Shear-induced migration and clustering mechanisms of kaolinite clay particles under the oscillating face seal by Jinchul Hong
The migration and clustering mechanisms of clay particles under the contact band of an oscillating face seal are investigated. There are two seperate stages in the wear, which are called the break-in period and the aggressive wear period. First small particles in the slurry penetrate through a short distance under the seal lip, where a thin oil film is present and there is no sign of significant wear. This period is called breakin period. However, after a number of cycles, the particles aggregate and start to form clusters. These clusters grow and the seal wears rapidly. Thus cluster formation plays a critical role in the whole wear process. As a first step, we have compared the possible forces which drive particles inwards. These include the effects of Van der Waals interactions, hydrodynamic shear, Brownian diffusion, etc. In the initial stages of the process, when the particle concentration is not high, prior experiments are consistent with shear-induced migration as the primary mechanism. Particles migrate inwards due to gradients in concentration, shear rate, viscosity and the effects of curved-streamline. Van der Waals force are likely to be dominant when the concentration is high enough so that the distance between the particles is small. In order to confirm these mechanisms, a new experiment using steel seals was carried out and corroborates earlier studies. Finally, some clustering and dispersion mechanisms such as the effects of dissolved ions (leading to aggregation) and thermal expansion of the seal lip (leading to dispersion) were also studied. Thesis Supervisor: L.Mahadevan Title: Associate Professor
Transition frictionnelle/visqueuse pour une suspension granulaire
Resume A partir d'une serie d'experiences de cisaillement sur des suspensions de billes de verre dans differents fluides interstitiels, on montre qu'il y a une transition de comportement d'un regime frictionnel (aux faibles vitesses) a un regime visqueux (aux fortes vitesses). L'evaluation des differents types d'interactions montre qu'une telle transition est sans doute due a la lubrification des contacts sous l'effet du cisaillement.
A method for correction of the wall-slip effect in a Couette rheometer
A simple method for correction of the wall-slip effect in a Couette rheometer was derived. The method requires only two series of measurements (two flow curves) performed in two measuring sets of any dimensions, and therefore it may be applied for the results obtained in each rheometer with a standard cup and bob set. The method was checked for experimental data and also verified theoretically for a hypothetical liquid.