Water, generally cavitation pressure

The choice of the solvent has a profound influence over the observed sonochemistry as well. The effect of vapor pressure has already been mentioned. Other liquid properties, such as surface tension and viscosity, will alter the threshold of cavitation (8), but this is generally a minor concern. The chemical reactivity of the solvent is often much more important. As discussed below, aqueous sonochemistry is dominated by secondary reactions of OH- and H- formed from the sonolysis of water vapor in the cavitation zone. No solvent is inert under the high temperature conditions of cavitation even linear alkanes will undergo pyrolytic-like cracking during high intensity sonication (89). One may minimize this... 

The final factor to be considered here, and known to affect the cavitation threshold, is the temperature. In general, the threshold limit has been found to increase with decrease in temperature. This may in part be due to increases in either the surface tension (a) or viscosity (rj) of the liquid as the temperature decreases, or it may be due to the decreases in the liquid vapour pressure (P ). To best understand how these parameters (a, q, Py) affect the cavitation threshold, let us consider an isolated bubble, of radius Rq, in water at a hydrostatic pressure (Pjj) of 1 atm. 

Question by R. J. Good, General Dynamics/Astronautics Do you have an explanation (1) for your observation that the critical negative pressure for cavitation-or. noncavitation is so much larger for liquid nitrogen than for water and (2) for the independence of air saturation, for water The expectation based on the Kelvin equation (i.e., that the vapor pressure in a bubble is less than that over a flat surface) would be the reverse of your observation. 

Avoiding cavitation in a pump is a concern in all services but particularly when the liquid operates close to the vapor pressure. Boiler feed pumps, shown in Exhibit 8-27, generally operate close to the vapor pressure of the feed water. As a result, it is imperative that changes in direction be minimized. Designers may add flexibility to the suction line when it is convenient to support it, but this may disrupt the flow and increase the possibility of cavitatioa The preferred... 

The NPSHr characteristics should be requested from the manufacturer who usually evaluates these with water using the well-known 3% A//-criterion (Figure 9.29a). For solvent close to their vapour pressure the manufacturer should be asked for special recommendations as general information [30] may not be sufficiently reliable. As centrifugal pump cavitation is rather dangerous for pump life, the actual NPSH should include a safety margin. A factor between 1.5 and 2.0 is recommended. 

Identification The attack was cavitation. This attack is generally encountered in diesel motor cylinders. The attack is observed when a body vibrating in a liquid attains high values of amplitude and frequency and the sluggish liquid cannot keep in pace with body. Implosion of bubbles on the point of maximum vibration occur and high shock wave pressures are produced on the metal surface. It may be pointed out that at the moment of reversal, the cylinder is subjected to bending vibrations by the sideways, pressure of the piston and the cooling water may not be unison with the cylinder vibrations. 

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