Posted by Darrick on May 11, 19104 at 15:24:44:

In Reply to: Re: Compressibility of Water posted by MathGrad on January 21, 19104 at 13:58:33:

Compressibility is a partial differential quantity. It is defined as -(1/V)(dV/dP) at constant temperature. It is simplest to think of it as the fractional change of volume that occurs when the pressure is increased a unit amount. For example, let's say that the value of the compressibility of water at room temperature and pressure is 3.59 x 10^-5 bar^-1. If we increased the pressure bearing down on the liquid by 100 bar, then the liquid would contract. The fraction of volume lost would be
(Vf - Vi)/Vi = (3.59 x 10^-5 /bar)(100 bar)
= 3.59 x 10^-3

In other words, the final volume would be about 1 - 3.59 x 10^-3 = 0.99641 of its initial volume.

Let's say the volume of the liquid was 1.0000 L at the start. After increasing the pressure by 100 bar, the liquid would be 0.9964 L. Not much of a change for such a large pressure increase.

Compressibility is a function of temperature and pressure, so the numbers must be valid for the T,P range you are interested in if you are interested in calculating accurately.

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