Liquid Receiver Pressure Control in CO2 Refrigeration Cycles
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Solution Overview
Problem
In refrigeration devices using carbon dioxide or other supercritical refrigerants, the transition from a supercritical to a subcritical state complicates the control of the refrigerant level in the liquid receiver, especially when the refrigerant flowing into the radiator has low temperatures, leading to an unstable gas-liquid two-phase state.
Innovation Solution
A refrigeration device with a control unit that minimizes the degree of pressure reduction by the first expansion mechanism when the high-pressure-side refrigerant transitions to a subcritical state, using sensors to detect pressure and temperature conditions, and an appropriate expansion valve to maintain the refrigerant in a near-saturated state, thereby stabilizing the refrigerant level in the liquid receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the first expansion valve is used to reduce pressure of the high-pressure-side refrigerant, then the refrigerant can be expanded to drive the refrigeration cycle, but when the refrigerant transitions to subcritical state, the refrigerant level in the liquid receiver becomes unstable and difficult to control
Solution Approach 1:
The patent applies dynamics by making the first expansion valve fully openable to maximize its opening degree. This dynamic adjustment allows the valve to adapt to subcritical state conditions where minimal pressure reduction is needed, preventing refrigerant level instability in the liquid receiver while maintaining normal refrigeration cycle operation during supercritical states
Solution Approach 2:
The patent changes the operational parameters of the first expansion valve by allowing it to operate at maximum opening degree during subcritical states. This parameter change minimizes pressure reduction across the valve when refrigerant transitions to subcritical state, thereby stabilizing the refrigerant level in the liquid receiver without compromising refrigeration effectiveness
2Productivity
If the first expansion valve reduces pressure significantly, then the refrigerant expands effectively, but the refrigerant that flows out attains a gas-liquid two-phase state making liquid receiver level control difficult
Solution Approach 1:
The patent makes the first expansion valve dynamically adjustable with full opening capability. During subcritical operation, the valve opens fully to minimize pressure reduction, preventing excessive expansion that would create gas-liquid two-phase flow and control difficulties, while still allowing effective expansion during supercritical states
Solution Approach 2:
The patent changes the pressure reduction parameter of the first expansion valve based on refrigerant state. By minimizing pressure reduction when refrigerant is subcritical (through maximum valve opening), the system avoids creating gas-liquid two-phase conditions that complicate liquid receiver level control, while maintaining adequate expansion when needed
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
The solution allows for stable control of the refrigerant level in the liquid receiver even when the high-pressure-side refrigerant is in a subcritical state, ensuring efficient operation by maintaining the refrigerant in a near-saturated state and facilitating easy determination of the subcritical state through pressure and temperature detection.
Implementation Method 1
The refrigeration device further comprises a pressure detector. The pressure detector is provided between the refrigerant discharge side of the compression mechanism and the refrigerant inflow side of the first expansion mechanism.
Implementation Method 2
the control unit minimizes the degree of pressure reduction by the first expansion mechanism when the high-pressure-side refrigerant has undergone a transition from a supercritical state to a subcritical state
Implementation Method 3
the high-pressure-side refrigerant sometimes transitions from a supercritical state to a subcritical state when the refrigerant flowing into the radiator has a low temperature
Implementation Method 4
The refrigeration device further comprises a first temperature detector and a second temperature detector. The first temperature detector is provided to a first specific region of the radiator.
Data Source
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AI summary
An object of this invention is to enable the refrigerant level in a liquid receiver to be stably controlled even when the high-pressure-side refrigerant is in a subcritical state in a refrigeration device that comprises a refrigerant circuit in which a compressor, a radiator, a first expansion valve, a liquid receiver, a second expansion valve, and an evaporator are connected in sequence. The refrigeration device (1, 101) of this invention is provided with a compression mechanism (11), a radiator (13), a first expansion mechanism (15), a liquid receiver (16), a second expansion mechanism (17, 33a, 33b), an evaporator (31, 31a, 31b) and a control unit (23). The control unit minimizes the degree of pressure reduction by the first expansion mechanism when the refrigerant that flows from the refrigerant discharge side of the compression mechanism to the refrigerant inflow side of the first expansion mechanism has reached a subcritical state.