最新刊期
卷 45 ， 期 5 ， 2024
- 摘要：Supersonic expansion cooling combined with swirl separation technology is a novel method for gas liquefaction separation that has been mainly employed to separate high freezing point components from multi-component gases in recent years. In this study, two typical structures of supersonic swirl separators are introduced. Thereafter, the theoretical development, numerical simulation, experimental research, and molecular simulation of the condensation phase transformation in the Laval nozzle are summarized. Subsequently, the shockwave problem and structural optimization are analyzed and recapitulated. Numerous experiments and field applications demonstrate the advantages of the device; for example, it saves energy and is environmentally friendly, it has no moving parts, and it eliminates the need to add chemical agents. It has thus been widely used in the field of natural gas purification treatment. Future research can focus on the condensation phase transformation mechanism of single-component and multi-component gases and on improving liquefaction efficiency to promote the application of supersonic swirl separation technology in liquefaction and refrigeration processes, particularly in the refrigeration temperature range and cryogenic temperature range of hydrogen and helium.关键词：supersonic swirl separation device;Laval nozzle;shock wave;structural optimization285|125|0发布时间：2024-10-09
- 摘要：Improvements in heat transfer performance and efficiency through a single heat transfer enhancement technology are limited. Hence, composite-enhanced heat transfer technologies must be developed to improve resource utilization rates and reduce energy consumption and carbon emissions. Refrigerants exhibit physical properties that significantly affect the energy transport in refrigeration systems. Based on the development trend of refrigeration systems characterized by miniaturization, reduced weight, energy savings, and efficient heat transfer, refrigerant composite-enhanced heat transfer can effectively improve the energy efficiency of refrigeration systems, which has been widely studied in recent years. This work summarizes the latest research progress in composite-enhanced flow boiling heat transfer for refrigerants, focusing on nanoparticles, metal foam, external field (ultrasonic/magnetic field/electric field), and environmentally friendly refrigerant mixtures. It also highlights the prospects and existing problems in the application of multi-field synergy and nanoparticle-metal-foam-refrigerant composite-enhanced heat transfer as a future research direction. The review provides insights and references for establishing a new multi-element refrigerant composite-enhanced system.关键词：refrigerant;composite-enhanced;Nanoparticles;metal foam;external field146|115|0发布时间：2024-10-09
- 摘要：Interfacial frosting is ubiquitous in daily life and has many industrial applications. Owing to the poor heat transfer performance induced by packed air pockets, the frost layer usually manifests itself as a thick porous medium, which compromises the operational effectiveness of heat exchangers. Despite extensive studies spanning centuries, condensation frosting has achieved significant advancement only in the last decade. These advancements include the discovery of new physical features during condensation frosting that were too fast or too small to be captured and the development of new anti-/defrosting techniques. This study aims to provide a comprehensive up-to-date review on condensation frosting, particularly its progress in the last decade. The stages of condensation frosting, namely, condensation nucleation, growth of condensed microdrops, icing nucleation, formation of frost halos, frost spreading via ice bridging, and the final densification process, are introduced chronologically. Recent engineering efforts to solve the frosting problem, either by anti-frosting or defrosting, are also discussed. This review sheds light on the existing understanding of condensation frosting and promotes the development of anti-/defrosting techniques.关键词：condensation frosting;interfacial phenomena;frost characteristics;anti-frosting techniques165|65|0发布时间：2024-10-09
- 摘要：A closed-loop pulsating heat pipe within atmospheric temperature relies on the pulsation and phase change of the internal working fluid. It has been widely used for the heat dissipation of electronic components owing to its high heat transfer efficiency, simple structure, and low cost. In this study, the factors affecting the startup and heat transfer performance of pulsating heat pipes are divided into three categories, namely, structural parameters, operating conditions, and working fluid properties. First, the structural parameters, including factors such as diameter, cross-sectional shape, number of U-bends, and length ratio of each section, are summarized. Second, the influence of operating conditions, including the heating power, inclination angle, and liquid filling rate, is analyzed. Finally, the physical parameters of the working fluid are divided into flow and heat transfer properties. To improve the start-up and heat transfer performance of pulsating heat pipes, future research should focus on conducting in-depth investigations into the critical number of U-bends. The anti-gravity performance of heat pipes must be improved for adapting to small inclination angles and negative angle conditions. A comprehensive evaluation criterion describing the influence of physical parameters on performance should also be established.关键词：closed-loop pulsating heat pipe;structural parameters;operating conditions;working fluid properties92|85|0发布时间：2024-10-09
- 摘要：In this study, mathematical models for the motion and force analysis of the important components of miniature rolling piston compressors, such as sliders and rolling rotors, are established. Using the calculation formula for the friction losses of main friction pairs, this study analyzes the proportion of friction losses of the main friction pairs in a miniature rolling piston compressor and compares the distribution of friction losses with that of conventional rolling piston compressors in air conditioners. The effects of discharge pressure and structural parameters on the friction loss of the main friction pairs of the compressor are subsequently investigated. The results show that compared with the conventional rolling piston compressor used in air conditioners, the miniature rolling piston compressor has higher piston rotation speed. Moreover, the proportion of friction loss between the sliding plate and the sliding plate groove increases by 9.5% while the proportion of friction loss between the main and auxiliary bearings decreases by 16.1%. The total friction power consumption of the compressor increases by 13.5% as the discharge pressure increases from 1 070 kPa to 1 470 kPa. The total friction power consumption increases by 3.1% as the thickness of the sliding plate increases from 1 mm to 3 mm. The eccentricity of the miniature rolling piston compressor increases from 0.08 to 0.18, resulting in a 69.7% rise in total friction power consumption. Meanwhile, the aspect ratio of the miniature rolling piston compressor increases from 0.25 to 0.5, resulting in a 10% reduction in total friction power consumption. The appropriate eccentricity range for miniature rolling rotor compressors is 0.08-0.18. The research results can provide a reference for the design and structural parameter optimization of miniature rolling piston compressors.关键词：miniature rolling piston compressor;kinematic analysis;force analysis;mathematical model;friction loss114|69|0发布时间：2024-10-09
- 摘要：Refrigerants exhibit different diffusion and distribution characteristics when they encounter obstacles after leaking into confined spaces. The influence of the thermophysical parameters of refrigerants on their diffusion and distribution after encountering obstacles thus needs to be analyzed to facilitate the prediction of flammable areas during the leakage of flammable refrigerant. In this study, R717, R290, R32, and R1234yf were selected. The diffusion and distribution characteristics of the refrigerants encountering high and low obstacles in a confined space were investigated, and the influence of the thermophysical parameters of the refrigerants on the diffusion process and flammable area were analyzed in detail. The results indicated different patterns of rigid collision when the refrigerants encountered a high obstacle after leakage. Refrigerant with lower densities diffused rapidly in the direction opposite to the leakage direction and gathered at the top of the space, whereas refrigerants with higher densities diffused along the surface of the obstacle to the ground. As the height of the measurement point decreased, the mass concentration of R717 decreased from 2.04% to 0.024%, and the mass concentration of R1234yf increased from 0.192% to 1.64%. The mass concentrations of R290 and R744 below the leakage hole were 0.92% and 1.27%, respectively. When the densities of the refrigerants were similar, the refrigerant with a higher viscosity had a higher mass concentration. The flammable area was primarily located above the high obstacle, and as the refrigerant leakage increased, the flammable area in the y-z section of the space gradually extended to the ground. When refrigerants encountered low obstacles after leakage, they accumulated below the leakage hole and gradually diffused to other low mass concentration areas of the space along the surface of the low obstacle. The distribution of refrigerants with lower densities was more uniform. As the densities of refrigerants increased, they accumulated significantly below the leakage hole. As the height of the measurement point decreased, the mass concentrations of R1234yf and R717 increased from 0.066% and 1% to 2.12% and 1.14%, respectively. The flammable area was mainly located in the corner surrounded by the low obstacle and the wall below the leakage hole. With an increase in refrigerant leakage, the flammable area extended to the ground along the surface of the obstacle.关键词：flammable refrigerant;leakage;obstacle;thermophysical parameter;flammable area117|80|0发布时间：2024-10-09
- 摘要：In this study, artificial snow is produced under natural conditions using a snowmaking machine, and the microscopic morphology of the snow crystals is obtained. The sizes of snow particles and the factors that influence them under various working conditions are subsequently analyzed, and the formation of artificial snow is deduced. The results show that the falling position, environmental temperature and humidity, and nozzle atomization particle size are important factors affecting snow particle diameter. Lower environmental temperature and humidity, as well as a smaller nozzle diameter, facilitate the formation of larger snow particles. When the snowmaker operates stably, the distribution of snow particle diameter is more non-uniform in distant areas than at the edges and middle regions. The measured snow particle size is approximately 0.3 mm, which is significantly larger than the atomization particle size of the nozzle (0.12 mm). This result indicates that snow particles collide during flight. Overall, this study is important for understanding the mechanisms of snow formation and the regulation of snow quality.关键词：snow particle size;snowmaker;artificial snowmaking;snow quality54|34|0发布时间：2024-10-09
- 摘要：Radiant cooling air conditioning systems offer energy savings and thermal comfort; however, the dew problem limits their application and popularization. In this study, a method of applying an infrared high-permeability film to a cold plate was proposed to increase the temperature of the contact surface between the infrared high-permeability film and indoor air while ensuring the radiation cooling capacity of the air conditioning system. This reduces the risk of condensation. A heat transfer model of an infrared transmitting film for radiation refrigeration was constructed, and the influence of the infrared transmittance of the highly permeable film on dew point temperature and radiant cooling capacity was calculated. In addition, the minimum transmittance and corresponding maximum cooling capacity of natural ventilation for preventing condensation in typical cities of different climate zones were predicted, and the effect of the infrared transmittance of the high permeability film on human thermal comfort was evaluated. The results show that the radiant heat transfer model can accurately predict the heat transfer process at the membrane surface. Under the premise of ensuring radiation cooling capacity, the transmission film can increase the dew point temperature by 4 ℃-17 ℃. The minimum transmittance required by different cities vary, with Hohhot and Chongqing having the lowest and highest rates of 0.4 and 0.95, respectively. Infrared transmission films can be used as a novel method to prevent condensation on the cold walls of radiant air conditioning systems. This study thus provides a reference for the design and selection of transmission films.关键词：radiant air conditioning;anticondensation;refrigerating capacity;high permeability film60|57|0发布时间：2024-10-09
- 摘要：To solve the contradiction between the surplus of low-temperature waste heat resources and the shortage of high-temperature heat demand, this study designed a set of high-temperature heat pump unit based on quasi-two-stage compression. The cycle was analyzed theoretically, and the design was optimized. A combination of a flash tank and an internal heat exchanger was used to improve the performance of the unit, and a performance test of the unit was carried out. The performance of the unit was analyzed under conditions in which the outlet water temperature of the condenser was 85 ℃-120 ℃ and the inlet water temperatures of the evaporator were 50 ℃, 60 ℃, and 70 ℃. Heating capacity, coefficient of performance (COP), exergetic efficiency, condensing pressure, and discharge temperature were taken as the performance indicators. The performance of the experimental unit was consistent with the theoretically calculated performance. The inlet water temperature of the evaporator was 49.8 ℃, and the outlet water temperature of the condenser was 118.1 ℃. The maximum heat produced by the unit, COP, and exergy efficiency were 916.3 kW, 2.51, and 46.3%, respectively. Meanwhile, the condensing pressure of the unit was 1.8 MPa, and the discharge temperature was 137 ℃; these values meet the safety requirements of the unit.关键词：high-temperature heat pump;flash tank;internal heat exchanger;heating performance;exergy analysis143|74|0发布时间：2024-10-09
- 摘要：Optimal discharge pressure is the most important factor affecting the performance of a transcritical CO2 heat pump. In this study, the reasons for the optimal discharge pressure were theoretically analyzed based on the heat transfer pinch point. The factors influencing the optimal discharge pressure and their influence mechanism were determined by constructing a transcritical CO2 heat pump simulation model using the AMESim software. The model took into consideration the internal heat transfer pinch point of the gas cooler. Under inlet water temperature of 10 ℃-40 ℃, outlet water temperature of 60 ℃-90 ℃, and ambient temperature -30 ℃-25 ℃, the influence of inlet temperature, outlet temperature, ambient temperature, and heat recovery rate on the optimal discharge pressure was studied quantitatively. The results showed that the lower the inlet, outlet, and ambient temperatures, the lower the optimal discharge pressure of the system. Moreover, the optimal discharge pressure could be reduced by using an internal heat exchanger. The influence mechanism of each factor on the optimal discharge pressure was found to be closely related to the heat transfer pinch point and the physical properties of CO2 near the critical point and supercritical zone. The research results can provide a reference for the design and performance optimization of CO2 heat pump systems.关键词：transcritical CO2 heat pump;optimal discharge pressure;heat transfer pinch point;heat recovery rate123|40|0发布时间：2024-10-09
- 摘要：Electronic expansion valves (EEVs) in air conditioner systems may induce serious flow noise when the refrigerant flows into them with unstable two-phase flow patterns. The addition of a flow pattern regulator in the flow path of an EEV is expected to stabilize the refrigerant flow pattern, thereby reducing flow noise. Therefore, determining the influence of flow pattern regulators on the flow noise of EEVs is essential for optimizing their structural parameters. In this study, a method for flow pattern simulation was verified through experiments. Then, the influence of the structural parameters of the flow pattern regulator, including the hole interval, thickness, and hole diameter, on the flow noise of the EEV under the typical unstable slug flow pattern was determined. Finally, the structure of the flow pattern regulator was optimized by reasonably combining the parameters to minimize the flow noise of the EEV. The results showed that the flow noise increased as the hole interval increased, whereas it initially decreased and subsequently increased as the thickness or hole diameter increased. The hole diameter is the most important factor affecting flow pattern regulation, and flow noise can be significantly reduced by appropriately designing the hole diameter. Under the working conditions of this study, noise was reduced by 6.88 dB.关键词：electronic expansion valve;flow noise;two-phase flow pattern;flow-pattern regulator;noise reduction75|76|0发布时间：2024-10-09
- 摘要：A vapor-liquid adjustment evaporator exhibits superior heat transfer performance by adjusting vapor quality and mass flux. In this study, two vapor-liquid adjustment evaporators with circuitries of 4-2-4-6-4 (evaporator 1) and 5-4-3-4-4-4 (evaporator 2) are applied to heat pump water heaters (respectively referred to as systems A and B), and an experimental comparative study is conducted. The results show that compared with that in evaporator 1, the refrigerant is more uniformly distributed in evaporator 2, and its pressure drop is reduced by 10.91%. Under nominal working conditions, the heating capacity and power consumption of system B are reduced by 1.69% and 1.45%, respectively, compared to system A; the coefficients of performance (COPs) of the two systems are generally the same. The pressure at the compressor outlet of system B is 26.35-84.78 kPa lower than that of system A; this range is conducive to the safe operation of the compressor. At different ambient temperatures, the power consumption of the compressor of system B is lower than that of system A. When the ambient temperature is 30 ℃, the COP of system B is 2.1% higher than that of system A.关键词：air-source heat pump water heater;evaporator circuit design;pressure drop;refrigerant distribution71|48|0发布时间：2024-10-09
- 摘要：This study investigates an air-source heat pump (ASHP) with an economizer in terms of its heating conditions and designs four groups of experiments to evaluate its heating performance. The results show that under each experimental condition, the main electronic expansion valve has the best opening, which is the maximum opening corresponding to a certain superheat range. Under the best opening conditions, the maximum heat of the heat pump unit is 85.99%, 76.58%, 57.46%, and 38.25% of the rated working condition. The corresponding energy efficiencies are 2.21, 2.08, 1.95, and 1.55, respectively. The opening of the replenishment electronic expansion valve can effectively improve the heating capacity; however, with an increase in the opening of the replenishment valve, the energy efficiency of the system decreases. If energy efficiency is used as the optimization objective of the heat pump unit, it may lead to insufficient heating capacity. Liquid return is also the main factor affecting the heating capacity and energy efficiency of the heat pump unit. When the replenishment port does not return the liquid, the heating capacity of the heat pump unit increases by 18.35%, 12.14%, and 25.95%; when the replenishment port returns the liquid, the heating capacity is reduced by 15.22%.关键词：ultralow-temperature environment;air-source heat pump;quasi-two-stage compression;heating capacity85|48|0发布时间：2024-10-09
- 摘要：Global warming has emerged as a world-wide concern; therefore, research on the fourth generation of new environmentally friendly refrigerants is an urgent requirement. The boiling heat transfer characteristics of a refrigerant in an evaporator are directly related to its application. Thus, the R513A refrigerant is a suitable alternative to R134a. The boiling heat transfer characteristics of R513A and R134A in a 12.7 mm horizontal smooth tube and microfin tube were experimentally studied. The effects of mass flow rate, evaporation temperature, heat flux, and internal thread structure on heat transfer coefficient and pressure drop were also analyzed. The experimental mass flow rate of refrigerant was 100-200 kg/(m2·s) and the evaporating temperature was 5 ℃-10 ℃. The results showed that the boiling heat transfer coefficient changed significantly with an increase in the heat flux. With an increase in mass flow rate, the boiling heat transfer coefficient increased by 15.06% to 42.33%, and the pressure drop increased by 26.16% to 61.83%. As the evaporating temperature increased, the boiling heat transfer coefficient increased by 13.27% to 38.25%, and the pressure drop decreased by 19.53% to 33.27%. The heat transfer coefficient of the microfin tube was significantly higher than that of the smooth tube, with a reinforcement multiplier of up to 2. Under the same conditions, the boiling heat transfer coefficient of R513A was 25.61%-30.74% higher than that of R134a. The pressure drop inside the microfin tube of R134a was approximately 12.33% higher than that of R513A. With an increase in the heat flux, the flow pattern transition of R513A occurred earlier than that of R134a, and the boiling heat transfer coefficient decreased sharply.关键词：microfin tube;flow boiling;heat transfer coefficient;frictional pressure drop;R513A84|92|0发布时间：2024-10-09
- 摘要：In this study, the flow boiling heat transfer and pressure drop of R245fa in a dimpled flat tube were experimentally measured. The effects of vapor quality and heat flux were analyzed accordingly. The experimental results showed that with an increase in vapor quality, the surface coefficient of heat transfer first increased and then decreased, and the corresponding vapor quality at the maximum surface coefficient of heat transfer was affected by the heat flux. When the heat fluxes were 2 kW/m2, 5 kW/m2, and 10 kW/m2, the surface coefficient of heat transfer reached its maximum value at vapor qualities of 0.35, 0.40, and 0.45, respectively, and then gradually decreased. Increasing the heat flux had little effect on the frictional pressure gradient, but it was beneficial for improving the surface coefficient of heat transfer. The decrease in the surface coefficient of heat transfer with an increase in vapor quality was due to the suppression of nucleate boiling. A comparison of the experimental results for R245fa and R134a indicated that vapor quality and heat flux have different effects on the surface coefficient of heat transfer. Under the same conditions, the ratio of the surface coefficient of heat transfer between R245fa and R134a ranged from 0.64 to 1.31.关键词：flow boiling;surface coefficient of heat transfer;dimpled flat tube;refrigerant52|37|0发布时间：2024-10-09
- 摘要：Ice slurry is a good cold storage medium with a large heat capacity and efficient heat transfer properties. In this study, a microemulsion was prepared with the addition of water, soybean oil as the oil phase, Tween-80 and AEO-3 as surfactants, and amyl alcohol as co-surfactants. The effects of the mass ratio of the oil phase to surfactant, hydrophilic and oleophilic balance of the surfactant (HLB value), and mass ratio of the surfactant to co-surfactant (Km value) on the water solubility of the microemulsion were investigated. A 1∶4 mass ratio of oil phase to surfactant, a 6∶4 mass ratio of Tween-80 to AEO-3 (HLB value of 11.6), and a 2∶1 Km value were the best ratios for the preparation of the microemulsion. An ice slurry was prepared by selecting the microemulsion with 50% water content under the above mass ratios. The influence of ice crystal particle size on the melting process of the ice slurry was studied using ice crystal melting images. The grain size of the ice crystals gradually decreased with increasing melting time. The melting time of the ice crystal particles with large grain size was greater than that of the particles with small grain size. The effects of storage time and ice content on the grain size distribution and average grain size of the ice crystals were analyzed using ice crystal images of the microemulsion ice slurry stored for 1 h and 2 h. The longer the storage time, the larger the grain size of the ice crystals. The number of ice crystals decreased while the ice percentage factor did not change. For the same storage time, the higher the ice content, the faster the growth rate of the ice crystal particle size.关键词：microemulsion;ice slurry;melting;storage;ice percent factor;soybean oil49|45|0发布时间：2024-10-09
- 摘要：The moisture content of seeds poses a significant challenge in their cryopreservation. Previous studies have shown that the hydrolysis of seed globulins can improve the freezing resistance of hydrated seeds. In this study, Brassica seeds were selected as the experimental material, and the effect of 5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB) on the freezing tolerance of hydrated Brassica seeds was investigated under the cooling rate of -1 ℃/min. The results showed that DTNB significantly improved the germination rate of Brassica seeds after rapid cooling. The initial temperature of ice crystal formation in seeds was delayed in DTNB treatment (control group vs. DTNB group: -14.78 ℃ vs. -16.43 ℃). Compared with the control, two different protein spots accumulated below 25 kDa; which were identified as 12 s storage globulins by mass spectrometry. The sulfhydryl group content, globulin, and its hydrolyzed polypeptide were significantly increased in the DTNB treatment. The non-enzymatic oxidants AsA and GSH increased by 1.26 times and 1.22 times, respectively, relative to the control. DTNB also promoted the expression of cold stress-responsive genes, including ICE1 and CBF. In conclusion, DTNB can improve the freezing tolerance of Brassica seeds after rapid cooling through molecular and physiological regulation.关键词：rapid cooling;Brassica seeds;5,5′-dithiobis-(2-nitrobenzoic acid);seed storage globulin;proteolysis45|29|0发布时间：2024-10-09
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