Flash Tank Economizer Control for Pressure Reversal Prevention
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Solution Overview
Problem
In vapor compression systems with flash tank economizers, pressure imbalances between the compressor mid-stage and the flash tank can cause flow reversal in the economizer vapor line, reducing system efficiency and preventing proper separation of refrigerant phases when the flash tank pressure exceeds the critical pressure, leading to suboptimal operation, especially in transcritical conditions with carbon dioxide as the working fluid.
Innovation Solution
A control system is implemented with flow control devices in the economizer vapor line, responsive to pressure differences between the flash tank and the compressor mid-stage, to prevent flow reversal and maintain operation below the critical pressure, including the use of sensors to measure or estimate pressures and a controller to manage the flow control devices, such as solenoid valves, to ensure proper refrigerant flow and phase separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the economizer operates in transcritical conditions with flash tank pressure above critical pressure, then the system can handle high temperature heat rejection, but the separation of refrigerant into liquid and vapor phases will not occur as desired
Solution Approach 1:
The system dynamically adjusts the flash tank pressure parameter by controlling the economizer valve opening degree. When the flash tank pressure approaches or exceeds the critical pressure, the control system reduces the economizer valve opening to lower the pressure below critical level, thereby restoring proper liquid-vapor phase separation while maintaining the ability to handle high temperature heat rejection conditions
Solution Approach 2:
The control system continuously monitors the flash tank pressure and uses this feedback signal to adjust the economizer valve position. When pressure exceeds the critical threshold, the feedback loop automatically reduces valve opening to decrease pressure, ensuring the flash tank operates below critical pressure for proper phase separation while still accommodating varying heat rejection temperatures
2Power
If the compressor mid-stage pressure exceeds the flash tank pressure, then the system can maintain compression performance, but flow reversal occurs in the economizer vapor line
Solution Approach 1:
The economizer valve acts as an intermediary flow control device between the flash tank and compressor mid-stage. By precisely regulating the valve opening, the system maintains a pressure differential that ensures unidirectional flow from the flash tank to the compressor, preventing flow reversal while preserving compression performance across varying operating conditions
Solution Approach 2:
The system dynamically adjusts the economizer valve opening degree based on real-time pressure conditions. When compressor mid-stage pressure approaches flash tank pressure, the control system modulates the valve to maintain adequate pressure differential, ensuring continuous forward flow and preventing reversal while adapting to changing compression demands
3Reliability
If a check valve is used to prevent flow reversal, then flow direction is controlled, but the system requires separate economizer valve control and the economizer cannot be flash tank type
Solution Approach 1:
The invention merges the flow direction control function with the economizer valve into a single integrated component. The economizer valve performs both the primary function of controlling refrigerant flow for economization and the secondary function of preventing flow reversal through its position-controlled flow restriction, eliminating the need for separate check valves and simplifying the overall control system architecture
Solution Approach 2:
The economizer valve is designed to perform multiple functions: it controls the amount of refrigerant flowing to the economizer for efficiency enhancement, regulates pressure differential to prevent flow reversal, and serves as the sole control element for both subcritical and transcritical operation modes, replacing what would traditionally require multiple specialized components
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 effectively prevents flow reversal and maintains system efficiency by ensuring the economizer operates only when pressures are appropriate, allowing for efficient cooling capacity and energy efficiency, even in transcritical conditions, by actively managing the flow based on sensed pressures and critical thresholds.
Implementation Method 1
Refrigerant collects in the flash tank as part liquid and part vapor
Implementation Method 2
The vapor refrigerant is used to cool refrigerant exhaust as it exits a first compression device
Implementation Method 3
A control system is implemented with flow control devices in the economizer vapor line, responsive to pressure differences between the flash tank and the compressor mid-stage, to prevent flow reversal
Data Source
AI summary
A flash tank economizer includes a sensor for sensing a condition indicative of pressure in the flash tank, and when that pressure is found to equal or exceed the critical pressure of the particular refrigerant being used, a controller responsively closes a valve in the economizer vapor line to shut off the economizer. A sensor is also provided to sense the pressure at the compressor mid-stage, and if that pressure is found to exceed the pressure in the flash tank, the controller causes the flow control device to function so as to prevent the flow of refrigerant from the compressor mid-stage to the flash tank. Provision is also made for selectively draining refrigerant from the flash tank to reduce the pressure therein from a supercritical to a subcritical condition.