Withdrawing a non-Newtonian fluid by a moving inclined plate with account for the near-wall split effect

A fluid withdrawn by a moving inclined surface with account for the near-wall slip effect is analyzed theoretically. A non-Newtonian fluid task is stated in general form. The solving of this task enables revealing the basic physical principles and mechanisms of the process over the entire withdrawal velocity range realized in practice. The case of withdrawing a finite yield stress viscoplastic fluid is considered.

Dip-coating with a particulate suspension

The coating of a plate withdrawn from a bath of a suspension of non-Brownian, monodisperse and neutrally buoyant spherical particles suspended in a Newtonian liquid has been studied. Using laser profilometry, particle tracking and local sample weighing we have quantified the thickness $h$ and the particle content of the film for various particle diameters $d$ and volume fractions ($0.10\leqslant \unicode[STIX]{x1D719}\leqslant 0.50$). Three coating regimes have been observed as the withdrawal velocity is increased: (i) no particle entrainment ($h\lesssim d$), (ii) a monolayer of particles ($h\sim d$), and (iii) a thick film ($h\gtrsim d$), where the suspension behaves as an effective viscous fluid following the Landau–Levich–Derjaguin law. We discuss the boundaries between these regimes, as well as the evolution of the liquid and solid content of the coating over the whole range of withdrawal capillary number and volume fractions.

Temperature Field Measuring and Simulation of CMSX-6 Superalloy during Directional Solidification

A three-dimensional model of CMSX-6 superalloy coupons was built in the paper, temperature field was calculated with software ProCAST. The temperature values of coupons were indicated from the measurement at the rate of 3 mm min-1 withdrawal velocity during directional solidification process, and the temperature gradient of different location of the coupons were calculated. It turned out that: the simulated results and the measured results are in good agreement; due to the different medial and lateral affected by radiation, isotherms showed sloped distributions in the process of the withdrawal; the temperature gradient of the measured positions in the coupons which are 10 mm, 50 mm, 100 mm, 150 mm far from the copper chill, are 8.0 Kmm-1, 3.0 Kmm-1, 2.5 Kmm-1, 1.8 Kmm-1 respectively.

Preparation of Porous Ti Plate with Nanograde Pore Size by Dip-Coating Method

The porous Ti plates with nanograde pore size were successfully prepared by dip-coating technique, using stainless steel plates as support and 400mesh Ti powders as raw material. The stainless steel plates were firstly dipped into Ti slurry and then pulled out with desired withdrawal velocity. After sintered in a vacuum furnace, stainless steel supports were removed by aqua regia. The obtained products were characterized by X-ray diffraction, sanning electron microscope and N2 adsorption–desorption isotherms. The results had shown that the thickness and pore characters of porous Ti plates could be controlled by adjusting the withdrawal velocity. When the withdrawal velocity was controlled between 0.2mm/s and 1mm/s, the porous Ti plates had smooth surface without cracks and the most pores were interconnected. The maximum pore diameters could be less than 300nm and the porosities of porous Ti plates are more than 4.9%. The kind of preparation method has advantages of simple technology, easy operation and high purity. These indicated that the porous sintering Ti plates were promising to be used as ultrafilter membranes.

Coating of a textured solid

We discuss how a solid textured with well-defined micropillars entrains a film when extracted out of a bath of wetting liquid. At low withdrawal velocity V, it is shown experimentally that the film exactly fills the gap between the pillars; its thickness hd is independent of V and corresponds to the pillar height hp. At larger velocity, hd slowly increases with V and tends towards the Landau–Levich–Derjaguin (LLD) thickness hLLD observed on a flat solid. We model the entrainment by adapting the LLD theory to a double layer consisting of liquid trapped inside the texture and covered by a free film. This model allows us to understand quantitatively our different observations and to predict the transition between hp and hLLD.

Application of the flotation process to thicken the sludge from a DAF plant

Dissolved air flotation (DAF) was evaluated for thickening of the sludges from a water treatment plant which uses DAF. Solid flux theory for gravity thickening was applied to the solid flux of DAF sludge. The higher the polymer dosage, at fixed solid concentration, the greater the rising velocity becomes. When applied with solid flux equations, a similar relationship to that of gravity thickening has been found. However, the values were much higher than in gravity thickening, because both the inflow solid concentration and the floating velocity were higher than for settled sludge. With this result, the proper dosage of polymer could be derived from the relationship between total solid flux and withdrawal velocity of DAF sludge.