Optical Fiber Refractive Index Sensing for Phase Change Material State
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Solution Overview
Problem
Phase change material (PCM) storage tanks face challenges due to poor thermal conductivity in the solid state and high costs, along with inaccurate state of charge (SoC) measurements caused by non-uniform phase changes and pressure-induced local cavities, which require numerous sensors and complex designs.
Innovation Solution
A heat storage vessel with optical fibers having sections without cladding, allowing direct contact with PCM, measures light intensity to determine the refractive index change and calculate the SoC, using a light source and optical measuring means to provide accurate, global measurements of solid and liquid phases within the vessel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If numerous optocouplers are installed inside the thermal storage vessel to obtain accurate PCM state measurements, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
Multiple discrete optocoupler measurements are merged into a single integrated optical fiber measurement system. The optical fiber traverses the entire PCM volume and integrates refractive index information from all phases, replacing numerous separate sensors with one unified measurement device that provides global PCM state assessment.
Solution Approach 2:
The optical fiber serves multiple functions simultaneously: it acts as a light transmission medium, a refractive index sensor, and a global measurement probe for the entire PCM volume. This multi-functional approach eliminates the need for multiple specialized sensors while providing comprehensive measurement capability.
2Measurement precision
If numerous optocouplers with cables and sealed feedthroughs are installed to measure PCM state at various locations, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent combines multiple discrete measurement components (optocouplers, cables, feedthroughs) into a single optical fiber probe, dramatically reducing the number of parts required and simplifying the manufacturing process while maintaining measurement accuracy across the entire PCM volume.
Solution Approach 2:
The measurement function is extracted from complex multi-component sensor assemblies and concentrated into a simple optical fiber probe that can be easily manufactured and installed, removing the need for expensive sealed feedthroughs and cable management systems.
3Measurement precision
If numerous sensors are distributed throughout the vessel to capture non-uniform phase changes, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent transitions from point measurements (0D) or line measurements (1D) with multiple sensors to a volumetric measurement approach (3D) using a single optical fiber that samples refractive index throughout the entire PCM volume, capturing non-uniform phase changes without requiring spatial distribution of multiple sensors.
Solution Approach 2:
The patent merges multiple spatial measurement points into a single integrated optical measurement that captures the average refractive index state across the entire PCM volume, effectively combining information from all phases and locations into one measurement value.
4Measurement precision
If pressure sensors are used to estimate PCM phase ratio, then measurement precision may be improved, but reliability decreases due to inability to register local cavities
Solution Approach 1:
The patent replaces mechanical pressure sensing with optical refractive index measurement. Instead of using pressure sensors that infer phase ratio indirectly and fail to detect local cavities, the optical fiber directly measures the refractive index of the PCM material, providing reliable detection of phase changes regardless of pressure conditions or cavity formation.
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 method allows for quick and precise determination of the SoC without extensive sensor readings, reducing complexity and cost, while avoiding pressure-induced issues and providing reliable energy content estimation.
Implementation Method 1
the refractive index at the wavelength λ of the core is higher than that of the phase change material in a first phase and lower than that of the phase change material in a second phase
Implementation Method 2
measuring the amount of light at the output at a second end of the at least one optical fiber wherein the at least one optical fiber comprises one or a plurality of sections with the cladding removed so that at these sections the core is in direct contact with the phase change material
Data Source
AI summary
A device for measuring the state of a phase change material inside a vessel, the device includes at least one optical fiber arranged inside the vessel, the optical fiber including a cladding around a core, a light source emitting light coupled into a first end of the at least one optical fiber at a wavelength λ, optical measuring devices for measuring the amount of light at the output at a second end of the at least one optical fiber. The at least one optical fiber also includes a plurality of sections with the cladding removed so that at these sections the core is in direct contact with the phase change material inside the vessel and where the refractive index at the wavelength λ of the core is higher than that of the phase change material in a first phase and lower in a second phase.