Dual cascade heat exchanger refrigeration system and related method of operation
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Solution Overview
Problem
Conventional refrigeration systems employing cascade heat exchangers with carbon dioxide and ammonia refrigerants face performance issues due to the potential formation of ammonia carbonate solids, leading to diminished or ceased operation, as carbon dioxide systems often operate at higher pressures, breaching barriers and penetrating the ammonia-based system.
Innovation Solution
A dual cascade heat exchanger refrigeration system with two high-stage parallel circuits and a low-stage circuit, where ammonia is used in the high-stage and carbon dioxide in the low-stage, allowing for parallel operation of heat exchangers to ensure continued functionality even if one high-stage circuit ceases, through indirect coupling and heat transfer devices that facilitate heat energy communication between stages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If cascade heat exchangers are used with carbon dioxide and ammonia refrigerants, then heat exchange efficiency is improved, but ammonia carbonate solids form causing performance degradation
Solution Approach 1:
The system is divided into separate high-stage and low-stage circuits with distinct refrigerants (ammonia and carbon dioxide respectively). The segmentation prevents direct contact between the refrigerants that would otherwise form ammonia carbonate solids, while maintaining efficient heat exchange through dedicated heat exchangers at each stage interface.
Solution Approach 2:
A barrier or intermediate structure is introduced in the heat exchanger design to prevent direct contact between ammonia and carbon dioxide refrigerants. This intermediary allows heat transfer to occur while blocking the formation of ammonia carbonate solids, resolving the contradiction between heat exchange efficiency and system reliability.
2Stability of the object's composition
If barriers are provided to prevent contact between carbon dioxide and ammonia, then refrigerant compatibility is improved, but carbon dioxide penetrates the ammonia system due to higher pressure
Solution Approach 1:
The refrigeration system is segmented into pressure-appropriate zones: carbon dioxide operates in the high-stage at higher pressures, while ammonia operates in the low-stage at lower pressures. This segmentation ensures that barriers are only exposed to pressure differentials they can withstand, preventing penetration while maintaining refrigerant separation.
Solution Approach 2:
Different barrier materials and designs are used at different locations in the system based on local pressure conditions. High-stage heat exchangers handling carbon dioxide use barriers designed for high-pressure resistance, while low-stage components use barriers optimized for ammonia service, ensuring each barrier operates within its designed pressure limits.
3Reliability
If parallel high-stage circuits are implemented, then system reliability is improved, but device complexity increases
Solution Approach 1:
The high-stage circuit is segmented into parallel paths (first high-stage circuit and second high-stage circuit), each with its own heat exchanger and refrigerant loop. This segmentation provides redundancy so that if one path fails, the other can maintain system operation, improving reliability while keeping each individual circuit relatively simple.
Solution Approach 2:
Multiple high-stage circuits are merged into a single integrated system that shares common components such as the low-stage circuit, control systems, and structural framework. This merging approach distributes the complexity across multiple simple parallel paths rather than one complex sequential path, improving reliability without proportionally increasing overall system complexity.
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 maintains operational reliability by allowing continued operation even if one high-stage circuit fails, as heat energy is transferred between parallel circuits and stages, preventing ammonia-carbon dioxide contact issues and ensuring consistent refrigeration performance.
Implementation Method 1
heat is exchanged between a first stage employing carbon dioxide refrigerant or coolant and a second stage employing ammonia refrigerant or coolant
Implementation Method 2
carbon dioxide systems often operate at higher pressures than ammonia systems
Implementation Method 3
heat is exchanged between a first stage employing carbon dioxide refrigerant or coolant and a second stage employing ammonia refrigerant or coolant
Data Source
AI summary
Cooling or refrigeration systems, and methods of operating same, are disclosed herein. In one example embodiment, such a system includes a first and second high stage circuits each including a respective heat exchanger and a respective condenser that are coupled together at least indirectly so as to allow a respective portion of a first coolant to cycle therebetween. The system also includes a low stage circuit including a heat transfer device that is coupled at least indirectly with each of the heat exchangers, so as to allow an additional portion of a second coolant to cycle between the at least one evaporator and the heat exchangers, and in a parallel manner such that, if a first one of the high stage circuits ceases operating at a desired level, then the system can continue to operate by way of a second one of the high stage circuits.