[show abstract][hide abstract] ABSTRACT: Blending is often used to reduce the viscosity of vegetable oil lubricants. Experimental rheological results were compared with traditional blending charts and calculation methods. Kinematic viscosities of 90% oleic sunflower, canola, and soybean oils blended with adipates, oleates, polyalphaolefins, and mineral oil were determined at 40°C using capillary viscometers. Blending charts related the viscosities to blend composition with 5% inaccuracy compared with more than 10% deviation made by the cubic equation of Kendall and Monroe. Even more accurate and simpler correlations could be derived. A semilog relationship between viscosities and composition was more accurate than a cubic model. Higher accuracy was also achieved when relating viscosities to volume fractions rather than to weight or mole fractions. Mineral oil blends did not follow the observed rules.
[show abstract][hide abstract] ABSTRACT: The present study investigates experimentally the evolution of two-phase flow pattern and pressure drop in the converging and diverging, silicon-based microchannels with mean hydraulic diameter of 128 μm and CO2 bubbles produced by chemical reactions of sulfuric acid (H2SO4) and sodium bicarbonate (NaHCO3). Three different concentrations of 0.2, 0.5 and 0.8 mol/L of each reactant at the inlet before mixing and 10 different flow rates from 1.60 × 10−9 m3/s to 16.0 × 10−9 m3/s are studied. Flow visualization is made possible by using a high-speed digital camera. It is found that the present design of the microchannel, with the inlet chamber, results in much more intensive chemical reactions in the diverging microchannel than that in the converging one. The void fractions at the entrance and exit regions and pressure drop through the channel are also measured. The results reveals that the presence of small void fraction, <0.1, at the inlet may promote CO2 generation in the microchannel, irrespective of the channel is converging or diverging, indicating the agitation effects of bubbly flow in the microchannel. The increase of inlet concentration of reactants does not increase the pressure drop in the converging microchannel significantly, while the inlet concentration presents significant but mild effects on the pressure drop in the diverging microchannel. The two-phase frictional multiplier may be positively correlated with the mean void fraction in the channel linearly, and the data agree well with predictions from the correlations in the literature.
International Journal of Heat and Mass Transfer. 10/2006;
[show abstract][hide abstract] ABSTRACT: In this work, a model for calculating the dynamic viscosity of polymer solutions was developed. The model is based on the Eyring absolute rate theory and on the solution theory of McMillan−Mayer. An equation of state is used for the calculation of the solution osmotic pressure and, thus, the excess molar McMillan−Mayer free energy. The final expression shows an explicit dependence between the viscosity of the polymer solution and the applied shear stress. The proposed model contains three terms. The first term describes the viscosity of an ideal polymer solution. The second term takes into account non-Newtonian behavior of the polymer solution. Finally, the third term represents the deviation from the thermodynamic ideal behavior. The whole model presented five adjustable parameters, with two of them also considered as being a function of the applied shear stress. To test the proposed model, we have measured experimental rheological data for poly(ethylene glycol) aqueous solutions (nominal molecular weight 6000 g/mol) for nine different polymer concentrations, at different shear rates, at 313.15 K and 0.1 MPa. The proposed model has been used for correlating the experimental viscosity data of these polymer solutions at different values of the applied shear stress and polymer concentration. It has been found that the agreement between the experimental and calculated values is within the experimental error.
Industrial & Engineering Chemistry Research - IND ENG CHEM RES. 12/2005; 45(2).
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