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3.4.2 Vapour pressure of water at temperatures between 0 and 360°C

The table has been calculated from the equation given by Wagner and Pruss (1993)

ln(p/p_c) = (a₁τ + a₂τ^1.5 + a₃τ³ + a₄τ^3.5 + a₅τ⁴ + a₆τ^7.5)T_c/T,

where p is the pressure, T = T₉₀, and subscript c indicates the values at the critical point; τ = 1 − T/T_c. The values for substitution in the equation are:

T_c = 647.096K     p_c = 220 64 kPa     a₁ = −7.859 51783     a₂ = 1.844 082 59

a₃ = −11.786 6497     a₄ = 22.680 7411     a₅ = −15.961 8719      a₆ = 1.801 225 02

Pressures are tabulated in kPa for Celsius temperatures t₉₀. For example, at 34 °C the pressure is 5.3240 kPa and at 102°C is 108.87 kPa.

The pressure at the triple point, 273.16 K, is 0.611 657 kPa and the temperature at which the pressure is one standard atmosphere, 101.325 kPa, is 372.124 K (99.974 °C). Change in the temperature T with change in pressure p in the region of atmospheric pressure may be calculated from the following equation applicable in the range 95 °C to 105 °C (85 kPa to 120 kPa):

   ln(p/kPa) = 16.166 29 − 3736.276/((T/K) − 49.577)

Reference

W. Wagner and A. Pruss (1993) J. Phys. Chem. Reference Data, 22, 783–787.

D.Ambrose

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