最新刊期
卷 41 ， 期 6 ， 2020
- 摘要：At present, different fields have different requirements for humidity. The industry does not have a unified standard for the division of dehumidification levels, which is likely to cause confusion and inconvenience when multiple fields are crossed. To solve the above-mentioned problems, this study analyzes the existing dehumidification technology. It introduces the dehumidification requirements of comfort air conditioning, equipment air, industrial production, and other fields. The dehumidification level is uniformly divided. After dehumidification treatment, a dew point >?20 ℃ is considered as shallow dehumidification, a dew point between ?20 ℃ and ?65 ℃ is considered as deep dehumidification, and a dew point 65 ℃ is considered as extremely deep dehumidification. The latest research progress in deep dehumidification technology can be summarized as follows: for freezing dehumidification, direct evaporative refrigeration and pressurized freezing dehumidification can reduce the dew point of the outlet air to less than ?10 ℃ to ?20 ℃; for solution dehumidification, the dew point of the outlet air can reach ?10 ℃ to ?20 ℃, or even lower, by cooling the dehumidifying liquid or compressing the humid air.关键词：dehunidification level;deep dehumidification;dew point;dehumidification requirement;dry environment1673|2340|3发布时间：2024-12-12
- 摘要：Swirl separation technology based on the supersonic refrigeration effect is a new method to remove water, heavy hydrocarbons, and other impurities from natural gas. In this article, first, the typical structure of a supersonic swirl separator and Laval nozzle design are reviewed; thereafter, the condensation phase transition theories of one-component and two-component gases are summarized. Subsequently, the effects of inlet and outlet parameters and nozzle structure parameters on the condensation characteristics of supersonic flow are summarized; finally, new applications in the fields of natural gas liquefaction and acid gas removal are reviewed. Although many domestic and international scholars have conducted considerable research, some problems still remain, and future prospects for supersonic swirl separation technology have been proposed.关键词：supersonic refrigeration effect;swirl separator;Laval nozzle;condensation characteristics;natural gas1707|1744|0发布时间：2024-12-12
- 摘要：When operated under low ambient temperature conditions, the frosting rate of a microchannel evaporator is high, which restricts its application in refrigeration systems. In terms of the frosting phenomenon of a microchannel heat exchanger, this paper summarizes the factors that affect the frosting characteristics, the research on inhibition of frosting, and simulations of frosting characteristics. The factors that affect the frosting characteristics of a microchannel heat exchanger primarily include external factors (environmental parameters, surface temperature, and condensate), structural factors (heat exchanger installation direction, fin structure, fin density, coating, and fouling), and internal factors (refrigerant distribution). To improve the frosting characteristics of a microchannel heat exchanger, the fin structures can be optimized to obtain better drainage performance and more uniform frosting characteristics. Future research focuses on the development of a microchannel heat exchanger with better frost suppression performance and the establishment of a higher-precision simulation model.关键词：micerochannel heat exchanger;frosting characteristics;impact factors;fin structure1615|1888|2发布时间：2024-12-12
- 摘要：Responding to the applied air-conditioning requirements for electric cars, an experimental bench for the R290 heat pump system with a secondary medium cycle was established. The cooling and heating performances of the system were tested under various working conditions. As the compressor speed increases from 1800 r/min to 6600 r/m, the cooling capacity increases from 1789 to 4027 W under standard conditions (35 ℃), while the COP decreases from 3.65 to 1.82. As the compressor speed increases from 2700 r/min to 4500 r/min, the cooling capacity increases from 1973 to 3031 W under extremely warm conditions (45 ℃), while the COP decreases from 2.10 to 1.88. Under cold conditions (?20 ℃), the heating capacity of the system reaches 2911 W at 6000 r/min, and the corresponding COP is 1.80. Under extremely cold conditions (?25 ℃), the heating capacity reaches 1685 W at 3600 r/min, and the COP is 2.16. Meanwhile, the system adopted the form of secondary heat transfer, which improved the safety and reliability. However, compared with the primary circuit, the cooling capacity is attenuated by 300–500 W, and the heating capacity is attenuated by 200–400 W.关键词：heat pump;eletric vehicle;R290;performance of the system1574|2693|1发布时间：2024-12-12
- 摘要：Heat pump air-conditioning systems play an important role in meeting the winter heating needs of electric vehicles. In this study, the new refrigerant R1234yf, which has a low GWP value, was used for the working medium. The low-temperature heating performance of the electric vehicle heat pump air-conditioning system was tested at ?20 ℃ to 7 ℃. The winter heat load of the electric vehicle was calibrated. The refrigerant charge amount, heating performance, COP, and discharge temperature of the system were studied and compared with those of refrigerant R134a. Exergy loss of system components was analyzed, and the system was also optimized. The results show that the optimal refrigerant charge amount of the system was 1551 g, and the heating capacity and COP reached greater than 2 kW and 1.8, respectively, under most working conditions, which could meet the needs of heating at low temperatures. When directly substituted, the heating capacity and COP of the system were 7.1% and 6.6% lower than that of the R134a system. The discharge temperature of the R1234yf heat pump system is 5.3 ℃lower than that of R134a, which could make the system more stable and reliable. The exergy loss of the inner condenser and compressor accounts for more than 80% of the total exergy loss of the system, which is the key optimization parameter for heat pump air conditioning. Increasing the heat transfer area of the inner condenser, increasing the air volume, and improving the compressor speed can significantly improve the heating performance of the system, making it basically equal to or even better than the R134a system.关键词：electric vehicle;heat pump;R1234yf;system performance;exengy loss analysis1648|2218|3发布时间：2024-12-12
- 摘要：Focusing on the problem wherein the outdoor heat exchanger of a vehicle heat pump system is prone to frost in winter, this study designs and builds a corresponding experimental system for testing. The frost and defrost characteristics of the outdoor heat exchanger were studied. Then, the effects on defrosting time of two different electronic expansion valve (EXV) calibers,?2.1 mm and ?3.0 mm, were compared. The experimental results show that the degree of frosting on the heat exchanger can be judged by the change rate of the suction temperature or pressure relative to the non-frosted state, and the completion of defrosting can be judged by the temperature by which the outdoor heat exchanger outlet exceeds 0 ℃. For defrosting conditions with different ambient temperatures and different frost layers, the impact of EXV caliber on defrosting time is not consistent. The EXV with a large caliber has a good defrosting effect in the early stage, but in the later stage, it is not as good as the EXV with a small caliber because the compressor exhaust pressure of the large-caliber EXV rises slowly, causing the inlet temperature of the outdoor heat exchanger to increase slowly. Therefore, in real vehicle applications, a larger caliber EXV can be used in combination with intelligent control to achieve the best overall defrosting effect.关键词：heat pump;electric vehicle;frost and defrost;defrost efficiency1545|2081|3发布时间：2024-12-12
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Experiment on Temperature- and Humidity-Controlled Air Conditioner with Dual Evaporation Temperature
摘要：To address the problems of energy waste and imbalance between heat and humidity in traditional combined heat and moisture treatment, the annual hourly energy consumption of a residential building in Shanghai was simulated by EnergyPlus software in this study. According to the simulation results, the independent temperature and humidity control technique was combined with dual evaporative temperature compressor, and a temperature- and humidity-controlled air conditioner test bed was established based on dual evaporation temperature. Relevant theoretical calculations were performed, and the operational characteristics of the air conditioner under whole-year operation conditions were experimentally investigated. The results show that it is feasible to use an air-conditioning unit with a double evaporative temperature compressor in an air-conditioning system with separately controlled temperature and humidity, which meets the design requirements and has obvious energy efficiency. In summer, the energy efficiency ratio of the compressor is 3.5, which is 14.8% higher than that of the inverter compressor of conventional air conditioning with the same cooling capacity (3.04). At the same time, the energy efficiency ratio of the unit compressor under the design conditions in winter is 4.3. Compared with the inverter compressor of conventional air conditioning with the same cooling capacity, the air conditioner with dual evaporation temperature shows remarkable energy savings.关键词：air conditioner unit;independent temperature and humidity control;dual evaporation temperature;energy efficiency ratio1572|1643|0发布时间：2024-12-12 -
Defrosting Characteristics of Refrigeration, Heating, and Hot Water Combined Air-conditioning System
摘要：Frost on the surface of an outdoor heat exchanger will seriously affect the operating performance and safety factor of a refrigeration-, heating-, and hot-water combined air-conditioning system when it is operating in winter. According to the defrosting strategy of the system, the influence of different defrosting temperature sensor positions on the defrosting characteristics of the unit is explored by carrying out experimental research. The results show that when the position of the defrosting temperature sensor is located at measuring point 2 and measuring point 5 on the surface of the outdoor heat exchanger, the duration of the system fluctuation during the frosting process is 2280 s and 220 s, respectively. The defrosting time was 5 min and 12 min, respectively, when the defrosting temperature sensor was located at measuring point 2 and measuring point 5. In addition, the time during which the superheat degree of the system continued to be negative in this process was 185 s and 80 s, respectively. Considering the safety of the system, it is recommended that the defrosting temperature sensor be placed at measuring point 5.关键词：air-conditioning;refrigeration, heating and hot water combined system;operating characteristics;degree of superheat;defrosting temperature;defrosting time1499|1736|0发布时间：2024-12-12 - 摘要：The power consumption of a data center cooling system accounts for approximately 40% of the total energy consumption of the data center, so establishing an evaluation strategy to evaluate the efficiency of the data center cooling system is very important for energy conservation. This paper presents an comprehensive COP evaluation strategy with the index COPdc for evaluating data center cooling systems. Based on the simulation results of the cooling system operation, the energy efficiency of the data center cooling system is evaluated using the COPdc evaluation strategy. The characteristics of the comprehensive COP strategy are discussed by comparing them with the PUE. The results show that under a variety of load and temperature conditions, the variation range of COPdc (4.51~5.44) is larger than that of PUE (1.19~1.21), which suggests that COPdc can more prominently show the change in power consumption of the data center cooling system. The comprehensive COP evaluation strategy of the data center cooling system proposed in this paper can quantify the energy efficiency of the data center cooling system and evaluate the energy efficiency more specifically compared with PUE.关键词：cooling system;data center;PUE;COPdc1607|3848|2发布时间：2024-12-12
- 摘要：To reduce the energy consumption of air conditioning and improve heat exchange efficiency in data center, this paper proposes a composite air conditioning system combined dew-point indirect evaporative cooling, which involves a combination of counter-flow and cross-flow heat exchangers, with mechanical refrigeration. A test bench was built for the composite air conditioning system, and the system performances under dry conditions and high-humidity conditions with return air temperatures of 26 ℃ and 35 ℃were tested. The experimental results show that: (1) In the wet mode, when the return air temperature is lower than 26 ℃, the maximum wet-bulb efficiency of the unit under dry conditions is 97%; when the return air temperature of the simulated data center is higher than 35 ℃, the wet-bulb efficiency of the unit under dry conditions is approximately 110%, and the wet-bulb efficiency of the unit under high-humidity conditions is also 99%; (2) In the mixed mode, the wet-bulb efficiency of the dew-point indirect evaporative cooler under dry conditions and high-humidity conditions is approximately 120% and 110% respectively. The test results show that the dew-point indirect evaporative cooling technology is more suitable in dry areas, and auxiliary mechanical refrigeration is required in medium- and high-humidity areas. In particular, when the return air temperature is low, the effect of evaporative cooling under high-humidity conditions is limited and the auxiliary mechanical refrigeration is needed to meet the air supply requirements. When the return air temperature is high, evaporative cooling can reduce the time required for mechanical refrigeration.关键词：dew-point indirect evaporative cooling;mechanical refrigeration;data center;wet bulb efficiency1748|2060|0发布时间：2024-12-12
- 摘要：To explore a microemulsion with stable performance and repeatable ice slurry preparation, liquid paraffin was used as the oil phase, compounded with fatty alcohol polyoxyethylene ether (AEO-9), sodium oleate as the surfactant, and hexanol as the surface agent. The active agent was used to prepare a microemulsion, and a stability test of the prepared microemulsion was conducted and an ice slurry was formed. The results of conductivity and temperature experiments indicate that when the water content is less than 36.9%, a clear and transparent W/O type microemulsion can be prepared, and the microemulsion can remain stable in the temperature range of 0.2–30 ℃. Centrifugation tests and storage tests suggest that the microemulsion has good stability. The microemulsion remained stable after 300 thermal cycles between ?3℃and 30 ℃, which demonstrates the reusability of the microemulsion for cold storage. The ice slurry was prepared using a microemulsion. The microemulsion system has a crystallization point of ?0.8 ℃ and a subcooling degree of 0.2℃, which can overcome the defects of a large degree of subcooling and low crystallization point in the traditional ice slurry preparation. Meanwhile, the ice crystals do not adhere to the wall surface, and the fluidity of the ice slurry is suitable.关键词：ice slurry;cold storage;microemulsion;surfactant;phase change1475|1625|0发布时间：2024-12-12
- 摘要：As a type of functional material, nanofluids are widely used to enhance heat transfer; however, as a cold storage agent, there are few studies on its initial freezing temperature. In this study, Al2O3 particles with a particle size of 500 nm were used, and three different cooling rates (1, 5, and 10 ℃/min) and three different mass fractions (0.01%, 0.05%, and 0.1%) were used to study the freezing point of the Al2O3-H2O nanofluid. The relationship between the cooling rate and particle concentration was investigated. The samples were divided into nine groups, and each group was tested 60 times; the initial freezing temperature was recorded to obtain its probability distribution. The results show that the initial freezing temperature value is approximately Gaussian; increasing the cooling rate will reduce the initial freezing temperature of the fluid during freezing; however, at different cooling rates, the initial freezing temperature and nanofluid mass fraction do not show the same trend: with an increase in the cooling rate, the initial freezing temperature gradually changes, first decreasing and then increasing with an increase in the nanofluid concentration. Moreover, the degree of influence of heterogeneous crystallization on the initial freezing temperature is greater than that of the solution viscosity.关键词：Al2O3-H2O nanofluid;initial freezing temperature;distribution probabilit;cooling rate1390|1598|0发布时间：2024-12-12
- 摘要：To study the surface temperature distribution characteristics and related control methods of cryogenic non-thermal equilibrium cylinders under complex heat transfer conditions, this study establishes two models of heat transfer enhancement methods appended to pure top ventilation: an additional local nozzle air supply and a radiation screen. The temperature characteristics, such as radial temperature gradient, body temperature non-uniformity, and surface temperature non-uniformity of the cylinder, are analyzed by numerical simulation methods. The accuracy of the numerical simulation results was verified by experiments. On this basis, the influence of different heat transfer methods and operating parameters was quantitatively analyzed. The results show that, compared with simple top ventilation, the local nozzle air supply can increase the average temperature decrease of the cylinder by 5.1%, the temperature non-uniformity of the cylinder can be increased by 38.3%, and the temperature unevenness of the cylinder surface can be reduced. The temperature gradient of the cylinder was controlled on the side near the heat-conducting surface. With the addition of a cryogenic radiation screen, the coupled heat transfer of convection and radiation can reduce the average temperature decrease of the cylinder by 2.3%, increase the temperature unevenness of the cylinder by 57.5%, and reduce the temperature unevenness of the cylinder surface.关键词：convective heat transfer;radiative heat transfer;coupling effect;temperature uniformity1471|1715|0发布时间：2024-12-12
- 摘要：Among all cold chain equipment, the energy consumption of an open refrigerated display case is usually high, especially the dual-temperature display cabinet, which provides simultaneous heating and cooling and consumes even more electricity. The condensing heat can be used for heating and therefore will lead to significant energy savings for the dual-temperature display cabinet. This paper simulates a dual-temperature display cabinet with condensing heat recovery. Employing COP and effective heating power as the indices, the optimization direction of each component in the refrigeration system is determined, and its performance is compared with the baseline cabinet with an electric heater. The simulation results of the baseline cabinet are validated by experimental results, and the energy-saving potential of the new system is studied. Simulation results suggest that the dual-temperature display cabinet with condensation heat recovery has significant energy-saving advantages. The key is the air volumetric flowrate of the condenser. It is recommended to install a variable-speed fan, which can produce optimal air volumes of 0.018 m3/s, 0.03 m3/s, 0.045 m3/s, and 0.095 m3/s at ambient temperatures of 15 ℃, 20 ℃, 25 ℃, and 32 °C, respectively. When the condenser air flow rate is kept at 0.06 m3/s, the cabinet has a decent energy-saving potential when the ambient temperature is high. The best energy savings is achieved when the ambient temperature is 25 ℃, with a reduction in power consumption of 52%.关键词：open display cabinet;condensing heat recovery;steady state simulation;air flowrate1485|1630|0发布时间：2024-12-12
- 摘要：In this study, an experimental study of the axial force on twin-screw compressor rotors was conducted to improve operating reliability. The variations in the axial force under different operating conditions and built-in volume ratios were investigated. Furthermore, the axial force of the end face was also calculated by employing the mean pressure model and sector pressure model and was compared with the experimental results. It was concluded that the sector pressure model is more accurate for predicting the axial force on the rotors in comparison with the mean pressure model. However, the mean pressure model was more accurate under operating conditions with a large built-in volume ratio. Moreover, the built-in volume ratio was found to have a larger influence on the axial force of the rotor end face than that on the rotor helical surface, where the former is approximately 50% larger than the latter.关键词：twin-screw compressor;rotor axial force;gas axial force;axiaal force of end face1381|1909|1发布时间：2024-12-12
- 摘要：In the environmental test of precision electronic components, the uniformity and fluctuation of temperature field in the environmental test chamber are very important to the test result. To develop an environmental test chamber with high performance, sevarel chamber structure models were proposed first from the view point of temperature field and velocity field on the basis of traditional clockwise and counterclockwise box structures. Then, the temperature field with different air flow patterns were simulated, in which different angle, position and velocity of supply air are included and considered. Finally, the simulation results were verified based on a test chamber prototype with return air in the center. The results showed that the average temperature and temperature standard deviation were similar for the three cases: 0°angle of supply air with clockwise structure, return air at the center position with counterclockwise structure, and multiple outlets. There was still a gap between the experimental and simulation data regarding the standard deviation of temperature uniformity. The average temperature and temperature standard deviation of all measuring points was ?71.55 ℃ and ?1.55 ℃. The maximum temperature deviation of all measuring points was 1.8 ℃. However, after the data were decentralized, the temperature at each point had a similar distribution.关键词：environmental test chamber;temperature field;structural design;uniformity1503|1791|1发布时间：2024-12-12
- 摘要：Open rack vaporizers are basic load vaporizers that are widely used in LNG terminals. However, there are few experimental studies on the fluid flow and heat transfer behaviors of supercritical natural gas. In this study, nitrogen was used to replace natural gas, and the heat transfer characteristics of supercritical nitrogen in a heated vertical tube were investigated experimentally. The effects of various operating parameters, including nitrogen pressure, inlet temperature, and mass flow of water, on the heat transfer characteristics were investigated. The surface coefficient of heat transfer decreased with increasing pressure below the pseudocritical temperature, while the variation of the surface coefficient of heat transfer was opposite to that of the pseudocritical temperature. The outlet temperature of nitrogen was determined by the water temperature instead of the mass flow rate when the mass flow rate of water was sufficiently large. A new correlation was developed for the heat transfer of a supercritical cryogenic fluid based on the experimental data, and the mean absolute relative deviation between the predicted values and the experimental data was 8.42%. This new correlation can be used to accurately predict the surface coefficient of heat transfer of supercritical nitrogen in a vertical heating tube.关键词：vaporizer;cofficient of heat transfer;supercritical nitrogen;vertical tube;correlation1395|1609|1发布时间：2024-12-12
- 摘要：To optimize the thermal performance of small-volume vaccine cold storage, a 20 m3vaccine cold storage with a working temperature of 2–8 ℃ belonging to the Jiangsu Province CDC was investigated. Steady temperature fields under different working conditions and unsteady temperature fields 60 s after opening the door at opening angles of 30°or 90°were measured. By establishing a mathematical model, the structure of cold storage was simulated, and the optimized refrigeration effect and temperature field uniformity in cold storage were systematically analyzed considering both the measurement period and stable running time; in addition, the existing evaluation indexes were extended in the evaluation. The results show that when the length L≥width W, the optimal arrangement scheme for the small-volume vaccine cold storage is two air coolers with proper refrigerating capacity located in the L direction. When L=W, the vaccine cold storage is the optimal structure. Considering the influence of door opening, the positions of the vaccine boxes should be given sufficient attention. It is suggested that the stacking height of vaccine boxes be kept within 1.5 m, the distance from the doorway should be within 1.5 m, and the overall stacking height should not exceed 1.8 m.关键词：cold storage;vaccine storage;thermal performance;temperature field1439|1755|5发布时间：2024-12-12
- 摘要：For the high-power insulated gate bipolar translator (IGBT) module, which is presently used in the converter of CRH2, four types of high-efficiency cooler for the traction converter of CRH2 were designed. Using FLUENT to simulate four types of cooler models and comprehensively analyzing and comparing the simulation results, cha-30×10 was determined to be the best cooler model, and the optimal model was quadratically optimized. The optimal scheme was determined to be the 160° cooler, and the relationship between the maximum temperature, maximum thermal resistance, pressure drop, and the flowrate of coolant was obtained. With an inlet mass flow rate 0.1 kg/s, the simulation results show that the maximum temperature of the cha-30×10 (160°) cooler is 3 K lower than that of shun- 20×10, and the maximum thermal resistance is 7.8% lower than that of shun-20×10.关键词：radiator;insulated gate bipolar translator(ICBT);numerical simulation;cofficient of performance1662|1635|1发布时间：2024-12-12
- 摘要：The effects of cooling rates (5, 10, 20, 50, 100 ℃/min) and solution concentration (0.5, 1, 2, 3, 4 mol/L) on the thermo-physical parameters of typical amino acid aqueous solutions ，such as L-lysine, L-proline, glycine ，and L-serine, were investigated viadifferential scanning calorimetry ( DSC). The results indicated that the effect of solution concentration on thermos - physical parameters of cryoprotectant solution was more significant than that of the cooling rate. At low concentrations (0. 5 mol/L and 1 mol/L) ，the unfrozen water content of L-proline was higher than that of other three amino acids. This indicates that the water-binding capacity of L-proline was higher than that of other three amino acids in low concentration solution. At high concentrations ( 2 mol/L and 3 mol/L) , the unfrozen wa-ter content of L-lysine was higher than that of the other three amino acids. Given that the concentration of the L-lysine functional group is higher than the other three amino acids in the same concentration solution and the longer molecular chain thereof leads to a lower probabili-ty of self-bonding of the functional group, a higher unfrozen water content was exhibited in the solution system.关键词：thermophysical parameters;diferential scanning calorimetry (DSC);amino acid cryoprotectants;ice crystals inhibition;um-frozen water content1451|1922|4发布时间：2024-12-12
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