57 



Figure 33 - The Effect of Air Content on Cavitation— Prom 

 Bureau of Reclamation Photographs 



coefficient may be taken as the critical cavitation number for cavitation in- 

 ception by changing the sign of the coefficient and replacing the local pres- 

 sure by the vapor pressure. For flows with very high air contents, it may be 

 appropriate to replace the vapor pressure by some higher pressure— perhaps 

 that given by Henry's law for equilibrium saturation of the gas in the liquid. 

 An equally important reason for a knowledge of the pressures is the 

 possibility of occurrence of cavitation in zones of separation (as discussed 

 in the foregoing). Although, in general, it will not be possible to predict 

 pressures in such zones, the possible existence of such zones can be recog- 

 nized from the form of the pressure distribution on the boundary. Since the 

 occurrence of separation is associated with positive pressure gradients, those 

 systems which show sharply rising gradients may be subject to cavitation even 

 though the minimum pressures at the boundary do not fall below the vapor 



