Refrigeration system for a transport unit
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Solution Overview
Problem
Refrigeration systems for transport units face challenges in achieving high cooling capacity while minimizing size and environmental impact, and in reducing costs and inefficiencies, particularly in maintaining low temperatures for perishable goods during transportation.
Innovation Solution
The refrigeration system incorporates a suction gas heat exchanger to superheat refrigerant, reducing liquid entry into the compressor and enhancing efficiency, and uses a cascade refrigeration system with non-azeotropic refrigerants and a multi-stage compressor to achieve high compression ratios and efficient heat exchange, along with a pre-cooler and economiser expansion valve to optimize temperature and pressure conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the refrigeration system uses a larger compressor and condenser to achieve high cooling capacity, then the cooling capacity is improved, but the system size increases reducing cargo space
Solution Approach 1:
The patent changes the thermodynamic parameters of the refrigeration cycle by implementing a two-stage compression process with intercooling and a cascade refrigeration system with two different refrigerant cycles. This allows achieving higher cooling capacity through optimized temperature and pressure parameters rather than simply increasing component sizes
Solution Approach 2:
The refrigeration system is divided into two separate refrigeration cycles (first and second cycles) with different refrigerants, each optimized for specific temperature ranges. The cascade heat exchanger separates the two cycles while enabling heat transfer between them, allowing each cycle to operate at optimal parameters without compromising overall cooling capacity
2Productivity
If the refrigeration system uses conventional single-stage compression, then the device complexity is low, but the efficiency and cooling capacity are limited
Solution Approach 1:
The compression process is segmented into two stages with an intermediate cooler between them. The first compressor compresses refrigerant to an intermediate pressure, the intermediate cooler reduces the temperature, and the second compressor completes the compression to final discharge pressure. This segmentation improves efficiency by reducing the work required compared to single-stage compression
Solution Approach 2:
The intermediate cooler performs preliminary cooling of the compressed refrigerant between the two compression stages. This preliminary action reduces the temperature and volume of the refrigerant before it enters the second compressor, improving the overall compression efficiency and reducing the work required
3Loss of energy
If the refrigeration system uses non-azeotropic refrigerants with temperature glide, then the heat exchange efficiency is improved, but the device complexity increases due to multiple refrigerants
Solution Approach 1:
The patent utilizes the temperature glide characteristic of non-azeotropic refrigerants by designing heat exchangers that accommodate the varying temperature during phase change. The cascade heat exchanger and evaporators are configured to match the temperature profile of the refrigerants, improving heat exchange efficiency by eliminating temperature differences throughout the heat transfer process
Solution Approach 2:
The system uses composite refrigerant mixtures (non-azeotropic blends) in each cycle, where multiple refrigerant components work together to achieve desired thermodynamic properties. The first cycle uses a refrigerant blend optimized for higher temperature operation, while the second cycle uses a different blend optimized for lower temperature operation, with each blend acting as a composite material with tailored properties
4Productivity
If the refrigeration system operates at high compression ratios, then the cooling capacity is improved, but the compressor reliability and longevity decrease
Solution Approach 1:
The high compression ratio is segmented into two smaller compression ratios by dividing the compression into two stages. Each compressor handles a moderate compression ratio, reducing mechanical stress, heat generation, and wear compared to a single-stage high ratio compression, thereby improving reliability while maintaining overall cooling capacity
Solution Approach 2:
The intermediate cooler acts as a mediator between the two compression stages, cooling the refrigerant between compressions. This reduces the temperature and volume of the refrigerant entering the second compressor, allowing for more efficient and less stressful operation of both compressors while achieving the required overall compression ratio
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 improves the cooling capacity, efficiency, and longevity of the compressor, reduces pressure drop, and allows for lower Global Warming Potential refrigerants, achieving cooling temperatures below -40°C while minimizing system size and environmental impact.
Implementation Method 1
a suction gas heat exchanger comprising a liquid line side and a suction line side, wherein the liquid line side is fluidically coupled downstream of the condenser and upstream of the expansion valve, and the suction line side is fluidically coupled downstream of the evaporator and upstream of the compressor, whereby the suction gas heat exchanger is configured to transfer heat between refrigerant in the liquid line side and refrigerant in the suction line side
Implementation Method 2
an expansion valve fluidically coupled downstream of the condenser and upstream of the evaporator
Implementation Method 3
an evaporator; a condenser fluidically coupled downstream of the compressor and upstream of the evaporator
Implementation Method 4
This may further improve an efficiency of the evaporator, such as by supplying refrigerant having a higher liquid-phase content to the evaporator, thereby increasing an amount of heat storable in the refrigerant as latent heat
Implementation Method 5
a compressor; an evaporator; a condenser fluidically coupled downstream of the compressor and upstream of the evaporator
Implementation Method 6
a condenser fluidically coupled downstream of the compressor and upstream of the evaporator
Data Source
AI summary
Provided is a refrigeration system for a transport unit. The refrigeration system has a refrigeration cycle comprising a compressor, an evaporator, a condenser fluidically coupled downstream of the compressor and upstream of the evaporator, an expansion valve fluidically coupled downstream of the condenser and upstream of the evaporator, and a suction gas heat exchanger comprising a liquid line side and a suction line side. The liquid line side is fluidically coupled downstream of the condenser and upstream of the expansion valve, and the suction line side is fluidically coupled downstream of the evaporator and upstream of the compressor. The suction gas heat exchanger is configured to transfer heat between refrigerant in the liquid line side and refrigerant in the suction line side.