Abstract
RECENTLY, Gadd1,2 and Hoyt3 reported results of experiments on the turbulent flow characteristics of dilute polymer solutions, and showed that the addition of very low concentrations of polymer molecules (of the order of 50 weight parts per million) to water greatly reduced the turbulent friction acting at surfaces moving relative to the fluid. This phenomenon was attributed to the formation of normal stress differences, because other physical properties such as density and viscosity are sensibly unchanged. Work carried out in this department on the flow of very dilute polymer solutions and other additives in water confirms these findings. Measurements have been made of the turbulent friction factor for flow of these solutions in glass and metal pipes of varying surface roughnesses for Reynolds numbers up to 12,000 and for flow past arrays of spheres. Up to 25 per cent reduction in friction factor was observed in flow in tubes. Although we agree on the formation of normal stress differences on addition of small traces of polymeric substances to water, we would also suggest that in some instances adsorption of the solute at the solid surface can occur which will influence the flow in the boundary layer near the solid surface. Similar work carried out by El'perin and Smolskii confirms this4. The importance of these surface effects can be easily demonstrated in pipes, because it has been shown that when the flow of the solution is stopped and water reintroduced the friction factor measured is initially lower than that expected. This effect can persist for up to 15 min, dependent on the flow conditions, and is several orders of magnitude greater than the residence time of the fluid in the tube.
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References
Gadd, G. E., Nature, 206, 463 (1965).
Gadd, G. E., Nature, 211, 169 (1966).
Hoyt, J. W., Nature, 211, 170 (1966).
El'perin, I. T., and Smolskii, B. M., Vesti. Akad. Navuk Belarusk S.S.R. Sev. Fiz-Tekhn, Navuk, 2, 39 (1965).
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DAVIES, G., PONTER, A. Turbulent Flow Properties of Dilute Polymer Solutions. Nature 212, 66 (1966). https://doi.org/10.1038/212066a0
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DOI: https://doi.org/10.1038/212066a0
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