最新刊期
卷 37 ， 期 2 ， 2016
- 摘要：A novel vapor injection structure on blade for rotary compressor is put forward. In the new mechanism, the inject port will keep close until the gas suction process is finished and the compression pocket is isolated from the suction tube, which avoids the back-flowing of the injection refrigerant into the suction tube and the decrease of the volumetric efficiency. Based on a verified numerical model, the performance of the new configuration is investigated. The results indicate that: (1) this vapor injection mechanism can well eliminate the back-flowing of the injected refrigerant; (2) compared with the traditional injection configuration, the novel structure can enhance the volumetric efficiency 2.62%~3.67%.关键词：rotary compressor;gas refrigerant injection;quasi two-stage compression;volumetric efficiency1945|2107|1发布时间：2024-07-18
- 摘要：Two-phase flow pattern is important for investigating heat transfer coefficients and pressure drops of condensation in horizontal tubes. And the flow pattern maps are the usual approach to predict flow regimes and their transitions. In this paper, a review on flow pattern maps and flow regime transitions of condensation in horizontal tubes of Breber et al. (1980), Tandon et al. (1982), Cavallini et al. (2002, 2006), El Hajal et al. (2003), Kim et al. (2012) and Nema et al. (2014) is presented. Furthermore, this paper presents that there are a few flow pattern maps on the condensation, especially for the microchannel. And the proposed maps could not apply to high pressure and low temperature refrigerants and most recent work didn’t well combine the flow regime with the investigation of heat transfer coefficient and pressure drop.关键词：flow condensation;flow pattern;flow pattern map;horizontal tube2074|2366|5发布时间：2024-07-18
- 摘要：Wavy finned-tube heat exchangers are widely used in outdoor units of air conditioners, and their performance will be decreased when covered by dust particles. The purpose of this paper is to investigate the characteristics of particle deposition on wavy-finned tube heat exchangers. The particle distribution has been observed and the mass of depositing particle has been measured. The range of fin pitch is from 1.6mm to 3.2 mm, the particle concentration is from 80 kg/m3 to 280 kg/m3, the air velocity is from 1 m/s to 3 m/s, and the particle injection time is from 15 s to 90 s. The results show that particles mostly deposit on the leading edge of fins and windward side of tubes. The mass of depositing particle per unit of area increases up to 52% as fin pitch decreases from 3.2 mm to 1.6 mm, meaning that small fin pitch is beneficial to particle deposition. The mass of depositing particle per unit of area increases up to 88.2% with increasing particle injection concentration from 80 kg/m3 to 280 kg/m3, indicating that high particle injection concentration is helpful to particle deposition. The mass of depositing particle per unit of area decreases up to 6.3% as air velocity increases from 1m/s to 3 m/s, revealing that high air speed can restrain particle deposition.关键词：finned-tube heat exchanger;particle deposition;wavy fin;experimental investigation2176|2041|5发布时间：2024-07-18
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Study on Application Scope for CO2 Cascade Refrigeration System and CO2 Secondary Refrigerant System
摘要：The employment of natural refrigerant have drawn widespread attention, since natural refrigerant are completely environmentally friendly and they have high potential in refrigeration application. Among them, the NH3/CO2 cascade refrigeration system and NH3 compression refrigeration system with CO2 as secondary refrigerant have been viewed as the most promising refrigeration methods in freezer and cold storage especially. Nevertheless, there is limited agreement on the scope of application for these two types of system since no strictly related investigation has been conducted. In this paper, the refrigeration performance of the two systems above is analyzed, and conclusion is drawn on the basis of practical engineering applications. The range of application for these two types of system is marked off and explained in detail, aiming at providing reasonable suggestion for design and optimization of CO2 refrigeration systems in the future. It is shown that NH3/CO2 cascade refrigeration system is more competitive when the evaporating temperature is below -25 ℃, and the maximum suction pressure and and the maximum discharge pressure of CO2 compressor should not be lower than 1.97 MPa and 4.07 MPa respectively.关键词：CO2 cascade refrigeration system;CO2 secondary refrigerant;application scope;natural refrigerant;refrigeration performance;CO2 compressor2250|2800|2发布时间：2024-07-18 - 摘要：Due to the poor instantaneity and adaptability, the current methods for sensors fault detection are still less applied in practical project. Based on the decentralized intelligent control system of building, a decentralized algorithm for the faults of slow drift in sensors is proposed. The basic idea of the method is to detect the consistency of variables under the equality and inequality constraints established through physic principle. In the decentralized control system, each sensor is fitted with a decentralized controller such that it become a sensor-agent, which can communicate with other sensors and thus operate collaboratively to check out the faulty nodes assited by Hopfield network. Unlike traditional centralized and distributed algorithms, this algorithm does not need to build a central node, regardless of increasing hardware or time redundancy, with good parallelism and simplicity. In the case of secondary chilled water pump system, this method is verified effective to detect the fault of sensors through simulation result.关键词：central air-conditioning system;building decentralized control system;hopfield network;sensors fault detection2288|2044|3发布时间：2024-07-18
- 摘要：Effects of mechanical vibration on the heat and mass transfer process of absorption refrigerating system had been researched in this paper. A performance appraisal test bench was set up, thus an electrodynamics vibration generator was installed on the bottom of the absorption refrigerating machine to add vertical vibration into the system. Enhancement effects of vibration frequencies and amplitude on the heat and mass transfer process of absorption refrigerating machine were analyzed respectively. The results showed that when amplitude was constant, vibration frequencies had a strong effect on enhancement effect; and under the optimum spray volume and same vibration frequency, the enhancement effect of vibration would be reduced with too high or too low vibration amplitude. And in the range of test, frequency ranges for the best enhancement effect was 20-30 Hz, in these conditions, the enhancement effect of heat transfer could be 8%-20%, the enhancement effect of mass transfer could be 10%-25%, and cooling capacity increased by 12%-18%.关键词：absorption refrigeration;vibration;heat and mass transfer;enhancement2384|1968|2发布时间：2024-07-18
- 摘要：To solve the problem caused by transcritical CO2 compression refrigeration system, a new absorption refrigeration system driven by double low-grade energy was presented based on the principle of energy cascade utilization. Based on mathematical model for each component of the system, an experimental equipment driven by the double low-grade energy were developed. The effect of operating parameters, such as hot source temperature, cooling water inlet temperature and cooled medium, on the system performances had been investigated under constant flow rate. The results showed that the new absorption refrigeration system owned a higher COP and the lowest refrigeration temperature ﹣15.2 ℃ under the same experimental conditions. The study results are helpful to the optimal design.关键词：double low-grade energy;CO2-[emim][Tf2N];absorption refrigeration system;heat and mass transfer;system performance1917|2304|1发布时间：2024-07-18
- 摘要：Heat pump can be used for renewable energy recovery. Several units of renewable energy can be obtained with the consumption of one unit of electric or mechanical energy. Therefore, heat pump is an important energy saving and environmental protection technology. With the significant increase in energy demand and rapid development of electric power industry, the proportion of renewable energy in our country needs to be improved. Thus, heat pump technology plays a critical role. Heat pump technology has been listed as renewable energy in European Union. Then, the corresponding policy for our country is proposed. Based on the data of the power generating efficiency and transmission efficiency, it is concluded that heat pump is a technology for renewable energy recovery. Two calculation methods, including primary energy multiple α and renewable energy contribution rate β, are introduced, to provide a reference for the industry. The target of flue gas emission for power plant is much more stringent than the common coal-fired boiler, so utilizing heat pump to replace coal-fired boiler can improve atmosphere environment. It is suggested that the calculation method of renewable energy contribution rate for heat pump should be listed as a national standard. The heat pump manufacturing industry should be further developed, and heat pump technology should be widely applied.关键词：heat pump;renewable energy;primary energy utilization ratio;SPF;renewable energy contribution rate2028|2104|2发布时间：2024-07-18
- 摘要：Printed circuit heat exchanger with its compact, efficient, reliable characteristics can meet the requirements of the main cryogenic heat exchanger in the offshore floating natural gas liquefaction. In recent years, it has gradually become the first priority of main cryogenic heat exchangers of offshore floating natural gas liquefaction. In this paper, the progress of research and application of printed circuit heat exchanger in recent years, including the basic principle, manufacturing process based on diffusion welding, heat transfer and pressure drop characteristics, and mechanical behaviors, is reviewed; the application status of printed circuit heat exchanger in offshore LNG platform is summarized; and the key technologies that requires to be overcome in future applications in offshore LNG platform is proposed, including thermal design, manufacturing process, detection technology.关键词：offshore floating liquefied natural gas;diffusion welding;heat transfer;pressure drop;printed circuit heat exchanger1985|2318|2发布时间：2024-07-18
- 摘要：The application of hydrate technology can be divided into hydrate dissociation and hydrate formation. Both area of gas hydrates technology have been reviewed in this paper. Regarding the trend of dissociation, the progress of gas hydrates exploitation, hydrate plug removal in pipe, hydrate inhibition and hydrate anti-agglomeration are introduced. Regarding the reverse of dissociation, i.e., formation, gas storage, carbon capture and sequestration, seawater desalination, solution concentration, sewage treatment, mixed gas separation and cool storage in the form of hydrate are also summarized. According to the development of the gas hydrate, great achievements and some challenges are pointed, which is expected to provide useful guide on the future development of gas hydrate technology.关键词：gas hydrates;dissociation;formation;review1849|2195|9发布时间：2024-07-18
- 摘要：Elliptical tube heat exchanger has been widely used in heat exchange equipment due to its good flow and heat transfer characteristics. In this paper we use computational fluid dynamics method to simulate the flow field and sound field generated by the indoor unit of air conditioner with elliptical finned tube heat exchanger , and make comparison with circular tube heat exchanger. The results show that for the inside the cross-flow, the structure of tubes in heat exchangers has no effect on the location and size of the eccentric vortex; compared with the circular tube finned heat exchanger with the same cross-sectional area, the air conditioners using elliptical tubes work better on increasing the air volume, improving cooling effect and reducing noise especially low-frequency noise under the same conditions. Above all, the conditioner using elliptical tubes in which the ratio of the long axis and short axis is 2.0 can reduce noise 4 dB.关键词：air-conditioner indoor unit;elliptical tube;noise reduction;numerical simulation1961|2022|1发布时间：2024-07-18
- 摘要：In order to develop a distributor for small-diameter air conditioner with a best distribution performance, a CFD model was established and experiments with air and water as working fluids were done to evaluate distribution performance of three types of commonly used distributors. The CFD model was validated by the experiments, the structure of the chosen distributor was optimized, and the optimized distributor was verified by its application in a room air conditioner. The results show that, the jack-type distributor has the best distribution performance, and its uneven index are less than 6% under rated cooling and rated heating conditions; the CFD model can predict the performance of distributors, with the deviation of uneven index less than 15%. The validated CFD model was used to optimize the structure of the jack-type distributor. Application of the optimized distributor shows that it can enhance the energy efficiency of room air conditioner by 2.2%~ 2.7%.关键词：small-diameter air conditioner;distributor;distribution uniformity;structure optimization1898|2270|3发布时间：2024-07-18
- 摘要：A multi-split variable refrigerant flow rate (VRF) air conditioning system with reheat dehumidification was built in the paper. With the VRF system, the dehumidification amount was experimentally studied under 6 operating conditions. The influences of opening degree of reheat electronic expansion valve (EVW) and reheat heat exchange area on outlet air temperature of indoor unit were experimentally investigated in detail. The experimental results indicated that the employment of parallel reheat heat exchanger increased the dehumidification amount of the VRF system effectively; the dehumidification amounts of indoor unit 1# and 2# increased by 11.7%~40.4% and 10.5%~28.9%, respectively. Optimal EVW opening degree existed for reheat heat exchanger to obtain the maximum reheat temperature difference; the optimal EVW opening degree increased with the decrease of indoor temperature Ti. For purpose of isothermal dehumidification mode, the required EVW opening degrees of indoor unit 1# and 2# were 9.6%~9.9% and 6.5%~7.0%, respectively. For purpose of dehumidification mode with To＞Ti, the required EVW opening degrees increased with the decrease of both indoor temperature and reheat heat exchange area.关键词：variable refrigerant flow rate system;air-conditioning system;electronic expansion valve;refrigeration performance test;dehumidification2132|2625|3发布时间：2024-07-18
- 摘要：In order to explore the effect of DC electromagnetic field of different field strengths on the shape and size of cells and ice crystals during the freezing phase transformation process of plant tissue cells, the third layers of onion cut into squares of 0.5 cm×0.5 cm were studied. Put the onion slices on the cold platform and the cooling rate of the experiment was: 10 ℃/min before 0 ℃, 3 ℃/min after 0 ℃, and the final temperature was﹣25 ℃, the DC magnetic field strengths were 0Gs (the control group) , 4.6 Gs, 18 Gs, 36 Gs, 72 Gs respectively. In the experiment, the changes of morphology of the cells and ice crystals under different strengths were observed, and the index of "two-dimensional cell retention rate ζ" was put forward to evaluate fruit and vegetable cells’ freezing effect. AutoCAD software was used to calculate the micrograph and the value of ζ. The results show that the magnetic field assisted freezing of the onion cells can make the formation of ice crystals tend to atomization and sand grains, which can inhibit the growth of ice crystals, thus reduce the size of the ice crystals, and it will also be more conducive to maintain the original cell morphology and decrease the cell damage rate. With the increasing of the magnetic field strength, phase transformation time of the onion cells decreases, supercooling degree decreases gradually, but it is always higher than that of non magnetic field.关键词：food processing technology;DC magnetic field freezing;morphology of ice crystals and cells;onion1986|1968|5发布时间：2024-07-18
- 摘要：A water-cooled tube-in-tube gas cooler was designed in this paper, and experimental researches on it were conducted. A triple tube is equipped in the gas cooler with CO2 in the inner tubes and water between inner and outer tubes. Experimental investigations were done about the effect of CO2 mass flow rate, inlet pressure and cooling water temperature on heat transfer coefficient, heat transfer and heat exchanger efficiency. The results show that both heat transfer coefficient and heat transfer firstly increase and then decrease while CO2 mass flow rate increases, and heat exchanger efficiency reduce gradually when CO2 mass flow rate increases. In the same CO2 mass flow rate, heat transfer coefficient, heat transfer and heat exchanger efficiency increase with the increase of CO2 inlet pressure and decrease while cooling water temperature increases.关键词：tube-in-tube gas cooler;heat transfer performance;triple tube1877|2021|4发布时间：2024-07-18
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