Accumulator-Expander Heat Exchanger to Prevent CO2 Liquid Slugging
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Solution Overview
Problem
Transcritical refrigeration systems, particularly those using CO2, face challenges in achieving high specific cooling capacity and coefficient of performance (COP) due to difficulties in liquefaction and liquid slugging, which can damage compressors and reduce system efficiency.
Innovation Solution
An integrated accumulator-expander-heat exchanger system where the expansion conduit is positioned within the accumulator chamber to isolate it from liquid refrigerant, allowing heat exchange predominantly with gaseous and two-phase refrigerant, thereby preventing liquid slugging and enhancing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the expansion device is simply assembled at the inlet of accumulator-heat exchanger without being functionally integrated, then the device complexity is reduced, but the system efficiency and cooling capacity are not improved significantly
Solution Approach 1:
The patent combines the expansion device with the accumulator-heat exchanger into a single integrated unit. The expansion device is positioned within the accumulator chamber, and its outer surface acts as a heat exchange surface. This merging of components allows the expansion device to simultaneously perform expansion function and heat exchange function, resolving the contradiction between device complexity and system efficiency.
Solution Approach 2:
The expansion device is designed to serve multiple functions: it acts as both an expansion device for pressure reduction and as a heat exchange surface for thermal transfer. The outer surface of the expansion device serves as a heat exchange surface, allowing it to perform dual functions within a single component, thereby improving system efficiency without significantly increasing device complexity.
2Temperature
If capillary coils are immersed in the liquid-phase of the accumulator, then heat exchange is enhanced, but liquid refrigerant evaporation increases consuming more energy and reducing specific cooling capacity
Solution Approach 1:
The patent extracts the expansion device from the liquid-phase environment and positions it within the accumulator chamber where it can exchange heat with gaseous and two-phase refrigerant instead of being immersed in liquid refrigerant. This extraction prevents excessive liquid refrigerant evaporation while still maintaining effective heat exchange, thereby reducing energy loss and improving specific cooling capacity.
Solution Approach 2:
The patent creates different local environments for heat exchange: the expansion device exchanges heat with gaseous and two-phase refrigerant in the upper portion of the accumulator chamber, while liquid refrigerant remains in the lower portion. This local differentiation allows heat exchange to occur without causing excessive liquid evaporation, maintaining energy efficiency.
3Reliability
If liquid refrigerant is used to dilute cycling oil and carry it back to the compressor, then oil return is ensured, but system efficiency is lowered and liquid slugging may damage the compressor
Solution Approach 1:
The integrated expansion device-accumulator system acts as an intermediary that separates liquid and vapor phases. The expansion device with its heat exchange surface facilitates controlled evaporation of liquid refrigerant, creating a two-phase mixture that ensures proper oil return to the compressor while preventing excessive liquid from entering the compressor, thus maintaining both reliability and efficiency.
4Productivity
If heat exchange occurs between refrigerants of different parts using internal heat exchanger, then specific cooling capacity is improved, but the system complexity increases
Solution Approach 1:
The patent merges the heat exchange function into the expansion device itself. The outer surface of the expansion device serves as a heat exchange surface, eliminating the need for separate internal heat exchanger components. This integration achieves the desired heat exchange for improved specific cooling capacity while minimizing system complexity through component consolidation.
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 configuration increases the refrigeration system's efficiency and cooling capacity by promoting heat exchange between refrigerant phases, reducing liquid refrigerant evaporation in the accumulator, and allowing more liquid to be available in the evaporator, while maintaining the refrigerant in a superheated state for the compressor, thus improving COP.
Implementation Method 1
said conduit having an impedance over at least a portion of its length to produce a pressure drop in fluid therealong
Implementation Method 2
allowing heat exchange predominantly with gaseous and two-phase refrigerant
Implementation Method 3
a phase change from supercritical fluid to liquid which occurs in trans-hypocritical systems
Data Source
AI summary
A refrigeration system with integrated accumulator-expander-heat exchanger is disclosed. Refrigerant from a condenser/gas cooler is throttled through a capillary tube while at the same time undergoing a heat exchanging process with refrigerant from an evaporator. This method can elevate the compressor efficiency, increase the specific cooling capacity, and enhance the system performance. The capillary tube, which has dual functions of expansion device and heat exchanger, is placed inside a canister which also functions as an accumulator. The new device combining three separate parts into one can simplify the manufacturing process, lower the system size and weight, and thus decrease cost of the whole system.