No abstract

A numerical investigation of aeolian sand particle flow in atmospheric boundary layer is performed with a Eulerian–Eulerian granular pseudofluid model. In this model, the air turbulence is modelled with a large eddy simulation, and a kinetic–frictional constitutive model incorporating frictional stress and the kinetic theory of granular flow is applied to describe the interparticle movement. The simulated profiles of streamwise sand velocity and sand mass flux agree well with the reported experiments. The quantitative discrepancy between them occurs near the sand bed surface, which is due to the difference in sand sample, but also highlights the potential of the present model in addressing near-surface mass transport. The simulated profiles of turbulent root mean square (RMS) particle velocity suggest that the interparticle collision mainly account for the fluctuation of sand particle movement.

The particle circulation rate of the clapboard-type internal circulating fluidized bed (ICFB) is investigated with the particle tracing method. For quantitative determination, the capacitance probe and the differential pressure sensor are used to measure the voidages in the high and low gas velocity regime. The mechanism governing the solid circulation in the ICFB is the competition between driven force, caused by pressure drop across the gap, and the resistance force of particle flow, derived by the flow friction in the wall surface and clapboard, the partial resistance loss of clearance, and the gas bypassing formed from the high to the low gas velocity regime. A modified La Nauze model helped to predict and to calculate the particle circulation rate without giving data of pressure drops.

With the gradual increase in the average exploration depth of domestic coal industry, the conflict between deep coal exploration technology and exploration requirements is becoming increasingly prominent. A series of exploration disaster accidents caused by geological disasters require a high level of survey technology before the deep coal exploration. In this study, a high-resolution single hole measuring system for aquifers in coal seam is proposed. The entire system can be divided into two parts: hardware and software. The hardware probe integrates various sensors for different physical parameters using optical fibre to communicate with the controlling part above the ground. The home-made software is then used to receive and process the signals of temperature, pressure and orientation, as well as the instantaneous image sequence of aquifer with flowing contaminants. A home-made novel particle tracking velocimetry algorithm based on Voronoi diagram is used as the core algorithm to analyse the image sequence and obtain the magnitude and direction of flow at the measuring spot of aquifer. After practical tests, the system is confirmed to be able to effectively monitor the hydrological conditions of the aquifer in coal seam. Therefore, the proposed algorithm can be applied to the evaluation of hydrogeological conditions before well establishment for coal-exploration and to the prevention of potential dangers during the exploration work.

The malfunctioning heart valve will compromise the cardiovascular circulation of the human body. Given that artificial valves can be used to replace a disabled one, a feasible in vitro evaluation system is important before any possible implantation. In this study, two types of transcatheter heart valves, namely, V-A (diameter: 23 mm) and V-B (diameter: 25 mm), are tested and compared by an in vitro experiment that incorporates a circulation system and a particle image velocimetry measuring module. Three dynamical indices, namely, the time-averaged wall shear stress, oscillatory shear index, and relative residence time, are applied for the evaluation. The results show that compared with V-B, V-A leads to lower probabilities of vessel wall damage and thrombosis formation, especially when the flow rate is close to that of the human body (4 l/min). Meanwhile, an independent analysis, which mainly concerns the mean pressure difference and regurgitation volume across the two ends of the valve, demonstrates that V-A has a better performance than V-B, thus verifying the above-mentioned analysis from the perspective of fluid dynamics. Therefore, the present in vitro measuring system is considered effective in evaluating the valve functionality.