International Journal of Refrigeration-revue Internationale Du Froid最新文献

Restrictions on high-GWP refrigerants have made the use of transcritical CO₂ refrigeration systems widespread. Using transcritical booster refrigeration cycle in warm climates is unsatisfactory due to its high energy consumption. This paper presents theoretical analysis and performance comparison of three different transcritical CO₂ supermarket refrigeration cycle configurations with ejector expansion in Türkiye, which has different climatic regions. Bin-hour data were derived using hourly dry-bulb temperature values for provinces from 7 different regions in Türkiye. The applicability of multi-ejectors to each modeled cycle was also investigated. Annual energy consumption and environmental impact reductions of up to 17% were obtained using ejector expansion cycle compared to booster cycle. Ejector expansion cycles achieved higher performance than booster cycle up to 46% in terms of exergy efficiency at investigated ambient temperatures. Unit product exergy costs of the ejector cycles were found up to 28% lower than booster cycle.

Household refrigerator compartments and cold chain systems are highly susceptible to microbial contamination. To minimize the surface-contact disease transmission, low-temperature surfaces must be inactivated. Currently, there is no environmentally friendly and convenient means for surface sterilization at low temperatures. This investigation proposed the use of low-pressure mercury lamps to sterilize the bottom surface of a refrigerator. The mercury lamps emitted UVC irradiation and were mounted horizontally on the sidewalls of the refrigerator compartment to inactivate Escherichia coli (E. coli) on the bottom surface. The measured irradiances and E. coli inactivation efficiencies were used to validate the surface-to-surface (S2S) model. The impacts of the refrigeration temperature (20 °C, 4 °C, and −18 °C, respectively) on the UVC output and E. coli sterilization efficiency were evaluated. And so did for the impacts of the relative humidity (ranging from 45 % to 85 % at 4 °C). The required time for operation of the UVC lamps to reach a 3-log reduction in E. coli was calculated for different lamp placements. The results revealed that the UVC emission of low-pressure mercury lamps decreases remarkably with the temperature. The necessary UVC irradiation dose to achieve the same inactivation efficiency increases as the temperature decreases. To extend the operating life of UVC lamps, the installed lamps should make the irradiance distribution on the target surface as uniform as possible.

1,1-difluoroethane (R152a) is one of the most prospective low GWP refrigerants but may trigger fires and explosions once it leaks. Understanding the flame propagation process and combustion mechanisms at different relative humidity conditions is essential to use flammable refrigerants safely. In this study, a high-speed camera has recorded the flame propagation of R152a combustion near the flammability limit. Combining with macroscopic experimental phenomena, we revealed the effect of H₂O on the microscopic mechanism of R152a combustion by using reactive force field molecular dynamics simulations with a reliable force field. The promotion effects of H₂O on the oxidation of R152a were revealed from an atomistic perspective. The differences of oxidation intermediates and products in different environments were analyzed for the first time. The H₂O/O₂ environment was the most potent promoter of R152a decomposition, followed by the O₂ and the pyrolysis environment. The O₂/H₂O environment reduced the apparent activation energy of R152a, significantly enhanced the consumption rate of R152a, and enriched the number of species. O₂ reacts with H₂O or H to form OH to accelerate the reaction process. The H₂O could provide more OH active fragments for the reaction. Moreover, it promotes the formation of HF and H_2, H₂O + F→HF + OH, H₂O + H→H₂ + HO. This study aims to provide a guiding theory for the safe application and disaster prevention of flammable refrigerants.

This study presents a simple correlation for describing the temperature and pressure dependence of the liquid dynamic viscosity of low GWP refrigerants, namely HydroFluoroOlefins (HFOs) and HydroChloroFluoroOlefins (HCFOs). The model has 3 input parameters (i.e., reduced temperature, reduced pressure, and acentric factor) and 6 coefficients which were regressed on 794 experimental data collated from the literature for 7 alternative refrigerants (i.e., R1233zd(E), R1234yf, R1234ze(E), R1234ze(Z), R1224yd(Z), R1336mzz(E), and R1336mzz(Z)). Moreover, a multi-layer perceptron neural network for the liquid dynamic viscosity of the studied fluids was developed from the selected dataset. The artificial network has the same 3 input parameters of the correlation and one hidden layer with 19 neurons. The results of the proposed correlation proved that it is an accurate model for calculating the dynamic viscosity of the studied liquid refrigerants, despite its simplicity. It ensured an average absolute relative deviation of the liquid dynamic viscosity (AARD(η)) of 2.88 %, lower than that given by other literature correlations. As expected, the multi-layer perceptron neural network provided the best results for all the selected refrigerants (AARD(η) = 0.86 % for the complete dataset), proving that it can be considered a reference for the development of other models.

Displacer type pulse tube refrigerator (DPTR) can get high efficiency with strong phase shifting and acoustic work recovery to advantages. However, the optimal match of gas driving displacer can only be reached at one point, while the linear motor driving displacer has a complex structure. And for two-stage DPTR, more parameters need to be optimized such as step ratio. A well-matched displacer costs a lot and asks high quality manufacturing. In this work, an orifice and an inertance tube were added to the single-stage DPTR and two-stage DPTR as an additional adjustment parameter. For single stage DPTR, the experimental results indicate that the lowest temperature decreases from 44.7 K to 42.1 K after a suitable inertance tube was added. The cooling power can be increased with almost same efficiency by adding an orifice with appropriate opening turn. After adding an additional inertance tube of the two-stage DPTR, the lowest temperature of 15.6 K was achieved, while the lowest temperature of 15.7 K was achieved by installing an orifice to the two-stage DPTR.

In order to guide the operation of the actual cascade system, this paper takes the cascade system as the research object and compares the use of six refrigerant pairs. Unlike the previous single-objective optimization of refrigeration system carbon emissions and other indicators, this research uses a multi-objective optimization algorithm, that is, we consider the cascade system's exergy efficiency and carbon emissions at the same time. We reduce carbon emissions while improving the system's exergy efficiency, and finally find out the specific operating conditions under which the system can realize low-carbon and high-efficiency operation, which further promotes the process of achieving energy saving and emission reduction in factories. The optimization results show that among the six refrigerant pairs, the use of R744-R134a and R744-R290 refrigerant pairs can make the system operate better, but considering the high global warming potential (GWP) of R134a refrigerant, the use of R744-R290 combination is more recommended.

The objective of this paper is to provide the reliable calculation procedure for determining heat and mass flow rates for plate finned tube heat exchangers in dehumidification regimes that can be used easily in engineering practice. For this purpose, the experiments are conducted on two heat exchangers, and datasets for six more heat exchangers are used from literature. Comprehensive database is established with total of 637 sets of data, and it gathers 365 new measurement sets and 272 sets from open literature. The new calculation procedure predicts heat transfer rate and condensate flow rate where new methodology approach (based on the porous velocity, the ratio of characteristic surfaces and hydraulic diameter) is used. Predicted results show 5–10 % deviation for heat duty and up to 20 % for mass flow rate from experimental results, which is of importance to industrial practice.

The current research investigates the effects of the swirl generator material, the tube length to diameter (L/D) ratio, and the vortex tube housing material on its performance. Two vortex tube were designed and constructed using either stainless or brass. In addition to testing different materials for the housing, 5 different materials were examined as potential options for the swirl generator, including stainless steel, brass, polyamide, acrylic and wood. All were having nozzle number of 6. The study encompassed three main areas: examining the impact of various L/D ratios on an entirely stainless vortex tube (ESVT) and an entirely brass vortex tube (EBVT), exploring various swirl generator materials at an optimal L/D ratio for the stainless vortex tube and the brass vortex tube, and investigating the influence of an optimal swirl generator material with varying L/D ratios for the stainless and brass vortex tubes. Operating conditions were controlled for all tests, the natural refrigerant, compressed air was used, the inlet pressure was set to 3.0 bar and the cold mass fraction was varied from 0.40 to 0.90. The results revealed that the performance of the ESVT was greater than the EBVT. The best combination was the polyamide swirl generator and brass vortex tube with an L/D ratio of 19.0. This resulted in the maximum isentropic efficiency of 0.27 at a cold mass fraction of about 0.47.

The advancement of ice-ball thermal energy storage systems is limited by the poor thermal conductivity of phase change materials(PCM). This paper presents a numerical investigation into enhancing heat transfer in ice balls by partially filling them with metal foam. Dynamic temperature changes, solid phase fraction, and cold storage capacity are analyzed for various filling radius ratios (2/13, 4/13, 6/13, 8/13, and 13/13). We quantitatively assess the specific impact of metal foam filling on heat transfer by calculating changes in the comprehensive thermal conductivity coefficient. Our findings reveal that the comprehensive thermal conductivity coefficient increases nonlinearly with the growing metal foam filling radius ratio, indicating that full filling may not the most optimal configuration. Furthermore, the energy storage capacity per unit time, per unit weight and per unit cost of the ice ball filled with metal foam under different radius ratios was evaluated by comprehensive evaluation criteria, and the optimal filling radius ratio was determined to be 6/13. Contrary to prior findings, this research highlights the efficacy of partial filling strategies, offering valuable insights for optimizing ice ball performance in thermal energy storage applications.

Semi-empirical models for predicting the suction flow rate, injection flow rate, input power consumption, and discharge temperature are proposed for scroll compressors with vapor injection. A data set containing four compressors wherein each compressor was tested over a range of operating conditions is used to evaluate the models. The fitted parameters of the models and the prediction errors of each data set are discussed. The accuracy and generalizability of applying the models to the same compressor with and without vapor injection are also discussed.