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.
•An experimental study of R1234yf as a drop-in replacement for R134a is presented.•An alternative methodology was proposed to estimate the optimal mass charge.•R1234yf optimal charge was 92.2 g, ...about 7.8% lower than R134a.•A thermal and energy comparison between R134a and R1234yf was analyzed.•The TEWI analysis for the R1234yf was 1.13% higher than for R134a.
This paper presents an experimental study for three identical domestic refrigerators using R1234yf as a drop-in replacement for R134a. An alternative methodology was proposed to estimate the optimal mass charge for R1234yf; with the use of such methodology, new evidences were sought on the thermal behavior of the refrigerator compartments as well as at the heat exchangers. Additionally, energy performance for both refrigerants was measured, and, finally, a TEWI analysis was conducted. For the type of refrigerator evaluated, results showed that R1234yf presented an average (for the 3 refrigerators) of 0.4 °C for the fresh food compartment, and 1.2 °C for the freezer, among different charges with respect to R134a. The optimal charge for R1234yf was 92.2 g, which is about 7.8% lower than the one for R134a, which represents a small increase of 4% in energy consumption in comparison to R134a. Finally, the TEWI analysis for the R1234yf was 1.07% higher than the R134a.
This paper presents an experimental analysis of a vapor compression system using R1234yf as a drop-in replacement for R134a. In this work, we compare the energy performance of both refrigerants, ...R134a and R1234yf, in a monitored vapor compression system under a wide range of working conditions. So, the experimental tests are carried out varying the condensing temperature, the evaporating temperature, the superheating degree, the compressor speed, and the internal heat exchanger use. Comparisons are made taking refrigerant R134a as baseline, and the results show that the cooling capacity obtained with R1234yf in a R134a vapor compression system is about 9% lower than that obtained with R134a in the studied range. Also, when using R1234yf, the system shows values of COP about 19% lower than those obtained using R134a, being the minor difference for higher condensing temperatures. Finally, using an internal heat exchanger these differences in the energy performance are significantly reduced.
► We present an experimental analysis of R1234yf as a drop-in replacement for R134a. ► Comparisons are carried out using the energy performance parameters. ► Cooling capacity obtained using R1234yf is about 9% lower than that using R134a. ► Volumetric efficiency obtained using R1234yf is 5% lower than that using R134a. ► Similar energy performance obtained using an IHX with high condensing temperatures.
•The energy performance of liquid chiller is compared using R1234yf and R134a.•The Buckingham π-theorem was applied to modeling drop-in.•The predicted and experimental data are correlated in order to ...study the accuracy of the model.•R1234yf shows that COP reduces about 2%–11.3% taking R134a as baseline.•Indirect emissions are similar for R1234yf and R134a using several energy sources.
This paper presents a model for a variable-speed liquid chiller integrating a compressor model based on Buckingham π-theorem to accurately predict the system performance when R134a is replaced with R1234yf, using a wide range of data obtained from an experimental setup. Relevant variables such as temperature, pressure, mass and volumetric flow rates, compressor power consumption and rotation speed were measured at several positions along the refrigeration and secondary circuits and were used to validate the developed model. Model results show that cooling capacity and power consumption predicted values are in good agreement with experimental data, within ±5%, being slightly higher for the deviation obtained for R134a than for R1234yf. Moreover, model results indicate that R1234yf has a reduction of coefficient of performance (COP) compared with R134a (between 2 and 11.3%), and that R1234yf COP reduction is diminished at intermediate volumetric flow rate and higher inlet temperature for the evaporator secondary fluid, respectively. On the other hand, an environmental analysis based on TEWI (total equivalent warming impact) method showed that direct emissions are almost negligible for R1234yf. However, there are no environmental benefits in terms of indirect greenhouse gas emissions using R1234yf without system modifications (as for instance the addition of internal heat exchanger or R1234yf new design components), which are required to reduce the liquid chiller climate change contribution using it as low GWP alternative in comparison with the typically used R134a refrigerant.
•A new approach to analyze the energy behavior of R134a, R450A and R513A is discussed.•An artificial neural network application to model a small refrigeration system is developed.•The performance of ...the model was verified using cross-validation.•Computer simulations were performed to build 3D color surfaces for each energy parameter.•Based on the results, R450A and R513A are adequate refrigerants to replace R134a.
In this paper, an artificial neural network application to model a small refrigeration system is presented. The main objective of this study is an energy comparison of three refrigerants: R134a, R450A and R513A. The application of the artificial neural network was designed to model individually three typical energy parameters: the cooling capacity, the power consumption and the coefficient of performance, as a function of the evaporating temperature and the condensing temperature. Each model was validated using a technique called cross-validation, producing minimum relative errors of 0.15 for the cooling capacity and the coefficient of performance, while 0.05 for the power consumption. Based on the appropriate validation results, computer simulations were performed to build 3D color surfaces. After inspecting these 3D color surfaces, it was concluded that R450A presented a slightly lower cooling capacity than R134a, actually a 10% reduction in the cooling capacity was estimated. Similar results were observed for the power consumption, that is, R450A had about 10% less power consumption than the other two refrigerants. On the other hand, it was observed that R134a and R513A presented very similar energy behaviors. With respect the COP, it was concluded that all three refrigerants showed a very similar behavior. After the analysis performed with the artificial neural networks and the use of 3D surface color, it was concluded that R450A and R513A are appropriate refrigerants to replace R134a in the short term in applications at medium evaporating temperature.
•Multi-objective optimization of a lower GWP R450A refrigeration system was performed.•RSM-CCD methodology was used to establish novel quadratic models.•The difference between predicted and adjusted ...R2 was lower than 0.2.•Middle evaporator temperature showed the greatest effect on cooling capacity.•The most optimum operating condition from an energetic point of view was provided.
The main objective of this work is to comprehensively investigate R450A behavior in refrigeration systems and subsequently optimize the main operating variables for the first time to reach the maximum performance. For this purpose, a hybrid multi-objective optimization model coupling response surface method and non-dominated sorted genetic algorithm II is established. The regression analysis results reveal a good agreement of experimental data samples with the quadratic polynomial models with a coefficient of determination exceeding 0.97. The optimum results for the first scenario indicate that the reduction in the motor-compressor electrical power consumption and discharge temperature is 18.39% and 53.51%, respectively, and percentage of growth in the refrigerant mass flow rate is 215.57% when the middle evaporator temperature, middle condenser temperature, superheating degree, and subcooling degree change from −14.95 °C to 8.71 °C, 31.28 °C to 24.50 °C, 13.12 K to 10.49 K, and 15.65 K to 15.66 K, respectively.
The purposes of this study are to demonstrate our experience in using the “lotus petal” suprafascial flap and to evaluate the postoperative complications. During the period ranging from July 2012 to ...March 2015, nine patients diagnosed with primary or recurrent vulvar cancer have undergone radical vulvectomy followed by reconstructive surgery. Seventeen lotus petal suprafascial flap surgeries were performed. The average age of the patients was 79 years. No intraoperative complications were reported. The surgery length was 180 min with an estimated blood loss of 400 cc. Severe postoperative complications were rare. There were no complications associated with the donor site, nor were there any losses due to total or partial flap tissue necrosis. There were 2 (22.2 %) cases of partial wound dehiscence, which did not require re-intervention. The lotus petal suprafascial flap is a simple procedure that can be done during the same surgery as the radical vulvectomy, improving the aesthetic results and reducing both the rate of complications and hospital stay.
The replacement of HFCs using lower GWP refrigerants in the coming years is a priority to reduce the predicted climate change. The exergy analysis of vapor compression systems can help to identify ...the feasibility of alternative fluids in existing installations and the potential to improve them. In this sense, this paper presents an exergy analysis of an experimental setup which operates with R134a and the alternative HFO/HFC mixture R513A. The evaporating temperature is ranges between −15 °C and 5 °C, while the condensing temperature is set at 30 °C and 35 °C. In this analysis, the highest amount of exergy destruction rate is obtained at the compressor, followed by the evaporator. The maximum exergy efficiencies are observed at the condenser and the thermostatic expansion device. Finally, the average global exergy efficiency of R513A when replaced R134a in this refrigeration experimental setup is 0.4% higher (absolute difference), and with respect to the components, there is only slight reduction in efficiency in the condenser using R513A. Therefore, the R513A replacement is acceptable according to the second law of thermodynamics.
•The experimental results on the exergy behavior of R513A versus R134a are discussed.•The global exergy efficiency of R513A is slightly higher than that of R134a.•The component that cause higher irreversibility and hence lower exergy efficiency is the compressor.•The second-law analysis confirmed that R513A does not needs redesign to be used in R134a refrigeration systems.
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