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Measurement and evaluation od drag coefficient for settling of spherical particles in pseudoplastic fluids

The drag coefficient is important hydrodynamic characteristic of the motion of particles in both, Newtonian and non-Newtonian fluids, and possibilities of its evaluation based on mathematical equations are very significant. Development of mathematical model for estimating drag coefficient values is primarily based on measurement accuracy. The experiment was run using carboxymethylcellulose water solutions in concentration range 1-4 wt% with different rheological properties which were determined using RV-3 HAAKE Viscometer. Approximately 200 experimental results were obtained using spherical particles of different materials and diameters. Measurements of the falling velocities were carried out in a glass tube. An optical method of measuring was developed for this purpose. Laboratory device contains three printed boards. Two are identical and each consists of 7 photodiode photoreceiver pairs while third is used for connecting with computer. Photodiodes emit 2 mm wide IR ray towards photoreceivers and their outputs give TTL levels. Output signals from these two boards are connected with RS flip-flop on third board, and his output is connected to computer. This technique enables time measurement accuracy of 0,02 s. By comparison experimental drag coefficient values with those obtained using proposed model for pseudoplastic fluids (1), the value of mean relative deviation is 25 %. Our proposed mathematical model simplify correlation of correction factor vs. flow behaviour index and achieve better results in wide range of Reynolds number (RePS < 1000) that gives a value of mean relative deviation 15%.

drag coefficient; optical method; pseudoplastic fluids; spherical particles

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