For liquids, which are relatively incompressible, the factors β and κ are generally show an weak dependence on T and P and hence averaged values of these parameters may be used for estimating the liquid volume at any temperature using the following integrated form of the equation (2.5):
(2.6)
For liquids the usual datum volume (i.e., V1 in eqn.2.6) can be the saturated volume at a given temperature, which may be obtained from the Rackett equation (H. G. Rackett, J. Chem. Eng. Data, 1970, vol. 15, pp. 514-517); i.e.,:
; where Tr=reduced temperature = T/Tc
(2.7)
Where ZC is the critical compressibility factor (see below).
Example 2.1
For a liquid ‘A’ at 350K and 1 bar, k = 50x10-6 bar-1. (i) To what pressure must water be compressed at 350 K to change its density by 0.5%? Assume that k is independent of P. (Click for solution)
;