混凝土中的爆坑实验研究

利用爆炸相似理论讨论了固体介质中的相同装药量在不同埋深爆炸情况时的爆坑、炸深与埋深的关系，将传统理论的1／3比例因子修正为1／3．4或1／3．6比例因子。据此设计了混凝土中的炸坑效应缩比实验，并利用某原型实验进行了验证。将实验结果与修正后的比例因子计算值进行了对比，符合较好，其精度可用于工程设计计算。     

Magnetically assisted gas–solid fluidization in a tapered vessel: First report with observations and dimensional analysis

The article presents first experimental results on gas–solid fluidization in a tapered bed in presence of an external transverse magnetic field that creates a novel branch in magnetically assisted fluidization. Phase diagrams similar to those used to describe cylindrical beds have been created to distinguish the bed regimes occurring under the action of two principle macroscopic variables such as field intensity and gas flow rate. A detailed analysis and parallelism to the bed behaviour exhibited by non‐magnetic spouted beds of cohesive particles have been performed. Principle process variables such as bed depth, field intensity, particle size, cone angle have been detected. A dimensional analysis utilizing a “pressure transform” of the initial set of variables has been applied to develop scaling relationships. Examples of scaling experimental data pertinent to the minimum spouting point and involving the magnetic granular Bond number have been developed.     

Shape dependence of resistance force exerted on an obstacle placed in a gravity‐driven granular silo flow

Resistance force exerted on an obstacle in a gravity‐driven slow granular silo flow is studied by experiments and numerical simulations. In a two‐dimensional granular silo, an obstacle is placed just above the exit. Then, steady discharge flow is made and its flow rate can be controlled by the width of exit and the position of obstacle. During the discharge of particles, flow rate and resistance force exerting on the obstacle are measured. Using the obtained data, a dimensionless number characterizing the force balance in granular flow is defined by the relation between the discharge flow rate and resistance‐force decreasing rate. The dimensionless number is independent of flow rate. Rather, we find the weak shape dependence of the dimensionless number. This tendency is a unique feature for the resistance force in granular silo flow. It characterizes the effective flow width interacting with the obstacle in granular silo flow. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3849–3856, 2018     

A method of modeling large cratering explosions

Summary Modeling a cratering explosion has made it possible to investigate the dependence of the crater radius on the depth of the charge and the energy of the gas in the cavity. The empirical formula thus obtained is in satisfactory agreement with the results of test explosions in alluvium and loam over a broad interval of charge weights (from 80 kg to 450 t). The model and full-scale experiments are also in agreement with respect to their kinematic characteristics.The role of the gravity field in the cratering process has been clearly established and a corresponding method of calculating the energy of the explosion at different charge depths is proposed.The possibility of modeling a cratering explosion with respect to its kinematic parameters suggests new means of solving a whole series of engineering problems involving the explosive displacement of soil masses.Fizika Goreniya i Vzryva, Vol. 3, No. 1, pp. 119–127, 1967     

Liquid‐like wave structure on granular film from granular jet impact

Results in the literature show that a granular film appears from a dense granular jet impacting on a circular target under certain conditions (Cheng X, Varas G, Citron D, Jaeger HM, Nagel SR, Phys Rev Lett. 2007; 99(18):188001). In current study, granular jet impacts are experimentally studied using a high‐speed camera, and interesting liquid‐like wave structures on the granular film are observed with increasing granular jet velocities or decreasing solid fractions of granular jets. Effects of the particle diameter, the granular jet velocity, and the solid fraction of granular jet on the wave structures are investigated. The dynamic characteristics of granular wave such as the wave frequency and velocity are demonstrated and compared with the liquid jet impact. Results reveal that increasing pushing pressure enhances the gas‐particle interaction inside the nozzle, which causes the granular jet instability and further gives rise to the granular wave at lower solid fractions and higher granular jet velocities. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3276–3285, 2017     

Orbitally shaken bioreactors—viscosity effects on flow characteristics

Phase‐resolved particle image velocimetry measurements were carried out to assess the flow dynamics occurring in orbitally shaken bioreactors of cylindrical geometry when working fluids of increasing viscosity are considered. Study of the phase‐resolved flow characteristics allowed to built a Re‐Fr map, where four quadrants associated to different flow regimes are identified: in‐phase toroidal vortex (low Fr and high Re), out‐of‐phase precessional vortex (high Fr and high Re), in‐phase single vortex (low Fr and low Re), out‐of‐phase counter‐rotating toroidal vortex (high Fr and low Re). Turbulence levels are found to be significant only in the top right quadrant (high Fr and low Re) and scaling of the turbulent kinetic energy obtained with fluid of varying viscosity is obtained using the ratio of the operating Froude number to the critical Froude number associated to the mean flow transition, . Estimates of the mean flow strain deformation as well as of the flow dissipative scale are provided, while a comparison is made between the flow circulation times obtained for different regimes. © 2014 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 60: 3951–3968, 2014     

Studies on Energetic Compounds Part 27: Kinetics and Mechanism of Thermolysis of Bis(Ethylenediamine)Metal Nitrates and Their Role in the Burning Rate of Solid Propellants

Four bis(ethylenediamine)metal(II) nitrate (BEMN) complexes, i.e. [M(EDA)₂](NO₃)₂, where M=Cu, Co, Ni and Zn, have been prepared and characterized. Thermolysis of these complexes induced by heat and drop‐weight impact has been investigated by TG‐DTG, DTA, explosion delay (D_E), explosion temperature (T_E) and impact sensitivity measurement. The kinetics of early thermolysis reaction prior to fast decomposition have been evaluated. Contracting area (CA, n=2) and contracting cube (CC, n=3) equations were found to give the best fits in isothermal TG data among all tested nine mechanism‐based kinetic models. The values of activation energy (E_a), T_E, D_E and activation energy for explosion (E*) have been found to be quite lower for the copper complex as compared to cobalt, nickel and zinc complexes. A mechanism of thermolysis has also been proposed. All these complexes were found to be insensitive towards impact of 2 kg weight up to the height of 110 cm. These complexes were used as energetic burning rate modifiers in the combustion of hydroxy‐terminated polybutadiene (HTPB)‐ammonium perchlorate (AP) composite solid propellants. A two‐fold increase in burning rate was observed with copper and cobalt complexes at low concentration (2% by wt.). The in situ freshly formed metal oxides with large number of active sites in their crystallites seem to be better additives for combustion of propellants.     

Computational Study of Impingement Jet Drying of Seeds Using Superheated Steam Based on Kinetic Theory of Granular Flow

A Eulerian model including the kinetic theory of granular flow (KTGF) and mass transfer in the period of saturated wet surface has been developed to simulate continuous drying of particulate solids using superheated steam in a radial impingement jet system. When applying this type of drying processes, the preliminary results obtained show good predictive ability of the Eulerian modeling based on KTGF. It is concluded that the present study and other works of modeling can be used to study the dynamics and control of this drying process and thus would facilitate the equipment design and scaling.     

Numerical simulation of particle dynamics in different flow regimes in a rotating drum

Flow regimes in a horizontal rotating drum are important to industrial applications but the underlying mechanisms are not clear. This paper investigated the granular flow dynamics in different regimes using the discrete element method. By varying the rotation speed and particle-wall sliding friction over a wide range, six flow regimes were produced. The macroscopic and microscopic behaviour of the particle flow were systematically analysed. The results showed that the angle of repose of the moving particle bed had a weak dependence on the rotation speed in the slumping and rolling regimes, and increased significantly as the flow transited to the cascading and cataracting regimes. The mean flow velocity increased with the rotation speed, but the normalised velocity against the drum speed in the continuous regimes collapsed into a single curve, which can be well described by a log-normal distribution. The particle bed at low rotation speed had a similar density to those of the random loose packing, and became more dilated with the increase of the rotation speed. Similarly, the mean coordination number showed linear dependence on the drum speed. Both the collision energy and collision frequency increased with the rotation speed. However, the normalised collision energy in different regimes can be fitted with a simple scaling law.     

Validating granular segregation rate models

One significant hindrance to the development of granular segregation rate models is the inherent difficulty of performing the dynamic experiments required for validation. Here, we seek to overcome this experimental hurdle by establishing an “equilibrium” between segregation and flow perturbation in free surface granular flows and use steady‐state—rather than dynamic—measurements for validation. That is, we combine the segregation rate expressions to be tested with a segregation control framework such that the perturbation rate enables us to infer the segregation rate by measuring simply the steady state extent of segregation. We use periodic flow inversions via an axially located baffle in a tumbler‐type mixer to provide the perturbations that ultimately alter the steady‐state distribution of particles. This work examines the efficacy of existing models for binary segregation driven by either size or density differences. For completeness, we test our model validation framework both computationally and experimentally. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3756–3763, 2017     

Impact of Contact Scaling and Drag Calculation on the Accuracy of Coarse-Grained Discrete Element Method

The accuracy of coarse-grained discrete element method (CGDEM) relies on appropriate scaling rules for contact and fluid-particle interaction forces. For fluidized bed applications, different scaling rules are used and compared with DEM results. The results indicated that in terms of averaged values as mean particle position and voidage profile, the coupling of computational fluid dynamics and CGDEM leads to accurate results for low scaling factors. Regarding the particle dynamics, the approach leads to an underestimation of RMS values of particle position indicating a loss of particle dynamics in the system due to coarse graining. The impact of cell cluster size on drag force calculation is studied. The use of energy minimization multiscale drag correction is investigated, and a reduced mesh dependency and good accuracy are observed.     

Dynamic densification of wet granular materials in continuous dense flows under gravity

The continuous granular flow under gravity extensively exists in chemical processes, and the dynamic behaviors of granular flow under different gas–liquid environments are investigated by synchronous slide-type high-speed photography. Results show that a hexagonal arrangement is observed after three-stage densification in wet granular flow, while these structures are almost absent in the dry system. Further analysis shows that under the induction of liquid, the special cavity collapse in stage І is the pre-condition of granular densification, and the subsequent densification in stage ІІ for the first time gives the experimental proof for the hypothesis that energy barriers exist and depend on the friction characteristics, and the cage effect in stage ІІІ provides a guarantee for the formation of a hexagonal contact network. Besides, three-stage densification in the three-phase system mainly occurs in the region with low gas and liquid velocities (G* < 0.716 and L* < 0.023 in this work).     

Development of a virtual Couette rheometer for aerated granular material

A novel rheometer to study the behavior of granular materials in an aerated bed of particles has been developed. The device, called the aerated bed virtual Couette rheometer, is shown to be able to measure the shear stresses in the quasi-static and in the intermediate flow regimes. To validate the instrument, a Newtonian fluid of known viscosity was first sheared. The device was then used for measuring the shear stress of nonaerated glass beads with three -3D printed cells of different sizes to validate the optimal radial position, r*, where both shear rate and shear stress are independent of the cell radius. The results for the nonaerated glass beads displayed Coulomb behavior. The same behavior was observed when the bed was aerated. These experiments also showed that for a fixed shear rate the shear stress decreases as the aeration velocity, U. increases.     

Flow of particles suspended in a sheared viscous fluid: Effects of finite inertia and inelastic collisions

We investigate in this article the macroscopic behavior of sheared suspensions of spherical particles. The effects of the fluid inertia, the Brownian diffusion, and the gravity are neglected. We highlight the influence of the solid‐phase inertia on the macroscopic behavior of the suspension, considering moderate to high Stokes numbers. Typically, this study is concerned with solid particles O (100 μm) suspended in a gas with a concentration varying from 5% to 30%. A hard‐sphere collision model (with elastic or inelasic rebounds) coupled with the particle Lagrangian tracking is used to simulate the suspension dynamics in an unbounded periodic domain. We first consider the behavior of the suspension with perfect elastic collisions. The suspension properties reveal a strong dependence on the particle inertia and concentration. Increasing the Stokes number from 1 to 10 induces an enhancement of the particle agitation by three orders of magnitude and an evolution of the probability density function of the fluctuating velocity from a highly peaked (close to the Dirac function) to a Maxwellian shape. This sharp transition in the velocity distribution function is related to the time scale which controls the overall dynamics of the suspension flow. The particle relaxation (resp. collision) time scale dominates the particulate phase behavior in the weakly (resp. highly) agitated suspensions. The numerical results are compared with the prediction of two statistical models based on the kinetic theory for granular flows adapted to moderately inertial regimes. The suspensions have a Newtonian behavior when they are highly agitated similarly to rapid granular flows. However, the stress tensors are highly anisotropic in weakly agitated suspensions as a difference of normal stresses arises. Finally, we discuss the effect of energy dissipation due to inelastic collisions on the statistical quantities. We also tested the influence of a simple modeling of local hydrodynamic interactions during the collision by using a restitution coefficient which depends on the local impact velocities. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Hydrodynamic drift ratchet scalability

The hydrodynamic drift ratchet provides a novel means to continuously separate particles at the microscale, based on particle size. Separation arises from a combination of diffusion and particle‐wall hydrodynamic interactions. As there are currently no verified experiments, our aim is to determine numerically how these systems scale so that appropriate experiments can be designed. Using nondimensional variables, we derive the correct scaling parameters governing drift ratchets by simulating individual particle motion using a model that treats the particle dynamics at pore walls as elastic reflections. While our model does not quantitatively resolve the detailed hydrodynamic interactions, we show that it does recover the correct scaling behavior for these interactions. Our simulations demonstrate that the drift velocity relative to the characteristic pore size is independent of pore size if all the relevant nondimensional groups remain constant. Dynamic similarity can be used to facilitate the appropriate design and testing protocols for experiments. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2358–2366, 2017     

Dynamic polygonal spreading of a droplet on a lyophilic pillar-arrayed surface

We experimentally investigated the dynamic polygonal spreading of droplets on lyophilic pillar-arrayed substrates. When deposited on lyophilic rough surfaces, droplets adopt dynamic evolutions of projected shapes from initial circles to final bilayer polygons. These dynamic processes are distinguished in two regimes on the varied substrates. The bilayer structure of a droplet, induced by micropillars on the surface, was explained by the interaction between the fringe (liquid in the space among the micropillars) and the bulk (upper liquid). The evolution of polygonal shapes, following the symmetry of the pillar-arrayed surface, was analysed by the competition effects of excess driving energy and resistance which were induced by micropillars with increasing solid surface area fraction. Though the anisotropic droplets spread in different regimes, they obey the same scaling law S ~ t^2/3 (S being the wetted area and t being the spreading time), which is derived from the molecular kinetic theory. These results may expand our knowledge of the liquid dynamics on patterned surfaces and assist surface design in practical applications.     

Energy release of mixed explosives during propagation of a nonideal detonation under conditions similar to the operation conditions of a blasthole charge

Detonation experiments were performed in a specially developed explosive device simulating a blasthole using charges of fine-grained and coarse-grained (granular) 30/70 TNT/ammonium nitrate mixtures of identical density 0.89 g/cm³ in steel shells with an inner diameter of 28 mm and a wall thickness of 3 mm at detonation velocities of 4.13 and 2.13 km/sec, respectively. Despite significant differences in detonation velocity (pressure), identical expansion of the charge shells was observed. On the other hand, numerical simulations of detonation propagation in the explosive device with the corresponding velocities ignoring the possibility of energy release behind the shock front show that the expansion of the charge shell is always greater in the case of a high-velocity regime. It is concluded that under the conditions simulating detonation propagation and the work of explosion products in a blasthole, effective additional energy release occurs behind the low-velocity (nonideal) detonation front. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 111–120, July–August, 2007.     

Self organization of granular flow by basal friction variation: Natural jump,moving bore,and flying avalanche

The article discusses the response of rapid granular downslope flow to an abrupt change in basal friction. Although granular discharge from silo and hoppers has received considerable attention in the past, the flow behavior for an abrupt change in basal friction is hitherto unexplored. In the present study, the channel floor comprises of a smooth surface (bed friction angle—δ_S) and a rough surface (bed friction angle—δ_R) such that the angle of repose of the granular material (θ_r) lies between δ_S and δ_R and the flow features are observed as the channel inclination (θ) is varied from ≈δ_S to >δ_R. Experiments are performed in two channels with different extent of rough surface for two grain sizes with the same angle of repose and different inlet depth of granular flow. The visualization studies reveal a rich variety of flow features namely moving bore, rapid granular flow, flying avalanche and granular jump. Natural granular jump formed by mere frictional dissipation without any external forcing has not been reported earlier. The variety of flow features primarily results from the interplay of downslope motion of variable depth, collision-driven piling of grains, and slope shaving avalanches. The observed flow phenomena have been satisfactorily analyzed by the well-known depth-averaged avalanche flow equations under conditions of incompressible granular flow.     

Rheology and viscosity scaling of the polyelectrolyte xanthan gum

The viscosity as a function of concentration for xanthan gum in both salt‐free solution and in 50 mM NaCl is measured and compared with a scaling theory for polyelectrolytes. In general, the zero shear rate viscosity and the degree of shear thinning increase with polymer concentration. In addition, shear thinning was observed in the dilute regime in both solvents. In salt‐free solution, four concentration regimes of viscosity scaling and three associated critical concentrations were observed (c* ≈ 70 ppm, c_e ≈ 400 ppm, and c_D ≈ 2000 ppm). In salt solution, only three concentration regimes and two critical concentrations were observed (c* ≈ 200 ppm and c_e ≈ 800 ppm). In the presence of salt, the polymer chain structure collapses and occupies much less space resulting in higher values of the critical concentrations. The observed viscosity‐concentration scaling is in very good agreement with theory in the semidilute unentangled and semidilute entangled regimes in both salt‐free and 50 mM NaCl solution. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009