Capacitive Electrotomography for Cryogenic Temperature Field Measurement
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Solution Overview
Problem
Conventional temperature sensors are inadequate for recording a complete three-dimensional temperature field, especially in cryogenic liquids like liquid hydrogen, as they require an infinite number of sensors and are unsuitable for obtaining precise measurements in such environments.
Innovation Solution
The method employs capacitive electrotomography to determine local liquid density, which is then used to derive local temperature, creating a three-dimensional temperature field by repeating the process multiple times, utilizing a capacitive electrotomography device, pressure measuring device, and substance databases to achieve precise measurements suitable for cryogenic liquids under various conditions, including microgravity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature sensors are used to record temperature fields, then point-by-point temperature information can be obtained, but a complete three-dimensional temperature field cannot be captured without an infinite number of sensors
Solution Approach 1:
The patent replaces the mechanical/physical temperature sensor system with an electrical field-based measurement system. Capacitive electrodes emit electrical signals that penetrate the liquid, and the dielectric constant variations caused by temperature-induced density changes are detected electrically, eliminating the need for numerous physical temperature sensors throughout the volume.
Solution Approach 2:
The patent introduces dielectric constant as an intermediary parameter that links temperature to measurable electrical properties. Temperature changes cause density changes, which alter the dielectric constant of the liquid, which in turn modifies the electrical capacitance between electrodes. This intermediary allows indirect but comprehensive temperature field measurement.
2Measurement precision
If conventional temperature measurement methods are used in cryogenic liquids, then point measurements are possible, but three-dimensional temperature field measurement is not suitable
Solution Approach 1:
The patent exploits the change in dielectric constant with temperature in cryogenic liquids. As temperature varies, density changes, which directly affect the dielectric constant. By measuring capacitance variations across multiple electrodes, the system captures three-dimensional temperature distribution without requiring sensors adapted to extreme cold.
Solution Approach 2:
The capacitive electrotomography system serves multiple functions: it measures temperature field, density distribution, and can potentially detect other dielectric properties. The same electrode array and measurement system work across different cryogenic liquids and conditions, providing a universal measurement approach.
3Measurement precision
If density changes of liquid hydrogen are measured using capacitive electrotomography, then temperature differences below 1 K can be resolved, but the measurement requires determination of local density and pressure
Solution Approach 1:
The patent divides the measurement process into separate determination steps: first local density is determined from capacitance measurements, then local pressure is determined (either from pressure sensors or hydrostatic calculations), and finally temperature is derived by combining these parameters. This segmentation allows each parameter to be measured independently with appropriate precision.
Solution Approach 2:
The patent uses material databases that contain pre-stored density-pressure-temperature relationships for cryogenic liquids. Instead of performing complex real-time calculations, the system copies pre-computed thermodynamic data into lookup tables, allowing rapid temperature determination from measured density and pressure values.
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 enables accurate and precise measurement of three-dimensional temperature fields in cryogenic liquids, such as liquid hydrogen, with temperature differences resolved to less than 1 K, and is applicable under terrestrial and space conditions, reducing the need for numerous pressure sensors.
Implementation Method 1
The electrical signals mutually emitted by the electrodes are received by neighboring electrodes. The liquid density is determined from the dielectric constant.
Implementation Method 2
Capacitive electrotomography (ECT) is characterized by the placement of a series of electrodes at the boundaries of the volume to be characterized. The electrical signals mutually emitted by the electrodes are received by neighboring electrodes.
Data Source
Figure 1~2
AI summary
Disclosed is a method for measuring a three-dimensional temperature field of a liquid in a container, in particular of cryogenic liquids, wherein a local liquid density is determined by means of capacitive electrotomography and the local temperature is derived from the local liquid density and a local liquid pressure, as well as a device for carrying out such a method.