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

Aneesh Somwanshi, Prabhat Ranjan Mishra, Y. Anupam Rao et al.

Abstract The authors have designed and developed a dual-purpose air cooler (DPAC) capable of both room cooling and refrigeration for storing fruits and vegetables. They proposed a design in which a box, made of mild steel plate and enveloped in jute cloth, is affixed at a specific distance from the cooler tank. This distance corresponds to the height at which the air temperature saturates. Water at saturation temperature is directed over the box to maintain its wetness, thereby indirectly cooling the interior space to prolong the freshness of stored items. The box's sidewall is perforated to introduce additional moisture, enhancing the preservation of vegetables and fruits. This innovative cooler was specifically designed for Raipur, Chhattisgarh, India, considering the region's maximum summer temperature (42 °C) and relative humidity ranging between 20 and 30% during the summer months. The authors conducted comprehensive computations to determine the optimal pad height, varying pad thickness from 10 to 15 cm, pad packing factor from 350 m2/m3 to 450 m2/m3, and relative humidity from 20 to 30%. Additionally, the cooling potential of the cooler was numerically evaluated as part of the study.

Hayder Mohsin Ali, Saif Ali Kadhim, Karrar A. Hammoodi et al.

Abstract The ingress of air into the vapor compression refrigeration system is a frequent occurrence, typically occurring during installation, maintenance, or charging. Air, being a non-condensable gas relative to the refrigerant gas within the system, leads to system degradation mostly due to elevated condensing pressure. This experimental study investigates the impact of non-condensable gas (air) contamination on the performance of a vapor compression refrigeration system using R134a refrigerant. A chest freezer was tested under steady-state conditions with air fractions of 0%, 1.7%, 2.5%, and 3.3% at an ambient temperature of 32 °C. Energy, exergy, and environmental analyses were conducted to evaluate system efficiency, power consumption, and sustainability. Results revealed that increasing air fractions significantly degraded performance: at 3.3% air, power consumption rose by 37.1%, while the coefficient of performance dropped by 42.8% compared to the air-free system. Also, exergy destruction rate increased by 189%, and exergy efficiency decreased by 119.1%, indicating severe thermodynamic inefficiencies. Additionally, higher air fractions led to elevated compressor temperatures, increased noise, and greater environmental impact due to higher energy-related emissions. The study highlights the critical need for rigorous system evacuation and leak prevention in refrigeration systems to maintain optimal efficiency and reduce operational costs.

Hua Yihuai, Li Qiuying, Cheng Hao et al.

Ortho-para hydrogen conversion in the hydrogen liquefaction process is significant for the long-term storage and long-distance transportation of liquid hydrogen. This paper outlines the differences in the properties of orthohydrogen and parahydrogen, reviews the research progress on the physical mechanisms and reaction kinetic models of the ortho-para hydrogen catalytic conversion process, and summarizes the performance of common catalysts. Finally, three mainstream schemes for ortho-para hydrogen conversion are compared. Research on the internal physical mechanisms and reaction kinetic models explores the conversion process from microscopic and macroscopic perspectives, respectively. Owing to the lack of experimental data, scholars have not yet formed a unified explanation for the surface characteristics of catalysts, which must be quantitatively validated. Furthermore, although nickel-based catalysts have higher catalytic efficiency, iron hydroxides and oxide catalysts are the main catalyst choices for ortho-para hydrogen conversion, considering the preparation, activation, and deactivation of catalysts and the characteristics of the liquefier. Among the three mainstream ortho-para hydrogen conversion schemes, the hydrogen liquefaction process with continuous conversion has the lowest energy consumption and is the future direction. Relevant research in China is still in its early stages and has great potential for development. This study provides theoretical guidance for the design and construction of ortho-para hydrogen catalytic conversion test benches.

Wang Fang, Yuan Qiuyan, Wang Shuaiqi et al.

It is difficult for single refrigerant used in heat pump systems to achieve optimum results. However, according to the principle of complementary advantages, new refrigerant blends may perform much better than single refrigerant. Based on this idea, a thermodynamic model of a heat pump system was established under the nominal working conditions of heat pump water heater, and a comparative analysis was made between the refrigerant blends R1234ze/HCs and the corresponding pure refrigerant through the EES program. The results show that the R1234ze/R600 blend has the best ratio in a mass fraction of (20/80) and R1234ze/R600a in mass fraction of (40/60). The corresponding maximum heating coefficient of performance (COP) are 3.414 and 3.321, respectively. The COP of R1234ze/R290 blend, however, exhibits monotonicity with the change of mass fraction. The heating COP of the R1234ze/R600 (20/80) system is 2.7%, 17%, 0.09%, 16.3%, and 17.8% higher than that of the R1234ze/R600a (40/60), R1234ze, R290, R600, and R600a systems, respectively. The discharge temperature, condensing pressure and compression ratio of the R1234ze/R600 (20/80) system are 76.9 oC, 0.711 MPa and 6.32, respectively. The results are promising for the development of a prospective alternative working fluid.

Chen Mingfeng, Yang Zhao, Chen Aiqiang et al.

In order to improve the superheat control precision of the variable capacity refrigeration system, and establish the simple superheat control method, an intelligent superheat control strategy based on the traditional PID control strategy was proposed, with various influencing factors considered. The actual superheat control effect of the intelligent control strategy was checked in a cold store with constant temperature and humidity, and was compared with the control effect of thermostatic expansion valve. The experimental results show that: the intelligent control strategy gives a better performance such as faster dynamic response, lower overshoot, and shorter oscillation time compared with traditional PID control strategy. It is advantageous to superheat stability, if the compressor frequency changes as the interference factors are inputted in advance. The intelligent control strategy is better than the thermal expansion valve on the superheat control effect, and the cold store cooling time is shortened by 37.14%.

Zhao Fei, Zhang Xu, Jing Hongpeng et al.

In order to determine optimal freezing methods for vegetable soybean, effect of three freezing rates of ﹣35 ℃ with 8 m/s wind, ﹣35 ℃ and ﹣18 ℃ on freezing temperature curve and the quality index changes of frozen vegetable soybean stored at ﹣18 ℃were investigated. The results showed that freezing at ﹣35 ℃ with 8 m/s wind had best freezing speed. Under the condition, the zone of maximum ice crystal formation in vegetable soybeans took the shortest time of 40 s, while freezing at ﹣35 ℃ and ﹣18 ℃ took about 6 minutes and 1 h, respectively. Freezing methods had significantly influence on the texture, drip loss rate, membrane permeability, MDA content, chlorophyll content, Vc content. In general, the lower temperature and faster freezing speed during freezing, the obviously lower speed of quality deterioration during storage. Quality of soybean frozen at ﹣35 ℃ with 8 m/s wind was significantly better than that frozen at ﹣18 ℃, so freezing at ﹣35 ℃ with 8 m/s is suitable for the rapid freezing of vegetable soybean.

Li Chunyin, Wang Shulin

By analyzing the motion of vane compressors for car air conditioner we proposed a mathematical model for the vibration of the discharge valve and determined its natural frequencies and mode shape in combination with the calculation using UG NX Nastran software. We show that the refrigeration efficiency can be maxima when the valve sheet takes the optimized thickness of 0.305 mm based on the vibration analysis. At the same time, test results revealed that the discharge flow pulsation and system noise are effectively controlled, and the both are lower than the upper limit of the "GMW Standard" of the U.S. General Motors Corporation. The study may be significant to enhance the refrigeration efficiency of the system and reduce discharge flow pulsation and noise of vane compressors.

王艳, 韩颖, 王捷熙 et al.

Yang Qiang, Dai Lisheng

Performance tests were conducted on three finned tube evaporators, which included one untreated copper fin evaporator, two hydrophilic treated copper fin evaporators. Each evaporator was tested with it being installed in the indoor unit of a cabinet- type air conditioner, which was used as the platform of the performance tests. Tests were conducted using the calorimeter method under the different humidity air conditions. The results showed that the evaporator surface wettability has notable effect on the air conditioner performance at high humidity air conditions because of strong ability to discharging great dew water, not at low humidity air conditions because of less water condensate.

梁工, 王蔚

丁力行, 包劲松, 陈宁

The experiments on different underground exchangers were carried out to research their exchange performance. The experimental datum on heat extraction and heat rejection of single U and double U models vertical underground pipes was analyzed using heat exchange capacity of unit pipe. The conclusion is that single U models vertical underground pipes is better than double U models. The influence of the flux and the temperature on exchange performance was investigated. The results show that the heat exchange capacity increase when the flux increase; The heat rejection increase and heat extraction decrease when the temperature increase.

黄逊青

吴业正