A new circulating accumulation emission model for assessing dust emission from open pit mine

To reduce the inaccuracy of using the monitoring data outside the pit to evaluate the unorganized emission dust source of open pit mine, the circulating accumulation emission model is established. Based on the model, the monitoring data in the pit can be converted into the dust emission from the pit. The main conclusions include: (1) the circulating accumulation emission model is suitable for the dust diffusion process in open pit mine. The ratio of diffusion $$\mu$$ μ and the ratio of surplus $$\varepsilon$$ ε were used to simulate the dust diffusion process in open pit mine, containing emission, retention and diffusion. (2) The initial value of the dust in the pit before the team operation has little influence on the final stable value. (3) When the external dust enters the pit, it will accumulate under the action of eddy current. The dust background value in the pit is different from that outside the pit. (4) The dust emission from the pit can be calculated from the monitoring data in the pit based on the circulating accumulation emission model. The model can deal with environmental changes such as the wind direction and speed, without arranging a lot of external monitoring equipment like the traditional external monitoring methods.

Coagulation Instability in Protoplanetary Disks: A Novel Mechanism Connecting Collisional Growth and Hydrodynamical Clumping of Dust Particles

We present a new instability driven by a combination of coagulation and radial drift of dust particles. We refer to this instability as “coagulation instability” and regard it as a promising mechanism to concentrate dust particles and assist planetesimal formation in the very early stages of disk evolution. Because of dust-density dependence of collisional coagulation efficiency, dust particles efficiently (inefficiently) grow in a region of positive (negative) dust density perturbations, leading to a small radial variation of dust sizes and as a result radial velocity perturbations. The resultant velocity perturbations lead to dust concentration and amplify dust density perturbations. This positive feedback makes a disk unstable. The growth timescale of coagulation instability is a few tens of orbital periods even when dust-to-gas mass ratio is on the order of 10−3. In a protoplanetary disk, radial drift and coagulation of dust particles tend to result in dust depletion. The present instability locally concentrates dust particles even in such a dust-depleted region. The resulting concentration provides preferable sites for dust–gas instabilities to develop, which leads to further concentration. Dust diffusion and aerodynamical feedback tend to stabilize short-wavelength modes, but do not completely suppress the growth of coagulation instability. Therefore, coagulation instability is expected to play an important role in setting up the next stage for other instabilities, such as streaming instability or secular gravitational instability, to further develop toward planetesimal formation.

A New Circulating Accumulation Emission Model for Assessing Dust Emission From Open Pit Mine

In order to reduce the inaccuracy of using the monitoring data outside the pit to evaluate the unorganized emission dust source of open pit mine, the circulating accumulation emission model is established. Based on the model, the monitoring data in the pit can be converted into the dust emission from the pit. Main conclusions include: (1) the circulating accumulation emission model is suitable for the dust diffusion process in open pit mine. The model contains three part, which correspond to dust emission, retention and diffusion in open pit mine. (2) The initial value of the dust in the pit before the team operation has little influence on the final stable value. (3) The dust background value of surrounding environment monitored outside the pit can not be directly used. When the dust enters the pit, it will accumulate under the action of eddy current. To eliminate the effect of background value, the monitoring data should be subtracted by the accumulated value. (4) The dust emission from the pit can be calculated in a certain monitoring period based on the circulating accumulation emission model. Hence the dust emission assessment of open pit can be completed more efficiently based on this model.

Particle Behavior Investigation for Different Structures of Hoppers

In this paper, two different kinds of hoppers were proposed. In order to investigate particle behavior in hoppers, the discrete element method (DEM) was introduced and soybeans were chosen as test material Particle behavior of four different samples were simulated under different flow rate. Results reveal that the deflection cone greatly affected the particle behavior. After adding the deflection cone in the hopper, the trajectory of particle material can be restrained and the dust diffusion can be reduced.different distances of the deflection cone showed different guiding effect on the particle movement.

Dynamics of small grains in transitional discs

ABSTRACT Transitional discs have central regions characterized by significant depletion of both dust and gas compared to younger, optically thick discs. However, gas and dust are not depleted by equal amounts: gas surface densities are typically reduced by factors of ∼100, but small dust grains are sometimes depleted by far larger factors, to the point of being undetectable. While this extreme dust depletion is often attributed to planet formation, in this paper we show that another physical mechanism is possible: expulsion of grains from the disc by radiation pressure. We explore this mechanism using 2D simulations of dust dynamics, simultaneously solving the equation of radiative transfer with the evolution equations for dust diffusion and advection under the combined effects of stellar radiation and hydrodynamic interaction with a turbulent, accreting background gas disc. We show that, in transition discs that are depleted in both gas and dust fraction by factors of ∼100–1000 compared to minimum mass Solar nebular values, and where the ratio of accretion rate to stellar luminosity is low ($\dot{M}/L \lesssim 10^{-10}\, \mathrm{ M}_\odot$ yr$^{-1}\, \mathrm{ L}_\odot ^{-1}$), radiative clearing of any remaining ${\sim}0.5\, \mu\mathrm{ m}$ and larger grains is both rapid and inevitable. The process is size-dependent, with smaller grains removed fastest and larger ones persisting for longer times. Our proposed mechanism thus naturally explains the extreme depletion of small grains commonly found in transition discs. We further suggest that the dependence of this mechanism on grain size and optical properties may explain some of the unusual grain properties recently discovered in a number of transition discs. The simulation code we develop is freely available.