最新刊期
卷 57 ， 期 3 ， 2023
- 摘要：The bubble dynamics in solar photocatalytic hydrogen production involves the interaction between multiple physical fields and photocatalytic reactions, which is unique and more complicated than the classic bubble dynamics in the field of boiling heat exchange and water electrolysis. Based on the basic principle of photocatalytic water splitting, this paper reviews the research progress in the dynamics of bubble nucleation and growth on the catalyst surface and the regulation of bubble behavior. The scale and supersaturation of bubble nucleation for photocatalytic water splitting can be estimated by the classical nucleation theory, however, the information of bubble nucleation process with high spatial and temporal resolution cannot be obtained simultaneously yet due to the constraints of existing testing methods. For the bubble growth on the catalyst surface, it can usually be described by three mechanisms: inertia control, diffusion control and chemical reaction control, and the key to determine the bubble growth control mechanism is the relative size of the effective reaction surface to the bubble size. The negative impact of bubble coverage on the photocatalytic reaction system can be effectively reduced by directional regulation of bubble behavior, including passive regulation methods based on the addition of surfactants and modulation of catalyst surface structure and wettability, and active regulation methods based on the application of external flow field, acoustic field, magnetic field and periodic illumination. The primary challenges of current research are to reveal the mechanisms of interphase interactions and energy-mass transport under the action of complex physical fields, thereby providing guidance for future low-cost and efficient solar photocatalytic hydrogen production applications.关键词：solar hydrogen production;photocatalytic water splitting;photoelectric conversion;bubble dynamics;behavior regulation878|30|0更新时间：2025-07-09
- 摘要：To solve the intermittent power supply problem of the solar thermal power generation system, perovskite oxides are proposed as energy storage materials based on the thermochemical energy storage system. A series of A-doped La1-xMxCoO3(M=Sr, K, Ba, and x is the percentage of mole fraction of M element doping)are prepared using the sol-gel method. The series of samples are tested in an air atmosphere by a synchronous thermal analyzer, and the effects of A-site doping element type, doping amount and calcination temperature on the synthesis and thermochemical energy storage performance of samples are investigated. The crystal structures of the perovskite samples are characterized and analyzed by X-ray diffraction. There are some results shown as follows: Due to the lower calcination temperature, the samples is impure. The weight loss during the first cycle of reduction is excessively large, and the quality change of the samples deteriorate with the cycle in the thermogravimetric analysis. Samples with higher purity and crystallinity can be obtained at a higher temperature.The doping of K has no effect on the energy storage performance of the samples. The weight changes of Sr-doped samples first increase and then decrease with the increase of Sr doping amount, and LS28C has the best energy storage performance. The mass change and reaction rate of the samples increase with the increase of Ba content. The experimental research in this paper is carried out under air conditions without adding a vacuum pump and other equipment, which not only simplifies the system, but also reduces the operating cost.关键词：perovskite oxide;A site doping;air;thermochemical energy storage;thermogravimetric analysis114|25|0更新时间：2025-07-09
- 摘要：In order to research the heat transfer problem of organic phase change materials melting in the square cavity heat storage unit, liquid fraction and mean Nusselt number of composite phase change materials under different filling rates during melting are analyzed. To solve the problem of heat accumulation at the top of the square cavity unit, the layered model is constructed to simulate the melting process of the composite phase change materials in different models The results show that when the contents of graphene nanosheets are 1%, 3% and 5%, the complete melting times of the nanoparticle-enhanced phase change material are 32.1, 20.0 and 17.5 min, respectively, which are 70.47%, 81.62% and 83.92% shorter than those of pure paraffin. When the square cavity is equally divided at the top and bottom, the melting time is reduced by 11.88% compared to the unlayered one. When the upper and lower parts of the square cavity are filled with 1% and 5% volume fraction of the composite phase change materials respectively, the melting time of the composite phase change model with an overall filling of 3% is reduced by 25.83% compared to that when it is not divided into layers. From the simulation results, it can be concluded that the addition of graphene nanosheets to paraffin wax can lead to a large degree of improvement in its thermal conductivity, as well as a smaller degree of viscosity growth and a smaller effect on natural convection. When considered together, it can be found that the addition of graphene nanosheets to paraffin can strengthen its heat transfer performance; the layered model can shorten the melting time of the phase change materials, and a suitable filling scheme can further accelerate the melting process of the rectangular cavity.关键词：phase change heat storage;nanoparticles;numerical simulation;structural optimization116|5|0更新时间：2025-07-09
- 摘要：In this paper, the boiling heat transfer characteristics of the new R32 alternative refrigerant with low pollution, high energy efficiency, poor flammability and low toxicity are investigated under low-temperature conditions in horizontally orientated tubes. The flow boiling system is established and applied to study the R32 flow boiling heat transfer and pressure drop in small-diameter tubes with 3 mm and 4 mm diameters in horizontal orientation. The impact of mass flow rate, heat flux, saturated temperature and vapor quality on the R32 two-phase thermohydraulic performance is experimentally considered. The heat transfer jeopardization by the dry-out mechanism is also observed. The result shows that the heat transfer coefficient of the 3mm tube can be improved by 8%～12% compared to that of the 4mm tube while the critical heat flux is independent of tube diameter at a high flow rate. Meanwhile, compared with heat transfer characteristics, R32 saturation temperature is more sensitive to the two-phase flow resistance, the resistance loss increases by about 23% when the saturation temperature is reduced from 13 ℃ to 11 ℃. Finally, the corrected Fang's correlation is applied to precisely predict the two-phase heat transfer coefficient of R32 in which over 88.56% of data can be controlled within the error of ±10%.关键词：refrigerant R32;horizontal small-diameter tube;flow boiling heat transfer;correlations88|22|0更新时间：2025-07-09
- 摘要：In the process of suspension control of the rotor system of the maglev permanent magnet synchronous motor, inaccurate magnetic parameters affect the optimal design of the controller and even destroy the stability of the system, therefore in this paper, a magnetic parameter identification method based on Gaussian modulation function method is proposed, and the sliding mode control law is designed to control the steady-state suspension of the rotor. Firstly, the closed-loop stability of the maglev rotor system is made under PID control. Then, the continuous dynamic model of the maglev rotor system is digitally modulated and integrated with a multi-sine signal excitation system using the Gaussian function as the modulation function, and thereby the discrete equivalent parameter identification model is established. Next, the scale parameters matching the frequency band coverage of the magnetic suspension rotor system are selected to construct the Gaussian modulation function, and the magnetic parameters of the magnetic suspension permanent magnet synchronous motor experimental platform are identified. Finally, according to the identified model parameters, a sliding mode controller is designed to realize the steady-state suspension of the PMSM rotor. The proposed method avoids the direct processing of differential signals and the problem of the integral initial value, and it can identify the magnetic parameters conveniently and effectively. The sliding mode controller makes the magnetic suspension rotor system have better steady-state and dynamic performance. The experimental results show that the sliding mode controller designed according to the proposed method can make the rotor reach the target position within 0.2 s and keep stable, and the adjustment time only 40% of that of PID control.关键词：permanent magnet synchronous machine;magnetic suspension rotor system;PID control;parameter identification;sliding mode control;modulation function71|13|0更新时间：2025-07-09
- 摘要：In order to develop an advanced design system for high performance multistage transonic compressors, a multi-circular arc(MCA)airfoil parametric modeling method, an MCA thickness-distribution airfoil parametric modeling method and a modified NACA 6-series airfoil parametric modeling method are proposed. The quasi-3D design results of the front 6.5 stages of the energy efficient engine(E3)high pressure compressor co-designed by NASA/GE are utilized to construct the parametric compressor model. Then the computational fluid dynamic method is used to numerically simulate the internal flows and pressurization characteristics of the parametric compressor under variable rotational speed conditions. The results show that compared with the design target and prototype compressor's experimental result at near peak efficiency point of 100% design speed, the errors of the mass flow rate are 0.4% and 0.6%, respectively, and the errors of adiabatic efficiency are 1.9% and 0.9%, respectively. The total pressure ratios of the parametric compressor and of the prototype compressor are both lower than the design target. The total pressure ratio deficiency is mainly accounted for the severe shock detachment caused by the excessive aerodynamic load of the front transonic rotor. By reasonably adjusting the aerodynamic load distribution and decreasing the flow spillage, the compressor aerodynamic performance especially the total pressure ratio at the design condition can be improved. The outcomes have reference values for the design optimization of multistage transonic compressors.关键词：E3 high pressure compressor;geometric parameterization;pressurization characteristics;shock detachment59|23|0更新时间：2025-07-09
- 摘要：Given the bottleneck problems of a traditional three-dimensional force sensor, such as non-linear error and large error of inter-dimensional coupling, and the measurement demand of the three-dimensional force with heavy load, high frequency, and strong impact, a piezoelectric thin film three-dimensional force sensor with a diamond configuration of pillars is designed by innovatively using the overturning moment generated by impact force based on polyvinylidene fluoride(PVDF)piezoelectric thin film and combined with parallel load sharing principle. The diamond configuration of the pillars enables the sensor to compensate for inter-dimensional coupling. Each pillar is approximated to be affected by a single overturning moment and therefore combined measurements can be made. The optimal arrangement of PVDF piezoelectric thin films is investigated. The feasibility of the sensor design scheme is verified by combining theoretical analysis, finite element simulation analysis and experimental verification. A combined self-decoupling piezoelectric thin film three-dimensional force sensor prototype is developed. Quasi-static and dynamic calibration experiments are carried out respectively. The experimental results show that the improved sensor has the characteristics of high sensitivity and high natural frequency, the three-direction non-linear error is less than 0.2%, and the inter-dimensional coupling error is less than 1.2%. Its structure design can counteract the inter-dimensional coupling. The three-dimensional force sensor has important application value and potential in high-precision bearing ball cold upsetting and transient strong impact scenarios.关键词：three-dimensional force sensor;polyvinylidene fluoride;piezoelectric thin film;inter-dimensional coupling;heavy load88|23|0更新时间：2025-07-09
- 摘要：In response to the difficulty of composite fault diagnosis when cracks and wear faults occur simultaneously in gear system, a dynamic characteristic analysis model of gear transmission system considering profile wear and root cracks is proposed. Firstly, a numerical simulation model of gear transmission system wear is established based on Archard formula to solve the tooth profile wear under different wear cycles. Then, the meshing stiffness calculation model of single tooth under the action of crack and wear is established by the potential energy method. The relationship between meshing teeth and wear is considered in the contact area of double teeth, and the meshing stiffness calculation model of double teeth is established combined with deformation coordination. Finally, a 4-DOF dynamic model of the gear system is established by using the centralized mass method, and the dynamic response is solved by using the Newmark-β method with time-varying mesh stiffness with faults as the input. The dynamic characteristics of the gear under different degrees of cracks and wear are obtained. The experimental results show that the model can reflect the wear and crack characteristics of composite faults well. Compared with the crack and wear composite fault model without considering the actual deformation of the double teeth region after wear, the accuracy of the stiffness calculation of the double teeth region of the composite fault model is improved by about 22%. The proposed model can provide an effective dynamic supplement for the fault diagnosis of the gear transmission system with wear and crack.关键词：time-varying mesh stiffness;gear root cracks;gear tooth profile wear;dynamical model;dynamic response100|13|0更新时间：2025-07-09
- 摘要：In view of the large amount of common mode voltage(CMV), high-frequency dv/dt and other harmonics generated during the operation of the three-level PWM inverter, a subregion PWM modulation strategy is adopted to suppress the common mode voltage of the PWM converter. The three-level space vector is redivided into several different modulation regions by modulation index. In different modulation regions, the three-level PWM modulation algorithm is realized by using large vector, medium vector, and small vector of four basic vector types. The subregion PWM modulation strategy(Ma-PWM)divides the small region inside the sector into high and low modulation regions, and uses the nearest basic voltage vector to synthesize the reference vector. The simulation results show that the common mode voltage amplitude of the proposed Ma-PWM modulation strategy under different load types is 1/6 of the DC bus voltage. In addition, the common mode voltage amplitude of the PWM inverter under variable speed load can be reduced to 1/2 of the original, and the total harmonic distortion(THD)of the output current waveform of the PWM inverter is less than 5%. This method can not only suppress the common mode voltage but also reduce the total harmonic distortion of the PWM inverter output current.关键词：three-level PWM inverter;common-mode voltage suppression;pulse width modulation;sector division;voltage vector83|24|0更新时间：2025-07-09
- 摘要：The communication base station management system mostly adopts an empirical test method at present, which cannot simulate the test cases with a long period and reasonable occurrence time. To solve this problem, a test case modeling method based on the base station alarm log is proposed. Firstly, taking the log generation time interval of the base station as the research object, it is found that the log generation time interval obeys power-law distribution by analyzing data entirety, device type, log type, and device combination log type. Then, the least square method, maximum likelihood estimation, and maximum posterior estimation are compared and analyzed. Based on the estimation error, it is found that the least square method has the fitting of a higher degree and the smallest residual error, the value of goodness of fit is 0.96%, and mean absolute percentage error is 3.5%. Finally, the least square method is used to estimate the log time interval by power exponent, and the alarms with the value of goodness of fit greater than 0.7 are reserved to form test cases within a location. The model is applied to estimate the interval distribution of alarm logs of communication base stations in different cities throughout the country. The experimental results show that the proposed model can calculate more than 85% of log distribution law, which lays a foundation for arranging test cases close to the actual operating environment and further improves the reliability of test results.关键词：communication base station management system;test case;power-law distribution;parameter estimation;least square method45|6|0更新时间：2025-07-09
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Two-Phase Flow Parameter Measurement Using Multi-Task Learning and Electrical Capacitance Tomography
摘要：A two-phase flow parameter measurement method, which combines multi-task learning and electrical capacitance tomography, is proposed to solve the problem of the interference in parameter measurement caused by the low accuracy of the images reconstructed by the reconstruction algorithm in terms of electrical capacitance tomography. Firstly, the residual module is used as the feature extraction module to extract the features of the images reconstructed by the Landweber algorithm, so as to eliminate the interference of artifacts of reconstructed images on parameter measurement. Secondly, a dual output multi-task neural network with hard parameter sharing is built to finish the task of initial measurement of the phase fraction in order to further improve the anti-noise ability of the model. Then, a method of fusing neural network and classification models, such as extreme random forests, is proposed to achieve flow identification. Finally, regression models such as extreme random forests are used to obtain the final phase fraction by fusing the results of flow pattern identification and initial results of the phase fraction in order to further improve the accuracy of phase fraction measurement. The experimental results show that the proposed algorithm can improve the accuracy of phase fraction measurement when compared with the method of only using the neural network. In the actual measurement, the relative error of phase fraction measured by the proposed algorithm is within 5%, and the accuracy of flow identification is beyond 98%, which shows a good anti-noise ability of the model and can meet the demands of practical industrial applications.关键词：electrical capacitance tomography;multi-task learning;two-phase flow;flow identification;noise interference38|13|0更新时间：2025-07-09
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