Refrigeration cycle system
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Solution Overview
Problem
The transient increase in discharge refrigerant pressure in the secondary-side refrigerant circuit of dual refrigeration systems using carbon dioxide poses a design challenge, particularly at the start of the secondary-side refrigerant circuit.
Innovation Solution
A refrigeration cycle system with a first cycle using carbon dioxide and a second cycle using a different heat medium, where the first compressor of the first cycle is started after the heat medium flow generates in the cascade heat exchanger of the second cycle, utilizing a cascade heat exchanger as both a radiator and a heat sink.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the primary-side compressor is started before the secondary-side compressor, then the transient increase in discharge refrigerant pressure is suppressed, but the system complexity and control difficulty increase
Solution Approach 1:
The patent applies preliminary action by starting the primary-side compressor before the secondary-side compressor to pre-cool the cascade heat exchanger. This preliminary cooling action reduces the temperature difference between the heat exchanger and the incoming refrigerant, thereby suppressing the transient pressure increase when the secondary-side compressor starts. The control unit coordinates the startup sequence to achieve this pressure suppression effect.
2Stress or pressure
If the primary-side compressor is started after heat medium flow is generated in the cascade heat exchanger, then the transient pressure increase is effectively suppressed, but the startup time is extended
Solution Approach 1:
The system generates heat medium flow in the cascade heat exchanger before starting the primary-side compressor as a preliminary action. This pre-established flow creates favorable thermal conditions that suppress transient pressure increases during compressor startup. The control unit monitors and manages this preliminary flow generation to optimize the startup timing.
Solution Approach 2:
The patent employs dynamic control by adjusting the startup timing of the primary-side compressor based on the real-time state of heat medium flow in the cascade heat exchanger. The control unit dynamically determines the optimal startup moment to balance pressure suppression with minimizing startup time loss, adapting to varying operational conditions.
3Stress or pressure
If a bypass flow path is added to manage refrigerant pressure, then pressure stability is improved, but the device structure becomes more complex
Solution Approach 1:
The bypass flow path acts as an intermediary mechanism that provides an alternative route for refrigerant flow during transient conditions. When the primary-side compressor starts, the bypass allows refrigerant to circumvent certain components, preventing excessive pressure buildup. The control unit activates the bypass flow path as needed to maintain pressure stability without requiring permanent structural modifications.
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 approach effectively manages the transient pressure increase, ensuring stable operation and efficient heat exchange in dual refrigeration systems.
Implementation Method 1
the case of using the cascade heat exchanger as a radiator of the first cycle and a heat sink of the second cycle
Data Source
AI summary
A refrigeration cycle system includes a first cycle and a second cycle. The first cycle is connected with a first compressor, a cascade heat exchanger, a first expansion unit, and a first heat exchanger, and includes a first flow path that connects the first compressor to the cascade heat exchanger, a second flow path that connects the cascade heat exchanger to the first expansion unit, a third flow path that connects the first heat exchanger to the first compressor, and a bypass flow path that connects at least one of the first flow path and the second flow path to the third flow path. The second cycle includes the cascade heat exchanger. In a case of using the cascade heat exchanger as a radiator of the first cycle and a heat sink of the second cycle, the first compressor of the first cycle is started after a flow of a heat medium generates in the cascade heat exchanger in the second cycle.