By now it seems that no pure refrigerants will be available to substitute R502 as of 1996, when CFCs will be banned in compliance with the most recent international agreements. The substitutes for R502 are expected to be binary or ternary mixtures and they will probably be obtained as combinations of the pure refrigerants listed in table I. This opinion is supported by the current availability on the world market of the following mixtures: R290/22/218(6/74/20), R290/22/218(6/55/39), R125/290/22(60/2/38), R125/290/22(38/2/60), R125/143a/134a(44/52/4), R32/125/134a(30/40/30), proposed as substitutes for R502 /seq bib sund1,seq bib shif2,seq bib pear3/. These are non-azeotropic mixtures but the refrigerant manufacturers claim that they are near-azeotropic. It is worth noting that the definition "near-azeotropic" has no scientific significance, but indicates mixtures with a temperature glide sufficiently small that it may be disregarded without consequential error in analysis for a specific application /seq bib ash4/. The components R22 and R290 are worth careful consideration. R22 belongs to the group of substances that will have to be substituted in the future, in compliance with the Copenhagen update of the Montreal Protocol. Refrigerant mixtures containing R22 are therefore more suitable for retrofitting equipment currently operating with R502. R290 is a highly flammable refrigerant and the mixtures containing it may be flammable even when the mass fraction of R290 in the mixture is very low. On the other hand, R290 is particularly interesting because it is environmentally one of the safest refrigerants. The maximum mass fraction of R290 acceptable in a mixture is very difficult to define: it depends on the priority level that is attributed to two fundamental and often conflicting requirements in a refrigerant, i.e. safety and environmental acceptability. In this work, the R125/290/134a mixture was considered as a possible substitute for R502. The mixture is probably flammable when the mass fraction of R290 is greater than 0.05, due both to the high flammability of R290 and because R125 and R134a are not good extinguishers. In our opinion, when the mass fraction of R290 in a mixture exceeds the flammability threshold, the mixture is only suitable for replacing R502 in refrigerating equipment with hermetic circuits. The mixture's performance as a function of composition was calculated to find the composition range in which the mixture achieves a performance similar to that of R502. Then five different compositions of the mixture were tested in a closed refrigerated display cabinet. In order to gain information about the suitability of the mixture for replacing R502 in retrofitting, the lubricant oil was not changed.

The R125/290/134a mixture as a substitute for R502 in commercial refrigeration

Bobbo S;Camporese R;Scattolini M
1993

Abstract

By now it seems that no pure refrigerants will be available to substitute R502 as of 1996, when CFCs will be banned in compliance with the most recent international agreements. The substitutes for R502 are expected to be binary or ternary mixtures and they will probably be obtained as combinations of the pure refrigerants listed in table I. This opinion is supported by the current availability on the world market of the following mixtures: R290/22/218(6/74/20), R290/22/218(6/55/39), R125/290/22(60/2/38), R125/290/22(38/2/60), R125/143a/134a(44/52/4), R32/125/134a(30/40/30), proposed as substitutes for R502 /seq bib sund1,seq bib shif2,seq bib pear3/. These are non-azeotropic mixtures but the refrigerant manufacturers claim that they are near-azeotropic. It is worth noting that the definition "near-azeotropic" has no scientific significance, but indicates mixtures with a temperature glide sufficiently small that it may be disregarded without consequential error in analysis for a specific application /seq bib ash4/. The components R22 and R290 are worth careful consideration. R22 belongs to the group of substances that will have to be substituted in the future, in compliance with the Copenhagen update of the Montreal Protocol. Refrigerant mixtures containing R22 are therefore more suitable for retrofitting equipment currently operating with R502. R290 is a highly flammable refrigerant and the mixtures containing it may be flammable even when the mass fraction of R290 in the mixture is very low. On the other hand, R290 is particularly interesting because it is environmentally one of the safest refrigerants. The maximum mass fraction of R290 acceptable in a mixture is very difficult to define: it depends on the priority level that is attributed to two fundamental and often conflicting requirements in a refrigerant, i.e. safety and environmental acceptability. In this work, the R125/290/134a mixture was considered as a possible substitute for R502. The mixture is probably flammable when the mass fraction of R290 is greater than 0.05, due both to the high flammability of R290 and because R125 and R134a are not good extinguishers. In our opinion, when the mass fraction of R290 in a mixture exceeds the flammability threshold, the mixture is only suitable for replacing R502 in refrigerating equipment with hermetic circuits. The mixture's performance as a function of composition was calculated to find the composition range in which the mixture achieves a performance similar to that of R502. Then five different compositions of the mixture were tested in a closed refrigerated display cabinet. In order to gain information about the suitability of the mixture for replacing R502 in retrofitting, the lubricant oil was not changed.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.14243/199868
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