Compressor with an oil separator between compressing stages
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Solution Overview
Problem
Carbon dioxide refrigeration systems with two-stage compressors face challenges due to increased miscibility of oil at high pressures, leading to oil accumulation, viscosity issues, and maintenance problems, which existing oil separators are ineffective in addressing, especially when requiring pumps and complex valve arrangements.
Innovation Solution
A two-stage compressor design with an oil separator positioned outside the shell casing, featuring an expansion chamber, J-tube, and oil drain, which reduces refrigerant velocity and facilitates oil separation without complex pumps or valve arrangements, allowing oil to drain back into the shell casing, thereby reducing oil content before the second stage compression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a two-stage compressor is used to improve efficiency, then system performance is improved, but oil miscibility increases leading to accumulation and maintenance issues
Solution Approach 1:
The oil separator extracts oil from the refrigerant stream between compression stages. The separator chamber allows oil to separate from the carbon dioxide refrigerant through density differential, and the oil is removed via the oil drain before the refrigerant enters the second stage compression mechanism, preventing oil accumulation that would compromise system reliability
Solution Approach 2:
The oil separator acts as an intermediary component between the first and second stage compression mechanisms. It mediates the oil contamination problem by intercepting and removing oil from the refrigerant stream, allowing the two-stage compression system to maintain high efficiency without the harmful effects of oil accumulation
2Reliability
If known oil separators are used, then oil separation may occur, but complex pumps and valve arrangements are required due to pressure differential
Solution Approach 1:
The oil separator utilizes the natural density differential between oil and carbon dioxide refrigerant, combined with the pressure differential already present in the two-stage compression system, to achieve oil separation without requiring external pumps or complex valve arrangements. The system uses its own operating conditions to perform the separation function
Solution Approach 2:
The oil separator employs fluid dynamics principles where the refrigerant flow carries oil into the separator chamber, and the pressure differential drives the separated oil toward the oil drain. The expansion chamber allows velocity reduction and phase separation based on density differences, utilizing pneumatic and hydraulic principles rather than mechanical pumps
3Reliability
If oil is removed from the refrigerant stream, then oil content is reduced, but system balance and oil return to shell casing must be maintained
Solution Approach 1:
The oil drain provides a feedback mechanism that allows separated oil to return to the shell casing, maintaining the oil inventory needed for lubrication. This closed-loop approach ensures that while oil is removed from the refrigerant stream to prevent accumulation, the system retains sufficient oil through the drain connection to maintain proper lubrication and operational balance
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 enhances overall system performance and efficiency by minimizing oil content in the refrigerant, reducing maintenance needs, and eliminating the need for complex components, while maintaining system balance and preventing oil bypass.
Implementation Method 1
The miscibility of oil in carbon dioxide in such carbon dioxide refrigeration systems, however, may be greater as compared to typical synthetic refrigerants at high operating pressures. Moreover, the miscibility of oil in carbon dioxide may increase as the pressure increases.
Implementation Method 2
an expansion chamber and/or a J-tube positioned within the expansion chamber and/or an oil drain in communication with a shell casing
Data Source
AI summary
The present application provides a compressor for use with a flow of carbon dioxide. The compressor may include a first stage compression mechanism for compressing the flow of carbon dioxide from a low pressure to an intermediate pressure, an oil separator downstream of the first stage compression mechanism, and a second stage compression mechanism positioned downstream of the oil separator for compressing the flow of carbon dioxide from the intermediate pressure to a high pressure.