Cascade refrigeration system with modular ammonia chiller units
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Solution Overview
Problem
Conventional refrigeration systems face challenges in efficiently managing ammonia refrigerant and oil circulation within modular chiller units, particularly in minimizing toxicity and flammability hazards while maintaining effective cooling for both low and medium temperature subsystems.
Innovation Solution
A cascade refrigeration system with a modular chiller unit that incorporates a critically-charged ammonia refrigerant, an oil recycling circuit with an oil separator, filter, pressure regulator, and return line, and an oil management system to ensure positive oil return from the evaporator, reducing oil collection and minimizing ammonia refrigerant charge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional refrigeration system uses ammonia refrigerant in modular chiller units, then effective cooling for low and medium temperature subsystems is achieved, but toxicity and flammability hazards increase due to larger ammonia charge
Solution Approach 1:
The system is divided into modular chiller units, each with its own ammonia refrigerant circuit and oil management system. This segmentation allows each module to operate independently with minimized ammonia charge, reducing overall hazards while maintaining cooling effectiveness through multiple distributed units
Solution Approach 2:
The patent changes the physical and chemical parameters of the refrigerant system by using a critically-charged ammonia refrigerant with optimized charge quantity, and by implementing an oil recycling circuit that maintains specific oil-to-refrigerant ratios. These parameter changes enable effective cooling while minimizing ammonia charge and associated hazards
2Reliability
If conventional refrigeration systems use oil lubrication in ammonia refrigerant circuits, then compressor lubrication is maintained, but oil collection in evaporator reduces system efficiency
Solution Approach 1:
The oil recycling circuit extracts oil from the ammonia refrigerant circuit at strategic points (compressor discharge and evaporator outlet). The oil separator removes oil from the refrigerant stream, and the oil return line actively returns extracted oil to the compressor, preventing oil accumulation in the evaporator that would otherwise reduce cooling efficiency
Solution Approach 2:
The oil management system implements feedback control through level sensors in the oil separator and oil return line that monitor oil accumulation. When oil reaches critical levels, the system automatically activates the oil return mechanism to extract and return oil to the compressor, maintaining optimal system efficiency while ensuring continuous compressor lubrication
3Object-affected harmful factors
If modular chiller units use minimal ammonia charge, then toxicity and flammability risks are reduced, but refrigerant charge sufficiency becomes challenging to maintain
Solution Approach 1:
The system performs preliminary action by pre-charging the ammonia refrigerant to a critically-optimal level during manufacturing or initial setup. The refrigerant charge is precisely calculated and installed to provide sufficient cooling capacity while minimizing charge quantity, eliminating the need for later adjustments and ensuring reliable operation from startup
Solution Approach 2:
The ammonia refrigerant serves multiple functions simultaneously: it provides the primary cooling effect in the evaporator, acts as the working fluid for heat transfer in the condenser, and maintains pressure differential throughout the system. This multi-functionality allows the minimal critical charge to sustain reliable operation across all system components
4Reliability
If cascade refrigeration system uses modular chiller units with oil management systems, then oil return from evaporator is improved, but device complexity increases
Solution Approach 1:
The oil management functions are merged into a single integrated circuit system comprising the oil separator, oil return line, and level control mechanism. These components work as a unified system rather than separate devices, reducing overall complexity while maintaining effective oil return from the evaporator to the compressor
Solution Approach 2:
The oil return line incorporates a level sensor and automatic return mechanism that operates autonomously based on oil accumulation levels. When oil reaches a predetermined level in the evaporator, the system automatically activates the return pump or utilizes pressure differential to return oil to the compressor without requiring external monitoring or manual intervention, simplifying operation despite increased component count
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 effectively provides cooling for both low and medium temperature loads while minimizing ammonia usage, reducing toxicity and flammability risks, and enhancing maintainability by using a minimal ammonia charge and an efficient oil management system.
Implementation Method 1
heating the oil being returned from the evaporator in order to boil-off entrained ammonia refrigerant
Implementation Method 2
uses warmed coolant (e.g. glycol, etc.) to heat the oil being returned from the evaporator
Data Source
AI summary
A cascade refrigeration system includes an upper portion. The upper portion includes at least one modular chiller unit that provides cooling to at least one of a low temperature subsystem having a plurality of low temperature loads, and a medium temperature subsystem having a plurality of medium temperature loads. The modular chiller unit includes a refrigerant circuit, an ammonia refrigerant, an ammonia refrigerant accumulator, and an oil separation system. The refrigerant circuit includes at least a compressor, a condenser, an expansion device, and an evaporator. The ammonia refrigerant is configured for circulation within the refrigerant circuit. The ammonia refrigerant accumulator is configured to receive the ammonia refrigerant from the evaporator. The oil separation system is configured to remove oil from the ammonia refrigerant. The oil separation system includes an oil separator that is configured to remove oil from the ammonia refrigerant flowing from the compressor to the condenser, an oil drain pot that is configured to collect oil from the evaporator, and an oil reservoir that is configured to collect oil from the oil separator and the oil drain pot.