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As one of the early weapons used by the ancient Chinese military, the gravity-powered trebuchet is listed as a mandatory program in science and technology games in several provinces. Due to its entertaining and informative features, this program has received continuous attention and discussion from scholars. Currently, most of the studies on this program are empirical, and few studies have been conducted quantitatively based on theoretical models. Therefore, this study established a theoretical model of the trebuchet projection process from the perspective of system energy conservation and gave an accurate analytical expression of hitting target points. In order to verify the reliability of the theoretical model, experimental tests were conducted. The results showed that the experimental results were relatively consistent with the theoretical predictions. These findings could provide a new research idea for facilitating gravity-powered trebuchets to hit targets accurately.

Since China set forth the goal of “dual carbon”, studies on heat transfer characteristics of evaporators have been one of the hot spots in the field of refrigeration and heating. This paper conducts an experimental study on the heat transfer performances of evaporators under different flow rates by changing the water flow of the evaporator and condenser. The results shows that on the premise of unchanged water flow of condenser, cooling coefficient of performance (COP) and heat transfer coefficient (HTC) grow with the increases in flow rates of evaporator and temperatures of inlet and outlet water. However, the changes in HTC are relatively smooth; the compressor’s inhalation and expulsion temperatures grow with the increases in water flow rates of the evaporator, and the changes are quite evident. The paper also discusses and analyzes deeply those manifestations, which provides experimental evidence for the experiments and improvement of the evaporator, optimization of evaporator design, and the enhancement of the economic performance of the system.

As a classic research topic of fluid mechanics, the research on the problem of flow around a circular cylinder is essential both from the perspective of academic research and application in the engineering industry. In this paper, the surface pressure of the cylinder is measured by the experimental research on the flow around the circular cylinder, the three-dimensional modeling of the key parts of the experiment is carried out according to the one-to-one size, and the three-dimensional CFD software is used to numerically simulate the velocity field and the pressure field. The research shows that under different air volumes, the relative error between the experimental value and the simulated value of the inlet velocity in the convergence section and the working section is less than 5%. It can be considered that the results of the numerical simulation and the experimental results are within the allowable range. The relative error between the experimental value and the simulated value of pressure is less than 2%, and the numerical simulation results are consistent with the experimental results. It lays a theoretical foundation for the improvement of the flow around the cylinder experiment and its engineering application in the future.

In this paper, the performance experiments and simulation studies on air conditioning heating under various fan frequencies were conducted using the air conditioning heating experimental device, and the key factors affecting air conditioning were studied. The experimental study concluded that with the gradual increase of fan frequency, the suction and discharge temperatures of the compressor, the outlet temperature of the heat exchanger, the mass flow of the air duct, and the thermal power consumption showed a gradually increasing trend. From the simulation study, it was found that by simulating the temperature field of the outlet temperature of the heat exchanger under different fan frequencies, and making a relative error with the outlet temperature of the experimental heat exchanger, the relative error is 2.5% at most; while simulating the velocity field of the experimental velocimetry tube flow rate and making a relative error with the experimental velocimetry tube flow rate, the maximum relative error was 1.8%. The research shows that the simulation calculation is highly consistent with the experimental results, which provides a direction and theoretical basis for the study of better air conditioning performance and optimal design.

Interface control and dispersion of graphene base nanomaterials in polymer matrix are challenging to develop high comprehensive nanocomposites due to their strong interlayer cohesive energy and chemical inertia. In this research, an efficient approach is presented to functionalize reduced graphene oxide nanosheets by N-[3-(trimethoxylsilyl)propyl]ethylenediamine, which is dispersed into polyacrylonitrile to prepare N-[3-(trimethoxylsilyl)propyl]ethylenediamine – reduced graphene oxide/polyacrylonitrile nanocomposites. A thermogravimetric analysis technique was employed to evaluate thermal properties of the nanocomposites. The tribological properties of the polyacrylonitrile/graphene nanocomposites were investigated. The morphologies and volume of the worn surface were examined using a 3D profilometer. The impact of loading ratio on friction coefficient, carry-bearing capacity and durability were studied. The N-[3-(trimethoxylsilyl)propyl]ethylenediamine – reduced graphene oxide/polyacrylonitrile nanocomposite with appropriate loading ratio of reduced graphene oxide exhibited a high load-bearing capacity and durability. Therefore, the polyacrylonitrile/graphene nanocomposite shows promising potential to industrial applications involving the lubrication and anti-wear.

A facile one-pot synthesis of ZnS hollow spheres has been carried out via a chemical transformation induced inside-out Ostwald ripening process from a single source precursor. The size and shell thickness of the ZnS hollow spheres can be controlled by adjusting the reaction temperature and reaction time, respectively. Photoluminescence spectra show a dominant emission peak at 470 nm accompanied by several weaker peaks. UV–vis measurement reveals that the obtained ZnS hollow spheres exhibit “hollow effect”. The formation process of ZnS hollow spheres has been discussed.

Monodisperse α-Fe2O3 microspheres of different shapes have been selectively synthesized through the hydrothermal process. The products were characterized by powder X-ray diffraction and scanning electron microscopy. All the α-Fe2O3 microspheres have good dispersibility, uniform size, and well-defined shapes. The ferromagnetic investigation of the egg-like α-Fe2O3 microspheres gave extremely high coercivity of 3800 Oe at room temperature. The formation mechanism of these microspheres was preliminarily discussed. Nanorods and branched nanorods of a hydroxide precursor Fe8O8(OH)8Cl1.35 have been captured. Monodisperse Fe3O4 microspheres have also been prepared, and their magnetization saturation value is about 40.1 emu/g.