最新刊期
卷 43 ， 期 6 ， 2022
- 摘要：The development of machinery manufacturing and heat recovery technologies has resulted in the development and adoption of environment-friendly reverse Brayton cycle air refrigeration systems. This study introduces the principle of the reverse Brayton cycle and describes the composition, performance, advantages and disadvantages, and applications of seven types of systems, i.e. regenerative cycle, two-stage compression cycle, two-stage expansion cycle, cascade cycle, positive and negative pressure cycles, open and closed loop cycles, and mixed working fluid cycle. Three regenerative schemes (non-regenerative, first-stage regenerative, and two-stage regenerative), positive and negative pressure cycles, and open and closed loop cycles were compared. The optimization methods and advantages and disadvantages of the expander, heat exchanger, and dehumidification devices as well as their development status, are summarized. Finally, the key technologies and future research directions of reverse Brayton cycle air refrigeration systems are discussed.关键词：air refrigeration system;reverse Brayton cycle;regeneration;dehumidification;system processes1151|1212|0发布时间：2024-07-18
- 摘要：In this study, a CO2 heat pump system test bench for electric vehicles with an oil circulation rate testing device was built to investigate the influence of the oil circulation rate on the performance of the compressor and the heat pump under typical vehicle operating conditions. Under refrigeration conditions, the increase in the oil circulation rate from 1.17% to 5.26% increased the volumetric and isentropic efficiencies of the compressor by 13.6% and 5.6%, respectively, Under heating conditions, when increasing the oil circulation rate from 1.51% to 6.68%, the volumetric and isentropic efficiencies of the compressor increased by 7.19% and 15.7%, respectively, while the discharge temperature of the compressor decreased from 155.5 °C to 146 °C. Unlike the flow resistance and heat exchange capacity of the air cooler in the high-temperature section, the oil circulation rate exhibited a significant effect on the evaporation process in the low-temperature section. The analysis of the influence of the oil circulation rate on the overall performance of the heat pump system demonstrated that the heat pump system performance improved when the oil circulation rate is approximately 4%.关键词：oil circulation rate;CO2;electric vehicle;heat pump system958|827|1发布时间：2024-07-18
- 摘要：Seawater temperature is a critical factor in the design and operation of new energy systems that utilize ocean energy, such as seawater-source heat pumps and power generation systems that use seawater as the cooling medium. In this study, statistical data on the water temperatures in the Yellow Sea and the Bohai Sea near Dalian, China, from 2005 to 2021, were obtained. Thereafter, the daily variation formulas of the annual seawater temperatures were derived, which can provide more reasonable fundamental data for the design and research of ocean energy utilization systems. It was observed that the typical seawater temperatures increased in 2021. The maximum increase in the mean monthly temperature was 0.98 ℃ compared with that in 2014. From 2005 to 2021, the extreme water temperatures in the Yellow Sea were 26.2 °C in the summer and ?0.4 °C in the winter, and the extreme temperatures in the Bohai Sea were 28.6 °C in the summer and ?1.8 °C in the winter. Because the temperatures in the Yellow Sea were lower in the summer and higher in the winter compared with those of the Bohai Sea, the Yellow Sea is more suitable as a heat source for seawater-source heat pumps.关键词：typical year;seawater temperature;seawater-source heat pump;ocean energy868|1121|0发布时间：2024-07-18
- 摘要：When selecting the type of pressure-drop distributor for air conditioners with good distribution performance, the divergence of the distribution uniformity among the existing types of pressure-drop distributors should be checked. In this study, an experimental rig for testing the distribution homogeneity of distributors was designed and established. Thereafter, the distribution unevenness of existing reflection-type, jet loop-type, Venturi-type, and filter-type distributors were measured and compared. The testing conditions include a refrigerant volumetric flow rate of 32–125 L/h and a vapor quality of 0.15–0.22, which represent the normal operating conditions of room air conditioners. The installation angle of the distributor between the central axis of the distributor and the vertical direction ranged from 0° to 90°. The results demonstrate that a large mass flow rate of the inlet refrigerant or the vertical installation of the distributor is beneficial to distribution uniformity. The filter-type distributor exhibited good distribution uniformity under various experimental conditions, with a distribution unevenness of less than 0.05. Thus, the filter-type distributor is most suitable for air conditioners.关键词：air-conditioner;distributor;distribution uniformity;two-phase flow930|885|1发布时间：2024-07-18
- 摘要：The electronic expansion valve is regulated by considering the superheat at the outlet of the evaporator as the control object. However, the traditional proportion integration differentiation (PID) control strategy fails to simultaneously consider the dynamic pull-down and steady-state performance of the refrigeration system. In this study, a segmented variable-gain PID scheme involving double feedback of the superheat and compartment temperature deviation is analyzed and compared with the traditional constant-gain PID scheme with single feedback. The results of the environmental test chamber demonstrate that at a constant temperature, the variable-gain PID scheme increased the pull-down rate by 11.8%–49.3%, decreased the overshoot time by 7.1%–57.7%, and reduced the temperature fluctuation to 0.1 ℃. This method also adapted well to variable working conditions at compartment temperatures of ?40, ?20, 0, and 20 ℃.关键词：EEV;PID;variable gain;environmental test chamber1003|1084|2发布时间：2024-07-18
- 摘要：An approach based on phase-change cold thermal energy storage is proposed for the emergency cooling of an air-cooled modular data center to improve its operational reliability. An experimental setup was built for the cold thermal energy storage unit. The influence of various inlet temperatures on the charging and discharging process of the cold thermal energy storage unit was investigated. In addition, sensitivity analysis was performed on the length, height, spacings of the arcuate fins, and spacings of cold thermal energy storage plates in the unit. The results demonstrate that the experimental cold thermal energy storage unit can meet the emergency cooling demand for at least 5 min. The height of the arcuate fins indicated the greatest influence on the comprehensive heat transfer performance, followed by the fin length. The spacings of the fins and cold thermal energy storage plates have a trivial effect. When the fin height of the experimental cold thermal energy storage unit was reduced from 2.0 mm to 1.5 mm, the comprehensive heat transfer performance is improved by 57%.关键词：data center;emergency cooling;phase-change cold thermal energy storage;heat transfer enhancement843|1109|1发布时间：2024-07-18
- 摘要：The main energy requirements of indoor ice rinks are refrigeration and heat. If the refrigeration system can simultaneously meet the refrigeration and heating loads, the system efficiency can be significantly improved. In this study, the CO2 refrigeration system of an indoor ice rink with heat recovery is analyzed, considering an 1800 m2 ice hockey rink in Tianjin, China, as the research object. The actual comprehensive utilization coefficient (ACOPhc) is proposed. Four heat recovery systems that maximize the use of discharged heat were compared based on the actual heat consumption requirements of the system. The results demonstrate that the CO2 refrigeration system with heat recovery runs more smoothly. The two-stage compression refrigeration system of the ice rink that directly utilized the heat from the discharge gas leads to the highest annual operating efficiency of 6.77; in winter, this value can exceed 7.0.关键词：refrigerating system;ice rink;heat load;coefficient of performance;carbon dioxide883|806|1发布时间：2024-07-18
- 摘要：Against the backdrop of carbon neutralization, CO2 has attracted increasing attention as a natural working medium for refrigeration and heating applications. Based on pinch point analysis, a CO2 refrigeration and heat recovery system for an ice rink is optimized and analyzed. Under the assumption of two-stage heat recovery (water temperatures at the inlet and outlet are 40 °C and 60 °C for low-temperature heat recovery and 60 °C and 80 °C for high-temperature heat recovery), the following results were obtained by changing the water mass flow rate at a specific stage. The existence of the pinch point increased the CO2 outlet temperature for heat recovery in the heat exchanger and reduced the amount of recovered heat, heating coefficient of performance (COPh), and comprehensive COP of the system. The optimal discharge pressure corresponding to the maximum COP also moved backward until it exceeded the upper limit. When the mass flow ratio of the second stage is 0.4, the influence of the pinch point can be eliminated by adjusting the mass flow ratio of the first stage. When the mass flow ratio of the first stage is 0.4, the optimal discharge pressure increased from 10.2 to 10.9 MPa, while the maximum comprehensive COP decreased from 3.538 to 2.843. To improve the system performance, the mass flow rate of water at the second and first stages should be decreased and increased, respectively, while the discharge pressure should be increased within a reasonable range.关键词：ice rink;refrigeration and heat recovery system;pinch point analysis;CO2;coefficient of performance864|1016|1发布时间：2024-07-18
- 摘要：The flow rate, spray cone angle, and droplet diameter of swirl nozzles are key parameters in the snow-making process of an outdoor snow-maker. Aimed at the swirl nozzle of a domestic outdoor snow-maker, a mathematical model was established based on the volume of fluid method (VOF) and RNG k-ε turbulence model. The atomization process for the water in the nozzle was studied, and the effects of the water injection pressure and inner wall roughness of the nozzle on the atomization performance were analyzed. The results demonstrate that the spray cone angle and liquid film thickness are less sensitive to changes in the injection pressure, while the droplet diameter decreases with the increase in injection pressure. The decrease in droplet diameter is attributed to the increased water velocity, which enhanced the instability of the liquid film and the secondary breakup of droplets. As the smoothness of the nozzle wall decreased, the air vortex and water atomization cone angle generated by atomization also decreased, however, the reduced smoothness of the nozzle is helpful to obtain a larger atomization flow rate.关键词：outdoor snow-maker;swirl nozzle;atomization characteristics;VOF882|699|1发布时间：2024-07-18
- 摘要：Composite phase-change cold thermal energy storage materials have attracted significant attention in recent years; however, studies on their microscopic phase-change mechanism have garnered insignificant interest. In this study, the ice-water system with a high latent heat was mixed with polyethylene glycol (PEG) of mass fractions of 0%, 3%, and 5%, and using 10% glycerol and 20% ammonium chloride as the nucleating and cooling agents, respectively. The molecular dynamics method was used to simulate the phase transition process. The phase transition temperature was predicted and analyzed based on parameters such as the bonding and conformation, bond length, bond angle, radial distribution function, diffusion coefficient, and density. The results demonstrate that the lower the temperature, the lower the molecular kinetic energy, the smoother the molecular motion, and the greater the probability that the hydroxyl bond length will decrease. The temperature had a slight effect on the bond angle but a great impact on the bond length. With regard to the phase change, as the temperature decreased, the diffusion coefficient of the solution system decreased; the density increased; the solution viscosity increased; the orderliness increased. In the 10% glycerol-20% ammonium chloride aqueous system, the inflection point of the phase transition temperature was 255.2–256 K, which is very close to the experimental result of 255.5 K. After adding 3% and 5% PEG polymers, the phase transition temperature of the solution system was predicted to be 254.1–254.3 K and 253.5–253.8 K, demonstrating a decrease of 1.1–1.7 K and 1.7–2.2 K, respectively.968|708|1发布时间：2024-07-18
- 摘要：The infectious isolation intensive care unit (ICU) is an isolation unit where medical care is provided for patients with severe infectious diseases, which plays an important role in epidemic prevention and control. In this study, the application of a fresh air system combined with a radiant ceiling in an infectious isolation ICU was simulated using computational fluid dynamics models. The effects of different heating or cooling capacities of the radiant ceiling and heights of exhaust outlet on the indoor thermal environment and contaminant removal efficiency were examined. Experiments were also conducted to verify the accuracy of the model. The vertical temperature difference in the room, draft rate near the patients, and contaminant removal efficiency decreased by 5%–58%, 68%–86%, and 13%–50%, respectively, with the increase in the cooling capacity of the radiant ceiling in the summer. The exhaust outlet installed on the upper part of the room discharged gaseous pollutants and heat during the summer. In winter, the use of the radiant ceiling combined with the exhaust outlet reduced the room vertical temperature difference by 7%–43% and improved the contaminant removal efficiency by 43%–59%. However, the combined use of the radiant ceiling and exhaust outlet in the lower part of the room in the winter reduced the contaminant removal efficiency. These results are applicable to the operation of fresh air systems combined with a radiant ceiling in infectious isolation ICUs.关键词：radiant ceiling;infectious isolation ICU;contaminant removal efficiency;draft rate;vertical air temperature difference777|635|1发布时间：2024-07-18
- 摘要：The air-conditioning system of an independent ventilation cage (IVC) often controls the cage-level and room-level environments. However, compared with the room-level macroenvironment, the surrounding environment of laboratory animals, known as the animal feeding microenvironment, plays a key role in improving their welfare. To optimize the control method of the feeding microenvironment and the performance of the IVC air-conditioning system, a heat transfer model was established and the IVC mouse feeding microenvironment was simulated using computational fluid dynamics models. The microenvironment and macroenvironment parameters were also measured experimentally. The results demonstrate differences between the IVC mouse feeding microenvironment and macroenvironment parameters. The air supply speed in the IVCs at different locations in the same cabinet ranged from 2.79 to 4.94 m/s, which changed the velocity field in the cage. At supply air speeds of 2.97 and 4.94 m/s, the average wind speed at the inlet side was 54.7% and 60.4% higher than that at the outlet side, respectively. When the air supply speed reached 4.94 m/s, the wind speed behind the mouse exceeded 0.3 m/s, which is beyond the specified limit. The velocity field also affected the temperature, humidity, and pollutant concentration distribution. These results demonstrate that the IVC air-conditioning system should be designed based on cages with the worst hydraulic balance to improve the feeding microenvironment and ensure the welfare and quality of laboratory animals.关键词：IVC;feeding microenvironment;control method;laboratory animal welfare821|626|0发布时间：2024-07-18
- 摘要：The experimental system of household air-source heat pump water heater with flash tank was set up, and its operation perform- ance at different temperatures was studied in the environmental control room, and compared with the single-stage compression system. The results show that the heating capacity and heating COP of the household air-source heat pump water heater with flash tank are greater than that of the single-stage compression system, and the heating capacity increases 21. 3% when the ambient temperature is -15 ℃ . The heat- ing time of air-source heat pump water heater with flash tank system is shortened by 20. 1% compared with that of single-stage system un- der the same water volume and initial and ending temperatures. The discharge temperature of the compressor is reduced by 11. 3 ℃ , which ensures the operation safety of the unit. The calculation of APF shows that the system of flash tank replenishment is better in the ar- ea with lower ambient temperature.关键词：heat pump water heater;vapor-injection;flash tank;heating performance988|777|0发布时间：2024-07-18
- 摘要：To determine the influence of cold surface temperatures on the frosting characteristics and anti-frosting performance of superhydrophobic fins, the frosting process on superhydrophobic fins under different cold surface temperatures was studied. A visual frosting experimental system was built and the results were compared with those of bare fins without surface treatment. As the cold surface temperature decreased, the onset freezing time of condensate droplets, half freezing time, and complete freezing time on the superhydrophobic fin surface were shortened. The lower the cold surface temperature, the smaller the critical radius of the crystal nucleus, the denser the crystal nucleus, and the higher the surface coverage when the droplets were completely frozen. The frost thickness of the superhydrophobic and bare fins increased as the cold surface temperature decreased. After frosting for 45 min, the frost thickness on the superhydrophobic fins at cold surface temperatures of ?5, ?10, ?15, and ?20 °C were 78.8%, 95.6%, 94.6%, and 78.8% of those on bare fins, respectively. This indicates that superhydrophobic fins have an anti-frosting effect at different cold surface temperatures.关键词：frosting;superhydrophobic fin;cold surface temperature;condensate droplet1002|691|1发布时间：2024-07-18
- 摘要：Air-source heat pump systems with vapor injection have promising potential applications in cold areas in China owing to their high efficiency at low temperatures. This study investigates the effect of the refrigerant charge on the energy efficiency and operating parameters of air-source heat pump systems with vapor injection at low temperatures. The results demonstrate that as the charging amount increased from 18 kg to 25 kg, the suction temperature and pressure of the compressor slowly decreased from ?11 to 14 °C and from 0.295 to 0.32 MPa, respectively; the discharge pressure slowly increased by 5.6%; the heating capacity and compressor power steadily increased; the energy efficiency gradually increased. When the refrigerant charge exceeded the critical charging amount of 25 kg, the operation of the compressor degraded; the temperature of discharge gas increased by more than 11%; the discharge pressure increased by more than 13.6%. At the optimal refrigerant charging amount of 26 kg, the maximum energy efficiency of the unit was 2.12, which demonstrated a 14.6% increase compared with the case of 19 kg refrigerant charge. As the charging amount increased from 26 to 28 kg, the coefficient of performance slowly decreased.关键词：air-source heat pump;enhanced vapor injection;refrigerant;R410A1048|889|0发布时间：2024-07-18
- 摘要：This study examines the influence of the physical properties of the secondary refrigerant and cooler combinations on the performance of an indirect refrigeration system used in cold storage. An indirect refrigeration system test-bed was built and the performance of two new secondary refrigerants, LM-4 and LM-8, were compared using different coolers to determine the secondary refrigerant with the best performance and the optimal cooler combination. The results demonstrate that the cooling time of the system was affected by the physical properties of the secondary refrigerant and cooler combination. Under the same conditions, the cooling time of the LM-8 system with a finless wall-mounted cooler and a top-mounted fin-tube cooler was the shortest compared with the standalone top-mounted fin-tube cooler and a finless wall-mounted cooler with a finless top-mounted cooler; the cooling time of the LM-8 system is approximately 30.4% less than that of the LM-4 system. The Reynolds numbers corresponding to the optimal working parameters were derived. The optimal refrigeration coefficient of performance (COPr) and comprehensive coefficient of performance (COPc) of the LM-8 system were higher than those of the LM-4 system by 10.7% and 10.9%, respectively. Among the three types of coolers, the total energy consumption of the LM-8 system was 5.8%–13.6%, 2.2%–9.1%, and 3.3%–7.2% lower than that of the LM-4 system. In conclusion, the LM-8 system with a finless wall-mounted cooler and a top-mounted fin-tube cooler is recommended for indirect refrigeration systems in cold storage applications.关键词：indirect refrigeration system;cooler;secondary refrigerant;COP918|780|0发布时间：2024-07-18
- 摘要：A novel compression-assisted decomposition chemisorption refrigeration system is proposed to reduce the desorption pressure and temperature and increase the suction pressure of the compressor, which may contribute to the reduction of the power consumption of the compressor and increase the coefficient of performance (COP) of the system. A solidified composite sorbent performance test platform was built, which used ammonia as the refrigerant, and strontium chloride with expanded natural graphite treated with sulfuric acid was used as the sorbent. The decomposition and sorption reactions of the composite sorbents were tested under different working conditions. The results demonstrate that the novel system decomposed at the heat source temperature of 70–90 ℃. At an evaporation temperature of ?10 ℃ and a heat source temperature of 90 ℃, the optimal desorption pressure of the novel system was 0.62 MPa. The compressor pressure ratio was 2.60. The COP of the novel system was 5.21, which is 74% higher than that of traditional vapor compression refrigeration systems.关键词：adsorption refrigeration;vapor compression refrigeration;compressor-assisted desorption;consolidated composite sorbent863|746|0发布时间：2024-07-18
- 摘要：The application of enhanced tubes in an evaporator inevitably results in a higher pressure drop. Herein, a novel active liquid feeding evaporator is proposed to reduce the pressure drop by actively adjusting the mass flow rate and vapor quality along the flow path. Physical and mathematical models are established and experimentally verified. Comparisons of the vapor quality, mass flow rate, and pres- sure between the new and conventional evaporators are performed in the flow rate ranging from 14 g / s to 26 g / s. Results indicate that the quality and pressure drop in the conventional evaporator increased, whereas the mass flow rate decreased as the number of tubes increased under an inlet pressure of 1. 2 MPa using R410A. The inlet quality at the third path of the novel evaporator can be increased by 1. 82 times compared with that of the conventional evaporator, and the mass flow rate can be reduced by 43. 2%. Moreover, the new evaporator exhibits a lower pressure drop by 21. 5% at an inlet mass flow rate of 26 g / s.关键词：evaporator;active liquid feeding;heat transfer enhancement;pressure drop;vapor-liquid separator1022|813|0发布时间：2024-07-18
- 摘要：The effects of the vortex chamber radius and cold flow ratio on the performance of a vortex tube are studied using R41 gas as the working medium. The standard k-? turbulence model is adopted, where the inlet pressure and temperature were set as 4.0 MPa and 323.15 K, respectively. The cold flow ratio ranges from 0.1 to 0.9, and the vortex chamber radius ranges from 2.5 to 4.5 mm. At a cold flow ratio of 0.4, the tangential velocity first increased and then decreased with the increase in the radial distance of the vortex tube. When the vortex chamber radius was 3.5 mm, the maximum tangential velocity was 159.5 m/s. As the vortex chamber radius increased, the axial velocity of the internal and external swirls decreased. When the vortex chamber radius was 2.5 mm, the maximum axial velocity of the external swirl was 47.6 m/s. The maximum cooling effect was achieved at a flow rate and vortex chamber radius of 1.5 and 0.5 mm, respectively. At a cooling flow ratio of 0.9 and vortex chamber radius of 3.0 mm, the maximum heating effect was 36.3 K. At a cooling flow ratio of 0.6 and vortex chamber radius of 3.0 mm, the maximum cooling capacity and COP were 364.5 W and 0.21, respectively.关键词：vortex tube;vortex chamber radius;vortex tube performance;flow field;cold flow ratio1173|999|0发布时间：2024-07-18
- 摘要：Ice formation during freezing and rewarming processes is a key factor that affects the success rate of cell cryopreservation. The discovery of the formation and inhibition mechanism of ice crystals in various scenarios is highly significant for clinical applications, such as fertility treatments and assisted reproduction. A new cryomicroscopy system based on the instant contact method was developed, which achieved a cooling rate of up to 1600 K/min. The system was used to study the freezing process of pure water and dimethyl sulfoxide solution on a plate and in a circular channel under different supercooling conditions. The crystallization behavior of rat seminiferous tubules in pure water and 10% dimethyl sulfoxide solution was compared. Compared with pure water, the ice formation process of the dimethyl sulfoxide solution occurred more randomly at different positions on the plate with a slower growth rate. In the circular channel, the ice formed by pure water was mainly in the shape of a sharp needle, whose growth rate increased with the increase in the degree of supercooling. The ice formation outside the seminiferous tubules of rats was weakened by the addition of dimethyl sulfoxide; hence, the seminiferous tubules retained their physiological morphology.关键词：cell cryopreservation;ice formation;cryoprotectant;cryomicroscopy954|764|0发布时间：2024-07-18
- 摘要：The demand for oocyte vitrification has increased. However, the current step-by-step loading and removal of cryoprotectants by manual or automatic storage devices may cause osmotic injury and the loss of cells. In this study, low-cost polymethyl methacrylate (PMMA) microfluidic chips and quartz capillaries were used to build a microfluidic system that achieved not only the continuous loading and removal of cryoprotectants but also the subsequent immersion in liquid nitrogen to realize automatic vitrification. MII mouse oocytes were loaded or unloaded with cryoprotectants by manual multistep and microfluidic methods, and the cell volume changes, survival, and oocyte development rates were compared. The results demonstrate that the survival, cleavage, and blastocyst rates of oocytes were 93. 25%, 77. 12%, and 53. 00%, respectively, for the 8 min loading / unloading duration group. These are significantly higher than those of the manual multistep group but not significantly different from those of the control group (P <0. 05). In conclusion, the microfluidic system using the PMMA chip and quartz capillaries significantly reduced osmotic injury and cell loss, and simplified the operational steps. This system may provide key technical support for the development of automated devices for oocyte and embryo vitrification based on microfluidic technology.关键词：vitrification;microfluidics;oocyte;quartz capillary;PMMA chip688|706|2发布时间：2024-07-18
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