Optimization Design of a Pneumatic Wheat-Shooting Device Based on Numerical Simulation and Field Test in Rice–Wheat Rotation Areas

In rice–wheat rotation areas of China, traditional wheat seeders have severe blockage, low working efficiency and poor seeding quality. In this study, a pneumatic shooting technology was designed, consisting mainly of a nozzle, shell and acceleration tube. To improve the sowing depth of the pneumatic shooting device, the response-surface methodology of structure parameters and CFD simulation technology was adopted in this work. The effects of working pressure, acceleration-tube diameter and throat distance on the steady airflow length (SAL) and steady airflow velocity (SAV) were studied by airflow field analysis, and the response-surface method was introduced to obtain the optimal parameter combination of the pneumatic shooting device for wheat. The optimal parameter combination was working pressure 686 kPa, acceleration tube diameter 8 mm and throat distance 20 mm. The simulation result showed that the optimized device of pneumatic shooting performs faster and has more stable airflow field characteristics in comparison to the initial device. The field test demonstrated that the optimized device has about 68% higher seeding depth than the initial device. The average field-seeding depth of the optimized device was 19.95 mm, which is about 68% higher than the initial device. The emergence rate for the optimized device was about 88.7% without obvious reduction. CFD and response-surface methods positively affect the optimization of pneumatic wheat-shooting devices, and the significance was also confirmed.

Optimization of fluid characteristics in the main nozzle of an air-jet loom

As part of the propulsion system, the fluid dynamic features of the main nozzle can immediately affect the stability and efficiency of an air-jet loom. This study aims to optimize the fluid characteristics in the main nozzle of an air-jet loom. To investigate ways of weakening the effect of airflow congestion and backflow phenomenon occurring in the sudden expansion region, the computational fluid dynamics method is employed. Three-dimensional turbulence flow models for a regular main nozzle and 12 prototypes with different nozzle core tip geometry are built, simulated, and analyzed to get the optimum performance. Furthermore, a set of modified equations that consider the direction of airflow are proposed for better estimation of the friction force applied by the nozzle. The result shows that the nozzle core tip's geometry has a significant influence on the internal airflow, affecting the acceleration tube airflow velocity, turbulence intensity, and backflow strength of the sudden expansion region, and other critical fluid characteristics as well. Several proposed models have succeeded in reducing the backflow and outperforming the original design in many different aspects. Models A-60 and C-P, in particular, manage to increase the propulsion force by 37.6% and 20.2% in the acceleration tube while reducing the maximum backflow by 57.1% and 52.2%, respectively. These simulation results can provide invaluable information for the future optimization of the main nozzle.

MATHEMATICAL DESCRIPTION OF THE TWO-PHASE FLOW MOTION AT THE OUTLET OF THE VERTICAL ACCELERATION TUBE OF A JET MILL WITH A PLANE GRINDING CHAMBER OF TORUS FORM

Nowadays building material industry as well as other industry branches exercise bigger demand to use powders with high dispersion. Jet mills are used to produce such powders that is why development of new jet mill designs, increase of grind efficiency, reduction of specific energy consumption is an important objective. This article provides a mathematic description of the two-phase flow motion at the outlet of the vertical acceleration tube of a jet mill with a plane grinding chamber of torus shape. The part of the acceleration tube above the impact plate is essential for grinding, as the initial particle grind occurs at this very section, in the grind chamber. Moreover, the initial grind defines the size of particles, that are further reground at the mill chamber. As a result of theoretical calculations, a formula is obtained that allows to determine the height of the acceleration tube from the bump element at the specified speed parameters of the two-phase flow. The article also contains the graph, that shows how particle velocity depends on the current (specific) height point (value) of the acceleration tube. This graph demonstrates that particle size strongly affects the way they move in the grind chamber. The formula allows to calculate the effective propulsion range of particles, depending on theirs' size, by presuming they have the maximum velocity

Simulation of ENACCEF2 Premixed Hydrogen-Air Mixture Deflagration Experiment Using OpenFOAM

During a severe accident in a nuclear power plant, hydrogen would be generated due to the oxidation of metallic components in steam atmosphere. In the containment hydrogen would form a combustible mixture, posing a deflagration or even detonation risk threatening the integrity of the containment. In order to estimate possible loads generated by the hydrogen combustion, reliable numerical tools are needed to simulate the deflagration process. Recently, the French MITHYGENE project consortium and the European Technical Safety Organization Network (ETSON) organized a benchmark on hydrogen combustion to identify the current level of the computational tools in the area of hydrogen combustion simulation under a severe accident typical conditions. The benchmark was based on the experiments performed in the ENACCEF2 facility. This paper presents post-benchmark simulations of the selected ENACCEF2 facility premixed hydrogen combustion experiment. The presented simulations were performed using a custom-built turbulent combustion OpenFOAM solver based on the progress variable model. Turbulent flame acceleration phase in the acceleration tube was well predicted. Furthermore, the simulations were able to capture the interaction between the flame and shock wave which was generated by the turbulent deflagration flame and reflected at the end of the ENACCEF2 tube. The overall numerical results show good agreement with the qualitative and quantitative behavior of the velocity results and flame front propagation.