EXPERIMENTAL EVALUATION OF DRAG COEFFICIENT FOR FALLING SPHERE IN NEWTONIAN AND NON-NEWTONIAN FLUID

Abstract

The present study investigated the effect of drag coefficient (C_D) in Newtonian and non-Newtonian fluids which were the rheological properties, size particles. Experiments were conducted using two types of drilling fluids, water represented Newtonian fluid and suspension of bentonite represented non-Newtonian fluid. Stainless steel spheres were used as falling particles. A plastic transparent cylinder of 200 mm inner diameter and 1850 mm length was used as a column for fluid container. Metal particle dedicator was designed and constructed with FPGA kit to perform the experimental work as electronic system to record accurate time of falling particles and high speed camera (1000fps) was also used in order to enhance results. A CFD software ANSYS FLUENT 15.0 was utilized. The study showed drag coefficient (C_D) and particle Reynolds’ number (Re_P) relationship and the effect of rheological properties on this relationship. The drag coefficient decreased with increasing particles Reynolds number in laminar slip regime in non-Newtonian fluid while remained approximate constant in fully turbulent regime in Newtonian Fluid. Smaller particles showed lower drag coefficient and higher Reynolds numbers for the same material. The range of Reynolds Number was (1.4 *10⁴ < Re < 7.1 *10⁴) and the range of drag coefficient was (0.39 – 0.41) for tap water whereas for the suspension of bentonite, the range of Reynolds Number was (48 < Re < 260) and the range of drag coefficient was (0.64 < C_D < 0.76).