Bernd 



SURFACE OF WATER 



ACOUSTICALLY TRANSPARENT 

 CONTAINER USED FOR SOME 

 SAMPLES 



TANK I'x I' X 2' 

 (FILLED WITH WATER) 



TrZ'Zr^ / ^^""'^'' ACrSTl'^ANSDUCER 



UN lANR WALL / ^q STRESS WATER 



CALIBRATING PROBE 



(NORMALLY WITHDRAWN) 



a. TEST SET-UP 



IDEAL DISSOLVING 

 '(NO SURFACE FILMS) 



NO DISSOLVING (HEAVY 

 SURFACE FILMS) NUCLEI 

 RISE TO SURFACE 



T = TIME 

 *. IDEAL TEST RESULTS 



Fig. 4 - Test for the effect of surface films 

 on gas nuclei dissolving (tensile strength) 



The nuclei produced are sorted out as to size by rising toward the open top 

 of the test tank in accordance with Stokes' law. The maximum diameter of nuclei 

 retained in the water is approximately 0.01 cm. Dissolving is produced essen- 

 tially by the surface tension of the water creating pressure within the nuclei. 

 The water is maintained at saturated equilibrium with dissolved air. The trans- 

 ducers are of such size and frequency (18 kc/s) that the acoustic intensity de- 

 creases rapidly with increasing distance from the active face of the transducer. 

 Thus nuclei and water are stressed at maximum intensity very close to the face 

 of the transducer at a given height in the water. This height is held constant. 



If no surface films are present, the curve for "ideal dissolving" is followed, 

 making for a rapid acquisition of tensile strength, as shown in Fib. 4b. If no 

 dissolving takes place, the subsequent increase in tensile strength due to rising 

 of nuclei to the surface is slow, following the "no dissolving" curve shown in 

 Fig. 4b. Waters possessing different film effects fall between these two 

 extremes. 



Tests on Nuclei Dissolving in Different Waters 



The first step in looking for surface film effects in water would be to 

 establish test results for nuclei when no films are present, and thus be able to 



90 



