# Cavitation

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 February 8, 2005, 11:49 Cavitation #1 Christian Guest   Posts: n/a Hi. Q1: Does anyone know what the sizes of cavitation bubbles are ? Q2: Does cavitation only occur when the pressure is below the vapor pressure, or does it initiate much sooner? If it occurs sooner, when does it occur? Any thumb rules, links or articles I should know of ? Cheers

 February 8, 2005, 12:19 Re: Cavitation #2 Angen Guest   Posts: n/a A1: There is no unique cavitation bubble size. They appear as critical bubbles (~1e-6m) and grow until under-saturation disappears. A2: Cavitation can occur because of pressure decrease below the saturation pressure of the same substance (e.g. vapor and liquid are H2O) or below the saturation pressure of dissolved gases (e.g. in coca-cola bubbles are CO2 in mostly liquid H2O). Angen

 February 8, 2005, 13:59 Re: Cavitation #3 CFDtoy Guest   Posts: n/a Hi Cavitation and bubble dynamics by Brennen 1995 is available for reference online. That should resolve all your questions. Further read, Cavitation by Knapp, 1970. Should be available in all libraries. If you still have questions, Lemme knw. I have been workin with cav simulations. CFDtoy

 February 10, 2005, 05:36 Re: Cavitation #4 Christian Guest   Posts: n/a Hi. I can see that the litterature tries to find a critical value for the cavitation number. And it seems to me that there is no universal value (like one can use Re>2300 is turbulent in tubes and Re>5e5 on surfaces). The critical number in the texts I have seen ranges from below 1 to above 100. I cannot find any grouping. Do you know of any? Christian

 February 11, 2005, 17:41 Re: Cavitation #5 CFDtoy Guest   Posts: n/a Hello Christian, Cavitation number is defined as sigma=Pv-Pinf/(0.5*rho*v*v) where Pv = vap pressure. So, essentially the cav number of the system with P< Pv is dependent on v which defines the reynolds number. So yeah, cav number could be anything. A No flow/creeping flow region with less pressure < Pvap can also result in cavitation with a low Reynolds number ! CFDtoy

 February 16, 2005, 09:18 Re: Cavitation #6 Christian Guest   Posts: n/a Is it safe to say that cavitation will _never_ occur when p_stat > p_vapor ?

 February 16, 2005, 14:10 Re: Cavitation #7 Angen Guest   Posts: n/a No, it is not. In case of multi-component liquids (e.g. H2O and CO2) it should be replaced with P_b < P, where P-b is a bubble pressure and P is an actual local pressure in liquid. In general, P_b = P_sat only in case of single component liquids. So, in single component liquid the condition for not having cavitation would be P_sat < P. If there are external fields (e.g electric) that can still be more complicated. Angen

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