Capacitance Void Fraction Sensing for Cryogenic Hydrogen Flow
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Solution Overview
Problem
Accurate measurement of the flow rate of liquid hydrogen is challenging due to its tendency to vaporize and fluctuating gas-to-liquid ratio, leading to inaccurate determination of flow rates in transfer pipes.
Innovation Solution
A void fraction sensor with an insulating inner pipe and electrodes, combined with a heat insulating layer, measures the void fraction of cryogenic liquids like liquid hydrogen, using capacitance to improve measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If liquid hydrogen is measured in transfer pipes, then flow rate measurement is required, but the low temperature and high thermal conductivity cause significant fluctuations in gas-to-liquid ratios and void content, making accurate measurement difficult
Solution Approach 1:
The patent replaces conventional flow measurement methods with capacitance-based sensing. The capacitance type void fraction sensor measures the dielectric constant of the two-phase flow, which varies with void content. This electrical field-based measurement method is insensitive to temperature fluctuations and thermal conductivity variations, enabling accurate flow rate measurement despite significant gas-to-liquid ratio changes in liquid hydrogen transfer pipes.
Solution Approach 2:
The patent utilizes the change in dielectric constant as a measurement parameter. By measuring capacitance between electrodes, the system detects void fraction through changes in the dielectric properties of the two-phase flow. This parameter change approach allows the sensor to distinguish between gas and liquid phases and calculate void content, thereby enabling accurate flow rate determination despite composition fluctuations.
2Measurement precision
If a void fraction sensor is introduced to measure gas phase volume percentage, then measurement capability is improved, but the sensor structure becomes more complex
Solution Approach 1:
The patent designs a multi-functional sensor assembly where the same structure performs multiple functions: the insulating pipe serves as both the measurement chamber and thermal insulation barrier, the electrodes provide both electrical isolation support and capacitance sensing, and the heat insulating layer simultaneously protects against external temperature and enables accurate void fraction measurement. This integration reduces overall system complexity despite the advanced measurement capability.
Solution Approach 2:
The patent introduces an insulating pipe as an intermediary element between the two-phase flow and the external environment. This insulating pipe with mounted electrodes creates a controlled measurement environment that isolates the sensing mechanism from external thermal interference while maintaining electrical isolation. The heat insulating layer acts as another intermediary that blocks external temperature effects, allowing the capacitance sensor to accurately measure void fraction without being affected by external thermal conditions.
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
The sensor provides precise measurement of void fraction, enhancing the accuracy of flow rate determination by minimizing the impact of external temperature fluctuations and reducing void generation.
Implementation Method 1
a heat insulating layer covering an outer peripheral side of the insulating inner pipe
Implementation Method 2
a capacitance type void fraction sensor that measures capacitance using a pair of electrodes
Data Source
AI summary
A void fraction sensor according to the present disclosure includes an insulating inner pipe having a through hole through which a low-temperature liquid flows, at least a pair of electrodes mounted on an outer peripheral surface of the insulating inner pipe, and a heat insulating layer covering an outer peripheral side of the insulating inner pipe. A flowmeter according to the present disclosure measures a flow rate of a cryogenic liquid flowing through the through hole of the insulating inner pipe, and includes the void fraction sensor described above, and a flow velocity meter that measures a flow velocity of the cryogenic liquid flowing through the through hole.