China
Africa
Explore chapters and articles related to this topic
Environmental Impacts from Groundwater Control
Published in Pat M. Cashman, Martin Preene, Groundwater Lowering in Construction, 2020
The settling rate of a solid particle is controlled by Stokes’ law – the smaller the particle, the slower its rate of settling. Hence, the larger the tank, the longer the retention time, allowing more time for smaller particles to settle out. In order to settle out silt and clay size particles by conventional means, very large tanks or lagoons may be needed.
Formulation of Depot Delivery Systems
Published in Sandeep Nema, John D. Ludwig, Parenteral Medications, 2019
Christopher A. Rhodes, Nikita Malavia
Stokes’ law assumes uniform and noninteracting particles. In reality, interactions between suspended particles are significant and include attractive van der Waals forces and repulsive electrical double layer and solvation/hydration forces.24 One of the primary failure modes in the formulation of suspensions is caking, which results from the settling of particles and the formation of a densely packed layer of solids.22 The distance between particles is sufficiently decreased within the cake such that attractive van der Waals forces dominate and cause irreversible aggregation of the particles, preventing their re-dispersion. One technique used to prevent caking is to formulate the suspension to flocculate. Flocculated particles interact to form a loosely aggregated structure where interparticle distances are large enough that the system is easily resuspended (e.g., by brief shaking). Formulation at the secondary minimum of the potential energy function can maximize the stability of the flocculated system.23
Micron Fines and Nanodiamonds
Published in James C Sung, Jianping Lin, Diamond Nanotechnology, 2019
Stokes’ Law is applicable only to spherical particles. As diamond particles are not spherical, so their settling time are longer than that predicted Eq. (5.2). In the case of irregular shaped diamond, the increase of settling time may be excessive. Hence, large irregular shaped diamond may settle at the similar speed as small round ones. Sometimes the size difference can be as large as 3 times. Hence, the more irregular the shape, the broader the diamond size distribution. The size distribution is critical for precision polishing, so more blocky shapes are preferred. In this way, the chance to cause scratch to work piece is less because less sharp protrusion is associated with blocky shape.
An overall review on the tribological, thermal and rheological properties of nanolubricants
Published in Tribology - Materials, Surfaces & Interfaces, 2021
Wani Khalid Shafi, M. S. Charoo
Dispersion stability of nanoparticles in lubricant governs their effectiveness in improving the thermal, rheological and tribological properties. Colloidal stability of nanoparticles signify that agglomeration do not take place at a remarkable rate. High colloidal stability ensures uniform homogeneity, less clogging and low sedimentation rate [25]. The sedimentation rate of nanoparticles is governed by stokes law given bywhere is the settling velocity, represent the density of nanoparticles and fluid respectively, r is the radii of the nanoparticles and represents the dynamic viscosity of fluid. It is observed that the settling velocity is directly proportional to the square of nanoparticles radii. Larger cluster size due to the agglomeration, faster the settling of nanoparticles and poorer the tribological and thermo-physical properties of nanolubricants. Different methods for improving the dispersion stability of nanoparticles include (a) surface modification techniques and (b) surfactants. The effect of surface modifying agents and surfactants on the stability, consequently on thermal conductivity, viscosity and tribological properties is shown in Table 2 [26–33].