Drag-reduction effectiveness of xanthan gum in a rotating disk apparatus

Drag reduction, achieved by introducing a minute amount of a homologous ser ies of polysaccharide xanthan gum in an aqueous solution, is investigated u sing a rotating disk apparatus. In this paper, the ultrasonic degradation m ethod is adopted to obtain different fractions of molecular weights of xant han gum. The dependence of drag reduction on various factors, including pol ymer molecular weight, polymer concentration, rotational disk speed, ionic strength of solution, and temperature, is investigated. Drag reduction indu ced by the xanthan gum is found to increase with polymer concentration, rea ching a maximum at its critical concentration, while the concentration requ ired for maximum drag reduction decreases with increasing molecular weight. Polymer degradation due to the high shear forces, which occur during drag- reduction experimentation, is also found to increase with turbulence intens ity. Furthermore, tests show that xanthan gum is a suitable drag reducer ev en at relatively high temperatures. (C) 2001 Elsevier Science Ltd. All righ ts reserved.