# Distribution and Deposition of Cylindrical Nanoparticles in a Turbulent Pipe Flow
## 1 Introduction  
Transport of particles through pipes has the advantages of small space occupied, no backhaul, no pollution, flexible setting, long distance transport and so on. Therefore, the transport of particles has been widely used in various industries such as machinery manufacturing, metallurgy, power generation, material engineering, pharmaceutical and food production. The transport of particles is usually accompanied by the process of particle deposition upon the wall surface. It is crucial to reduce the particle deposition in order to improve the conveying efficiency of particles. The mechanism of nanoparticle deposition on a wall is complicated because it is related to the thermophoretic force [1], inertial force of particle, gravitational force [2], Brownian and turbulent diffusion [3]. In the past several decades the transport and deposition of particles in the pipe turbulent flow have been studied a lot for the spherical particles, but very few for non-spherical particles. Actually, the major amount of particles is non-spherical in shape, e.g., cylindrical particles. The transport and deposition of cylindrical particles are very complicated because particle rotation and its orientation distribution are strongly coupled with the translation motion [4]. Moreover, inhomogeneity in the spatial and orientational distribution of particles affects the turbulent flow properties. There are several published works in the literature discussing the transport and deposition of cylindrical particles. In the case of laminar flow with no turbulent diffusion, [PERSON] [5] indicated that the deposition rate for the particles with an intermediate size was mainly dependent on the thermophoresis, turbophoresis and roughness. [PERSON] et al. [6] developed a new model for predicting particle deposition and analyzed the impact of the particle aspect ratio on the deposition. In the case of inertial cylindrical particle with no Brownian diffusion, [PERSON] et al. [7] measured the deposition velocity of particles with a diameter of 1-2 \(\upmu\)m for different Reynolds numbers. They showed that the deposition velocity was mainly dependent on gravitation when Re \(\leq\) 26,000, while dependent on the comprehensive effects of particle size, gravitation and turbulent fluctuations when Re \(>\) 26,000. [PERSON] and [PERSON] [8] measured the deposition velocity of particles of 0.6-2.5 \(\upmu\)m in diameter for different Reynolds numbers and particle aspect ratios, and found that the aspect ratios significantly affected the deposition velocity of particles. [PERSON] et al. [9] studied the particle deposition from a gas stream. They found that the deposition rate of flexible particles was the lowest, while stiff particles had the highest deposition rate. [PERSON] et al. [10] studied the dispersion and deposition of particles with considering the particle inertia and hydrodynamic forces. They found that particles tended to align with the flow direction near the wall, but such a state was unstable for particles with higher inertia. The deposition rate of particles with a larger aspect ratio was higher, but particle inertia had less effect on the particle deposition in the centerline. [PERSON] et al. [11] showed that the deposition rate of particles was proportional to the particle aspect ratio, and the fluctuating velocity gradient had an insignificant effect on the deposition rate. [PERSON] et al. [12] indicated that oscillatory breathing had an important effect on the particle deposition in the lungs. As is shown above, the transport and deposition of cylindrical particles are related to the inertial force of particle, gravitational force, thermophoretic force, Brownian diffusion and turbulent diffusion. For the transport of cylindrical nanoparticles in a turbulent flow with no temperature gradient, the deposition of a particle is mainly resulted from the Brownian and turbulent diffusion, while the thermophoretic force, inertial force of particle and gravitational force are negligible.