Cryogenic Flowmeter Using Capacitance-Based Void Fraction Sensing
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Solution Overview
Problem
Existing void fraction meters for cryogenic liquids like liquid hydrogen face challenges in accurately measuring the gas-liquid two-phase flow due to significant temperature changes affecting electrostatic capacitance, leading to inaccurate flow rate determination.
Innovation Solution
A void fraction sensor with an inner pipe, electrodes, conductive pins, and a filling member with controlled temperature coefficient of permittivity, combined with a housing and vacuum space to reduce impedance changes and improve measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitive void fraction meter is used to measure gas-liquid two-phase flow, then void fraction can be measured, but temperature changes cause significant variations in electrostatic capacitance leading to measurement inaccuracy
Solution Approach 1:
The patent introduces a filling member as an intermediary substance placed in the space between the electrode and the housing. This filling member has a temperature coefficient of relative permittivity that is equal to or less than that of the inner pipe material, thereby mediating the temperature effect and reducing its impact on electrostatic capacitance measurements. The filling member acts as a buffer that compensates for temperature-induced capacitance variations.
Solution Approach 2:
The patent changes the physical parameter (relative permittivity temperature coefficient) of the filling member to be equal to or less than that of the inner pipe. By selecting materials with specific permittivity characteristics, the system optimizes the electrostatic capacitance stability across temperature variations, thereby improving measurement accuracy under varying thermal conditions.
2Productivity
If liquid hydrogen is transported in a transfer pipe, then cryogenic liquid flow is achieved, but immediate vaporization occurs due to high thermal conductivity and low latent heat
Solution Approach 1:
The patent converts the harmful effect of vaporization into a beneficial measurement opportunity. By placing electrodes inside the transfer pipe and measuring electrostatic capacitance, the system can detect and quantify the void fraction generated by vaporization. This allows for accurate flow rate measurement of the liquid phase despite the presence of gas bubbles, turning the vaporization problem into a measurable parameter that enables precise flow control.
3Measurement precision
If flow velocity is measured in a pipe with gas-liquid two-phase flow, then velocity data is obtained, but accurate flow rate determination cannot be made due to fluctuating void content
Solution Approach 1:
The patent creates a multi-functional measurement system where the same electrode structure serves multiple purposes: measuring both flow velocity (through time-of-flight or other velocity measurement techniques) and void fraction (through electrostatic capacitance measurement). By combining these two measurement functions in one instrument, the system can simultaneously obtain velocity data and gas-liquid ratio information, enabling accurate flow rate calculation despite composition fluctuations.
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 accurately measures void fraction in cryogenic liquid flows by minimizing the impact of temperature changes on electrostatic capacitance, ensuring precise flow rate determination.
Implementation Method 1
an absolute value of a temperature coefficient τε1 of relative permittivity of the filling member at -196°C to 20°C is equal to or less than an absolute value of a temperature coefficient τε2 of relative permittivity of the inner pipe at -196°C to 20°C
Implementation Method 2
measuring an electrostatic capacitance between the pair of electrodes
Data Source
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AI summary
A void fraction sensor of the present disclosure includes: an insulating inner pipe including a through hole through which a cryogenic liquid flows; at least one pair of electrodes mounted on an outer peripheral surface of the inner pipe; a conductive pin connected to each of the one pair of electrodes; a housing surrounding the inner pipe and including a first insertion hole into which the conductive pin is inserted: and a filling member disposed at least between an inner wall surface of the housing and a back surface on an opposite side to a facing front surface of each of the at least one pair of electrodes. An absolute value of a temperature coefficient τε1 of relative permittivity of the filling member at -196°C to 20°C is equal to or less than an absolute value of a temperature coefficient τε2 of relative permittivity of the inner pipe at -196°C to 20°C.