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Parametric analysis and optimization of a cascade refrigeration cycle using HFCs/DMAc and natural refrigerants.

Number: pap. 2446

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

Summary

Cascade refrigeration cycles may be used to obtain very low temperatures, which are suitable for many different applications. These cycles offer a higher coefficient of performance reducing energy consumption. Kigali's Amendment on Montreal Protocol has recognized the great influence of hydrofluorocarbons (HFCs) on climate change, impacting the choice of refrigerants for future applications. The Environmental Ministry of Brazil forecasts that the use of HFCs as refrigerants will be reduced to only 25% of the current usage in the next 25 years. The F-Gas Regulation (European Union) controls the use of HFCs responsible for increasing GWP (Global Warming Potential), limiting their use in several applications. The possibility of using alternative refrigerants, with low GWP in cascade refrigeration systems have regained the interest of researchers and their use combining an absorption refrigeration cycle with a traditional vapor compression cycle has been studied recently, considering the existence of wasted heat sources present in industrial processes that can be recovered, allowing a reduction in electric energy consumption. In this work a cascade refrigeration cycle combining a single-effect absorption cycle (ABS) and a vapor compression cycle (VCC) was studied. Three different pairs refrigerant/absorbent (R32/DMAc - dimethylacetamide, R134a/DMAc and R152a/DMAc) were tested in the high temperature cycle (ABS) with a pure natural refrigerant (CO2) in the low temperature cycle (VCC). Simulations were performed using a process simulator with PRSV EOS as the thermodynamic package, allowing a parametric analysis to evaluate the performance of the cascade refrigeration system. A base case using NH3/H2O in the ABS cycle was also tested by means of comparison. Evaporating temperature at the evaporator of the VCC was fixed in 228.15 K (-45 °C) together with a cooling rate of 50 kW. Parametric analysis considered the influence of following variable parameters over the COP and exergy destruction rate: generator outlet stream temperature and condensing temperature of the pure refrigerant in the cascade heat exchanger. Then an optimization procedure was performed to maximize COP. When the condenser temperature increased, COP was reduced in 17% and when the generator temperature of the cycle increased, COP increased as well. The overall COP of the optimized system has increased up to 50% and total exergy destruction rate was minimized, being concentrated in the solution heat exchanger (25%) and generator (20%). The pair R152a/DMAc presented the highest performance, very close to the one of NH3/H2O, but with the advantage of presenting a lower GWP.

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Pages: 10

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Details

  • Original title: Parametric analysis and optimization of a cascade refrigeration cycle using HFCs/DMAc and natural refrigerants.
  • Record ID : 30024554
  • Languages: English
  • Source: 2018 Purdue Conferences. 17th International Refrigeration and Air-Conditioning Conference at Purdue.
  • Publication date: 2018/07/09

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