Two-Stage CO₂ Refrigeration Compressor to Reduce Mechanical Load
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Solution Overview
Problem
Existing refrigeration systems for transport refrigeration are complex and inefficient, particularly when using CO2 as a refrigerant, as they lack a straightforward method for compressing the main and additional mass flows to high pressure effectively.
Innovation Solution
The refrigeration system incorporates a refrigerant compressor unit with a first compressor stage for compressing the refrigerant from low to medium pressure and a second stage for compressing from medium to high pressure, with a medium-pressure heat exchanger for cooling before the second stage, and an external heat exchanger for additional cooling, optimized for CO2 operation with pressures ranging from 1 bar to 160 bar.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-stage compressor is used to compress refrigerant from low pressure to high pressure, then the device complexity is reduced, but the mechanical load on the compressor increases and efficiency decreases
Solution Approach 1:
The compression process is divided into two stages: a first compression stage compressing refrigerant from low pressure to intermediate pressure, and a second compression stage compressing from intermediate pressure to high pressure. This segmentation reduces the pressure ratio per stage, thereby reducing mechanical load and improving efficiency while maintaining reasonable device complexity
2Device complexity
If refrigerant is compressed from low pressure to high pressure in one stage, then the number of components is reduced, but the energy efficiency decreases due to excessive pressure ratio
Solution Approach 1:
The compression process is segmented into two stages with an intermediate pressure level. The first stage compresses from low to intermediate pressure, and the second stage compresses from intermediate to high pressure. This reduces the energy loss associated with high pressure ratios in a single stage, while the number of components remains manageable
3Reliability
If CO2 is used as refrigerant in transport refrigeration, then environmental performance is improved, but the system requires higher pressure operation which increases mechanical stress
Solution Approach 1:
The two-stage compression system segments the high pressure ratio required for CO2 refrigeration into two smaller pressure ratios. This reduces the mechanical stress on individual compressor components while maintaining the high pressure operation necessary for CO2's excellent environmental performance
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 allows for optimal compression and cooling of CO2, reducing mechanical load on components and enhancing the efficiency and simplicity of the refrigeration system, particularly in transport applications.
Implementation Method 1
a first compressor stage for compressing the refrigerant of the main mass flow supplied at low pressure to medium pressure
Implementation Method 2
the first compressor stage of the refrigerant compressor unit is connected to a medium-pressure-side heat exchanger, which cools the main mass flow compressed to medium pressure
Implementation Method 3
a second compressor stage for compressing the refrigerant of the main mass flow compressed at medium pressure to high pressure
Implementation Method 4
an expansion element arranged in the refrigerant circuit downstream of the high-pressure-side heat exchanger, which in the active state cools the total mass flow of the refrigerant by expansion
Implementation Method 5
a high-pressure-side heat exchanger arranged in the refrigerant circuit and cooling the high-pressure-compressed refrigerant
Data Source
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AI summary
A refrigeration system, in particular a transport refrigeration system, comprising a refrigeration circuit, in particular one that operates using CO2 as the refrigerant, in which a total mass flow of the refrigerant is conveyed; a heat exchanger arranged in the refrigerant circuit and cooling, on the high-pressure side, refrigerant compressed to high pressure; at least one cooling stage which expands the principal mass flow from the intermediate pressure manifold to a low pressure in at least one cooling expansion member, and in so doing makes refrigeration power available at a low-pressure-side heat exchanger; and a refrigerant compressor unit that compresses the principal mass flow from a low pressure to a high pressure, wherein the refrigerant compressor unit has a first compressor stage for compressing, to an intermediate pressure, the refrigerant of the principal mass flow supplied at low pressure, and a second compressor stage for compressing, to a high pressure, the refrigerant of the principal mass flow that has been compressed to an intermediate pressure.