Expander Bypass Pressure Control in Refrigeration Cycles
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Solution Overview
Problem
Refrigeration cycle apparatuses face instability and overexpansion issues due to high discharge pressure from expanders, leading to inefficient power recovery and unstable rotation of components.
Innovation Solution
A refrigeration cycle apparatus with a first compressor, radiator, expander, and evaporator, featuring a bypass piping system and physical quantity detecting means to control the flow rate of refrigerant through a bypass valve, ensuring appropriate discharge pressure is maintained by bypassing refrigerant to the suction side of the compressor when discharge pressure exceeds a determined threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the supercooling expansion valve is opened in the bypass circuit to supercool the refrigerant, then the refrigeration cycle efficiency is improved, but the discharge pressure of the expander cannot be made low and may rise instead
Solution Approach 1:
The bypass circuit is segmented into two separate valve control systems: a supercooling expansion valve for controlling refrigerant flow to achieve supercooling and efficiency improvement, and a newly introduced bypass valve for controlling discharge pressure. This segmentation allows independent optimization of both functions without interference.
Solution Approach 2:
A bypass valve is introduced as an intermediary control element in the bypass circuit, positioned to regulate the discharge pressure of the expander independently from the supercooling expansion valve. This intermediary valve acts as a pressure management mediator, preventing backpressure from affecting the expander while allowing the supercooling function to operate.
2Reliability
If the opening/closing valve is closed after the second compressor starts to stabilize the system, then the pressure differential between suction side and discharge side of the expander is increased, but the rotation of the second compressor and expander becomes unstable until discharge pressure reaches appropriate level
Solution Approach 1:
The bypass valve is designed with dynamic control characteristics, allowing it to remain open during startup to maintain stable rotation, then close automatically when discharge pressure reaches the appropriate level. This dynamic behavior enables the system to adapt to different operational phases, providing stability during startup and proper pressure differential during normal operation.
Solution Approach 2:
The bypass valve is opened in advance during the startup phase to prevent instability in the expander and compressor rotation. By maintaining the bypass open before normal operation begins, the system ensures stable rotation is achieved first, then the valve closes to establish the proper pressure differential for efficient operation.
3Power
If the expander operates with high discharge pressure, then power recovery is reduced due to overexpansion, but reducing discharge pressure requires additional control mechanisms
Solution Approach 1:
The bypass valve is designed to serve multiple functions: it controls discharge pressure to prevent overexpansion, maintains stable rotation during startup, and works in conjunction with the supercooling expansion valve to optimize overall system efficiency. This multi-functionality allows a single valve to address multiple issues without proportionally increasing system complexity.
Solution Approach 2:
The control system incorporates pressure detection means that continuously monitors the discharge pressure of the expander and provides feedback to the bypass valve control. This feedback mechanism allows the bypass valve to automatically adjust its opening degree to maintain optimal discharge pressure, ensuring efficient power recovery while preventing overexpansion without requiring complex manual control.
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 stabilizes the rotation of the expander and prevents overexpansion, ensuring efficient power recovery and maintaining a stable operating state by adjusting the discharge pressure of the expander.
Implementation Method 1
an expander that expands the refrigerant that has passed through the radiator and recovers power from the refrigerant
Implementation Method 2
a first compressor that compresses a refrigerant
Implementation Method 3
a radiator that rejects the heat of the refrigerant compressed by the first compressor
Implementation Method 4
an evaporator that evaporates the refrigerant expanded by the expander
Data Source
AI summary
A refrigeration cycle apparatus includes a refrigeration cycle formed by a first compressor, a radiator, an expander that expands a refrigerant that has passed through the radiator, and an evaporator. A bypass piping has one end connected to a discharge piping of the expander and the other end connected to a suction piping of the first compressor. A pressure sensor and a temperature sensor detect the suction pressure and suction temperature of the expander as physical quantities of the refrigerant to be sucked into the expander. A bypass valve controls the flow rate of the refrigerant. A control device determines the appropriate discharge pressure of the expander on the basis of the suction pressure and suction temperature of the expander, and opens the bypass valve when the pressure at which the expander discharges the refrigerant is higher than the determined appropriate discharge pressure.