Refrigerant vapour compression system
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Solution Overview
Problem
Refrigerant vapor compression systems in transport refrigeration face challenges with high operating pressures, particularly in transcritical systems using CO2, which increase the risk of refrigerant leaks and reduce efficiency due to loss of charge.
Innovation Solution
A refrigerant vapor compression system with a secondary expansion device and a flash tank assembly featuring a balanced plurality of modular tanks, which includes a first and second header connected to multiple tanks, allowing for balanced pressure distribution and reduced risk of leaks, while maintaining efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high operating pressure is used in transcritical CO2 refrigeration systems, then refrigeration efficiency is improved, but the risk of refrigerant leaks increases and system reliability deteriorates
Solution Approach 1:
The system divides the flash tank into multiple smaller tanks (first flash tank, second flash tank, third flash tank) instead of using a single large tank. Each tank operates at a lower individual pressure while collectively maintaining the required refrigeration capacity. This segmentation reduces the pressure stress on each individual tank wall, lowering the risk of leaks while preserving overall system efficiency.
2Productivity
If high operating pressure is used in transcritical CO2 refrigeration systems, then refrigeration efficiency is improved, but system reliability deteriorates due to loss of charge
Solution Approach 1:
The refrigeration system uses multiple flash tanks instead of a single tank, distributing the refrigerant charge across several smaller vessels. This segmentation reduces the consequence of potential charge loss in any single tank and improves overall system reliability while maintaining the high-pressure transcritical cycle efficiency.
3Device complexity
If a single large flash tank is used, then system complexity is reduced, but the risk of leaks increases due to high pressure requirements
Solution Approach 1:
The flash tank is segmented into multiple smaller tanks (first, second, and third flash tanks) with individual expansion devices for each. This segmentation allows each tank to operate at lower individual pressures, reducing leak risk, while the modular design actually simplifies installation and maintenance compared to a single large high-pressure tank.
Solution Approach 2:
The system introduces a multi-stage expansion process with intermediate flash tanks as mediators between the high-pressure refrigerant source and the final heat absorption heat exchanger. Each flash tank acts as an intermediary that progressively reduces pressure and separates refrigerant phases, reducing the overall leak risk while maintaining system functionality.
4Ease of manufacture
If copper or aluminum materials are used for tanks, then ease of manufacture and design flexibility are improved, but this requires reducing individual tank pressure
Solution Approach 1:
The system segments the flash tank volume into multiple smaller tanks made of copper or aluminum. By dividing the total refrigerant charge and pressure load across multiple tanks, each individual tank experiences lower pressure stress, making it feasible to use softer materials like copper and aluminum that would be unsuitable for a single large high-pressure tank. This segmentation enables easier manufacture and greater design flexibility.
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
The system enhances reliability and efficiency by reducing pressure on individual tanks, enabling the use of copper or aluminum materials and avoiding the need for welding dissimilar metals, thus improving design flexibility and operational stability.
Implementation Method 1
a flash tank assembly disposed downstream from the heat rejection heat exchanger
Implementation Method 2
A secondary expansion device is disposed downstream from the heat rejection heat exchanger and upstream from the flash tank assembly
Implementation Method 3
a heat rejection heat exchanger
Implementation Method 4
a heat absorption heat exchanger downstream from the main expansion device
Implementation Method 5
A secondary expansion device is disposed downstream from the heat rejection heat exchanger and upstream from the flash tank assembly
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
A refrigerant vapor compression system includes a refrigerant circuit having a compressor (30), a heat rejection heat exchanger (40), a heat absorption heat exchanger (50) and a main expansion device (55) arranged between the heat rejection heat exchanger (40) and the heat absorption heat exchanger (50) relative to a flow of refrigerant. A secondary expansion device (45) is disposed downstream from the heat rejection heat exchanger (40) and a flash tank assembly (70) is disposed downstream from the heat rejection heat exchanger (40). The flash tank assembly (70) includes a first header (72) arranged downstream from and in fluid communication with the second expansion device (45), a second header (74) arranged upstream from and in fluid communication with the main expansion device (55), and a plurality of tanks (76) connected at a first end to the first header (72) and at a second end to the second header (74). A load of the flash tank assembly (70) is equally balanced between each of the plurality of tanks (76).