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To address the problem that there are many limestone particle decomposition reaction models and it is difficult to accurately select the appropriate one, this paper established two typical one-dimensional unsteady numerical calculation models for single-particle limestone decomposition, coupling the convective heat transfer, thermal conduction, and CO2 mass transfer processes. Two numerical calculation models were solved through the Matlab R2021a platform, and the internal temperature, CO2 concentration distribution, and decomposition reaction rate of the limestone particles during the period from the beginning of temperature rise to the end of decomposition were obtained. Compared with the experimental data, Model 1 has a better agreement with a relative error of less than 10%. The simulation results have shown that the average decomposition reaction rate is 20% higher than the average mass transfer rate. As the particle size increases from 20 mm to 80 mm, the time required for temperature rise in the initial stage changes from 6.6 min to 42.7 min. It is noted that the CO2 volume fraction increment increases by 0.42% with a particle size of 80 mm and a heating temperature of 1050 °C, indicating that the influence of the distribution of CO2 on the limestone decomposition may not be ignored. [ABSTRACT FROM AUTHOR]

The applications of molecular simulation in supercritical carbon dioxide (S-CO2) and its mixtures are reviewed. First, an overview of physical properties of S-CO2 and CO2 models is given. Secondly, the accuracy of S-CO2 thermodynamic and transport properties calculated by different models is compared. It shows that Zhang's model has relatively better global accuracy in calculating thermodynamic properties. EPM2, Zhang and Cygan models have similar accuracy when calculating transport properties based on equilibrium molecular simulation (EMD) method, but generally have higher deviations when calculating thermal conductivity. Therefore, EMD and non-equilibrium molecular simulation (NEMD) methods have been compared in calculating thermal conductivity. The results show that NEMD is better than EMD but the process is complicated. The structural properties are also discussed in this part. Thirdly, the applications of molecular simulation in S-CO2 binary organic, binary inorganic and multiple mixtures are reviewed. Finally, the summary and the prospect of future works are given. [ABSTRACT FROM AUTHOR]

Regenerative cooling technology is the most widely used cooling technology in liquid rocket engines, and flow distribution is very important for regenerative cooling heat transfer. In this work, the flow distribution characteristics of Z -type parallel channels were studied through numerical simulation, and the effects of flow area ratio, inlet header shape, and inlet aspect ratio were analyzed. Results showed that changing the inlet cooling header can improve the uniform distribution of flow rate effectively. The nonuniformity coefficient and fuel temperature varied with change in the flow area ratio, inlet header shape, and inlet aspect ratio. The maximum temperature of the wall decreased from 1334.52 K to 1220.61 K when the flow area ratio was changed from 1 to 0.25. An appropriate decrement in the inlet header shape was beneficial to the uniform flow distribution. The inlet aspect ratio should be reduced properly to ensure that each channel experiences similar pressure drop. This research has a certain reference value for the structural design of regenerative cooling channels. [ABSTRACT FROM AUTHOR]

Platelet injectors are quite different from other injectors because of the specificity of the manufacturing technology and spray characteristics. In this study, a splash platelet injector was designed to obtain its combustion characteristics. Gaseous oxygen and methane were used as the propellants. A three-dimensional (3D) model was used with a reduced mechanism involving 16 species and 41 reactions. The influence of the structural parameters of the splash platelet injector, that is, the nondimensional parameter (Δ), nozzle space (D), and scale factor (ξ), on combustion characteristics were analyzed. Results indicate that the temperature was nonuniform near the injector faceplate in all cases, and large corner recirculation zones were formed at the head of the combustion chamber. Combustion length (LC) decreased as Δ increased, and the shortest combustion length was obtained when Δ=3.5. The combustion characteristics at D=2.4 mm slightly differed from those at D=3.6 mm , and the combustion characteristics in the front part of the combustor at D=4.8 mm were worse. The scale factor had little effect on component and temperature distribution. [ABSTRACT FROM AUTHOR]

Fine particulate matter (PM2.5) is a major air pollutant worldwide. Characterizing its chemical compositions and source contributions is a critical prerequisite for effective control of PM2.5 pollution. This paper systematically reviews the sampling methods, chemical compositions, and source apportionments of PM2.5. Sampling methods have significant influences on the identification of chemical compositions and source contributions, with Quartz and Teflon filters being the most widely used. Receptor models are commonly adopted for identifying the sources of PM2.5, such as positive matrix factorization, chemical mass balance, principal component analysis, and UNMIX models, which have their respective advantages and limitations that determine their applications. The variations of PM2.5 compositions and sources in the past two decades in Beijing are also reviewed, which is the political, economic, and cultural center of China and is experiencing severe haze pollution events frequently. It was found that organic matters were the largest component (28.2%) in PM2.5, followed by sulfate (15.1%) during 2004–2013, which was overtaken by nitrate (14.9%) after 2013. Each PM2.5 source demonstrated significant seasonal and annual variations due to changes in climatic conditions and anthropogenic activities. Future research on the impacts of these external factors is urgently needed. This review is expected to provide valuable advice and evidence for those fast-growing megacities like Beijing to identify and control their PM2.5-related air pollution problems. [ABSTRACT FROM AUTHOR]

Based on the lumped mass method, a torsional vibration model of the planetary gear system is established considering the nonlinear factors such as friction, time-varying meshing stiffness, backlash, and comprehensive error. The Runge–Kutta numerical method is used to analyze the motion characteristics of the system with various parameters and the influence of tooth friction on the bifurcation and chaos characteristics of the system. The numerical simulation results show that the system has rich bifurcation behavior with the excitation frequency, damping ratio, comprehensive error amplitude, load and backlash, and experiences multiple periodic motion and chaotic motion. Tooth friction makes the bifurcation behavior of the system fuzzy in the high frequency and heavy load areas, makes the chaos of the system restrained in the low-damping ratio and light load areas, advances the bifurcation point of the system in the small comprehensive error amplitude area, and makes the period window of the chaos area larger in the large-backlash area, which makes the bifurcation behavior of the system more complex. [ABSTRACT FROM AUTHOR]

In order to effectively identify and extract the composite fault characteristics of the gear transmission system, a composite fault diagnosis method combining nonlinear mode decomposition (NMD) and Teager energy operator demodulation is proposed. Because the envelope demodulation of Hilbert transform has the disadvantages of large amount of calculation and end effect, it uses Teager energy operator to solve the problem of large amount of calculation, and NMD solves the problem that the fault signal features is not easy to extract under the mode aliasing. First, the NMD method is used to decompose the fault simulation signal, and the nonlinear modal component with practical physical significance is obtained. Secondly, the Teager energy operator demodulation is carried out for the nonlinear modal components, and the demodulation results are analyzed to verify the feasibility of the method. Then, the method is applied to the composite fault diagnosis of gear pitting wear in gear transmission system, and the characteristic frequency obtained from the test data is compared with the calculated characteristic frequency. The comparative analysis shows that the method can separate the fault characteristic frequencies of large and small gears. The comparative analysis with EMD and EEMD methods in simulation signal analysis and experimental research shows that this method is superior. [ABSTRACT FROM AUTHOR]

Abstract: Surfaces of plants and animals are evolved to optimal states to accommodate environments better after billions of years of natural selection. As the development of further study on bionics, surfaces with special wetting properties in nature are discovered, extremely related to the micro‐/nanostructures on surface. The wetting models and wetting mechanism of several surfaces in nature are investigated, followed by lifting the veil of superhydrophobic field. Various facile, effective, and convenient methods for fabricating superhydrophobic surfaces are obtained and optimized in scientific research and practice. The possibility of wide application for superhydrophobic surface on production and life is improved via the promotion in fabrication ability. This paper is ranged from four main parts, including wetting models, wetting mechanism on various typical surfaces in nature, frequently used fabricating methods for superhydrophobic surfaces in recent years, and application of superhydrophobic material surfaces in three main aspects. It is really hoped that this review article can provide a useful guide for development of superhydrophobic surface in further study. [ABSTRACT FROM AUTHOR]

In order to solve the hysteretic character of the piezoelectric material for application, the initial weight factors of the hysteretic units are calculated by the Preisach theory and the first-order reversal curves test data, a hysteretic Preisach model based on the improved fuzzy least square support vector machine (improved FLS-SVM) is established. In the established model, the fuzzy least square support vector machine is introduced to calculate more weight factors of the hysteretic units and the adaptive variable chaos immune algorithm is introduced to optimize the penalty factor and the kernel parameter of the FLS-SVM (the penalty factor c = 35 and the kernel parameter σ = 1.35 are obtained). Moreover, the quadratic polynomial interpolation method is used to eliminate the sawtooth phenomenon. The validity of established model reveals that fuzzy least square support vector machine method based on adaptive variable chaos immune algorithm (FLS-SVMAVCIA) is more accurate than FLS-SVM method according to application results of the real actuators (the absolute mean error of the FLS-SVMAVCIA model is less than 1 mm and its maximum error is less than 2 mm). As a result, the hysteretic phenomenon can be effectively eliminated by the hysteretic Preisach model based on the FLS-SVMAVCIA method. [ABSTRACT FROM AUTHOR]

To study the influences of microwave drying on the combustion characteristics of food waste, this study conducted thermogravimetric analysis of cooked rice and vegetable leaves dried using a microwave at four intensities. The results suggested that dried rice and vegetable leaves were both favorable fuels, with higher comprehensive combustion characteristic indices than that of other biomass types such as straw, sawdust, etc. Microwave drying improved the combustion performance of food waste. The more intensive the microwave drying, the better the combustion performance of the food waste. Microwave drying significantly enhanced the combustion property of the selected vegetable leaves, while it exerted a slight influence on that of cooked rice. After microwave drying at 1500 W, the combustion characteristic index of vegetable leaves was increased by 34.47% compared with electrically dried samples. However, the combustion characteristic index of rice merely showed an improvement of 8.12%. Analysis of the combustion kinetics of food waste using the Coats–Redfern equation revealed that microwave drying changed the combustion kinetics of food waste. That is to say, the combustion rate of the food waste was accelerated by reducing the activation energy at low temperatures and increasing the activation energy at high temperatures. [ABSTRACT FROM PUBLISHER]

In order to effectively improve the composite regeneration performance of the diesel particulate filter in vehicle, a fuzzy gray correlation analysis model based on the composite regeneration influencing factors of diesel particulate filter was established using the cosine value of fuzzy membership and Euclidean distance formula. And, on the basis of experimental data from three-dimensional computational fluid dynamics simulation, the fuzzy gray correlation analysis on important degree of characteristic indexes, which has influence on the composite regeneration performance of diesel particulate filter, was conducted. Moreover, the method of Lagrange function was used to solve the fuzzy gray affiliate degree based on the results of this fuzzy gray correlation analysis. The effectiveness indexes of overall performance of the diesel particulate filter composite regeneration time, regeneration peak temperature and regeneration efficiency were also obtained. The results showed that the amount of ceria-based additive had the greatest influence on the regeneration time among all the characteristic performance indexes of diesel particulate filter composite regeneration. Similarly, it could be concluded that the exhaust oxygen concentration and exhaust temperature respectively had the greatest influence on the regeneration peak temperature and regeneration efficiency. In addition, the regeneration time had the greatest influence on the overall performance of diesel particulate filter composite regeneration while the regeneration efficiency took the second place and the influence of the regeneration peak temperature was the minimum. The results of this article showed theoretical significance and reference value for optimization analysis and control of diesel particulate filter composite regeneration process. [ABSTRACT FROM AUTHOR]

Based on models A, B, and C of three kinds of diesel particulate filter (DPF) with microwave regeneration, a DPF microwave regeneration model is established according to the laws of conservation of mass, momentum, and energy. The trends of internal temperature under different velocities of exhaust gas in channels are simulated and analyzed. The results show that: (1) Regeneration temperature in the process of microwave regeneration will begin to increase from the front to the rear end of along the axial direction, and the maximum temperature value will appear in the rear end of the monolith. (2) The internal flow velocity in the DPF of model C is the most uniform and the temperature gradient is the smallest among the three models. Therefore, it is the most useful for DPF regeneration. (3) The minimal thermal stress is exerted on the DPF of model C. Therefore, this model is most useful for prolonging the service life of a DPF. [ABSTRACT FROM AUTHOR]

In order to solve the nonlinear mechanism in the process of actual control application of six-degree-of-freedom parallel Stewart platform, the chaos theory was applied in the paper to analyze the acceleration control signal. The research included correlation dimension calculation by use of the G-P method, the maximum Lyapunov coefficient of the acceleration control signal, and Kolmogorov entropies of the acceleration control signal. The results show that the acceleration signals are of chaos characteristics, and there are lots of influencing factors to the acceleration variables. [ABSTRACT FROM AUTHOR]

Heat exchangers play an important role in power, the chemical industry, petroleum, food and many other industrial productions, while compact heat exchangers are more favored in industrial applications due to their high thermal efficiency and small size. This paper summarizes the research status of different types of compact heat exchangers, especially the research results of heat transfer and pressure drop of printed circuit heat exchangers, so that researchers can have an overall understanding of the development of compact heat exchangers and get the required information quickly. In addition, this paper summarizes and analyzes several main working fluids selected in compact heat exchangers, and puts forward some discussions and suggestions on the selection of working fluids. Finally, according to the existing published literature, the performance evaluation indexes of compact heat exchangers are summarized and compared, which is convenient for developers and researchers to better grasp the design direction. [ABSTRACT FROM AUTHOR]

Based on results of chaos characteristics comparing one-dimensional iterative chaotic self-map x = sin(2/ x) with infinite collapses within the finite region[−1, 1] to some representative iterative chaotic maps with finite collapses (e.g., Logistic map, Tent map, and Chebyshev map), a new adaptive mutative scale chaos optimization algorithm (AMSCOA) is proposed by using the chaos model x = sin(2/ x). In the optimization algorithm, in order to ensure its advantage of speed convergence and high precision in the seeking optimization process, some measures are taken: 1) the searching space of optimized variables is reduced continuously due to adaptive mutative scale method and the searching precision is enhanced accordingly; 2) the most circle time is regarded as its control guideline. The calculation examples about three testing functions reveal that the adaptive mutative scale chaos optimization algorithm has both high searching speed and precision. [ABSTRACT FROM AUTHOR]

Biomass pellet fuel is one of the development directions of renewable energy. The purpose of the article is to study the combustion characteristics of five kinds of biomass pellet fuel that can be used as biomass fuel and analyze their combustion kinetics. The thermogravimetric method (TG method) was used to analyze the combustion characteristics of five kinds of biomass pellet fuel and to calculate the index S of comprehensive combustion characteristic. The Arrhenius equation and the Coats–Redfern method were used to analyze the combustion kinetics of five kinds of biomass pellet fuel. The activation energy and pre-exponential factor were obtained according to different temperature ranges. Conclusions are as follows: The pyrolysis of five kinds of biomass pellet fuel mainly includes three stages: (1) water evaporation stage, (2) volatile component combustion stage, (3) fixed carbon oxidation stage. The TG curves of five kinds of biomass pellet fuel are roughly the same at the same heating rate. The peaks of thermal weight loss rate and maximum degradation rate are both in the high temperature range. The differential thermal gravity (DTG) curves of five kinds of biomass pellet fuel have an obvious peak. The peak temperature of the largest peak in the DTG curves is 280–310 °C. The first-order reaction equation is used to obtain the kinetic parameters in stages. The correlation coefficients are bigger than the value of 0.92. The fitting results are in good agreement with the experimental results. The activation energy of each sample is basically the same in each stage. The value in the volatile matter combustion stage is 56–542 kJ/mol, and the activation energy of the carbon layer slowly increases rapidly. The five kinds of biomass pellet fuels have good combustion characteristics and kinetic characteristics, and they can be promoted and applied as biomass pellet fuels in the future. [ABSTRACT FROM AUTHOR]

The NH3 uniformity and conversion rate produced by the urea–water solution spray system is an essential factor affecting de-NOx efficiency. In this work, a three-dimensional simulation model was developed with the CFD software and was employed to investigate the effects of two typical injection methods (wall injection and center injection) and three distribution strategies (pre-mixer, post-mixer, pre-mixer, and post-mixer) of two typical mixers on the urea conversion rate and uniformity. The field synergy principle was employed to analyze the heat transfer of different mixer flow fields. The results show that the single mixer has instability in optimizing different injection positions due to different injection methods and injection positions. The dual-mixer is stable in the optimization of the flow field under different conditions. The conclusion of the field synergy theory of the single mixer accords with the simulation result. The Fc of the dual-mixer cases is low, but the NH3 conversion and uniformity index rate are also improved due to the increase in the residence time of UWS. [ABSTRACT FROM AUTHOR]

The gasoline/natural gas dual-fuel combustion mode has been found to have unique advantages in combustion. The ignition timing has a significant impact on the combustion characteristics of gasoline engines. Thus, here we study the combustion characteristics of gasoline/natural gas dual-fuel combustion mode to determine the details of their respective advantages under cooperative combustion. A direct-injection turbocharged gasoline engine was modified, and an engine experimental platform was built for the coordinated control of gasoline direct-injection and natural gas port injection. A low-speed and low-load operating point was selected, and the in-cylinder pressure, heat release rate, pressure rise rate, combustion temperature, ignition delay, and combustion duration under the coordinated combustion of gasoline and natural gas dual fuel at the ignition moment were studied through bench tests among other typical combustion parameters. The results show that with the increase of the ignition advance angle, the maximum cylinder pressure, heat release rate, pressure rise rate, and maximum combustion temperature increase. The ignition advance angle is 28°CA-BTDC, and PES40 has the best fuel synergy effect and the best power performance improvement. The effect of the advance of the ignition advance angle on the ignition delay and the combustion duration reaches the peak at 20°CA-BTDC–22°CA-BTDC, and the improvement of the two periods is more significant at PES60. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various articles within the issue on topics including noise control, vibration, and mechanical and electrical systems.