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Blends of polystyrene/poly (4-vinylpyridine) have been prepared by casting from a common solvent. The compatibility of the blends was studied by using dilute solution viscometry (DSV), differential scanning calorimetery (DSC), Fourier transformation-infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The relative viscosity versus composition plots for the blends are not perfect linear. The corresponding intrinsic viscosity values show negative deviation from ideal behavior when plotted against composition. Also, the modified Krigbaum and Wall interaction parameter, Db, shows small and negative values for all compositions except for the blend PS/P4VP (25 : 75). The results indicate that the polymers are incompatible but small interaction values predict physically miscible blends which eventually show phase separation, as is observed in the present studies. However, the blends as obtained show a single, composition-dependent, glass transition temperature that fits the Fox equation well, indicating the presence of homogeneous phase. The constant, k obtained from Gordon-Taylor equation suggests intermolecular attraction between these polymers. FT-IR and SEM support the results of DSV and DSC.

This paper deals with the effects of heat and mass transfer on two-dimensional unsteady MHD free convection flow past a vertical porous plate in a porous medium in the presence of thermal radiation under the influence of Dufour and Soret effects. The governing nonlinear partial differential equations have been reduced to the coupled nonlinear ordinary differential equations by the similarity transformations. The resulting equations are then solved numerically using shooting method along with Runge-Kutta fourth order integration scheme. The numerical results are displayed graphically showing the effects of various parameters entering into the problem. Finally, the local values of the skin-friction coefficient, Nusselt number and Sherwood number are also shown in tabular form.Ó 2014 Production and hosting by Elsevier B.V. on behalf of Ain Shams University.

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The phenomena of fouling and corrosion in heat exchanger tubes commonly encountered in industrial practice are reviewed in two phases. In the first phase, the influence of physical and chemical properties of petroleum crude on scaling and fouling are reviewed. Further, in the second phase a generalized hypothesis is provided for unsteady analysis as function of time with the aid of logarithmic, exponential and Power law variation of fouling factors with time. The time dependent thermal characteristics of typical parallel and counter flow heat exchangers are established with the aid of time dependent fouling factors. The approach presented is in good agreement with the reported values of a petroleum refinery. Thus, a method to estimate the critical period for maintenance of the heat exchanger is established treating fouling as a time variable occurrence.