Hasil untuk "Low temperature engineering. Cryogenic engineering. Refrigeration"

赵巍, 韩雅倩, 张华 et al.

In order to investigate the critical snow formation height of the mixed single-aperture nucleator within the artificial snow machine, an industrial microscope was used to observe the microstructure of the snow crystals, measure the critical snow formation height threshold, and analyse the effect of the air-to-water pressure ratio (0.4MPa:0.4MPa, 0.5MPa:0.45MPa, and 0.5MPa:0.4MPa) and the ambient temperatures (-5℃, -10℃, and -15℃) on the critical snow formation height. The results showed that under the working condition of air-water pressure ratio of 0.4MPa:0.4MPa, when the temperatures were -5℃ and -10℃, the threshold of critical snow formation height did not exist, and when the temperature was -15℃, it was able to form snow, and the threshold of critical snow formation height was 50~55cm; when the air-water pressure ratios were 0.5MPa:0.45MPa, 0.5MPa:0.4MPa, the three ambient temperatures can form snow. And the gas-water pressure ratio and ambient temperature will have a certain effect on the critical snow height, under the same ambient temperature, the larger the gas-water pressure ratio, the smaller the critical snow height; The critical snow formation height increases as the ambient temperature increases from -15°C to -5°C while keeping the air-water pressure ratio constant. When the gas-water pressure ratio is 0.5MPa:0.45MPa, the trend of critical snow formation height with temperature is larger, and the temperature has a greater impact on the critical snow formation height. The results of the study can provide a basis for the design of the optimized arrangement between the nucleator and the nozzle of the snow-making machine.

Mohammed Saleh Alshaikh

The performance of Organic Solar Cells (OSCs) is intrinsically linked to the molecular, electronic, and structural properties of donor and acceptor materials. This study employs various machine learning techniques, namely the Generalized Regression Neural Network (GRNN), Support Vector Machine (SVM), and Tree Boost, to predict key performance metrics of OSCs, including power conversion efficiency (PCE), short-circuit current density (JSC), open-circuit voltage (VOC), and fill factor (FF). The models are trained and evaluated using an experimentally reported dataset compiled by Sahu et al. Correlation analysis demonstrates that material characteristics such as polarizability, bandgap, dipole moment, and charge transfer are statistically associated with OSC performance. The predictive performance of the GRNN model is compared with that of the SVM and Tree Boost models, showing consistently lower prediction errors within the considered dataset. In addition, sensitivity analysis is performed to assess the relative importance of the predictor variables and to examine the influence of kernel functions on GRNN performance. The results indicate that machine learning models, particularly GRNN, can serve as effective data-driven tools for predicting the performance of organic solar cells and for supporting computational screening studies.

Suman Lata Yadav

The concept of life skills is related to the way of life that emphasises the mutual exchange of knowledge, attitudes, and interpersonal skills in education. Its objective is to develop diverse skills among students and prepare them to face life’s challenges with determination. The World Health Organization has defined life skills as “the positive behaviours and tendencies that enable a person to adapt in day-to-day life.” Life skills are the abilities that enable a person to adapt and exhibit positive behaviour, allowing them to deal effectively with the problems and challenges of daily life. Life is a unique gift. Therefore, by equipping life with various skills, happiness, peace, and prosperity are created. In this research, with the objectives of the study in mind, an analytical examination of life skills among secondary-level students has been conducted. This research study examines the effects of living conditions, gender, and social class on students’ life skills and presents the findings. Future researchers can build upon this, and other factors affecting the research can also be explored.

Liang Anqi, Zeng Shuang, Ren Jiahang et al.

To improve the comprehensive utilization of regional energy and promote low-carbon development, this study constructs an integrated energy system for typical areas, such as parks, including a new energy power generation system driven by photovoltaic and wind power, heating and cooling energy supply systems for ground-source/air-source heat pumps, water chillers, and energy storage equipment. TRNSYS? software is used to simulate and study the dynamic characteristics of the system under six climate conditions in Beijing, and the game theory is used for intelligent operation, which is then compared with the logic control method. The results show that the logic control method can meet the load demand but cannot realize the efficient operation of the heat pump unit and the charge and discharge balance of the energy storage device. The integrated energy system after optimization via game theory can not only realize flexible energy scheduling and distribution through electric-thermal coordination, but also save the entire energy consumption of the heat pump unit and achieve the goal of regional energy economic benefits. The research presented in this paper provides an important theoretical basis for the intelligent operation of heat pump systems in integrated electric-thermal cooperative grids.

Liu Yu, Ma Guoyuan, Wang Lei et al.

To comprehensively consider temperature and humidity requirements, this paper proposed a room air conditioning system with adjustable temperature and dehumidification functions. Furthermore, the performance of the system in air conditioning and dehumidification modes were examined. The results indicated that the device can realize the air conditioning mode, dehumidification mode with rising temperature, and dehumidification mode with regulated temperature. In the dehumidification mode, under all test conditions, the outlet temperature of the dehumidification mode with regulated temperature was approximately 7% lower than that of the dehumidification mode with rising temperature, and the relative humidity of the outlet was approximately 27% lower. Furthermore, the former mode exhibited a dehumidification amount of approximately 2.8 times of that in the latter mode, and the unit power of dehumidification was approximately 2.6 times of that in the latter mode. Hence, dehumidification mode with rising temperature should be used when the outdoor temperature is lower than 18 ℃, and the compressor can be adjusted via variable frequency. Dehumidification mode with regulated temperature should be used when the outdoor temperature is between 18 ℃ and 26 ℃, and the compressor can be controlled with the "capacity adjustment + variable frequency" method. The system can effectively solve the problem of lower supply air temperature owing to the dehumidification in the middle and lower reaches of the Yangtze River.

Gao Jie, Wu Xiaozhou, L et al.

In this study, an electric-heating film was set up in a climate chamber to simulate the heat transfer in an external building envelope. Then, the indoor air distribution characteristics in a room with chilled ceiling and mixed ventilation were studied when the cooling loads were 83 or 111 W/m2. The results show that a uniform vertical temperature profile below 1.7 m as well as a non-uniform temperature profile above 1.7 m existed when the ceiling surface temperatures varied from 15 to 23 ℃ and the supply air temperature was 22 ℃. The CO2 concentration was large in the occupied zone and small near the ceiling or floor. Moreover, the average vertical air temperature difference, turbulence intensity, and contaminant removal effectiveness were 0.1–0.2 ℃, 32%–38% and 0.62–0.86, respectively. Therefore, the changes in the ceiling surface temperature slightly affected the vertical air-temperature difference and turbulence intensity, whereas they clearly influenced the contaminant removal effectiveness.

Xue Lianzheng, Ma Guoyuan, Zhou Feng et al.

The performance of gas-pump-driven free-cooling unit for heat dissipation was analyzed in a small data center in Beijing. The operating characteristics of the unit were fitted to its operating curve. The results show that the heat exchange capacity of the unit increases with the increase in the difference between the indoor and outdoor temperatures. When the indoor and outdoor temperature difference was 11 °C, the heat exchange capacity was approximately 10.4 kW, and when the difference reached 23 °C, the heat exchange capacity was approximately 13.6 kW. The difference between indoor and outdoor temperatures is the main factor affecting the heat exchange capacity of the unit. The power of the gas pump decreases with the increase in the temperature difference. For differences of 11 °C and 23 °C, the power of gas pump was 1300 W and 810 W, respectively. When the outdoor temperature was ?3.7 °C, the heat exchange capacity of the unit was 13.6 kW, and the EER reached 10.40. When the outdoor temperature was lower than 15 °C, the gas-pump-driven free-cooling unit could meet the cooling load of the data center. Compared with the original air conditioning, the electricity power was reduced by 6842.24 kW?h, and its annual energy saving rate was 25.78%.

Li Bei, Liu Daoping, Yang Liang

A phase change material is a popular functional material, and owing to its high heat storage density, maintains a constant temperature during the process of storing and releasing energy, or is stable within a certain temperature range, which makes the material be able to not only realize energy storage but also achieve temperature control functionality. Composite phase change materials have become a popular research area because of their variety of single material properties, and are widely used in building-energy conservation, the thermal management of electronic devices, and cold chain transport. Its application is quite extensive when the energy supply is not continuous. This paper divides composite phase change materials according to their chemical composition into organic-organic, inorganic-inorganic, and organic-inorganic materials, determines the advantages and disadvantages of different types of composite phase change materials based on the research in recent years, and summarizes their energy storage characteristics. The present applications of composite phase change materials are summarized, and the development of research in this area is further analyzed based on the current energy use and environmental conditions. The research objectives and directions of phase-change thermal storage are illustrated, and it is concluded that future composite phase change materials should be highly efficient, accurate, cheap, environmentally friendly, and biodegradable.

Wu Xuehong, Li Weiping, Wang Lixun et al.

In order to improve the performance of refrigerated display cabinet, decrease the food temperature and restrain the temperature fluctuation during defrosting, a kind of composite shelf is proposed in the food refrigerated display cabinet (RDC) based on the high-thermal conductivity of heat pipe and cool storage of phase change materials. The influence of three phase change materials of RT3, RT4, RT5 on the temperature of food packages, the characteristic of heat transfer and cool storage of composite shelf were investigated. Compared with the ordinary shelf, the food temperature on composite shelf of RT3 reduces by 13.7%-80%, temperature fluctuation decreases 53.3%-70%; the food temperature on composite shelf of RT4 reduces by 20%-83.3%, temperature fluctuation decreases 83.3%-87.5%; the food temperature fluctuation on composite shelf of RT5 decreases 66.7%-75%. Compared with the other two composite shelves, the average food temperature of each floor and each row on composite shelf of RT4 is the lowest and within 5℃, thus the cool storage performance of phase change material of RT4 is the best.

袁晓蓉, 高赞军, 王学会 et al.

According to the need for viscosity measurement of refrigerant mixtures, a new rotatable capillary viscometer is developed and designed. It is adequate for the viscosity investigation of the low boiling point liquid mixtures. A rotatable capillary viscometer is embedded in a pressure vessel. It combines the rotation method and the pressure vessel to realize the continuous experiment and eliminates the error brought from the deflation, which can repeat the viscosity measurement of the low boiling point liquid mixtures in the high pressure. The rotatable capillary viscometer was calibrated by R22 and R290 and checked by R410A. According to the results, the relative deviation of the viscometer has been controlled to be less than 0.81%.

Dong Man, Xia Zaizhong, Wang Ruzhu et al.

In this paper, heat and mass transfer during the process of ammonia vapor absorbed into the surface of stagnant ammonia-water solution under the condition of large pressure difference was studied. Physical and mathematical models of the absorption process with coupled heat and mass transfer were established. The temperature field, concentration field and the dimensionless number which represents the mass transfer at the interface were developed with constant ammonia vapor pressure. The results indicate that the concentration and temperature at the interface are fixed values which only depend on the initial conditions. By introducing the ammonia-water gas-liquid phase equilibrium equation, the semi-empirical correlation containing criterion number, initial pressure differential and initial parameters of ammonia-water solution was developed. The variation curve between time-averaged mass transfer and the absorption time was obtained. The curve shows that the time-averaged mass transfer is the largest at the beginning of the absorption and drops rapidly as the absorption time increasing.

Wang Wenyi, Mao Xiaoqian, Hu Bin et al.

Theoretical analysis of a heat pump with an economizer have been presented in this paper. The mathematic models of the heat pump system have been developed and experiments have been conducted to investigate the impacts of the gas injection on heat pump performance under low ambient temperatures. The results indicate that the heating capacity and the power consumption go up when the amount of gas injection increases under low ambient temperatures. The discharge temperature declines with the increment of gas injection, while the COP of the heat pump rises first and then descends. According to the test results, the optimal amount of gas injection is about 10%-14% of the total mass flow rate in the heat pump system.

Wu Zhaoguo, Ren Tao, Ding Guoliang et al.

The response surface method is applied to design the heat exchanger with decreasing tube diameter, for the traditional design methods are not suitable for the optimization of the performance and cost of heat exchanger simultaneously. The method fits the relationship among the tube length, fin pitch, performance and cost of heat exchanger into a quadratic continuous function that can be solved directly. The accuracy of the method is verified by applying it to the optimization of 7mm tube heat exchanger, the deviation from the experimental data is 0.3%. Using the method for the optimization of 9.52mm tube heat exchanger into 5mm tube heat exchanger, the cost and refrigeration charge of designed heat exchanger decrease by 28% and 39.8%, respectively, while the performance is unchanged.

王鑫, 史琳, 朱明善 et al.

According to special requirements of refrigerants used in centrifugal chillers, a new ternary mixture alternative, LXR2a, was proposed. The basic thermophysical properties and cycle performances of LXR2a were compared with those of R12. Moreover, the effects of different evaporating temperature, condensing temperature, super-heating temperature, and super-cooling temperature on the cycle performances were simulated. In addition, the leakage simulation was analyzed. The results show that LXR2a is a drop-in refrigerant with good performances and it may be a medium-term alternative to R12 in centrifugal chillers.