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Aging and Degradation in Dilute Polymer Solutions

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This paper describes studies of the properties of dilute solutions of polymers which have been found to reduce friction in turbulent flows. The substances tested, in solution in tap water, were guar gum, polyethylene oxide (Union Carbide 'Polyox' WSR 301) and polyacrylamide (Dow 'Separan' AP 30). It had been previously found that solutions of 'Polyox' and 'Separan' exhibit normal-stress difference effects. Correspondingly for'Polyox' solutions, it has been reported that the pressure increment at the mouth of a pitot tube, or open-ended tube facing into the flow, can be reduced below the value [formula] normal for Newtonian liquids, where [Greek rho] is density and V is speed. The present experiments began as a further investigation of this loss of pitot pressure. It was found that the pitot loss reduced with time, and that with 'Polyox' solutions other normal-stress difference effects showed a similar aging, without apparently impairing the ability of the liquid to produce turbulent drag reduction. Continued exposure of the liquid to intense turbulence does, however, lead to a degradation of the drag reduction.

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