Abstract
Aerosol nanoparticle deposition onto a surface under a temperature gradient is commonly applied in the chemical and medical industries. In this study, a numerical investigation with a two-phase model is used to investigate the deposition characteristics of nanosized particles in a 90° square bend. The effects of variations in the gas phase physical parameters, such as density, viscosity, and thermal diffusivity with changing temperatures are studied. The main forces acting on the particles are the drag forces, Brownian forces, and thermophoretic forces. A discrete phase model (DPM) based on the FLUENT software is used to investigate particle transfer. The results show that in a temperature gradient flow, particles move towards the colder wall, and some of them strike and deposit onto its surface. The particle deposition efficiency increases with the temperature gradient rising. The Brownian force plays a more important role in particle deposition when smaller particles are used. Because of inertia and gravity, particle deposition on the four surfaces of a 90° square bend tube is inhomogeneous. The deposition efficiency on the floor surface increases with increasing particle diameter. On the contrary, larger particles decrease the deposition efficiency on the ceiling surface.
Highlights
Aerosol nanoparticle deposition in bend surfaces is adopted in diverse scenarios, such as chemical and medical industries, environmental engineering, instrument andYin et al, Aerosol and Air Quality Research, 18: 1746–1755, 2018 semiconductor engineering (Garoosi et al, 2015a; Gupta et al, 2016; Tiwari et al, 2017; Zhu et al, 2017; Chen et al, 2018)
The results show that in a temperature gradient flow, particles move towards the colder wall, and some of them strike and deposit onto its surface
Particle behavior in a continuous bend flow field depends on the flow Reynolds number and the curvature ratio, which can be combined into another parameter, Dean number (De)
Summary
Aerosol nanoparticle deposition in bend surfaces is adopted in diverse scenarios, such as chemical and medical industries, environmental engineering, instrument andYin et al, Aerosol and Air Quality Research, 18: 1746–1755, 2018 semiconductor engineering (Garoosi et al, 2015a; Gupta et al, 2016; Tiwari et al, 2017; Zhu et al, 2017; Chen et al, 2018). Shimada et al (1993) first determined the deposition velocities for monodisperse aerosol particles with diameters of 10–40 nm at two cross-sections of pipe by considering Brownian and turbulent diffusive deposition Apart from this, he (1994) found that thermophoretic deposition was enhanced by the increase in the wall temperature variation, but this phenomenon did not depend on the particle. Chiou et al (2011) considered the particle transport mechanisms of Brownian and turbulent diffusion, eddy impaction, particle inertia, and thermophoresis, and discovered that in the presence of a temperature gradient near the container wall, the thermophoretic effect plays a more active role in movement through the viscous sublayer compared to the other mechanisms, and the smallest particles benefit most from this effect because of their low inertia. He concluded that Brownian diffusion and thermophoresis are the only important slip mechanisms in laminar flow. Zahmatkesh (2008) showed that depending upon temperature gradient, varying degrees of thermophoretic and Brownian diffusion may contribute to particle deposition. Lin et al (2009a, b) studied the transport and deposition of nanoparticles in bends for different angular velocities, Dean numbers, and Schmidt numbers. Healy and Young (2010) critically discussed the various expressions for the thermophoretic force on an aerosol particle. Chiou et al (2011) considered the particle transport mechanisms of Brownian and turbulent diffusion, eddy impaction, particle inertia, and thermophoresis, and discovered that in the presence of a temperature gradient near the container wall, the thermophoretic effect plays a more active role in movement through the viscous sublayer compared to the other mechanisms, and the smallest particles benefit most from this effect because of their low inertia. Abarham et al (2013) developed an axisymmetric model to predict thermophoretic deposition, and found that the axisymmetric model estimated the deposited mass more accurately. Guha and Samanta (2014) examined various thermophoresis expressions and computed the deposition of nano- to micro-sized particles on both vertical and horizontal surfaces. Lin et al (2010, 2014) studied aerosol particle deposition under the combined effects of Brownian diffusion, turbulent diffusion, particle coagulation, and breakage with a moment method
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