The rheological characteristics of liq. petroleum prods. are measured by aspirating a given vol. of the liq. through a filter or capillary under fixed suction and measuring the aspiration time. The temp. is lowered in steps and the aspiration time is measured at each temp. The data obtd. are continuously plotted to give a curve of aspiration time verous temp. Filter method can be used to measure the cloud point and the cold filter plugging point. Capillary method can be used to measure the kinematic viscosity, the viscosity index and the 'limiting temp. of laminar flow', i.e. the temp. at which the viscosity ceases to increase linearly with decreasing temp.
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