X-RAY FLOW VISUALISATION OF FLOW PATTERNS DURING THE MIXING OF YIELD STRESS, NEWTONIAN AND DILATANT FLUIDS

Abstract

Abstract This paper describes the use of an X-ray flow visualisation technique to visualise flow patterns in opaque fluids. Flow patterns were observed in a pseudoplastic fluid possessing a yield stress, in a dilatant clay suspension and in a Newtonian fluid for comparison. Impeller Reynolds numbers were in the range 4.5 ≤ Re≤ 74. The flow patterns observed in the fluid possessing a yield stress indicate that the predominant motion in the mixed cavern surrounding the impeller is circular in nature. Comparison of the flow patterns observed in the dilatant suspension, power law flow behaviour index n ≅ 3, with those in the Newtonian fluid al the same Reynolds number, shows that bulk motion throughout the vessel is greater but extensional flows seem reduced. The observed flow patterns support the prediction that when mixing a power law fluid with n > 2 an increase in impeller speed will lead to a reduction in impeller Reynolds number.