Coaxial Capacitance Sensing for Refrigerant Phase Control
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Solution Overview
Problem
Current refrigeration systems lack effective methods to detect and control the liquid/gas phase of refrigerant in the suction gas between the evaporator and compressor, leading to inefficiencies and potential damage to compressors due to liquid hammer and inadequate evaporator utilization.
Innovation Solution
A capacitive sensing system using coaxial tubes to measure the capacitance between an outer and inner electrode tube, allowing for precise detection of liquid or gas content, which triggers control mechanisms for the expansion valve and compressor operation to prevent liquid entry and optimize evaporator performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive sensors are used to detect liquid in suction gas, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent implements a nested electrode structure where an inner electrode tube is positioned within an outer electrode tube, both forming part of the capacitive sensor assembly in the suction line. This nested configuration enables precise dielectric measurement while maintaining a compact sensor design that integrates into the existing refrigeration system architecture.
Solution Approach 2:
The patent replaces mechanical liquid detection methods with capacitive sensing technology that measures dielectric constant changes to distinguish between liquid and gas phases. This substitution eliminates moving parts and mechanical wear while providing continuous, precise phase detection through electrical field measurements between the coaxial electrodes.
2Productivity
If expansion valve opening is increased to eliminate dry zone, then evaporator efficiency is improved, but risk of liquid hammer increases
Solution Approach 1:
The patent implements a feedback control system where capacitive sensors continuously monitor the dielectric constant of suction gas to detect liquid presence. The control unit receives these measurements and dynamically adjusts the expansion valve opening degree to maintain optimal evaporator utilization while preventing liquid carryover that could cause liquid hammer in the compressor.
Solution Approach 2:
The patent places capacitive sensors in the suction line before the compressor to detect liquid refrigerant in advance. This preliminary detection allows the control system to adjust the expansion valve or compressor operation before liquid enters the compressor, preventing liquid hammer damage while maximizing evaporator capacity utilization.
3Productivity
If superheat value is decreased to utilize evaporator efficiently, then productivity is improved, but reliability of compressor decreases
Solution Approach 1:
The patent uses capacitive sensors to provide real-time feedback on suction gas composition to the control unit. This feedback enables the system to maintain low superheat values for high evaporator efficiency while simultaneously detecting liquid presence and adjusting compressor operation or expansion valve positioning to prevent liquid entry, thus protecting compressor reliability.
Solution Approach 2:
The patent implements dynamic control where the expansion valve opening and compressor operation are continuously adjusted based on real-time capacitive measurements of suction gas dielectric constant. This dynamic adjustment allows the system to operate at low superheat for high efficiency while adaptively responding to liquid presence to maintain compressor reliability.
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 system enables effective indication of slight changes in refrigerant content, preventing liquid hammer and optimizing evaporator efficiency by ensuring dry gas reaches the compressor, thereby enhancing the overall performance and safety of the refrigeration system.
Implementation Method 1
which capacity censor at least measures the capacity between at least the first and at least the second electrode
Implementation Method 2
the detection circuit takes out the change of capacitance of the state detection means in accordance with the change of dielectric constant of the refrigerant liquid
Data Source
AI summary
A system or a method for performing capacitive sensing of humidity/liquid, primarily in conductive or non-conductive liquid/gas mixtures, having a control unit and at least first and second sensor electrodes, the capacitance between the first and the second electrodes being measured. To measure humidity/liquid in a circulating gas/liquid mixture at least one of the sensor electrodes is formed as a tube which is placed in the liquid/gas mixture. Based on the capacitance measurements, a calculation of at least one dataset for control of a second system is performed. The tube can be more or less filled up with liquid or gas and the capacitance can be measured as it depends on the content around or inside the tube, and if a dry gas is there will be one value of capacitance and in a situation where the gas is being replaced by liquid, the capacitance value will change rapidly.