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Parametric analysis and optimization of a cascade refrigeration system using a CO2/Propene mixed refrigerant.

Number: pap. 2436

Author(s) : MASSUCHETTO L. H. P., NASCIMENTO do R. B. C., CARVALHO S., et al.

Summary

Cascade Refrigeration Systems (CRS) are versatile due to the independent stages, which allow the combination of cycles with distinct operating principles and different pure refrigerants or mixtures in the High-Temperature Cycle (HTC) and Low-Temperature Cycle (LTC). Low GWP refrigerants, like carbon dioxide (CO2) or hydrocarbons like propene, have gained attention as potential substitutes for halogenated substances which present a harmful environmental impact. The use of zeotropic mixtures in CRS may achieve a higher coefficient of performance (COP) than the ones operating with pure refrigerants. This work presents a theoretical study of the thermodynamic performance of a CRS composed of two independent vapor compression cycles (VCC), both using a zeotropic mixture of CO2-Propene. A process simulator was used to simulate the cycle considering a fixed evaporator cooling rate of 100 kW. A parametric analysis was conducted to evaluate the thermodynamic performance of the CRS using mixture composition (wt%) in each cycle and condensation temperature of cascade heat exchanger as inputs. The outputs analyzed were: refrigerant mass flow rate, compression work, exergy destruction rate, exergetic efficiency and COP. After performing this parametric analysis, systems were optimized to maximize the COP, comparing the results obtained for the systems using mixed refrigerant to the ones with pure refrigerants. Mixed refrigerants in HTC and LTC promoted impacts on the performance of the CRS, however, the LTC mixture composition provided the most significant effect over the COP. Condensation temperature of the cascade heat exchanger presented a great influence in the CRS performance and for each operating condition a specific temperature gives a maximum COP. Optimization showed that the use of mixtures in both cycles enhanced the performance of CRS compared to the pure refrigerants. A mixed refrigerant CO2/Propene leads to a maximum COP (2.17) with 30 wt% CO2 in HTC and 10 wt% CO2 in LTC. The benefits achieved using mixtures were: reduction of the refrigerant mass flow rate (10 to 45% lower), reduction in the total exergy destruction rate (33 to 55% lower) and an increase of the exergetic efficiency and COP ranging from 17 to 25% higher than the pure refrigerants.

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Pages: 10

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Details

  • Original title: Parametric analysis and optimization of a cascade refrigeration system using a CO2/Propene mixed refrigerant.
  • Record ID : 30024548
  • Languages: English
  • Source: 2018 Purdue Conferences. 17th International Refrigeration and Air-Conditioning Conference at Purdue.
  • Publication date: 2018/07/09

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