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

Drag reduction, achieved by introducing a minute amount of a homologous series of polysaccharide xanthan gum in an aqueous solution, is investigated using a rotating disk apparatus. In this paper, the ultrasonic degradation method is adopted to obtain different fractions of molecular weights of xanthan gum. The dependence of drag reduction on various factors, including polymer molecular weight, polymer concentration, rotational disk speed, ionic strength of solution, and temperature, is investigated. Drag reduction induced by the xanthan gum is found to increase with polymer concentration, reaching a maximum at its critical concentration, while the concentration required 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 intensity. Furthermore, tests show that xanthan gum is a suitable drag reducer even at relatively high temperatures.