Subcooling Circuit for Centrifugal Compressor Surge Prevention
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Solution Overview
Problem
Vapor cycle systems face surge conditions due to varying heat loads and flow rates, leading to erratic compressor operation and potential mechanical damage, which existing active surge control mechanisms like valves cannot effectively manage without increasing complexity and cost.
Innovation Solution
A subcooling circuit that diverts a liquid fraction of refrigerant from the evaporator through a subcooler to evaporate and provide additional cooling, maintaining a high flow rate of superheated vapor refrigerant to the centrifugal compressor, eliminating the need for active surge control valves and reducing system complexity and failure points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a surge control valve is used to recirculate refrigerant, then surge conditions are reduced, but device complexity and cost increase
Solution Approach 1:
The invention extracts the surge control function from the traditional valve-based active control system and implements it through the natural thermodynamic behavior of the refrigerant cycle itself. The subcooling circuit is configured to automatically divert liquid refrigerant based on pressure differential, eliminating the need for mechanical surge control valves and their associated complexity.
Solution Approach 2:
The system uses the refrigerant's own phase change properties and pressure differential to automatically regulate flow and prevent surge conditions. The subcooling circuit self-regulates by diverting liquid refrigerant when compressor inlet pressure is high, without requiring external control mechanisms, sensors, or active valve operation.
2Reliability
If a surge control valve is used to recirculate refrigerant, then surge conditions are reduced, but system cost increases
Solution Approach 1:
The invention replaces expensive, complex surge control valves with simple, passive thermodynamic components that are already part of the refrigerant cycle. The subcooling circuit uses basic refrigerant flow diversion and phase change, eliminating the need for costly active control mechanisms while maintaining surge prevention functionality.
3Productivity
If refrigerant flow rate is reduced at low heat loads, then evaporator performance is maintained, but compressor surge conditions occur
Solution Approach 1:
The invention changes the thermodynamic parameters of the refrigerant entering the compressor by subcooling the liquid refrigerant before it enters the evaporator. This allows the system to maintain higher refrigerant flow rates at low heat loads while still achieving proper evaporator performance, preventing compressor surge by ensuring sufficient mass flow through the compressor.
4Reliability
If subcooling circuit diverts liquid refrigerant, then compressor receives superheated vapor, but liquid fraction must be separated
Solution Approach 1:
The invention uses the subcooling circuit as an intermediary mechanism that indirectly achieves compressor inlet superheat by subcooling liquid refrigerant before evaporation. This thermodynamic approach naturally produces superheated vapor at the compressor inlet without requiring direct mechanical separation devices, using instead the phase change process and pressure differential 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 solution maintains a high flow rate of superheated refrigerant through the compressor at various heat loads, reduces the risk of surge conditions, and operates at lower compressor pressure ratios, enhancing efficiency and reliability by eliminating the need for active surge control mechanisms.
Implementation Method 1
the subcooler to evaporate the liquid fraction of the refrigerant
Implementation Method 2
The excess liquid refrigerant is heated using the relatively warm pressurized refrigerant from the centrifugal compressor via the condenser
Implementation Method 3
The centrifugal compressor compresses and pumps the vapor refrigerant through the condenser
Implementation Method 4
cool and condense the vapor refrigerant prior to expanding and entering the evaporator
Implementation Method 5
an accumulator downstream of an evaporator separates and stores an excess liquid fraction of the refrigerant and discharges a vapor fraction of the refrigerant
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
The disclosure describes a system that includes an evaporator, an accumulator downstream of the evaporator, a centrifugal compressor downstream of the accumulator, a first heat exchanger stage downstream of the centrifugal compressor, and a second heat exchanger stage downstream of the first heat exchanger stage. The evaporator is configured to cool a conditioned air stream using a refrigerant. The accumulator is configured to store excess refrigerant. The centrifugal compressor is configured to compress the refrigerant. The first heat exchanger stage is configured to cool the refrigerant using environmental air. The second heat exchanger stage is configured to cool the refrigerant from the first heat exchanger stage using a portion of the excess refrigerant from the accumulator.