Title: Use of ejectors in cascade refrigeration systems for exergetic performance improvement

Authors: N. Ejemni; E. Nehdi; L. Kairouani

Addresses: Unité de Recherche Energétique et Environnement, ENIT, BP 37 le Belvèdére, 1002 Tunis, Tunisia. ' Unité de Recherche Energétique et Environnement, ENIT, BP 37 le Belvèdére, 1002 Tunis, Tunisia. ' Unité de Recherche Energétique et Environnement, ENIT, BP 37 le Belvèdére, 1002 Tunis, Tunisia

Abstract: In this paper an expansion cascade refrigeration system are compared to cascade systems using ejectors. This comparison is made for a variety of fluids. Natural fluids and hydrofluorocarbons (HFCs) are used in the two loops. Theoretical models are written using FORTRAN. The thermodynamic parameters of fluids are given using the software REFPROP 8.0. For fixed working conditions, using CO₂, R23 or R32 in LPL and R152a in HPL in an expansion cascade system gives the best Coefficient of Performance (COP) which attains 1.57 for T_i = −15°C. A comparison between the different systems with ejectors showed that a cascade system with two ejectors is the most powerful. It allows an optimum COP equal to 1.8 and a relative performance equal to 19.8% when propane is used in HPL and CO₂ in LPL for T_i = −25°C. But the best relative performance is given when R125 is used in HPL; it attains 24.2% when CO₂ is used in LPL. An exergetic analysis shows that introduction of two ejectors in cascade system ameliorate the exergy efficiency by 27.3% when CO₂ is used in LPL and R152a in HPL for T_i = −30°C.

Keywords: CO2; carbon dioxide; COP; ejectors; cascade refrigeration; exergy performance; HFC; fluids; hydrofluorocarbons; HFCs; thermodynamics; coefficient of performance.

DOI: 10.1504/IJEX.2012.045864

International Journal of Exergy, 2012 Vol.10 No.2, pp.171 - 189

Accepted: 05 Aug 2011
Published online: 15 Mar 2012 *

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