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Thermodynamic assessment of air-cycles for ultra-low-temperature refrigerated container applications.

Number: 2536

Author(s) : BREHM J. K., PERGANTIS E.N., BANI ISSA A. M. Abd, GROLL E. A., ZIVIANI D.

Summary

The demand for low-temperature refrigeration systems increased due to the ongoing COVID-19 pandemic, which resulted in the need for a distribution of vaccines. Some vaccines require storage at ultra-low temperatures (ULT) between -60 °C and -90 °C. Other medical supplies, for example, antibiotics and plasma, require storage temperatures of roughly -20 °C. Therefore, multi-temperature refrigerated containers are typically used to deliver medical supplies globally. Current technologies are characterized by capacity limitations, environmentally damaging refrigerants, inefficiencies and safety concerns. Although low-temperature refrigeration systems still benefit from HFC replacement exceptions, the ongoing phase-down of existing HFC refrigerants requires additional research to identify low Global Warming Potential (GWP) substitutes. This study investigated the use of a reverse Brayton cycle to overcome these issues. The performance of different open air-cycles on the ULT side is computed through a detailed thermodynamic model. Air-cycles have the advantage of being safe and environmentally harmless due to the use of air as a refrigerant. Furthermore, the air-cycle does not need a heat exchanger on the low side, which saves space and eliminates inefficient defrosting cycles. Additionally, the compressor is much smaller compared to compressors used in vapor compression cycles and the cycle architecture is relatively simple, which increases reliability. The proposed system was compared under the same operating conditions to a cascade vapor compression cycle. It was found that the efficiency of the air-cycle is 25% to 41% lower than the cascade vapor compression cycle in the expected operating range. However, the air-cycles have some advantages over the cascade system. The increasing wealth of legislation against HFCs and HFOs has made low or zero GWP refrigerants very attractive. Furthermore, space can be saved due to smaller compressor size and the lack of an evaporator, which can increase the storage volume for transported goods. Lastly, the air-cycles do not have frosting/defrosting losses, which reduces the real performance of the cascade system. Within the air-cycles, both cycle configurations showed very similar performance, which means that the parallel air-cycle configuration is advantageous due to low complexity. Overall, this makes the air-cycle a feasible alternative to more traditional approaches in low-temperature applications and the design requirements must be carefully weighted to choose the ideal system.

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Details

  • Original title: Thermodynamic assessment of air-cycles for ultra-low-temperature refrigerated container applications.
  • Record ID : 30030768
  • Languages: English
  • Subject: Technology
  • Source: 2022 Purdue Conferences. 19th International Refrigeration and Air-Conditioning Conference at Purdue.
  • Publication date: 2022

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