Two-Stage Compression Refrigeration System for CO₂ Defrosting Capacity
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Solution Overview
Problem
The use of carbon dioxide as a refrigerant in air conditioners increases the compression ratio, leading to a severe burden on compressors and reduces the driving efficiency, particularly during defrosting operations where the high pressure side compressor struggles with wet vapor suction, resulting in insufficient defrosting capacity and prolonged defrosting times.
Innovation Solution
A refrigerating apparatus employing a two-stage compression/two-stage expansion refrigeration cycle with an intermediate-pressure refrigerant gas-liquid separator, where the high pressure side compressor is driven to suck gas refrigerant from the separator and mix it with the refrigerant from the low pressure side compressor, and part of the refrigerant is returned to the suction side to prevent liquid refrigerant from entering the compressor, enhancing defrosting capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If carbon dioxide is used as refrigerant and compressed to critical pressure, then refrigeration effect is improved, but compression ratio increases causing severe burden on compressor and reduced driving efficiency
Solution Approach 1:
The compression process is divided into two stages: a low-pressure compressor compresses refrigerant to intermediate pressure, then a high-pressure compressor further compresses it to critical pressure. This segmentation reduces the compression ratio burden on each individual compressor while achieving the required high compression ratio for carbon dioxide refrigeration.
Solution Approach 2:
An intermediate-pressure refrigerant gas-liquid separator is introduced as an intermediary device between the low-pressure and high-pressure compressors. This separator divides intermediate-pressure refrigerant into gas and liquid phases, with the gas phase being injected into the high-pressure compressor suction side, enabling efficient two-stage compression.
2Productivity
If high pressure side compressor is driven during defrosting operation, then defrosting capacity is improved, but risk of liquid refrigerant entering compressor increases causing damage
Solution Approach 1:
During defrosting operation, the high-pressure compressor suction side is pre-filled with gas refrigerant from the gas-liquid separator before starting compression. This preliminary action ensures that only gas refrigerant enters the compressor, preventing liquid slugging and protecting the compressor while enabling high-capacity defrosting.
Solution Approach 2:
The gas-liquid separator acts as an intermediary that separates intermediate-pressure refrigerant into gas and liquid phases during defrosting. The gas phase is directed to the high-pressure compressor suction side, serving as a protective barrier that prevents liquid refrigerant from entering and damaging the compressor while still allowing high-capacity defrosting operation.
3Power
If two-stage compression cycle is implemented, then compressor efficiency is improved, but device complexity increases due to additional components
Solution Approach 1:
The gas-liquid separator performs multiple functions: it separates intermediate-pressure refrigerant into gas and liquid phases during normal operation, stores gas refrigerant for high-pressure compressor injection, and prevents liquid refrigerant from entering the high-pressure compressor during defrosting. This multi-functionality reduces the need for separate dedicated components for each function.
Solution Approach 2:
The invention merges the gas-liquid separation function with the refrigerant distribution function into a single integrated system. The gas-liquid separator is positioned to simultaneously serve as a separation device and a source of gas injection for the high-pressure compressor, reducing overall system complexity while maintaining two-stage compression efficiency.
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 configuration allows both compressors to be driven during defrosting, increasing the defrosting capacity and reducing the time required for defrosting, while preventing damage to the high pressure side compressor by ensuring only gas refrigerant is sucked in, thus improving the overall efficiency and comfort in heating operations.
Implementation Method 1
an intermediate-pressure refrigerant gas-liquid separator, where the high pressure side compressor sucks the gas refrigerant from the separator
Implementation Method 2
the high pressure side compressor sucks the gas refrigerant from the separator and mixes it with the refrigerant from the low pressure side compressor
Implementation Method 3
part of the refrigerant is returned to the suction side to prevent liquid refrigerant from entering the compressor
Data Source
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Figure 3
AI summary
An optional unit (30) including a high pressure side compressor (31) and a gas-liquid separator (33) is provided between an outdoor unit (20) including a low pressure side compressor (21) and an indoor unit (40). During a defrosting operation, refrigerant discharged from the low pressure side compressor (21) defrosts an outdoor heat exchanger (21) while refrigerant in the gas-liquid separator (33) is sucked into the high pressure side compressor (31) and is then discharged to the suction side of the low pressure side compressor (21). The optional unit (30) includes an injection pipe (36) for returning part of the refrigerant discharged from the high pressure side compressor (31) to the suction side of the high pressure side compressor (31) in the defrosting operation. Hence, the refrigerant flowing into the high pressure side compressor (31) from the gas-liquid separator (33) is gasified by the high-temperature discharged refrigerant.