Flash Tank Refrigerant Storage in Transcritical CO2 Cycles
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Solution Overview
Problem
Refrigerant vapor compression systems operating in transcritical cycles, particularly those using carbon dioxide, lack an adequate buffer volume for refrigerant storage due to the refrigerant heat rejection heat exchanger functioning as a gas cooler, which prevents the use of traditional receivers or accumulators for liquid refrigerant storage.
Innovation Solution
Incorporating a flash tank with an internal volume ranging from 10% to 30% of the total system volume, positioned between the refrigerant heat rejection and heat absorption heat exchangers, which also functions as an economizer and provides a buffer reservoir for refrigerant storage during low load demand or system inactivity, eliminating the need for additional accumulators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a refrigerant vapor compression system operates in a transcritical cycle with a gas cooler, then the system can reject heat at temperatures above the refrigerant's critical point, but the system lacks an adequate buffer volume for refrigerant storage because the gas cooler prevents traditional receiver or accumulator configurations
Solution Approach 1:
The flash tank is positioned to receive refrigerant from the gas cooler and perform both flash gas separation and refrigerant storage functions. By merging the separation and storage functions in one component, the system achieves adequate buffer volume without requiring traditional receivers or accumulators that would not function properly in a transcritical cycle with a gas cooler.
Solution Approach 2:
The flash tank serves multiple functions: it acts as a separator to remove flash gas from liquid refrigerant, provides buffer volume for refrigerant storage during low load demand or system inactivity, and enables the system to operate effectively in transcritical mode. This multi-functionality resolves the contradiction by providing storage capacity without adding separate components that would be incompatible with the gas cooler configuration.
2Quantity of substance
If the flash tank internal volume is increased to provide adequate buffer storage, then refrigerant storage capacity improves, but the system complexity and component size increase
Solution Approach 1:
By combining the separation and storage functions in the flash tank, the invention avoids the need for additional accumulators or receivers. The flash tank is sized to provide both separation capacity and buffer volume (10-30% of total system volume), thereby reducing overall system complexity while achieving adequate refrigerant storage.
Solution Approach 2:
The flash tank is designed to perform multiple functions simultaneously: flash gas separation and refrigerant buffer storage. This multi-functionality eliminates the need for separate storage components, thereby providing adequate buffer volume without increasing device complexity or requiring additional accumulators.
3Quantity of substance
If the flash tank volume is set between 10% to 30% of total system volume, then adequate buffer storage is provided without excessive system complexity, but the separation efficiency must be optimized to ensure unimpeded vapor-liquid separation
Solution Approach 1:
The flash tank is designed with specific internal characteristics (such as separation zones, baffle configurations, or geometric features) that optimize vapor-liquid separation within the constrained volume. By optimizing the local quality of the separation region, the system achieves reliable separation efficiency while maintaining the flash tank volume within 10-30% of total system volume.
Solution Approach 2:
The invention optimizes parameters such as flash tank geometry, internal flow patterns, and phase separation mechanisms to ensure efficient vapor-liquid separation within the reduced volume range of 10-30% of total system volume. By changing these parameters, the system achieves both adequate buffer storage and reliable separation efficiency without requiring excessive tank size.
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
Ensures unimpeded separation of refrigerant vapor and liquid, maintaining system efficiency and preventing over-pressurization by providing sufficient storage volume, thus optimizing refrigerant storage and operation in transcritical cycles without the need for additional accumulator components.
Implementation Method 1
ensures that the process of separation of the refrigerant vapor and refrigerant liquid will still occur unimpeded
Implementation Method 2
provides a buffer reservoir for refrigerant storage during low load demand or system inactivity
Data Source
AI summary
A refrigerant vapor compression system (10) includes a plurality of components, including a flash tank (70), connected in a refrigerant flow circuit by a plurality of refrigerant lines (2, 4, 6, 8). The system internal volume equals to the sum of the internal volumes of the plurality of components and the internal volume of the plurality of refrigerant lines. The internal volume of the flash tank ranges from at least 10% to about 30% of the total system internal volume.