Abstract: In the present work, detached eddy simulation (DES) of the turbulent flow in an unbaffled stirred tank agitated by a six-pitched-blade turbine was carried out. The sliding mesh (SM) approach was applied to simulate the rotation of the impeller. For comparison, the computations based on the large eddy simulation (LES) model and RANS equations closed with Reynolds stress model (RSM) were also performed. The instantaneous velocity fluctuations, mean velocity and turbulent kinetic energy profiles were analyzed and compared with the laser doppler velocimetry (LDV) results from literature. Results show that DES model can capture the unsteady turbulent flow characteristics accurately. The mean velocity and turbulent kinetic energy profiles by the DES model are in good agreements with the LES results and the LDV data. Besides, the computational cost of DES is only about 80% of LES. By contrast, the results obtained by RSM are not so good. It can be concluded that the DES model can produce as similarly good predictions as LES with less computational cost, and can work as an alternative of the LES model in predicting the hydrodynamics in the stirred tanks.
Abstract: Using tetraethoxysilane (TEOS) and novolac-PF as raw materials, SiO2/PF hybrid fibers were prepared via sol-gel associated with drawing process, and then sintered at different temperatures (500-1300 °C) under air atmosphere. The microstructure variation and reaction mechanism of the fiber were investigated by FT-IR, XRD, and SEM measurements. The results showed that the microstructure variation of the hybrid fiber was influenced greatly by sintering temperatures. When the sintering temperature was below 900 °C, the fibers were amorphous, and converted into porous SiO2/SiC fibers after being sintered at 1300 °C.
Abstract: Based on the analysis of production process in three phases and finite element analysis of silicon carbide (SiC) furnace temperature field, 2D thermal-seepage coupled finite element model was built to know production practical situation by temperature distribution and pressure distribution. The relation of SiC furnace inside pressure and power was obtained by pressure distribution as well. Then this paper built power curve optimization model that minimizing product energy consumption is objective function with extreme pressure of spouting as one constraint condition, and simplified optimal algorithm plan was proposed based on three production phases. To verify the optimization results, the powers of before optimization and after optimization were employed on the basis of actual industrial furnace data. Results show that energy consumption decreases about 5% and the SiC output increases about 10%. Besides, production period is nearly unchanged after optimization. All stated illustrate the effectiveness of the proposed method.
Abstract: This paper studied on the hydrokinetics and uniform distributed mechanics of supplying ink pressure for the inkjet printing system based on the, and the advanced testing equipment. According to the analysis of theoretical calculation and CFD, we designed a new type of equipment for supplying ink, including the structure of the transition pipe. This supplying ink equipment could make the ink droplets distribute under the equal pressure on the cross direction. The experiments showed that this new supplying ink equipment could make the ink droplets distribute under the equal pressure and uniform velocity on the cross direction, so it greatly improved the imaging effects for the inkjet printing system.
Abstract: With the help of Fluent 6.2 and supporting software, 3D numerical simulation of fluid flow and heat transfer enhancement of plastic spiral tubes were performed on computer, and the velocity, turbulence intensity and improvement of convective heat transfer coefficient distribution in plastic spiral tubes were analyzed and compared with those in smooth tubes, and characteristics of fluid flow and heat transfer were obtained. The results showed that there were obvious axial, tangential and radial velocities in spiral space, and they were bigger than those in smooth tubes. The turbulence intensity was also increased greatly because of the existence of spiral channels. The dirt production was prevented and the tube's convection heat transfer was effectively strengthened. Its surface average heat transfer coefficient had been enhanced by about 20% compared with the smooth tubes; The pressure drop caused by plastic spiral flange was in the permissible range of engineering application. It was suitable for the heat exchanger at a flow velocity lower than 0.8m/s.
Abstract: Real gas effect has great impact on unsteady flow behaviors in wave rotor refrigerator (WRR). In this work, the main thermal separation effect and propagation speed of gasdynamic wave of real gases are briefly studied. Numerical results have shown the large deviations between perfect gas model and real gas model for gasdynamic waves. A corrected wave diagram of WRR has been achieved based on real gas PVT relations, through which the problem of offset design of port timing can be completely solved.
Abstract: The SiC/FexSiy composites were synthesized by reaction sintering process with iron tailings as raw material and carbon as reductant. The room and high temperature flexural strengths and fracture toughness of composites were studied in this paper. Fracture surfaces were observed by means of a scanning electron microscope (SEM). The results showed that the room temperature flexural strength of SiC/FexSiy composites changed along with the different contents of FexSiy and sintering temperature. The flexural strength of composites reaches the maximum at 900°C. The correlation between flexural strength and temperature is consistent with curveⅠ.The fracture toughness of composites is related to the content of FexSiy. The fracture behavior of composites is mainly transcrystalline in room temperature and intercrystalline in high temperature.
Abstract: Flow field of gas and particles in a conveying vessel is investigated by use of a three-dimensional model combined Eulerian approach. Because of the nozzles’ arrangement in this study, the flow patterns of spouts and bubbles can be seen in the gas-solid flow field, which lead to a non-uniform distribution of gas velocity. Solid volume fraction is high near the bottom and low at the top part. The porosity rises with gas speed increasing, as well as time. An improvement is examined to remove the dead zone at the bottom, which results in particles remaining.
Abstract: A rich variety of two-phase microstructures have been shown to form in the directionally solidified Pb-30wt.%Bi alloy. The selection of microstructure is shown to be depended upon the value of G/V (temperature gradient in the liquid divided by growth rate). The microstructure evolution is also discussed based on the competitive growth of different phase at various G/V ratios in directional solidification. Experimental results indicate that the primary a phase is the leading phase and grows with a dendritic/cellular microstructure while the peritectic b phase grows with cellular/planar microstructure in interdendritic/intercellular region at low G/V value. In contrast, competitive structures but not the discrete banded structure is present at high G/V ratio which makes the primary and secondary phase to grow with planar/cellular interface.
Abstract: In fixed-fluidized bed reactor, laboratory evaluation of different catalyst, raw materials and process parameters can be implemented, so it has wide applications in the refining process. In this study, we focused on small fixed-fluidized bed reactor, using Eulerian-Eulerian two-fluid model, simulated the gas-solid flow behavior in it. Gas residence time distribution was measured in order to characterize macro-mixing. At the same time, by changing the reactor structure and operating conditions, we studied their effects on gas-solid macro-mixing characterization. The results show that the effects of structural parameters are larger than operating conditions, and different parameters have different effects. Different parameters can be adjusted to change the gas-solid macro-mixing characterization in small fixed-fluidized bed reactor. Therefore, the small fixed-fluidized bed reactor can provide better results in more application areas.