Near-wall particle depletion in a flowing colloidal suspension

Effects of particle size on near-wall depletion in mono-dispersed colloidal suspensions

“…For penetration depths of 0.5 µm or more (d/a 2.4), the measured concentration does not decrease further at higher shear rates, and for the penetration depth of 1 µm (d/a = 5.1) the measured concentration even increases. A similar phenomenon was seen in the experiments on suspensions with ethylcellulose particles [1]. It was shown to be caused by competing effects.…”

“…10a). This accounts for the effect where the measured concentration of particles first decreases and then For comparison the results for ethylcellulose (EC) particles in the radius range 50 to 300 nm [1] are also shown. The Peclet number and δ/a for the EC particles are based on the larger diameter of the bimodal particle size distribution.…”

“…However, the estimate of the equivalent wall slip layer thickness allows a qualitative check of the order of magnitude of the wall slip layer thickness determined from the spectroscopic experiments. The experimental details and procedure for analysis of the results are described in Hartman Kok et al [1].…”

“…The use of the ATR-IR technique for measurement of the concentration profile has been described in recent work [1]. The wall depletion in a suspension consisting of ethylcellulose particles (particle diameter ranging from 0.1 to 0.6 µm, concentration 24% v/v) was quantified and interpreted.…”

Heat transfer properties of nanoparticle-in-fluid dispersions (nanofluids) in laminar flow

“…Several mechanisms may lead to smaller improvements in heat transfer coefficient between the nanofluids and the base fluids at higher temperature. These include: (1) rapid alignment of \nanoparticles in lower viscosity fluids, leading to less contact between nanoparticles, and (2) depletion of particles in the near-wall fluid phase [23], leading to an intrinsically lower thermal conductivity layer at the wall. Understanding and isolating which mechanism or mechanisms might be responsible for the experimental results will require significant future work, including computational fluid dynamic modeling of the flows in nanoparticle dispersions.…”