P"Pco 



(2) 



so that the pressure is 



P = P V (TJ +q(a+c p ) (3) 



When the fluid pressure, p, is less than the vapor pressure, p , we expect 

 vapor to form and, hence, we may expect cavitation to begin. Thus, as a 

 first guess, we estimate that 



a < - c (4) 



— P • 



mm 



is the condition for the onset of cavitation. We follow Holl (1969) in 



calling the cavitation that occurs when p . <p (T ) vaporous cavitation as 



& mm v °° — ' 



we expect the cavitation process to be one of the formation and collapse 

 of cavitation voids filled primarily with the vapor of the liquid. 

 Observations show (Holl ibid) that it is also possible for p . to exceed 

 the vapor pressure at inception. This can happen wherever the test liquid 

 contains dissolved gas and the local pressure is below the gas saturation 

 pressure or bubble point. Cavitation inception, when so dominated by 

 diffusion of the gas into a cavity void, is termed gaseous cavitation by 

 Holl. As he has shown, this may be quite common in hydrodynamic appli- 

 cations (see also the reviews by Acosta and Parkin 1975, Morgan and 

 Peterson 1977) . A further type of cavitation inception termed by Holl 

 "pseudo cavitation," is said to occur when entrained bubbles of gas or 

 vapor respond quasi-statically to an imposed pressure history. This fea- 

 ture of cavitation is more characteristic of bubbly two-phase flow than it 

 is of cavitation inception and will not be considered further herein. 



