# Pressure Drop and Particle Settlement of Gas-Solid Two-Phase Flow in a Pipe
## 1 Introduction  
Particle transport through a pipe is quite common in the power generation, metallurgy, machinery manufacturing, pharmaceutical and food production, and material engineering industries, among others. In transport processes, it is important to characterize the pressure drops and particle settlement [1; 2; 3; 4], which are directly related to the transport efficiency and particle deposition to the wall-even blockage, well.  
Some research has already been published on particle settlement and pressure drops in gas-solid two-phase flow in a pipe. [PERSON] et al. [5] showed that vortex shedding resulting from natural convection changed the sedimentation velocity and induced horizontal oscillation. [PERSON] et al. [6] performed a study on particle sedimentation in suspensions with high particle concentrations and pointed out that Eulerian-Eulerian simulations could account for some of the detailed particle-settling processes. [PERSON] et al. [7] found that the initial geometric arrangement of multiple particles had a great effect on sedimentation behavior. [PERSON] [8] indicated that the transport of dense particles depended on the ratio of the shear velocity of the flow to the settling velocity of the particles and the Reynold's number of the sedimentation. [PERSON] and [PERSON] [9] reported that the pressure drops showed completely opposite trends in two situations with different particle concentrations were used. The pressure drops increased as the particle volume concentration increased. [PERSON] et al. [10] found that the pressure-drop increase rate depended strongly on the Archimedes number.  
[PERSON] et al. [11] indicated that at higher gas velocities, the pressure drops predicted using the standard \(k\)-\(\omega\) turbulence model are higher than those obtained when using the standard \(k\)-\(\epsilon\) model. [PERSON] and [PERSON] [12] presented the minimum pressure gradient point experimentally through pressure gradient versus gas velocity curves and indicated that the transition velocity between dense and diluted flows enhanced as the particle density and diameter increased. [PERSON] and [PERSON] [13] presented a pressure drop- and Froude number-dependence on the particle size and density.  
As shown above, although there have been some studies on particle settlement and pressure drop in gas-solid two-phase flow, few studied both at the same time. In addition, the factors affecting particle settlement and pressure drop include inlet velocity, particle volume concentration, particle mass flow, particle diameter, and so on, but there is no correlation expression between particle settlement, pressure drop, and these factors. Therefore, in the present study, the momentum equations based on a two-fluid model are solved numerically, and the distributions of velocity and particle concentration as well as pressure drop are analyzed. The effects of inlet velocity, particle volume concentration, particle mass flow, and particle diameter on particle settlement and pressure drop are discussed. Finally, the relationship between the settlement index, pressure drop, and related synthetic parameters is determined based on the numerical data.