Asymptotes of maximum friction and heat transfer reductions for drag-reducing surfactant solutions

A new maximum drag reduction asymptote (MDRA) for surfactant solutions is p resented. Various concentrations including cationic and non-ionic surfactan t solutions were used to experimentally determine this asymptote. It is sho wn that if solvent viscosity is used to compute Reynolds and Prandtl number s for viscous solutions, it leads to underestimations of the friction coeff icient. To avoid uncertainties in the selection of the fluids viscosity, mo st solutions used were intentionally conditioned so their shear viscosity w as water-like in the ranges covered. Using the same solutions, a maximum he at transfer reduction asymptote (MHTRA) was also determined - a correlation that did not exist for surfactants until now. Finally, by using slightly m odified definitions to quantify the heat transfer and drag reductions (TRH and TRD), it is possible to express the ratio between the MHTRA and MDRA wi th a constant value of 1.06, independent of Reynolds number. This relations hip can be used as an auxiliary criterion to determine whether or not a sol ution is asymptotic when there is an uncertainty about the shear viscosity. (C) 2001 Elsevier Science Ltd. All rights reserved.