promote boiling, unless there is already adsorbed air or surface-active ma- 

 terials on these chips which have little or nothing to do with the number of 

 points. That this conclusion is valid has been demonstrated in the experi- 

 ments of Dean 36 and Jakob 22 among others. On the other hand, deep crevices 

 with sharply pointed bottom contours are positions where vapor phase may 

 easily occur. Harvey, et al 11 showed by a series of experiments that "hydro- 

 phobic" surfaces cavitate more easily than "hydrophilic" surfaces; these ex- 

 periments evidently demonstrate the role of surface-active materials. The 

 latter experiments also showed very high tensile strength of water saturated 

 with air but completely de-nucleated. 



TENSIONS IN PLOWING WATER AND EFFECTS OF AIR-CONTENT ON CAVITATION 

 INCEPTION 



Although it is clear that the pressure for fracture of a liquid may 

 be raised toward vapor pressure rather easily, the presence of large amounts 

 of entrained air and of surface-active agents may raise the cavitation pres- 

 sure to well above the vapor pressure. In the oceans, for example, the pres- 

 ence near the surface of plankton and other marine growth and of a large 

 amount of entrained as well as dissolved air will promote cavitation. Experi- 

 ments by Crump 37 have shown cavitation inception at pressures corresponding 

 to as much as 5 feet of water above vapor pressure, Figure 13- 



1 









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Appearance of 

 Cavitation Inception 



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6.0 7.0 8.0 9.0 10.0 1 1.0 12.0 13.0 14.0 15.0 16.0 17.0 



Pressure Differential AH in inches of Mercury 



Velocity in Constriction in feet per second 



Figure 13 - Cavitation Inception in Sea Water — Prom Reference 37 



