Physico-chemical concept of drag reduction nature in dilute polymer solutions (the Toms effect)

• Updated model of drag reduction and turbulent flow intensification is proposed.
• The GV-equation allows calculating the size of coils and threshold shear stress.
• Hump in the curve of dependences of the volume flow increment vs C is explained.

The physicochemical concept of turbulent drag reduction (the Toms effect) integrates physicochemical characteristics of polymer solutions with hydrodynamic and rheological flow parameters into a generalized equation, where the increment in volumetric flow rate QP is a function of the external shear stress τw, temperature, volume of macromolecular coils with immobilized solvent Vc and a function of their volume fraction Ψ = C · [η]/(1 + C · [η]). The QP depends on the coil intrinsic elasticity [G] = kT/Vc as well. This model allows one: (1) to describe the Toms effect in terms of useful elastic work spent by macromolecular coils with immobilized solvent to overcome the frictional forces (i.e. the forces of intermolecular interactions), (2) to forecast the initial conditions of the Toms effect (τ* ≈ (RT)/(M · [η])) and (3) to explain the unusual temperature dependence of the polymer solutions flow.