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
1Loss of energy
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:
The suction line is segmented into multiple zones: the flooded evaporator section, the liquid separating device section, and the compressor inlet section. This segmentation allows liquid refrigerant to exist in the evaporator while being physically separated from the compressor through the liquid separating device, which uses centrifugal force and gravity to divide the refrigerant flow into liquid and vapor phases.
Solution Approach 2:
The liquid separating device acts as an intermediary component between the flooded evaporator and the compressor. It receives the refrigerant mixture from the evaporator, separates the liquid phase from the vapor phase using centrifugal separation and gravity, and directs only the vapor phase to the compressor while removing liquid refrigerant through the liquid outlet.
2Reliability
If a liquid separating device is added to prevent liquid refrigerant from reaching the compressor, then compressor safety is improved, but system complexity increases
Solution Approach 1:
The liquid separating device operates autonomously using the kinetic energy and gravitational potential energy of the refrigerant flow itself. The centrifugal separation is achieved by the rotation of the refrigerant flow through the device, and the gravity-driven liquid removal occurs automatically when liquid accumulates in the separation chamber, eliminating the need for external control mechanisms or additional energy input.
Solution Approach 2:
The liquid separating device utilizes hydraulic principles to achieve separation. The device creates a centrifugal hydraulic field that causes liquid refrigerant to move outward to the wall while vapor remains in the center, and uses gravity to drain the liquid through the outlet at the bottom, achieving separation without mechanical moving parts.
3Productivity
If flow rate control is implemented to manage liquid refrigerant removal, then liquid removal efficiency is improved, but control system complexity increases
Solution Approach 1:
The liquid separating device is designed with dynamic flow characteristics that automatically adapt to varying refrigerant flow conditions. The centrifugal separation effect and gravity-driven liquid removal adjust automatically based on the incoming refrigerant flow rate, maintaining effective liquid-vapor separation across different operating conditions without requiring active control.
Solution Approach 2:
The device changes the flow parameters of the refrigerant through the separation process. The refrigerant enters with certain velocity and pressure, and the device transforms these parameters through centrifugal acceleration and gravitational potential energy conversion, achieving phase separation based on the inherent physical properties of the two-phase flow.
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 method allows evaporators to operate in a flooded state for efficient 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
When refrigerant passes through an evaporator arranged in a vapour compression system, the refrigerant is at least partly evaporated while 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
AI summary
A vapour compression system (1) includes 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) 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.