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

With the increasing depth of coal mining, the hot and humid environment at the mining faces is becoming more severe. Mining in these conditions, coupled with the hazardous effects of coal dust, poses a significant risk to the health of coal miners. To improve the working conditions in underground coal mines, this study proposes a hybrid solution that combines evaporative cooling and dust suppression in fully mechanized working faces. Numerical models of the mining face are also created to simulate the cooling effects of the proposed solution. Additionally, the migration laws of water droplets from the spray system are also studied. The results indicate that the proposed solution can effectively improve thermal environments and suppress coal dust. This research can enhance the workplace safety in underground coal mines and provide valuable insights for addressing high airflow temperatures and concentrated dust levels.

This paper proposes an innovative two-stage ejector with a needle blocking the main nozzle area within 0%-60% to control the mass flow rate of the inlet. Based on this, under certain liquid volume fraction in two-phase inlet fluids, the nozzle exit positions (NXP₁ and NXP₂) and constant-area mixing chamber lengths (L₁ and L₂) of the first and second stages were optimized with blocking area ratio (BAR) of primary nozzle throat by using CFD simulation, the working fluid is R134a. The main results are as follows: (1) The maximum increase rate of the entrainment ratio (ER) of the first and the second-stage with optimization of four geometries without needle blockage are relatively slight, in comparison, both of them with optimization of L₁ can reach 23.47% and 20.38%, which obtain the best improvement; (2) Under the condition of a needle blockage at the primary flow inlet of the first-stage ejector, the increase rate of ER₁ with optimization of NXP₁ and L₁ are close to that without needle blockage; (3) Under the condition of a needle blockage at the primary flow inlet of the second-stage ejector, the first-stage ejector can achieve relatively large improvement of ER, especially, the optimization of NXP₂ can increase the maximum ER₁ by 258.73% of initial value, and the optimization of L₂ can increase the maximum ER₁ by 239.38% of initial value. The study in this work is helpful to understand the two-stage ejector performance improvement by adjusting the blocking area ratio of primary nozzle throat under certain liquid volume fraction in two-phase inlet fluids.

Atlantic salmon (Salmo salar) is the top imported fish in Japan. It is usually shipped in chilled form by air cargo to preserve its freshness but posts a high environmental impact. As a sustainable alternative, ocean freight can be implemented if the salmon is frozen. However, the question arises as to whether the quality of the frozen and thawed salmon is comparable. Therefore, the aim of this study is to evaluate the environmental impact and quality of Norwegian Atlantic salmon in chilled and frozen form. The CO₂ equivalent emissions of the key life-cycle stages were calculated, and the quality assessment was carried out by colorimetry and sensory evaluation with careful preparation and execution. The results showed that the CO₂ equivalent emissions of the packaging, transport, and overall cycle of the frozen salmon were 35 %, 90 %, and 60 % lower than those of the chilled salmon. Color measurements using digital imaging show that the frozen salmon is slightly redder, with a higher a* value and a lower b* value. Panelist ratings indicated that there was no statistically significant difference in perceived color, glossiness, fishy smell, texture, umami, and juiciness between chilled and frozen salmon. The study provides preliminary results that demonstrate the potential of frozen seafood and ocean freight transportation as a sustainable cold chain solution.

Refrigerant leakage is a situation that often occurs in refrigeration equipment such as heat pumps. However, certain alternative refrigerants, while exhibiting superior environmental performance, possess varying levels of flammability. The leakage of flammable refrigerants into confined spaces can pose a significant risk of explosion. The amount of lubricant in the leaking refrigerant will undoubtedly affect the flammability characteristics of the refrigerant. In this paper, the content of PVE32 oil in the leaking refrigerant during the operation of a heat pump was investigated. The results showed that, under the five leakage rate scenarios set up in the experiment, the oil concentration was highest when the leakage occurred at the condenser inlet and lowest when the leakage was at the evaporator outlet. During the leakage process of the experiment, as the mass flow rate of the leakage increased, the oil content in the early stage of the leakage increased, but the oil content in the late stage of the leakage decreased. The reasons for the change in oil content were analyzed by the oil circulation rate and the degree of phase separation. The decrease of the oil circulation rate and the change of the degree of phase separation were the key factors affecting the magnitude of the oil content as the leakage proceeded. The results of the study reveal the leakage characteristics of lubricating oil with refrigerant leakage.

The conventional approach of regulating cabin temperature and pressure on aircraft is to utilize engine-bleed air through an environmental control system (ECS). The extraction of bleed air from the engine leads to a decrease in thrust and an increase in drag on the ECS ram air duct, resulting in higher fuel consumption. Consequently, the ECS transitioned from being engine-powered to being electrically powered. In this study, the thermodynamic characteristics of three-wheel and split-wheel air cycle systems (ACSs) with a high-pressure water separation system (HPWS) were investigated by developing a parameter decomposition model and an iterative algorithm using MATLAB for a state-of-the-art electrically driven ECS (EECS) on the Boeing 787 Dreamliner. The efficiency of the ACS was assessed by establishing analytical correlations for the coefficient of performance (COP) using relevant literature on endo-reversible thermodynamic model (ETM). By employing these analytical correlations, the thermal performance of both ACSs can be accurately predicted without the need for system modeling and simulation, considering variations in the input variables and operating conditions, such as the temperatures of fresh air and ram air, the ratio of the mass flow rates of ram air and fresh air, and component parameters, including the efficiencies of the primary and secondary heat exchangers and the pressure ratios of the fan and compressor. The implementation of a split-wheel ACS instead of three-wheel ACS in the Boeing 787 EECS led to an improvement in the COP from 0.31 to 0.43, and also resulted in a reduction of 14.35 % in the input power.

Natural gas is a cost-effective energy supply for the development of low-carbon economy and environmental protection worldwide. Despite the environmentally friendly properties of natural gas, methane is a potent greenhouse gas. Therefore, efficiently recovering the boil-off methane gas (BOG) generated from liquefied natural gas (LNG) devices is becoming a pressing problem involving both the economy and the environment. The Stirling cryocooler is a promising technology in dealing with BOG. This technology has superior characteristics, including large cooling capacity, high efficiency, compact configuration, and flexible operating characteristics. In the study, a high cooling capacity Stirling cryocooler was developed. The influences of the regenerator on the cryocooler were studied. The refrigeration performance and the operating characteristics were systematically analyzed. A cooling power of 1050 W at 77 K with a relative Carnot efficiency of 33.28 % was achieved. Accordingly, the cryocooler outperforms the reported Stirling-type cryocoolers in terms of overall performance. A BOG liquefaction system based on the cryocooler was installed in an LNG refueling station. On-site test results demonstrated that the system can produce 27.3 L/h LNG with a power consumption of 14.5 kW. The present research lays a good foundation for future optimizations and applications of the cryocooler in liquefying BOG.

In this study, the impacts of various factors on the chattering phenomenon in sliding vane compressors, which is a crucial aspect that influences their performance and efficiency were explored. The analysis focused on the compressor rotational speed, pressure ratio, and operating temperature, considering both ambient and heated conditions. The aim was to provide a comprehensive understanding of the relationship between these factors and the occurrence of chattering at different operational intervals, as well as the vane sealing performance and adherence to the chamber wall.

The methodology involved examining vane behavior and the chattering occurrence across three intervals under various conditions, specifically looking at oil films formation and sealing performance degradation. The experimental results provided notable insights into the chattering phenomenon. It was shown that as the pressure ratio increased and the compressor rotational speed decreased, the sealing performance deteriorated. Moreover, when operating under heated conditions, a decrease in oil viscosity leads to reduced friction between the vane and bearing, improving vane adherence compared to ambient conditions.

The methodology and findings of this study provide insights into the chattering phenomenon in vane compressors by considering the interplay between various factors. The results emphasize the importance of optimizing the compressor oil refueling flow, rotational speed, pressure ratio, and operating temperature, to ensure proper lubrication and efficient interaction between the vanes and compression chamber walls for improved compressor performance and reduced operational challenges.

This study presents a method to calculate the freezing time of multidimensional objects using a pseudo-one-dimensional method. For example, the temperature of a rectangle in $\left(x,y,t\right)$ can be simulated from the two-dimensional heat conduction equation to obtain a pseudo-one-dimensional temperature $T\left(x,t\right)$, using the space grid $\Delta x=L_x/\left(n-1\right)$ (where $n=m$) and $\Delta y=\Delta x{L}_y/L_x$ as references. This procedure can be used to calculate the freezing time $\left(t_{\text{calc}}\right)$ at a selected point, such as the center of an object. A computer program with a runtime similar to that of a one-dimensional problem has been developed for the proposed model. The freezing times ($t_{\text{calc}}$) of 212 multidimensional objects (parallelepipeds, rectangles, and finite cylinders) were then compared with the experimental freezing times ($t_{\text{exper}})$. The calculations yielded the following parameters for all 212 objects: minimum error $E_{\text{min}}=-3.9\%$, mean error $E_{\text{mean}}=0.2\%$, maximum error $E_{\text{max}}=5.0\%$, standard deviation ${\sigma }_{n-1}=1.4\%$, and mean absolute error $E_{\text{abs}}=1.1\%$. The freezing times ($t_{\text{calc}}$) of 100 multidimensional objects (parallelepipeds and rectangles) were then compared with the freezing times of computational experiments (computational simulation) obtained from the literature using the finite element method ($t_{\text{comput}})$. The calculations yielded the following parameters for all 100 objects