A method for controlling a vapour compression system in a flooded state
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Solution Overview
Problem
Vapour compression systems face the challenge of operating efficiently while preventing liquid refrigerant from reaching the compressor unit, which could cause damage.
Innovation Solution
A method involving a liquid separating device in the suction line, which separates refrigerant into gaseous and liquid parts, ensuring only the gaseous part reaches the compressor, and adjusting flow rates to prevent liquid refrigerant accumulation, by increasing or decreasing the flow to the ejector or reducing the evaporator's flooded state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the evaporator is operated in a flooded state with liquid refrigerant, then heat transfer efficiency is improved, but liquid refrigerant may reach the compressor causing damage
Solution Approach 1:
A liquid separating device is introduced as an intermediary component between the evaporator and compressor. This device uses gravity and centrifugal force to separate liquid refrigerant from vapor, allowing the evaporator to operate in a flooded state while preventing liquid from reaching the compressor.
Solution Approach 2:
The suction line is segmented into separate pathways: one for vapor-refrigerant mixture going to the compressor and another for liquid refrigerant being diverted to the ejector through the liquid separating device. This segmentation allows simultaneous flooded evaporator operation and compressor protection.
2Reliability
If liquid refrigerant is removed from the suction line using a liquid separating device, then compressor safety is improved, but system complexity increases
Solution Approach 1:
The liquid separating device serves multiple functions: it separates liquid from vapor to protect the compressor, and simultaneously directs liquid refrigerant to the ejector to maintain proper evaporator flooding. This multi-functionality reduces the need for additional separate components.
Solution Approach 2:
The liquid separation function and liquid diversion to ejector are combined into a single integrated device rather than using separate components. This merging reduces system complexity while achieving both compressor protection and evaporator flooding maintenance.
3Productivity
If the flow rate of refrigerant to the ejector is increased to remove liquid from the liquid separating device, then liquid removal efficiency is improved, but the flow rate of liquid refrigerant from the evaporator may become insufficient
Solution Approach 1:
The system uses feedback control to monitor the flow rate of refrigerant to the ejector and adjust it dynamically. When liquid accumulation is detected in the liquid separating device, the flow rate is increased; when liquid levels are appropriate, the flow rate is reduced to maintain proper evaporator flooding.
Solution Approach 2:
The flow rate to the ejector is made dynamic rather than fixed, allowing the system to adapt to varying operating conditions. This enables the system to maintain both adequate liquid removal and proper evaporator flooding across different load conditions.
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
Enables efficient operation of evaporators in a flooded state for enhanced heat transfer while preventing liquid refrigerant from reaching the compressor, thus maintaining system integrity and efficiency.
Implementation Method 1
a liquid separating device arranged in a suction line of the vapour compression system, the liquid separating device comprising a gaseous outlet connected to the inlet of the compressor unit and a liquid outlet connected to a secondary inlet of the ejector
Implementation Method 2
detecting a flow rate of refrigerant from the liquid separating device to the secondary inlet of the ejector
Implementation Method 3
heat exchange takes place with the ambient or with a secondary fluid flow across the evaporator, in such a manner that heat is absorbed by the refrigerant passing through the evaporator
Data Source
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AI summary
A method for controlling a vapour compression system (1) is disclosed. The vapour compression system (1) comprises an ejector (6) and a liquid separating device (10) arranged in a suction line. At least one evaporator (9) is allowed to be operated in a flooded state. A flow rate of refrigerant from the liquid separating device (10) to the secondary inlet (15) of the ejector (6) is detected, and it is determined whether or not the flow rate is sufficient to remove liquid refrigerant produced by the evaporator(s) (9) being allowed to be operated in a flooded state from the liquid separating device (10). In the case that it is determined that the flow rate of refrigerant from the liquid separating device (10) to the secondary inlet (15) of the ejector (6) is insufficient to remove liquid refrigerant produced by the evaporator(s) (9), the flow rate of refrigerant from the liquid separating device (10) to the secondary inlet (15) of the ejector (6) is increased, and/or a flow rate of liquid refrigerant from the evaporator(s) (9) to the liquid separating device (10) is decreased.