Numerical study of instability of nanofluids: the coagulation effect and sedimentation effect

Abstract

This study is a numerical study on the coagulation as well as the sedimentation effect of nanofluids using the Brownian dynamics method. Three cases are simulated, focusing on the effects of the sizes, volume fraction, and ζ potentials of nano-particles on the formation of coagulation and sedimentation of nanofluids. The rms fluctuation of the particle number concentration, as well as the flatness factor of it, is employed to study the formation and variation of the coagulation process. The results indicate a superposition of coagulation and sedimentation effect of small nano-particles. Moreover, it is stable of nanofluids with the volume fraction of particles below the limit of "resolution" of the fluids. In addition, the effect of ζ potentials is against the formation of coagulation and positive to the stability of nanofluids.

A novel adjustable magnetorheological fluid gradient material of low frequency vibration isolation: a theoretical and experimental study

“…As shown in figure 7, r 14 , r 24 , and r 34 are the vectors from the centers of particles 1 ∼ 3 pointing to the center of particle 4, S i−1,i = l z -u i -u i−1 is the spacing between particle layer i and particle layer i−1 after moving, u i is the displacement of particle layer i, and u i−1 is the displacement of particle layer i−1. From the dipole theory, particle 4 is subjected to the repulsive forces F 14 ∼ F 34 generated by particles 1 ∼ 3, and each force can be calculated by equation ( 6) [34,35]…”

Study on the influence of composition parameters of magnetorheological fluid on its vibration transmission characteristics

“…In equation ( 8), r m is the particle radius, H = B/ µ 0 is the magnetic induction intensity, µ is the absolute permeability of the particle, µ s = µ/µ 0 is the relative permeability of the particle, µ 0 = 4π × 10 −7 N A −2 is the vacuum permeability, and χ e = µ s −1 is the effective magnetic susceptibility. Since the external magnetic field is uniform, so B = 0, the particles are only affected by the magnetic force generated by other particles [29,30]. Take particle chain a and b in figure 5 as the research object, and establish the coordinate system as shown in figure 6.…”

“…Particle 4 is affected by the repulsive forces F 14 , F 24 and F 34 of particles 1-3. According to the dipole theory, each force can be calculated by the following equation [29,31]…”