Hoyt and Fabula 



million, since 40% friction reduction or more for 2 wppm of high molecular 

 weight polymer is demonstrated in Fig. 15. 



It is interesting to speculate on the idea that some marine animals might 

 have evolved the release of friction reducing agents into their boundary layer. 

 This appears to be a possible area for further research. 



APPLICATIONS 



The only known present application of these materials as friction- reducing 

 agents is in oil-field pumping operations. However, the attractive power reduc- 

 tions which seem attainable should promote extensive interest in the further use 

 of these polymers. 



In considering applications, however, careful thought must be given to prac- 

 tical matters such as surface roughness, mechanical polymer degradation, and 

 economic feasibility. 



Surface Roughness 



A preliminary check on the effect of roughness was made with the large- 

 scale rotating disk facility. The data shown in Figs. 2, 3, and 5, and Table 1 

 were obtained with a smooth, polished disk. Another disk with about 100 micro- 

 inch rms machine -turned roughness was also tested, but showed no change in 

 torque required for either water or guar solutions. A rough surface was then 

 produced by means of wrinkle -finish paint. In water tests, the torque for a 

 given speed was increased about 35% due to the roughness. Figure 20 shows 

 that two or three times the concentration of guar gum was required to achieve a 

 given torque reduction with the rough disk. Also, effects of rotative speed ap- 

 pear at low guar concentrations in contrast to the smooth disk data. Neverthe- 

 less it seems clear that the additive can be effective on practical structures. 



Mechanical Degradation 



The polymer molecules are subject to mechanical degradation as the friction- 

 reduction process continues. For example, concentrations of 15 wppm of poly 

 (ethylene oxide) of 4 million molecular weight were repeatedly tested in the large 

 disk apparatus, with the results shown on Fig. 21. Each test was about 15 sec- 

 onds in duration, repeated at intervals of 3 minutes or 10 minutes. Each test 

 run with this polymer evidently contributed to the mechanical degradation. A 

 similar test with guar gum did not show this effect, and this is the main reason 

 for continued interest in this less effective, but apparently very sturdy polymer. 



Economic Feasibility 



The additive concentrations used in oil-field applications are about 1000 

 wppm and up [6]. Such concentrations, if assumed across the full turbulent 

 boundary layer thickness are out of the question for boundary- layer applications. 



956 



