The current European F-gas regulation establishes restrictions in the use of fluoride refrigerants with a high global warming potential (GWP) in applications of refrigeration and air conditioning ...(RAC) systems. Moreover, a gradual limitation on the GWP weight of the fluoride refrigerants placed on the market is ongoing and will end with approximately one-fifth of today's offer. In this context, many of the RAC systems operate with refrigerants R134a, R404A, and R410A that have GWP values of 1300, 3943 and 2088, respectively, are being forced to be replaced by environmentally friendly alternatives, like hydrofluoroolefin (HFO) refrigerants and their mixtures with hydrofluorocarbons (HFC), which can be designed to present intermediate characteristics and become the ideal candidate many RAC applications. This work presents the most recent HFC/HFO/HC/R744 refrigerant mixture options for an alternative to the refrigerants mentiond above and compares their energetic and performance with the early developed mixture prototypes.
This study presents the development of a new approximate model for a multilayer wire-on-tube condenser used in the domestic refrigeration industry. This model is based on physical foundations and ...empirical correlations, as well as on the ε-NTU thermal analysis methodology. It has been designed for three zones according to the state of the refrigerant. The input parameters to the model correspond to typical geometric characteristics of this type of condenser and operating conditions. As output parameters, the emphasis was placed on the thermal capacity of the condenser, and the refrigerant side and air-side outlet temperatures. For its validation, tests were carried out with real refrigerators, one of them operating with R134a and the other with R600a. The model prediction showed maximum relative errors of ±5% for thermal capacity and ±0.5K for temperatures. Finally, a parametric study was carried out analyzing the effect of varying the main geometric parameters such as tube and wire diameters, and wire and tube pitches.
•R513A showed a 9% reduction in energy consumption compared to R134a.•The TEWI for R513A presented a reduction of 8.85% with respect to R134a.•The optimal charge of R513A presented a reduction of ...16.7% with respect to R134a.
Today, hydrofluorocarbons continue to be used as part of a long transition towards the use of fluids with less impact on the environment. In this sense, the present work provides more information on the thermal and energetic performance of a domestic refrigerator using the R513A refrigerant as a direct replacement for R134a. Initially, the effect of the variation of the R513A charge on certain parameters such as operating pressures and temperatures, the superheating degree and subcooling, as well as the cooling capacity, is evaluated. The charge variations were made in increments of 10 g, until the optimal charge was defined for R513A concerning the minimum energy consumption, which was 100 g, representing a reduction of 16.7% compared to R134a (120 g). Once the optimal charge was defined, comparisons were made between both refrigerants under the same test conditions, resulting in a very similar average temperature of the refrigerator compartments; and for a test period of 24 h, R513A showed a 9% reduction in energy consumption compared to R134a. Finally, the analysis of the total equivalent warming impact presented R513A as a fluid with a lesser impact, around 8.85%, relative to R134a.
•Homogenization-based data-driven optimization method for designing graded cellular structures is developed.•The mapping relationships among the equivalent conductivity matrices, the relative ...densities, and the design variables are established based on the homogenization theory.•The cellular structure is composed of a series of basic microstructures generated from corresponding microstructure prototypes.•Both 2D and 3D examples of heat conduction problems are conducted for verifying the validity and effectiveness of the proposed method.
In this work, experimental tests were conducted on a domestic refrigerator to evaluate three faults with three levels: deterioration of the speed of the fan coupled to the condenser; degree of external fouling on the condenser; and area restriction on the rear cover of the refrigerator. The above, to analyze the effect of the type of fault on the performance of the refrigerator. Through a thermal analysis, it was observed that components such as the compressor and condenser presented a more noticeable variation in the thermal behavior of the refrigerant in the different faults. In fact, the fault corresponding to the fan speed was the one that caused the most inadequate performance in the refrigerator, compared to the refrigerator operating under normal conditions. The high level of this fault was reflected in an increase of 14.73 °C in the temperature of the refrigerant at the condenser inlet, it even caused an increase in the discharge pressure of 2.1 bar. Finally, this fault increased by 48% in energy consumption as well, which represented a 26% decrease in the coefficient of performance.
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