Method to increase the efficiency of polymer drag reduction for marine and industrial applications

A method for reducing polymer expenditure rates by establishing a drag-reducing viscoelastic coating on a marine or industrial surface, said method comprising the following steps, performed in the order indicated, but there may be intervening steps:

• (a) mixing a polymer with a solvent into a concentrated solution to produce a first fluid that has approximately the same density as a second fluid that flows over a surface, the friction drag of the second fluid flowing over the surface being desired to be reduced;
• (b) tangentially ejecting the first fluid formed in step (a) into the second fluid flowing over the surface in a manner that does not enhance diffusion of the ejected first fluid across the fluid flow boundary layer of the second fluid as the second fluid flows over the surface, with the ejecting of the first fluid being at a concentration and an ejection flow rate such that a coating of polymer is adsorbed onto the surface and the coating of polymer initially grows thicker with time, and further including temporarily relaxing the shear stress on the adsorbed coating of polymer one or more times by reducing the free stream velocity U∞ of the second fluid in order to control the potential entrainment of gases or other materials and to consolidate the resulting polymer adsorption entanglement layer(s);
• and
• (c) reducing the ejection rate of the first fluid such that the polymer adsorption entanglement layers become thinner with time;
• wherein, during step (b), one or more of:
• the concentration Ci of the first fluid,
• the ejection rate Qi of the first fluid, and
• the free stream velocity U28 of the second fluid are controlled so that the coating of polymer is adsorbed onto the surface within a desired time period.