Effect of external pressure on vapor bubble growth 



Some general remarks may be made concerning the growth of vapor bubbles 

 under various superheat conditions and for different ambient pressures. We are still 

 confining our interest to bulk liquid temperatures which do not change appreciably in 

 times of bubble growth of the order of some milliseconds. A comparison will be made 

 of the bubble growth in superheated water at 1 atmosphere with that in superheated 

 water first under high pressure and secondly under low, or even negative pressures. 



If water at 1 atmosphere pressure is superheated, for example, to 106°C, the 

 Rayleigh velocity is 408 cm/sec. Because of the cooling effect, the maximum bubble 

 growth velocity is 160 cm/sec. If we now consider water with a boiling point of 210°C 

 at approximately 19 atmospheres pressure and if we take the same superheat of 6°C, 

 the Rayleigh velocity is 1.39 X 10 3 cm/sec. The maximum bubble growth velocity is 

 only 16.9 cm/sec. Rayleigh velocities and maximum bubble growth velocities are given 

 in Table I for both 6°C and 3°C superheats for 1 atmosphere and 19 atmospheres- 

 pressure. The striking difference in velocity behavior between the high pressure situation 

 and the 1 atmosphere case is easily explained physically. The heat inflow to the bubble 

 is directly dependent upon the magnitude of the vapor density p', and the vapor density 



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T, DEGREES CENTIGRADE 



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Figure 9. These curves give the variations in the equilibrium water vapor density and water vapor 



pressure with temperature. 



310 



