The Effect of Additives on Fluid Friction 



would be required to achieve better friction-reduction performance by, say, an 

 order of magnitude, with this particular chemical. Such unusually large macro- 

 molecules would suggest the possibility of finite particles also producing the 

 friction reduction effect. Experiments with wood-pulp [7] show that this is in- 

 deed the case, but friction reductions were much lower than those reported 

 here. This is possibly because of the third requirement for maximum effec- 

 tiveness, solubility. 



Solubility 



Referring again to Table 1, tests with Carrageenan indicate the greater the 

 solubility the more the friction reduction effect. Further, molecules which 

 otherwise would be expected to be effective, such as Amylose, do not show up 

 well, probably because of poor solubility. 



FURTHER WORK WITH ROTATING DISKS 



Because the large-scale rotating disk apparatus described in the previous 

 section required large amounts of experimental solutions, a smaller apparatus 

 was developed consisting of a 7.6 cm diameter disk rotating in two liters of so- 

 lution. Figure 6 shows experimental data obtained with this equipment using 

 guar gum. The maximum torque reduction obtained was on the order of 40%. 

 Similar data are shown in Fig. 7 for solutions of poly(ethylene oxide). The 

 values of the torque reduction which were obtained on this apparatus as com- 

 pared with the large-scale equipment, together with the variation of torque re- 

 duction with rotative speed, suggest plotting these data as a function of Reynolds 

 number. 



Such a comparison is shown in Fig. 8 where data from the 7.6 cm, the 45.7 

 cm, and also a 76.2 cm disk are shown. The resultant envelope of maximum 

 torque reduction obtained in this way seems surprisingly similar for many poly- 

 mers, that is, the same maximum torque reduction at any given Reynolds num- 

 ber can be obtained with any of the "effective" polymers, with only the concen- 

 tration required to obtain this reduction varying from polymer to polymer. The 

 Reynolds number used in this plot is based on water viscosity without consider- 

 ing any viscosity increase due to the polymer. As some typical data for the 

 maximum torque reduction curve of Fig. 8, Table 2 gives concentrations of var- 

 ious materials required to attain 70% reduction at a Reynolds number of 1.3 

 million with the 45.7 cm disk facility. 



Effect of Sea Water 



The work presented so far has been based entirely on tap water or water 

 drawn directly from a fresh water lake. Additional tests were made with the 

 45.7 cm rotating disk to show the effect of sea water on the performance of 

 polymer additives. As shown in Fig. 9, friction reduction data taken in simu- 

 lated sea water agree closely with those obtained on fresh water for guar. The 

 tests shown are at three different temperatures, ranging from 13 °C to 27°C. 

 Poly(ethylene oxide) is even less affected by presence of sea water salts. 



951 



