Kuang, Pei Qiong.2009-03-232009-03-2319921992Source: Dissertation Abstracts International, Volume: 54-06, Section: B, page: 3220.9780315800076http://hdl.handle.net/10393/7597http://dx.doi.org/10.20381/ruor-6866Evaluations of apparent slip and surface effects characterizing polymer adsorption are reported for laminar capillary flow of dilute aqueous solutions of three homologous compounds of Polyox, denoted by WSR 301, Coagulant and FRA. Measurements were carried out using very dilute solutions in the polymer concentration range 5 to 200 ppm and very fine glass capillary tubes with diameters varying from 0.0054 to 0.047 cm. Results were obtained for glass capillary tubes coated with a silane compound (dimethyldiethoxysilane) as well as for the untreated glass tubes to provide a comparison between wall effects observed with a hydrophilic surface and a chemically modified surface. The results indicate that flow enhancement characterized by a positive effective velocity at the wall is dominant at the very low polymer concentrations and flow retardation characterized by a negative effective velocity at the wall is dominant at the higher concentrations comprising the polymer concentration range investigated. In general, it was found that the magnitude of the effective velocity at the wall increases with increasing wall shear stress and the contribution to the total flow rate becomes more significant in the tubes of smaller diameter. A transition from a positive to a negative effective velocity at the wall was observed with increasing polymer concentration. The critical concentration marking the transition was found to be higher for the silane-treated tubes than for the untreated tubes. The effective hydrodynamic thickness of the adsorbed polymer layer corresponding to zero shear was evaluated directly from the capillary flow data. The thickness in the plateau region at higher polymer concentrations was found to be greater than two times the root mean square radius of gyration of the polymer molecule for solutions of the three polymers in the untreated tubes while lower value was obtained for the same solutions in the treated tubes. A new analysis was applied to separate the contributions of polymer adsorption and slip in the evaluation of the effective velocity at the wall. In the analysis, the flow was modeled by postulating an adsorption isotherm for representation of the variation of the adsorbed layer thickness at zero shear with polymer concentration and assuming a linear dependence of the effective slip velocity on the wall shear stress. Effective hydrodynamic thicknesses of the adsorbed layers are presented as a function of the polymer concentration and wall shear stress for the three Polyox homologues investigated in the chemically treated and untreated glass tubes. The variation of the slip coefficients with polymer concentration of the solutions was also evaluated. End effect corrections based on flow measurements obtained by varying the tube lengths of the capillaries in the L/D range 750 to 2000 were applied to the data using a modification of the Bagley plot.249 p.Engineering, Chemical.Thesis