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-   -   How Accurate is the Tait Equation of State? (http://www.cfd-online.com/Forums/main/7906-how-accurate-tait-equation-state.html)

 Cary Kenny August 4, 2004 00:32

How Accurate is the Tait Equation of State?

So far Tait EOS is a standard EOS applied to water, particularly in the highly pressurised regime. The question is, how accurate is the Tait EOS when it is used to modelled region where the water pressure is negative (under tension)?

 Angen August 4, 2004 11:59

Re: How Accurate is the Tait Equation of State?

I think this equation has a simple mathematical form. Can you write it down for us?

Andy

 George August 4, 2004 12:20

Re: How Accurate is the Tait Equation of State?

I'm not sure what do you mean by a "negative pressure", as strictly speaking there is no such thing in a fluid. Generally, if the (absolute) pressure decreases sufficiently, then you get phase change, i.e. cavitation. I think you need to better specify your problem.

Regards, George

 jasond August 4, 2004 13:01

Re: How Accurate is the Tait Equation of State?

Water (and other liquids) can support some tension, or absolute pressures less than the vapor pressure, without phase change. The tensile strength is generally very small and depends on many factors. I could be mistaken, but I believe that the original poster is referring to pressure relative to the vapor pressure.

 Cary Kenny August 4, 2004 22:48

Re: How Accurate is the Tait Equation of State?

Thanks guys, your views are greatly appreciated. To redefine my earlier question, this is the scenario:

Water, similar to solid, posses a tensile strength, i.e. ability to withstand distortion. For solid, e.g. if a metal bar is pulled from both end, the bar will resist to be pulled apart (here tension refers to negative direction of force, as compression refers to positive one). So is water, if a "bar of water" is pulled, it will resist to break, but due to cavitation nuclei, it is very common to see the water bar "break" easily - and produce cavitation. The tension produced by the decrease in total pressure is the reason, as Jasond said.

In numerical simulations, Tait EOS is commonly used to represent "pure" water i.e. no cavitation exist in water, paticularly in the case of high pressure regime (<10GPa). But is Tait EOS still valid if inside the water there exist some pressure region of -10MPa?

Thanks