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• Low-GWP refrigerants were tested in a cascade refrigeration system as replacements in the high-temperature cycle. • The cascade-condenser temperature difference varied from 2.5 to 5.5 K. • Cooling capacity varied from 2.3 to 3.8 kW and cold room temperature from −23.1 to −9.4 °C. • All tested refrigerants proved to be adequate replacements for R134a. • R436A and R1234yf reduce equivalent CO 2 emissions by 46 and 42%, respectively. This work presents an experimental analysis of the energy and environmental performance of low-GWP refrigerants R513A, R1234yf and R436A as alternatives for R134a in a cascade refrigeration system that operates with R744 in low-temperature cycle. An apparatus was built using a well-insulated room, where tests were carried out in a steady state condition. In addition to the typical components of a cascade cycle, an intermediate heat exchanger was used to thermally communicate the low and high temperature cycles, thus providing additional superheating and subcooling, respectively. The cooling capacity of the system ranged from 2.2 to 3.8 kW, the evaporation temperature varied from -34 to -24.5 °C and the air temperature inside the cold room ranged from -23.1 to -9.4 °C. The results revealed that the alternative refrigerants are potential substitutes for R134a in cascade refrigeration systems, showing an average increase in the CRC coefficient of performance of 3.1% for R436A, while R1234yf and R513A exhibited a reduction of 3.7% and 4.4%, respectively. The environmental impact analysis considered the scenarios of Chicago (USA) and Curitiba (Brazil), the latter being a southern Brazilian city with a wet climate throughout the year, a warm and mostly cloudy summer, and a short and cold winter. Total TEWI values, compared to those obtained with the originally designed R134a system, showed reductions in CO 2 equivalent emission of 46%, 42.1% and 22.5% for refrigerants R436A, R1234yf and R513A, respectively, for the Curitiba scenario, while the values for Chicago were increments of 0.3%, 2.4% and 5.8%, respectively. [ABSTRACT FROM AUTHOR]

This experimental study evaluates the energy performance and climatic changes of a cascade cooling system operating with the R134a/R744 pairs (cooling capacity of 4.5‐6 kW) and R438A/R744. In both cases, the low‐temperature refrigerant, R744, operated under subcritical conditions. The experimental apparatus basically consists of two vapor‐compression cycles coupled by a plate cascade condenser. Two operational variables, from R744 cycle, were controlled: the degree‐of‐superheat and the compressor frequency. The experiment was initially assembled to pair R134a/R744. Subsequently, the R134a refrigerant charge in the high‐temperature cycle was replaced by R438A, on a drop‐in basis. The two systems, R134a/R744 and R438A/R744, were compared for similar cooling capacities and cold chamber air temperatures. Results showed that the energy consumption of the high‐temperature compressor, operating with R438A, was higher than R134a for all tests. As a result, the COP values for R438A/R744 were 30% lower than those for R134a/R744. The greenhouse gases emissions of the two systems were evaluated using the total equivalent warming impact factor, TEWI, whose value for the R438A/R744 pair was approximately 29.5% higher, compared with R134a/R744. Since R438A was originally designed to substitute R22, a few comparative tests were carried out with the latter, always with R744 as the low‐temperature cycle working fluid. [ABSTRACT FROM AUTHOR]

The invasion of exotic species of natural spaces constitutes a global conservation problem. In the Siboney-Juticí Ecological Reserve, Leucaena leucocephala is considered one of the main threats to the conservation of the semideciduous microphyll forest. The objective of this study is to characterize the richness and structure of the semideciduous microphyll forest in areas with different levels of Leucaena leucocephala coverage in said reserve. For the study, 15 plots of 400 m2 were established at three levels of coverage of the invasive species: ABSMNI (undisturbed forests), ABSM-PI (40-60 % coverage of Leucaena leucocephala) and ABSMTI (70 % cover of Leucaena leucocephala). The number of individuals per species and their presence in each of the stratus were estimated, in addition, the height of the woody species was considered. For each of the levels studied, the specific richness, the relative abundance of the species and the floristic composition by stratus were determined; as well as the floristic similarities between each of the levels. In ABSM-NI, 55 species were recorded, in ABSM-PI 51 and in ABSM-TI 43. At the three levels of cover, the strata (tree, shrub, herbaceous) and lianas were maintained. In ABSM-TI the epiphytes were not recorded. The greatest biological similarity was between ABSM-PI and ABSM-TI; some of the shared species are ruderal and colonize areas with some type of disturbance. The main transformation was in the composition and abundance of the species as the coverage of the invasive species increased. In ABSM-TI, the specific richness and abundance/cover of secondary vegetation species increased, to the detriment of other typical forest species. In the sites with the greatest coverage of the invasive species, a decrease in the specific composition and height of the tree stratus occurs. At this site, an increase in the specific composition of the shrub and herbaceous strata was also observed. Epiphytes were only recorded in ABSM-NI and ABSM-PI. [ABSTRACT FROM AUTHOR]

The floristic composition and the horizontal structure of the semideciduous microphyll forest of the ecological reserve Siboney-Juticí, a protected area of the biosphere reserve Baconao in the southeastern Cuba, were characterized. The data corresponding to ten 20 × 50 m plots were processed, where to each individual the diameter to 1,30 m of the floor and the height were measured. The basal area, the abundances, the frequencies and absolute and relative dominances, were calculated, as was the Index of Value of Importance by species and family. The Principal Coordinates Analysis was applied to the matrix of data as ordination method. Data of 3206 individuals corresponding to 54 infrageneric taxa and 27 families were analyzed, besides another companion plants. The species with higher number of individuals were Coccoloba diversifolia, Bursera simaruba, Sideroxylon salicifolium, Gymnanthes lucida, Nectandra coriacea, Eugenia axillaris and E. monticola, the same with higher Index of Value of Importance and with tendency to associate to each other. Structural regularities and of diversity among the parcels were observed. The arboreal stratum is dense but low, with a few emergent trees. [ABSTRACT FROM AUTHOR]