最新刊期
卷 41 ， 期 2 ， 2020
- 摘要：A pump-driven two-phase circulation loop system was built for data center cooling in order to make full use of the ambient energy. In this study, the cooling loss characteristic of working fluid pump was investigated by changing the system temperature difference, pump frequency, heat exchange area, temperature of the high and low-temperature water jacket. The results showed that the cooling loss rate would be minimum at a temperature difference of 16 ℃, frequency of 15 Hz, and a large heat exchange area when the temperature of high-temperature water jacket was kept constant. When the temperature of low-temperature water jacket was kept constant, the cooling loss rate with five evaporators and five condensers under different temperatures was the smallest and less than 3.20%. The higher the temperature of high- temperature water jacket, the lower the cooling loss rate. When the temperature of high-temperature water jacket was 26 ℃, the cooling loss rate was the lowest and did not exceed 2.82%.关键词：data center;free cooling;pump-driven loop;cooling capacity;cooling loss rate2005|2575|1发布时间：2024-07-18
- 摘要：The phase change materials can collect fluctuant solar energy and other low-grade energy to form a stable energy source for building insulation and the terminal equipment of the buildings. In this study, lauric acid and stearic acid were selected as the basic phase change materials. The binary equilibrium phase diagram was completed based on the step cooling curve method according to experimental tests data. The results showed that the phase transition temperature of the mixed acid at the lowest eutectic point was 31.2 ℃, and the latent heat value was 264.3 kJ/kg when the mixing ratio was 70% for lauric acid and 30% for stearic acid. Secondly, in order to improve the thermal stability and thermal conductivity of the mixed acid, silicon dioxide with a three-dimensional network structure was added to the mixed acid. The experimental results showed that when the proportion of the silicon dioxide in the hybrid materials was 35%, the mixed acid could be completely wrapped up by tetrahedral silica to form a stable phase unit change. Multiple cyclic experiments showed that the phase transition temperature of the hybrid phase change material was 30.8 ℃ and its latent heat value was 104.1 kJ/kg. Although the latent heat decreased, the thermal stability was greatly enhanced.关键词：lauric acid;stearic acid;silicon dioxide;phase change materials;step cooling curve1879|3171|0发布时间：2024-07-18
- 摘要：For the efficient operation of the cooling and dehumidification system, the relationship between dehumidification and the inlet air speed, dry bulb temperature, and relative humidity of evaporator is numerically analyzed. The results show that, when inlet air temperature and humidity are kept constant, dehumidification capacity increases first and then decreases with an increase in the inlet air speed. When the moisture content and the speed of the inlet air are constant, the dehumidification capacity gradually decreases with an increase in the dry bulb temperature of the inlet air. When the dry bulb temperature of inlet air is between 21-36 ℃ and its relative humidity is between 40% and 85%, the difference between the wet bulb temperature of inlet air- and its evaporation temperature at the optimum COP is about 10 ℃. There is a nearly linear relationship between the corresponding evaporation temperature at the optimal COP and the evaporation temperature with the maximum dehumidification capacity. After compared with the test data, it shows the error of the numerical model is less than 10%.关键词：dehumidification capacity;simulation;evaporator;linear relationship2089|2713|2发布时间：2024-07-18
- 摘要：An aircraft’s environment control system provides the proper environment for its safe and stable flying. The refrigeration and air-conditioning systems are the core parts of an aircraft. The functional requirements, thermodynamic principles and system processes of refrigeration and air-conditioning systems are introduced. Air compression refrigeration cycles (such as basic cycle, two-wheel booster refrigeration cycle, three-wheel booster refrigeration cycle, four-wheel booster refrigeration cycle, and reverse booster refrigeration cycle), vapor compression refrigeration cycles, and combined refrigeration cycles are compared. The advantages and disadvantages of high-pressure water separator and low-pressure water separator are also discussed. Advanced refrigeration and air-conditioning technologies, such as thermos-electric refrigeration system, pneumatic control, humidifying technology, loop heat pipe, etc. are also introduced. Research directions and key technologies for the future are summarized.关键词：aircraft environmental control system;air-conditioning;air compression refrigeration;vapor compression refrigeration;dehumidification1961|3837|4发布时间：2024-07-18
- 摘要：The uniformity of deuterium-tritium (DT) ice layer plays a key role in the successful ignition of indirective inertial confinement fusion (ICF), and is closely related to the temperature field of the cryogenic target, especially the temperature uniformity around the fuel capsule. In this study, CFD simulation is performed on the thermal field of cryogenic target using a spherical hohlraum under stable and unsteady cooling conditions. Two kinds of ablation layer material, i.e., the hydrocarbon (CH) and the high-density carbon (HDC) are considered, and the effects of DT ice profile on their temperature distribution are analyzed. The results show that the high thermal conductivity of the target material has a positive effect on improving the field uniformity of the target’s temperature. If the thermal conductivity of an ablative material is higher than 400 W/(m·K), the temperature difference on the outer surface of the target will be less than 0.01 mK. In the cooling process, the HDC target with higher specific heat capacity and thermal conductivity provides a much smaller temperature difference than the CH target.关键词：cryogenic target;temperature uniformity;ablative material;deuterium-tritium ice;numerical simulation1852|2394|0发布时间：2024-07-18
- 摘要：In order to study the evolution of the size of ice crystal during its flow in horizontal straight pipes, both experiment research and numerical simulation were performed in this study. The size distribution and evolution of ice crystals for different sub-cooling degrees, flow velocities, and Ice Packing Fractions (IPF) were studied by numerical simulation using the CFD-PBM coupling model, and the numerical simulation was then verified by experiment. The results show that the distribution of ice number density could be approximately described by Gaussian distribution at the entrance of the ice slurry pipe with an IPF of 15%. With the increase in velocity and IPF, the average size of ice crystal increases along the central axis. Additionally, the size distribution of ice crystals gets more uneven along the vertical direction. With the decrease of flow velocity and the increase of IPF, the peak value of the length number density distribution of the ice crystal’s particle size increases, and the average value of the corresponding ice crystal’s particle size decreases.关键词：ice slurry;CFD-PBM coupled model;kinetic model;numerical simulation;ice crystal size1956|2205|2发布时间：2024-07-18
- 摘要：Thermoelectric coolers (TEC) can enhance the cooling performance of the radiator but are greatly affected by parameters such as heat dissipation intensity, working current, and working heat-load. In this study, the finite element analysis model of TEC enhanced air-cooling module is established, and the system theory and experimental research on the temperature distribution and operating characteristics of the module are carried out. The study proposes a method to determine the effective operating current, heat load, and cooling coefficient range of TEC enhanced air-cooling module. Simulation and experimental results indicate that there is a limit heat-load Qc,max for a specific TEC enhanced air-cooling module, only when the working heat load Qc关键词：thermoelectric cooler;operating characteristics;air cooling;finite element analysis1973|2564|8发布时间：2024-07-18
- 摘要：Dynamic ice-making technologies with super-cooled water can produce ice slurry efficiently; however, the prominent problem in the stability of this method is that ice blocking easily takes place in the super-cooling heat exchanger. This study developed a dynamic ice-making system based on a modular super-cooling releasing device which was set inside a super-cooled heat exchanger. Its main structure are dismountable spiral blades that can release super-cooled state of solutions and scrape the ice on the heat transfer surface. The performance test of the ice making system under different working conditions shows that the ice making system can stably produce ice slurry and effectively improve the ice-blocking problem. The highest ice packing fraction reached 9.1%, the maximum continuous ice making time was up to 521 s. The ice packing fraction increases with the continuous ice-making time. When the mass fraction of sodium chloride solution was 6%, the ice packing fraction and continuous ice-making time were significantly improved. The experiment obtained the optimal operating parameters of the ice making system: the flow rate of the ice making solution is 0.50 m3/h, the secondary refrigerant temperature is ﹣15 ℃, and the rotating speed of the spiral blades is between 175~225 r/min.关键词：ice slurry;degree of subcooling;ice-making capacity;phase change1697|2064|2发布时间：2024-07-18
- 摘要：Desiccant materials play a key role on the dehumidification performance of desiccant coated heat exchanger (DCHE). The equilibrium water adsorption capacity and adsorption kinetics of Na+ and K+ modified polyacrylic acid salts were tested using an improved gas adsorption analyzer (ASAP 2020) and a constant temperature humidity chamber, with conventional silica gel as reference. Researches on equilibrium adsorption show that, Na+ modified polyacrylic acid salt had a water uptake much higher than that of silica gel, while the K+ modified one was inferior to silica gel at a relative humidity range higher than 0.8. Besides, sorption characteristic curves were fitted based on the Polanyi potential theory and can be used in simulating dehumidification performance. Adsorption kinetics tests displayed that the rate coefficients of both ions modified by polyacrylic acid salts were lower than that of silica gel; however, the dynamic water adsorption quantities of the Na+ modified one during an adsorption process of three hours were still higher than those of silica gel. Finally, the dehumidification performance of the Na+ modified polyacrylic acid salt was evaluated and compared to silica gel using a validated mathematical model of the DCHE system, with water as a refrigerant under three different ambient air conditions, i.e. ARI summer, ARI humid, and Shanghai summer. Simulation results suggested that the modified Na+ could remove 49%–118% more moisture from the process air and possessed greater superiority especially for conditions with lower atmospheric humidity.关键词：air-conditioning system;dehumidification;adsorbent;adsorption1628|2192|1发布时间：2024-07-18
- 摘要：Variable refrigerant flow (VRF) air-conditioning systems are widely used in various public buildings. If a fault occurs, it will result in reducing comfort and increasing energy consumption. The refrigerant charging level is an important parameter affecting the efficient operation of the air-conditioning system. In this paper, a fault diagnosis model based on Boosting integrated algorithm is proposed by taking refrigerant charge fault as the research object. Five basic classifiers, such as logistic regression, decision tree, random forest, support vector machine and BP neural network, are integrated. Chi-square test was used for feature selection, and the diagnostic model was established with experimental data for cooling and heating modes. The results show that the Boosting-based integrated model can efficiently detect the fault of VRF refrigerant charge, and the accuracy rate of the model is up to 96.8%. Compared with the traditional fault detection method, the proposed model greatly improves the response speed, accuracy and practicability of the diagnostic model.关键词：Boosting;integration;refrigerant charge;VRF;fault diagnosis1951|2241|1发布时间：2024-07-18
- 摘要：Based on the classification criteria of thermal space models, human thermal physiological models, and human thermal psychological models, this paper gives a comprehensive review of human comfort research in an asymmetric environment. Thermal space models directly predict the objective and subjective response of humans using air conditioning and environmental parameters. Human thermal physiological models predict the physiological parameters of humans by studying active and passive physiological regulation in human bodies. Human thermal psychological models focus on the relationship between physiological parameters and subjective responses or on how the human body adapts to the thermal environment. Finally, the advantages and limitations of each model is summarized. The results show that the thermal space model has a significant relationship with the selected space structure; once the space structure changes, many of the relationships established by the model cannot be established, which is more valuable in the field of vehicle applications; most thermophysiological and thermopsychological models are not comprehensive or limited to specific environments, and only a few can address human responses to non-uniform and transient conditions through detailed body temperature regulation; the Berkeley thermal comfort model covers both thermophysiological and thermopsychological models, but its coupling simulation process is too complicated; while the equivalent temperature model has relatively low accuracy, it is more widely used due to its simple operation; adaptive model fully considers human subjective initiative, but its research is still in its infancy.1859|3114|1发布时间：2024-07-18
- 摘要：The chiller fault data are often difficult to obtain in the field, which is one of the key obstacles hindering the field applications of chiller fault detection. Considering this reality, the fault detection task is transformed into a typical one-class classification problem by merging a distance rejection (DR) technique into a Bayesian network (BN); therefore, a method based on DR-BN is proposed in this study. The proposed method effectively overcomes the above-mentioned limitation by using the normal data alone to train the model. The performance of the proposed method is evaluated by using the experimental data from the ASHRAE RP-1043, and compared with the other traditional methods. The proposed method shows a better performance than the other traditional methods. Especially for the low serious level, the maximum accuracy of the proposed method is increased by 94%.关键词：chiller;fault detection;Bayesian network;distance rejection1571|2337|2发布时间：2024-07-18
- 摘要：The two-phase flow-condensation heat transfer experiment of R134a inside the micro-fin tube was operated on the test bench, the influence of working conditions and micro-fin tube structural parameters on the pressure drop was studied, and its correlations were also used to predict the pressure drop inside the tube in this study. The experimental results show that the pressure drop is positively correlated with mass flux and fin helical angle; however, they are negatively correlated with condensation temperature and Re of cooling water. Correlations of Cavallini et al., Haraguchi et al., and Pierre have good predictive effects on the pressure drop with an average prediction error of less than 17%, while the correlation Goto et al. overestimates the pressure drop. Based on the pressure drop experimental data of R134a, the functional relationship between Фv/Фl and Xtt was fitted again and referred to the computing mechanism of Goto et al. for correlation. Then, a new correlation for predicting the pressure drop inside the tube is put forward, and statistic test shows that the prediction error of the new correlation is within ±30% and the average prediction error is less than 10%.关键词：micro-fin tube;flow condensation;pressure drop;correlation1733|2278|0发布时间：2024-07-18
- 摘要：A cold storage air-conditioning system based on separated heat pipe heat exchanger was designed, and the effect of influencing factors on the discharge performance and their response surfaces were experimentally investigated. The results show that the discharging performance of the cold storage air-conditioning system with separated heat pipe was stable; the maximum refrigeration capacity could reach 5.09 kW under experimental conditions. Cooling capacity increases with an increase in the circulating air volume while there is an optimum circulating air volume for dehumidification. The optimum circulating air volume for dehumidification is about 620 m3/h and the dehumidification capacity is about 4.32 kg/h, and the cooling capacity increases with the increase in temperature and humidity of the environment. The regression equation of the cooling capacity under different working conditions was obtained, and the effect of different influence factors on the cooling capacity was analyzed. Under the conditions with low circulating air volume, the influence of the heat pipe valve on refrigeration capacity is weak; however, with an increase in circulating air volume, its influence on refrigeration capacity increases.关键词：ice storage;separated heat pipe;cooling and dehumidification;response surface method1648|1675|0发布时间：2024-07-18
- 摘要：For a domestic processor motherboard of an embedded computer, the heat dissipation technology of aluminous vapor chamber is adopted. Structure design, simulation analysis, and test research are carried out. An equivalent replacement for simulation analysis method for vapor chamber is proposed. The heat dissipation performance of the whole machine using aluminous vapor chamber at 65 ℃ is simulated, and the heat dissipation performance of the aluminous vapor chamber in its actual engineering prototype was tested by experiments. The test results show that the maximum error of the equivalent replacement for simulation results of vapor chamber is 4.8% compared with test results, and the simulation error of the junction temperature of domestic processors is 1% at a high temperature of 65 ℃. The maximum temperature difference at room temperature and a 65℃-high temperature environment in the vapor chamber is 4.7 ℃ and 5.6 ℃, respectively. The maximum junction temperature of the domestic processor is 100 ℃, which is lower than the allowable junction temperature of 105 ℃. It is concluded that the equivalent replacement simulation analysis method has high accuracy and can effectively predict the heat dissipation performance of vapor chamber. The aluminous vapor chamber can meet the heat dissipation requirements of the domestic processor board, which is present in fully sealed embedded computers.关键词：vapor chamber;thermal simulation;thermal test;embedded computer;domestic processor1974|2663|2发布时间：2024-07-18
- 摘要：The heat transfer performance of a tube type water-cooled radiator is numerically simulated, and this experiment is designed to verify it. The model is established from the pipe using the louvered and flat tube fin units to perform a comprehensive performance analysis. The louver angle of the tube-belt louver is analyzed, and the results show that the louver angle of the radiator is between 23°~27°, its heat dissipation effect is the best, and a scheme of fin structure optimization is verified by numerical simulation. Compared with the traditional structure, the heat dissipation effect is considerably improved. The test bench was set up and the orthogonal experiment table was designed to study the degree of influence of different factors on the overall heat dissipation effect of the radiator. The experimental results showed that in the scope of this experimental study, the degree of influence of three factors, namely, inlet water temperature, circulating water flow, and fan speed, on radiator heat dissipation is as follows: inlet water temperature > circulating water flow > fan speed.关键词：tubular radiator;numerical simulation;louvered fin;orthogonal experiment1967|2591|0发布时间：2024-07-18
- 摘要：A mathematical model of heat pump driven liquid desiccant (HPLD) fresh air system was established to investigate the system’s performance under different fresh air parameters. The results indicated that the average decline rate of the system’s coefficient of performance (COP) was 0.9% when the fresh air temperature increased by 1 ℃, while the average decline rate of COP was 3.6% when the fresh air moisture content increased by 1 g/(kg·dry air). The increase in air moisture content caused a significant reduction in COP, whereas the HPLD system had poor adaptability to the changes in fresh air humidity. In order to expand the range of the HPLD system’s adaptation, a dehumidification system combined with HPLD and cooling dehumidification was proposed. Taking the COP of the combined dehumidification system as the evaluation index, the optimal state of the fresh air parameters between HPLD and cooling dehumidification s was temperature 21 ℃ and moisture content 14.1 g/(kg·dry air). Under typical summer conditions, the COP of the combined dehumidification system was 5.4, which was 87.5% higher than that of a single HPLD system. Finally, an experimental prototype was built according to the design parameters, and simulation results were verified.关键词：fresh air dehumidification system;parameter optimization;liquid desiccant;coefficient of performance1853|2364|1发布时间：2024-07-18
- 摘要：Enhanced heat transfer in microscale has been highlighted in the field of microelectronics. The gas-liquid flow patterns and pressure drop analysis are fundamental for the design and control of microfluidic systems. In this study, two-phase flow characteristics in parallel rectangular micro-channels with sudden expansion were studied by flow patterns visualization, theoretical analysis, and experimental study. Through visualization experiments, four typical flows, i.e., bubble flow, plug flow, slug flow, and annular flow, were observed in parallel rectangular micro-channels with sudden expansion. When Qg = 110 mL/min and Ql = 20mL/min, the two-phase flow pattern achieves the maximum jet state, and a full fluid jet appears. By?means?of?setting?up?a?total pressure drop prediction?model of the parallel rectangular micro-channel with sudden expansion at the mass velocity of two-phase flow ranges from 367 kg/(m2·s) to 691 kg/(m2·s), their applicability and accuracy were analyzed. The results showed that the average prediction?error is 18.56%, which is superior to the prediction accuracy in classical literature. Additionally, with the increase in the overall pressure drop, the prediction accuracy increases.关键词：pressure drop;microchannels;gas-liquid flow;visualization1830|2442|3发布时间：2024-07-18
- 摘要：A multi-node model was developed to predict the vertical temperature profiles of a stratified air-conditioning system in a certain large space building with low-sidewall air supply and return. Then experiments were carried out in the building under 5 working conditions with a different air volume (1.5×104–2.5×104 m3/h) and outdoor meteorological parameters (28-34 ℃). The results show that the maximum relative errors of the calculated values of each condition are 6%, 7%, 14%, -6%, and 15%, respectively, and the average standard deviation of each condition is 2.05 ℃, which validated the multi-node model. Afterwards, the multi-node model was used to analyze the characteristics of the thermal environment of stratified air-conditioning system in large space buildings with low-sidewall air supply and return by changing air volume, outdoor air temperature, and solar radiation. Finally a graph is drawn to guide the adjustment of air volume as indoor and outdoor environmental parameters changes.关键词：large space building;low-sidewall air supply;stratified air-conditioning;vertical temperature profile;multi-node model1727|2091|2发布时间：2024-07-18
- 摘要：Thermal storage technology with phase change material (PCM) is one of the important ways to improve the utilization efficiency of solar energy. A hot water tank experimental system with sodium acetate trihydrate ball as PCM was built. The thermodynamic characteristics based on the temperature in the water tank were tested under an initial water temperature of 80 ℃ and inlet water temperature of 5 ℃. According to the change of water temperature in the tank with the dimensionless time, a filling efficiency analysis method was used to analyze the thermal stratification characteristics of the hot water tank with PCM. This analysis includes the curve of temperature change and filling efficiency when the water flow rates were 1, 3, 5, 7, and 9 L/min, respectively. The experimental results show that when the water tank temperature is 80 ℃, the energy of the ordinary water tank and the hot water tank with PCM are 18.81 MJ and 19.34 MJ respectively. When the water flow rate is the same, the closer the ball with PCM is to the water tank inlet, the better the heat stratification effect of the water tank is. The thermal stratification effect of the ordinary water tank is stronger than that of water tank with PCM when the ball is at the first, second, and third layers, but weaker than that of water tank with PCM when the ball is at the fourth layer. When the inlet flow rate is 9 L/min, the filling efficiency of water tank with PCM is 0.497 and 0.581 when the ball is in the first layer and the fourth layer, respectively, and the filling efficiency of the ordinary water tank is 0.573, when t*=1. As the water flow rate increases, the mixing degree of the hot and cold water increases, and the thickness of the thermocline layer in the water tank increases, which decreases the stratification effect. When the inlet flow rate is greater than 7 L/min and the PCM ball is at the bottom, the thermal stratification characteristics of the hot water tank with PCM are optimal.关键词：hot storage tank;phase change material;filling efficiency;thermal stratification1958|2507|3发布时间：2024-07-18
- 摘要：Micro-droplet spray vitrification system produces small droplets and can be vitrified at a lower concentration of cryoprotectant (CPA). In this study, HepG2 cells were vitrified using micro-droplet vitrification system; moreover, damages caused by CPA loading, spraying, receiving, and vitrification/rewarming processes were evaluated. In addition, CPA formulations were optimized by reducing the Me2SO concentration and adding an appropriate amount of trehalose. The results showed that each step in micro-droplet spray vitrification may cause damage to the cells. CPA loading, spraying, vitrification and rewarming processes caused severe damages, but mild damages were caused by the sheet receiving process. Cell activities after cryopreservation are significantly reduced with a decrease in the Me2SO concentration. When the CPA formulations are constant, cell activities in the vitrification group become better than those in the slow freezing group. Moderate amounts of trehalose can enhance the effect of cryopreservation, while excessive trehalose can be counteractive. When cells were preserved with 5% Me2SO + 0.3M trehalose as a cryoprotectant, the cell survival rate reached (92.42±0.95)% and the 24 h adherence rate reached (95.64±1.03)%; therefore, the droplet spray vitrification effect was found to be the best.关键词：micro-droplet spray;vitrification;process damages;cryoprotecant optimization1500|2176|1发布时间：2024-07-18
- 摘要：The major challenge to cell cryopreservation is intracellular ice formation (IIF), which can be reduced by controlling ice nucleation. In this review, the influence of ice nucleation on super-cooling and damage zone was analyzed. Physical, chemical, and biological methods have been applied to control ice nucleation during cryopreservation. The mechanisms of these methods were summarized and the influence of these methods on cell cryopreservation were discussed. Then it was proposed that biological and chemical methods should be superior methods of controlling ice nucleation. Additionally, the best ice seeding temperature was further proposed. At this temperature, ice crystals are initiated in the extracellular solution, which could result in minimal cell volume by reducing intracellularly active water properly, and then the incidence of IIF is reduced. The direction of ice seeding applied in the cell cryopreservation was pointed out.关键词：cryopreservation;intracellular ice damage;ice nucleation;suppressed nucleation;ice seeding1736|2090|5发布时间：2024-07-18
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