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External flows
Published in Zhigang Li, Nanofluidics, 2018
Thermophoresis is about the motion of particles suspended in a fluid caused by a temperature gradient. It is of great importance in quite a few areas, including aerosol science, combustion, and nanofluids (fluids dispersed with nanoparticles). The force acting on a particle induced by a temperature gradient is called the thermophoretic force. As the particle moves, a drag force is developed on it. When the drag force becomes equal to the thermophoretic force, the particle moves with a constant velocity, which is termed the thermophoretic velocity. The mechanism responsible for thermophoresis depends on the flow regime.
Fouling of Heat Exchangers
Published in Sadık Kakaç, Hongtan Liu, Anchasa Pramuanjaroenkij, Heat Exchangers, 2020
Sadık Kakaç, Hongtan Liu, Anchasa Pramuanjaroenkij
Thermophoresis is the movement of small particles in a fluid stream when a temperature gradient is present. Cold walls attract colloidal particles, while hot walls repel these particles. Thermophoresis is important for particles below 5 μm in diameter and becomes dominant at about 0.1 μm.
Mixed convective flow of Casson nanofluid in the microchannel with the effect of couple stresses: irreversibility analysis
Published in International Journal of Modelling and Simulation, 2023
A. Felicita, B. J. Gireesha, B. Nagaraja, P. Venkatesh, M.R. Krishnamurthy
Concentration profile for varying and is displayed in Figures 14 and 15. On enhancing thermophoresis parameter concentration reduces. Thermophoresis is a mechanism of particle transfer due to temperature gradient and finds its applications in the field of aerosol technology. It is worth noticing that concentration profile rises with increment in whereas depletes with escalation of . Increment of concentration with larger values of is because of the random motion of nano-sized particles which prohibit them to settle down, thus mass flux rises, consequently concentration is observed to rise throughout the flow. On the other side we visualize to reduce concentration. Thus, the results of the present work conclude that even though both Brownian motion and thermophoresis are the phenomenon concerned with nanoparticle migration, the former has direct relation and the latter holds inverse relation with the concentration profile. On enhancing we notice concentration profile to go upwards as in Figure 16, it’s as expected because Schmidt number is the ratio of momentum diffusivity to mass diffusivity which implies that rise in is nothing but rise in momentum diffusivity.
Heat and mass transfer analysis of radiative fluid flow under the influence of uniform horizontal magnetic field and thermophoretic particle deposition
Published in Waves in Random and Complex Media, 2022
B. C. Prasannakumara, R. J. Punith Gowda
Thermophoresis is useful in a wide range of industrial and micro-engineering applications like nuclear reactor safety, heat exchanger corrosion and gas cleaning. This phenomenon occurs when diverse kinds of transportable particles are exposed to a thermal gradient. The various kinds of particles react in diverse ways. Small particles may settle on a cold surface and move away from a warmth surface due to thermophoresis. The influence of thermophoretic particle deposition (TPD) in cross stream past a cylinder was first investigated by Garg and Jayaraj [21]. The nanomaterial flow across a moving disk with TPD was defined by Gowda et al. [22]. Kumar et al. [23] investigated the continuous stream of Casson fluid via a narrow needle with TPD. Wang et al. [24] investigated TPD and magnetic field impact on a liquid flow passing through a surface. The impact of thermophoretic diffusion on a nanomaterial fluid stream above a curved sheet was quizzed by Kumar et al. [25]. The upshot of TPD in a stable flow of micropolar NF on a surface with aggregation of nanoparticles was swotted by Yu et al. [26].
Analysis of Particle Dispersion and Entropy Generation in Turbulent Mixed Convection of CuO-Water Nanofluid
Published in Heat Transfer Engineering, 2019
Farzad Bazdidi-Tehrani, Seyed Iman Vasefi, Amir Masoud Anvari
Figure 7 depicts the distributions of CuO nanoparticles across the square duct cross section in the fully developed region (y/Dh = 50), and at and 8208. The nanoparticles are considered to disperse uniformly at the inlet and the average value of nanoparticles volume fraction is assumed as 0.1%. However, adding any surfactant to the mixture will change the nanoparticles dispersion and will alter the results [44]. It can be seen that the nanoparticles are dispersed non-uniformly and the particle volume fraction is higher in the core region of the duct. Based on the momentum equation, thermophoresis and Brownian motion alongside the turbulent eddies are the effective mechanisms regarding the particles dispersion across the duct cross section. Thermophoresis is the particle motion due to the existing temperature gradients. The higher molecular velocities on one side of a particle, because of an increasing temperature, enhances the momentum exchange and creates a force in the direction of a decreasing temperature. Therefore, along the lateral x-direction, the nanoparticles migrate in the direction of a decreasing temperature (from near wall to the core region) and cause a non-uniform distribution. On the other hand, the random movement of nanoparticles suspended in the water (Brownian motion) resulting from their collision with the fast-moving atoms or molecules of water, causes to counterbalance the thermophoretic effect. The Brownian force tends to move the nanoparticles in the opposite direction to the concentration gradient. Therefore, the Brownian motion and thermophoretic force act against one another.