最新刊期
卷 42 ， 期 2 ， 2021
- 摘要：The CO2 transcritical refrigeration system has become one of the most popular research topics in the refrigeration field owing to its numerous advantages such as environmental friendliness, excellent heating performance, low-ambient-temperature adaptability, and full range of working conditions. In this paper, the development status of transcritical CO2 refrigeration or heat pump technology in vehicle air conditioning, building heating and hot water supply, drying industry, commercial cooling chain, and other industries is discussed. Based on the development status, this paper also summarizes and presents a prediction on the future development trend of the transcritical CO2 technology. The CO2 refrigeration technology has a bright future in the field of vehicle thermal management. Its heating performance is higher than those of R134A, R407C, R1234yf, and other systems. However, its cooling performance should be further improved. For the application of building heating and hot water supply, the development of the transcritical CO2 technology has been relatively completed. Different structural optimization schemes have been proposed for different temperature requirements. The next step of the research will mainly focus on the industrialization of the existing mature technology. Additionally, although the transformation of distributed small-scale drying equipment into a new energy version has yet to be achieved, the transcritical CO2 technology, which has significant advantages in energy saving and environmental protection, has excellent promotion prospects in the field of heat-pump dryers. In addition, because of the mature state in the commercial cold chain field, its excellent energy conservation and environmental protection advantages will further advance the technology into the refrigeration field of ice-making and snow production in stadiums. In this new field, the integrated application of cooling and heating effects of the transcritical CO2 technology will be the main research direction in the next stage. In-depth research on pressure energy recovery technologies such as ejectors, vortex tubes, and expanders is an important means to improve the system energy efficiency. An intelligent control technology is necessary for real-time performance optimization of transcritical CO2 systems. These two aspects will become the main tasks of the transcritical CO2 technology research in the next stage.关键词：transcritical CO2 technology;automobile air conditioner;heat pump water heater;heat pump drying;commercial refrigeration technology2358|4445|18发布时间：2024-07-18
- 摘要：Liquefaction of unconventional natural gases, such as coalbed methane, synthetic natural gas, coke oven gas, and tail gas from chemical processes, is an effective method for recycling. Owing to the involvement of large amounts of oxygen, nitrogen, or hydrogen, they usually need to be purified by low-temperature distillation. Thus, the unconventional natural gas liquefaction technology is quite different from that for the conventional natural gas. In this paper, the research progress of unconventional natural gas liquefaction in recent years is reviewed. For coalbed methane, large-scale coalbed methane projects abroad employed a cascade process owing to the refrigerant supply, while the research and development in China focused on small-scale or skid-mounted liquefaction devices and specific characteristics of air-bearing coalbed methane liquefaction. For synthetic natural gas, the structure of the liquefaction–distillation processes was employed because of hydrogen removal and the energy integration between the two parts was recommended to increase the system energy efficiency. For coke oven gas, the mainstream technology scheme to produce synthetic natural gas was methanation, followed by liquefaction. The new technology scheme of separating and liquefying coke oven gas to simultaneously produce liquefied natural gas and liquid hydrogen should be analyzed. In addition, the safety, phase equilibrium, and solubility issues related to the unconventional natural gas liquefaction are discussed.关键词：liquefied natural gas;refrigeration cycle;liquefaction process;coalbed methane;synthetic natural gas;coke oven gas1689|3065|1发布时间：2024-07-18
- 摘要：With the development and popularization of variable refrigerant flow (VRF) systems, the research on the energy efficiency standard of VRF systems has gradually increased. Three major energy efficiency standard indices (SEER, HSPF, and IPLV(C)) are closely related to the cooling/heating hours for ambient temperature. From the perspective of geographical environment, the influence of different climate regions on the energy efficiency standards in combination with the development of international energy efficiency standards of the VRF system was analyzed in this study. Energy efficiency standard evaluation by zoning is a novel perspective.It is expected that the scholars and enterprises in the field of heating, ventilation, and air conditioning will actively participate in exploring the advantages and disadvantages of standard zoning or nonzoning from the perspectives of theory and experiment to jointly promote industrial progress.关键词：variable refrigerant flow system;energy efficiency standard;climaticzone;energy conservation;environmental protection1621|2074|1发布时间：2024-07-18
- 摘要：China is the world’s largest producer and consumer of refrigeration equipment and refrigerants. More than one-third of the global demand for refrigerants originates from China. It is estimated that, by 2030, the total refrigerant consumption in the refrigeration and air-conditioning industry will reach 154 000 t to 178 000 t in China. In this study, the current status of domestic and foreign refrigerant recovery and regeneration technologies and equipment has been presented. Moreover, the domestic and foreign standards for refrigerant recovery, purification, and reuse and detection methods of different contaminant contents in refrigerants were investigated and the carbon emission evaluation indicators and advantages and disadvantages of commonly used traditional refrigerants were analyzed. A type of refrigerant climate performance evaluation index suitable for the process of refrigerant recovery and regeneration has also been discussed. Finally, the opportunities and challenges of refrigerant recovery, purification, and reuse were discussed.关键词：refrigerant recovery;refrigerant detection;R134a;R407C1783|2441|0发布时间：2024-07-18
- 摘要：High-temperature heat pumps are an important means to solve the dual utilization of cold and heat and realize energy saving and emission reduction. Owing to the limitation of refrigerant use, natural working fluid has become the focus of research. As a natural working fluid, ammonia has excellent thermal properties. In this study, the performances of ammonia and other commonly used working fluids for heat pump were compared and analyzed by thermal calculations and the research progress on ammonia vapor compression high-temperature heat pumps were summarized. It is shown that ammonia has the highest overall performance in the range of 80–95 ℃ and is suitable for high temperatures of 60–110 ℃. Based on the single-stage vapor compression cycle, an ammonia high-temperature heat pump system using solar energy compensation is proposed and its feasibility is discussed in combination with the solar radiation conditions in Tianjin.关键词：high-temperature heat pump;ammonia;waste heat recovery;solar-assisted1759|1871|1发布时间：2024-07-18
- 摘要：The air-ground hybrid source heat pump system can realize indirect air source heat pump mode and heat compensation mode through an air-water heat exchanger, which could compensate for the difference between heat extraction and heat injection to the soil. This could solve the problem of soil heat imbalance caused by the long-term operation of the ground source heat pump system in northern China. In this study, the residential buildings in five cities of northern China were used as examples and a model of air-ground hybrid source heat pump system was established on the TRNSYS platform. To minimize the number of ground heat exchangers and ensure a good heating effect, the matching design of ground heat exchangers and air-water heat exchangers was explored and the performance and reduced number of ground heat exchangers of the air-ground hybrid source heat pump system were simulated and analyzed. The results showed that the maximum reduction ratios of the ground heat exchangers in Harbin, Changchun, Shenyang, Beijing, and Jinan were 29%–43%, and 0.029–0.050 m2 of air–water heat exchangers were needed per linear meter of ground heat exchangers. The air–ground hybrid source heat pump system with a reduced number of ground heat exchangers could provide a stable soil temperature during a long-term operation. Its total cost saving rates for ten years were 12.6%–25.3%.关键词：ground source heat pump;air source heat pump;residential building;matching design;clean heating1652|2237|1发布时间：2024-07-18
- 摘要：Fluid cooling plates are widely used in the heat dissipation of high-density components, which imposes stricter requirements for the temperature uniformity of the plate surface. In this study, to improve the temperature uniformity of the liquid-cooled plate, a liquid-cooled plate with a single inlet and single outlet was designed. Under a load of 300 W, the average temperature uniformities of the plate cooled by a single-phase water and multiple-phase-change working medium were evaluated to be within 2 ℃ and 2.6 ℃ (R236fa), respectively. To further improve the temperature uniformity, a scheme of a single inlet and multiple outlets for optimizing the flow channel was proposed. The effectiveness of the optimization scheme was verified by a simulation and experiment. The average temperature uniformity of the plate surface cooling with the R236fa working medium can be controlled to be within 2 ℃ after the optimization.关键词：high heat flux;cooling;fluid-cooling plate;temperature uniformity;optimization1572|2367|3发布时间：2024-07-18
- 摘要：A new type of air refrigeration cycle combined with a dew-point indirect evaporative cooler (IEC) is proposed. Corresponding thermodynamic calculations on the new cycle were carried out. A comparative analysis was carried out with the ordinary air refrigeration cycle and NH3 vapor compression cycle. The influences of operation conditions on the performances of the air refrigeration cycle before and after combining the dew-point IEC as well as the COP of the NH3 vapor compression cycle were analyzed. The results showed that the performance of the new air refrigeration cycle combined with the dew-point IEC was greatly improved. The maximum COP can be increased by 37.8% under the design conditions. In addition, compared to the NH3 refrigeration cycle, it can operate with simpler processes and equipment.关键词：refrigeration cycle;thermodynamic analysis;indirect evaporative cooler;COP;natural refrigerant1553|1862|1发布时间：2024-07-18
- 摘要：A theoretical analysis on the air-side flow characteristics of cylindrical fin-and-tube heat exchanger was carried out. Based on the existing heat transfer model, a correlation formula of lumped parameters, which can reflect the structural characteristics of the cylindrical fin-and-tube heat exchanger, was proposed. The heat transfer factors of the cylindrical and common types were experimentally studied and the theoretical analysis was verified. The average relative error of the existing heat exchanger model was 81.16% for the cylindrical heat exchanger, while that of the traditional heat exchanger was 7.53%. The average relative error of the new correlation was only 8.86% for the cylindrical heat exchanger and 8.80% for the traditional heat exchanger, and the error distribution was uniform, which indicates that the prediction accuracy of new correlation is significantly improved for the cylindrical heat exchanger and maintained for the traditional heat exchanger.关键词：fin-and-tube heat exchanger;heat transfer factor;experimental correlation;variable structure analysis1610|2207|0发布时间：2024-07-18
- 摘要：In this study, a micromachined array square micropillar metal surface was fabricated. Its frosting characteristics under natural convection were investigated experimentally at an ambient temperature of Tatm= 24 ℃ and relative humidity of 17%, with different cold surface temperatures Tw of ﹣5.2 ℃, ﹣10.1 ℃, and﹣15.2 ℃ and different specimen sizes. The effects of the surface temperature and time duration on the frost thickness and weight were analyzed. In addition, an antifrosting mechanism of the array square micropillar surface was proposed and validated by simulation. The results showed that when the surface temperature was -10 °C, the frost weight on the array square micropillar surface reduced by approximately 32% compared to that on a flat surface. Moreover, an air vortex was generated by natural convection, which prevented the water vapor from remaining in the groove. Frost formedonly on the top of the micropillar, rather than in the groove. The effective frosting surface was reduced significantly. When the micropillar spacing was too large, condensation droplets and frost were formed inside the groove.关键词：frosting characteristics;array square micropillar surface;natural convection;simulation1543|1833|1发布时间：2024-07-18
- 摘要：A spherical experimental device placed in a cylindrical hall of diameter 43 m and height 44 m was used to measure the radiation signal. Photomultiplier tubes (PMTs), which is used to receive the signal, were installed on the exterior surface of the sphere. The PMTs generated heat at 200 kW during operation. To maintain the surface temperature of the sphere at (21±1) ℃, a method for high-precision temperature control by immersing the sphere in circulated water and distributing water up and down simultaneously was proposed. A simulation method using computational fluid dynamics was applied to analyze the temperature field of the water. The results showed that the method of distributing water up and down simultaneously can achieve a precise local temperature control in large spaces. Owing to the limited flow channels in the irregular cavity, the angle of inclination for both upward and downward water distributors of the circulating system was adjusted to improve the performance of temperature control locally. The increase in the area with a low temperature using the upper water distributors can be up to 20%. To reduce the vertical temperature difference of the water, the water flow ratio of the upper and lower water distributors was increased. The temperature requirement can be met when the water flow ratio is 2.5:1.The water volumes that are effectively cooled are the porous media layer and outer water layer. To obtain temperature profiles with an accuracy of (21±1) ℃ under various heating intensities, the heat flux of the heating sources was determined. The variation ranges of the low-temperature volumes around the upper water distributors differed from that around lower water distributors of the inner water layer. The low-temperature volumes around the water distributors at the top decreased by 41%, while the volumes around the distributors at the bottom decreased by 62%. However, the low-temperature volumes around the lower water distributors were larger than those at the upper water distributor, regardless of the amount of heat flux from the heating sources.关键词：sphere heating source;water distribution;temperature control;numerical simulation1478|1725|0发布时间：2024-07-18
- 摘要：Vapor injection technology is widely used in variable refrigerant flow (VRF) system to solve the problem of severe decrease of capacity in low-temperature environments. In this study, the key parameters such as pressure, temperature etc. and performance of a VRF system were tested and analyzed to get the control strategy of VRF system at low ambient temperature. The results show that the mass flow and state of the refrigerant flowing through the heat exchanger of outdoor unit are the main factors in the control of vapor injection for the performance of VRF system at low ambient environment. The better heating effect will be observed when the quality x of the refrigerant in the inject circuit is closer to 1. Therefore, the saturated vapor state of the refrigerant at the compressor supplementary port can be used as an important parameter for the thermal control of the VRF system at low ambient environment. However, the theoretical optimal pressure calculated by the suction and discharge pressure is not universal, cannot be used as an effective input parameter control for the low-temperature VRF system with vapor injection.关键词：variable refrigerant flow system;vapor injection;vapor injection pressure;superheating degree;refrigerant flow rate1588|1738|0发布时间：2024-07-18
- 摘要：To address the multi-fault concurrency problem, which may occur in the actual operation of variable refrigerant flow air-conditioning systems, a multi-fault diagnosis strategy combining linear discriminant analysis (LDA) and random forest (RF) algorithms was proposed. After the completion of fault type identification, the best detailed diagnosis model was adaptively selected according to the fault type to further diagnose the fault level or determine the cause of the fault in detail. First, the original data set containing normal operating conditions, four-way valve failure, electronic expansion valve failure, and refrigerant charge failure was divided into a training set and test set with a ratio of 7:3. The training set was used to establish an RF algorithm-based fault type identification model. Then, the LDA method was used to reduce the dimensions of the three types of faults in the training set. The training set after the dimension reduction was used to establish a fault refinement diagnostic model. Finally, after the sample data in the test set were identified by the fault type, the test sample could adaptively input different fault refinement diagnostic models according to the recognition results. The results showed that the accuracy rate of the fault type identification model on the test set reached 99.99%, while the refinement diagnostic accuracy rates of the three types of faults were 96.12%, 100%, and 97.44%, respectively. The results indicated that the strategy proposed in this paper could better complete multiple types of fault diagnosis tasks for different refrigerant flow systems.关键词：variable refrigerant flow system;vapor injection;vapor injection pressure;superheating degree;refrigerant flow rate1562|1653|2发布时间：2024-07-18
- 摘要：To address the problem of unstable system operation caused by the jump of the target value of system operation parameters in the process of working condition switching, a steady-state optimization method of variable working condition operation parameters is proposed based on association rules. This method improves the original association rule mining strategy. The historical condition is regarded as one of the input conditions of association rule mining under variable working conditions and the steady-state operation parameters were optimized under the constraint of system stability. The quasi-steady-state operation conditions of the system under variable conditions were discussed. A chiller system of a shopping mall was chosen as the study object. Based on the division of typical working conditions, the Apriori algorithm was used to determine the relationship between the main operating parameters and performance indices under the quasi-steady operating conditions of chillers and the parameters were optimized. The simulation results showed that the comprehensive operation stability of the chiller increased by 50.4% and 62.7% in the transition season and summer, respectively. The energy consumption reduced by 14.48% and 16.5%in the transition season and summer, respectively, compared to the original operation mode.关键词：parameter optimization;association rules;chiller;quasi-steady;operating condition classification1458|1702|0发布时间：2024-07-18
- 摘要：For the problem of periodic heat release in the practical application of phase-change thermal storage materials, a response surface method was used to design an experimental program on an indirect heat accumulator, based on a circular erythritol/expanded graphite composite phase-change material. The performance evaluation of the thermal storage unit was carried out through the total heat release, potential heat, and effective energy utilization of the thermal storage material. The results showed that when the intermittent time was 20 min and the cumulative heat release time of the material was 40 min, with the increase in running time, the total heat release, Stephen number, and exergy efficiency had extremum values. In addition, the appearance time of the extremum of the exergy efficiency was 22% lagged behind those of the total heat release and Stephen number. It was concluded that the running time of 7.7 min is the best value that simultaneously satisfies the optimization of the three evaluation indicators.关键词：phase change thermal storage;erythritol;response surface method;periodic heat release1453|1717|0发布时间：2024-07-18
- 摘要：Heat source plumes are a type of airflow pattern that universally exists in daily life and work. However, it causes a considerable interference to the ventilation airflow which helps in creating a comfortable indoor environment. In this study, to avoid the interference of the test instrument on the heat source plume, a two-dimensional particle image velocimetry system with splicing technology was applied to measure the vertical area of the surface-source plumes with different heat source strengths and sizes so that more accurate motion characteristic equations and global airflow distribution can be obtained. Based on the measured data, the axial velocity and expansion radius of the surface-source plume were fitted by formulas and the fitting coefficients were discussed. A simple and accurate expression of the axial velocity of the plume from a circular area source was obtained and the coefficients in the formula were fitted and corrected. The radius of the heat source was in the range of 0.05–0.125 m, while the heat dissipation capacity was in the range of 40–120 W, which could better reflect the relationship between the axial velocity of the thermal plume and height away from the heat source.关键词：heat source plume;particle image velocimetry system;axis speed;heat source size1401|1650|2发布时间：2024-07-18
- 摘要：The carbon footprint calculation of our country’s food in the cold chain process is a prerequisite for its entry to the international market in the future. In this study, the life cycle assessment method was used to calculate the carbon footprint of various parts in the cold chain of certain fruit and vegetable. Based on the energy balance equation, the refrigerated transportation mode and carbon footprint under different duration of transportation were studied. The results showed that the carbon footprint of a 1-kg vegetable in the cold chain is0.098 kg; the transportation part accounts for 82% of the total emissions, while the precooling, storage (sales), and consumption (disposal) parts account for 7%, 6%, and 5%, respectively. When the duration of transportation is within 5 h, the precooled vegetables can be transported with heat preservation, and the carbon footprint is zero. When the duration of cold storage transportation is 60 h and the latent heat L of phase-change materialis270 kJ/kg,70kg of cold storage agent is needed per cubic meter. The 10-t refrigerated truck with a transportation duration less than 98h has a smaller carbon footprint for cold storage transportation than that for the mechanical refrigeration transportation. Therefore, to reduce the carbon footprint in the cold chain process, different refrigerated transportation methods should be selected according to the duration of transportation. Refrigerated trucks with a small shape coefficient H, cold storage agents with a large phase-change latent heat, and refrigeration units with a high COP should be the prior considerations while the thickness of the insulation layer of refrigerated trucks should be appropriately increased.关键词：fruit and vegetable cold chain;carbon footprint;transportation mode;calculation method1641|1967|4发布时间：2024-07-18
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