# Study on the Flow Velocity of Safe and Energy-Saving Transportation of Light-Particle Slurry
## 1 Introduction
[PERSON] [21] regarded the ice crystal particles as a simple cubic arrangement and determined the critical flow velocity by using the maximum filling rate of the particles at the top of the pipeline (52%) as a discriminant of the ice slurry flow pattern. Although the method can obtain a safer critical flow velocity, it is not possible to determine the critical flow rate due to the fact that the complexity of the solid-liquid two-phase flow in the transport process and the size of the critical flow velocity may be overestimated. [PERSON] [22] et al. established a multiphase flow model of Euler fluid in a pipe using Fluent software, studied the effects of initial IPF, particle size, and radius of curvature on the critical flow velocity of the pipe, and found that the critical flow velocity increased continuously with the increase in the initial ice content rate and the particle size, while the critical flow velocity decreased continuously with the increase in the radius of curvature of the bent pipe decreasing. [PERSON] [23] investigated the pressure drop and non-Newtonian behavior of ice slurries in horizontal pipelines with a reduced freezing point of methanol at different methanol concentrations (8-25%) and ice mass fractions (0-29%). It was found that the pressure drops of the ice slurry in the horizontal pipe increased with increasing flow velocity and ice mass fraction. The flow velocity and ice mass fraction showed a dominant effect on the Reynolds number. Newtonian fluid behavior was observed at ice mass fractions of 3% to 5%, while pseudoplastic behavior was observed at ice mass fractions of 9% to 26%. In addition, the critical velocity is closely related to the flow pattern, and the flow pattern of two-phase flow is also one of the focuses of research [24]. In view of this, this paper presents a numerical simulation method for determining the critical flow rate of a light particle slurry in horizontal circular pipe transport. We consider that the melting and agglomeration of ice crystals will affect the density and particle size of the slurry, and both the density and particle size will have an effect on the critical flow velocity. Therefore, in this paper, polyethylene particles with a density of about 922 kg/m\({}^{3}\) are selected to replace the ice crystal particles for the experimental and numerical simulation of slurry flow. The critical flow velocity under different working conditions is obtained through experimental observation, and the accuracy of the numerical simulation method is verified. Finally, the effects of solid-phase content and particle size on the critical flow rate are analyzed, and the flow pattern is compared with the pressure drop data. It was found that, when the slurry was in a moving bed or a stationary bed and transformed into a non-homogeneous suspended bed, there was an increase in the flow rate with a decrease in the pressure drop, which was favorable to the safe and energy-saving transportation of the slurry. When the flow rate is greater than the critical flow rate, the slurry is in a homogeneous suspended bed, where the flow rate increases the pressure drop of the slurry, which then increases rapidly, which is not conducive to the energy-saving transportation of the slurry. It was finally determined that the recommended flow rate for safe energy-saving transportation of slurry in the pipeline is the critical flow rate, and it was found that, when the solid-phase content is constant, the smaller the particle size is, and the more favorable it is for safe energy-saving transportation of slurry. This conclusion can achieve slurry transport in the horizontal circular pipe without clogging and can avoid increasing the transportation cost of the slurry, which is of great significance for the safe and energy-saving transportation of light-grained slurry in horizontal circular pipes in engineering applications.