Capacitive Void Fraction Measurement in Parallel Heat Transfer Circuits
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Solution Overview
Problem
Current methods for measuring void fractions in two-phase heat transfer systems are invasive, expensive, or limited to specific flow regimes, making it difficult to accurately determine void fractions in both steady and unsteady flow conditions, which is crucial for optimizing heat transfer systems like refrigerators where uneven evaporation can cause damage.
Innovation Solution
A heat transfer system with a distributor, multiple parallel circuits, and a collector, equipped with sensors and valves controlled by a processor that adjusts flow based on void fraction measurements, allowing for non-invasive and precise control of the system to ensure optimal evaporation across all circuits, regardless of changing conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical methods are used to measure void fraction, then measurement precision is improved, but the system requires transparent tubes which limits applicable temperatures and pressures
Solution Approach 1:
The patent replaces optical measurement methods with electromagnetic (capacitive) measurement methods. Instead of using light propagation through transparent tubes, the invention uses capacitance sensors that measure void fraction through electromagnetic field interaction with the two-phase flow, eliminating the need for transparent tubes and enabling operation across wider temperature and pressure ranges
2Measurement precision
If X-ray attenuation methods are used to measure void fraction, then measurement precision is improved, but cost and safety issues increase
Solution Approach 1:
The patent replaces expensive and safety-critical X-ray attenuation systems with low-cost capacitive sensors. The capacitive measurement system uses simple electrical components (electrodes, signal generator, amplifier) that are inexpensive, require no special safety precautions, and can be easily manufactured and installed
Solution Approach 2:
The invention substitutes the complex X-ray attenuation measurement system with an electromagnetic capacitive measurement system. Instead of using X-ray sources and detectors, the patent uses capacitance sensors that measure void fraction through changes in electrical capacitance caused by the dielectric properties of the liquid-gas mixture
3Difficulty of detecting and measuring
If ultrasonic transmission techniques are used to measure void fraction, then measurement capability is improved, but the technique is limited to total void fractions up to about 20%
Solution Approach 1:
The patent replaces ultrasonic transmission techniques with capacitive sensing. Instead of measuring acoustic impedance changes, the invention measures electrical capacitance changes that occur as the dielectric mixture of liquid and gas passes between the electrodes. This capacitive approach can detect the full range of void fractions from 0% to 100% without the limitations of acoustic wave reflection at gas-liquid interfaces
4Ease of operation
If capacitive measurements are used, then ease of implementation is improved, but the measured capacitance does not vary linearly with void fraction due to electrode curvature
Solution Approach 1:
The patent addresses the non-linear capacitance-void fraction relationship by changing the measurement parameters and data processing approach. The system measures capacitance values and uses calibration curves or lookup tables that account for the non-linear relationship between capacitance and void fraction. This allows the simple capacitive measurement to accurately determine void fraction across the full range despite the non-linear response
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 solution enables efficient and cost-effective design and operation of heat transfer systems by accurately determining void fractions in various flow regimes, reducing the risk of damage and optimizing performance, even under changing environmental conditions.
Implementation Method 1
Ultrasonic transmission techniques detect changes in acoustic impedance which is closely related to the density of the media.
Implementation Method 2
a gas-liquid interface acts almost as a perfect mirror for an acoustic wave
Implementation Method 3
measuring the volume averaged capacity between two curved electrodes mounted on the tube wall, the electrodes forming a capacitor
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The present invention relates to a method (100) and system for designing and/or controlling a heat transfer system comprising a set of at least two parallel circuits. The method comprises for at least one of the circuits of the set of parallel circuits, obtaining a void fraction dependent parameter of a substance flowing through the at least one circuit, and controlling a valve in at least one circuit of the set of parallel circuits so as to induce a flow in the at least one circuit that only has an evaporated fraction of the substance in the circuit at the position where the at least one circuit is combined with other parallel circuits or so as to obtain an identical evaporation state in more or each of the parallel circuits or so as to obtain a variable evaporation state of more or each of the parallel circuits. The controlling thereby takes into account the obtained void fraction dependent parameter or a void fraction determined based thereon.