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
Some rheological and electrokinetic properties of kaolinite suspensions
The rheological behaviour of kaolinite sols has been studied as a function of pH and in the presence of adsorbates. The Bingham yield value shows a pronounced maximum at about neutral pH due, it is suggested, to the presence of extended chains of particles attached together by electrostatic interactions between edges and faces, as has been suggested by Street. At high pH values the particles behave as individuals and the yield value can be very effectively correlated with the attractive and repulsive forces between them, using the basic notions of colloid stability theory. Adsorption of long-chain quaternary ammonium compounds on the clay surface at high pH enabled the particle interaction energy to be altered over a wide range and this adsorption itself allowed a study of the van der Waals interaction energy between the CH2 groups of the adsorbate; a value of 1.2kT was found for this latter energy, in excellent agreement with estimates based on micellization in solution.
Gill diseases of cultured salmonids in Ontario.
Between 1977 and 1981, the Fish Pathology Laboratory of the Ontario Veterinary College received 239 cases from trout farms of southern Ontario, 51 (21.3%) of which had diseased gills. Branchial lesions in 86.3% of these 51 cases were characterized by marked lamellar epithelial hyperplasia with epithelial hypertrophy and lamellar fusion. Filamentous bacteria were seen on the surface of the branchial filaments and lamellae in 68.6% of the cases. Our observations highlight the importance of gill diseases as a production problem of farmed salmonids in southern Ontario.