The patent replaces mechanical measurement systems with an optical system that has no moving parts. The optical waveguide remains stationary and uses light transmission to detect liquid level and state variables, making it suitable for low-temperature cryogenic environments where mechanical systems would fail.
4Measurement precision
If a single optical waveguide with extended sensor surface is used, then liquid level can be detected, but the amount of fuel in gas form above liquid level cannot be accurately accounted for
Solution Approach 1:
The patent extends the measurement capability from only liquid level detection to three-dimensional spatial mapping of state variables throughout the container. By distributing multiple optical waveguides or sensor elements throughout the container volume, the system can detect not only the liquid level but also the distribution and amount of gas phase fuel above it, providing comprehensive fuel quantity information.
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 a comprehensive, accurate, and reliable 'image' of state variables, enabling precise fuel level and mass determination, even in severe conditions, without the need for electrical lines or mechanical parts, thus enhancing safety and operational efficiency.
Implementation Method 1
light which is emitted from a lighting unit is carried in an optical waveguide to a contact point with the content of the container
Implementation Method 2
where it is partially reflected and the light intensity of the reflected light is measured
Implementation Method 3
Scattering losses occur in consequence as a function of the refractive index of the container content touching the sensor surface
Data Source
AI summary
A method and a device for optically determining state variables inside a container (1) for liquefied gases. In the method and device, light emitted by an illumination unit (2) travels within an optical waveguide (7, 9) to a contact point (33) with the content of the container (1) and is partially reflected there, the intensity of the reflected light is measured by an image sensor (4), and a state variable is determined from the intensity. In order to create a comprehensive “image” of the state variables in the container and of the container content, several optical waveguides (29, 29′) are guided to contact points (33) which are distributed within the container (1) and form measurement points (9.1, 9.2, 9.3, . . . , 9.n). Locally assigned state variables (refractive index, density, temperature, etc.) of the container content are determined from the measured values obtained at the measurement points (9.1, 9.2, 9.3, . . . , 9.n) and are evaluated along with the spatial coordinates of the measurement points (9.1, 9.2, 9.3, . . . , 9.n) in the container (1).