is 16 times greater at 210° C than at 100°C (cf. Fig. 9 and Table II). One must there- 

 fore expect a larger cooling effect in the high temperature, high pressure condition. With 

 this larger cooling effect goes also a larger decrease in the driving pressure 



p v (T) - P ^ P A(T - T h ) (30) 



since the slope of the vapor pressure curve increases with temperature (cf. Fig. 10). For 

 the specific case considered here, one has 



A(210°C) 



pa 12. (31) 



^(100° C) 



2 

 o 



\ 



>- 



Q 



120 



100 



80 



60 



40 



20 



0.6 



0.5 



0.4 



0.3 



en 

 u 

 cc 



U 

 I 

 CL 

 (^ 



o 

 s 



H 



0.2 



a.' 

 ■o 



0.1 



50 100 150 



T, DEGREES CENTIGRADE 



200 



250 



Figure 10. These curves give the variations of the surface tension of water and of the vapor pressure 



derivative with temperature. 



We may consider the vapor bubble growth in incipient cavitation with the same 

 arguments. Vapor bubble growth in incipient cavitation at, for example, a water tem- 

 perature of 15°C is the same phenomenon as that which we have been considering here. 

 A difference to be remarked is that the ambient pressure is often significantly less than 

 zero, but the fact that one is dealing with tensions associated with negative external 



311 



