Water Substance and the Atmosphere

Abstract

Water is the working substance in so many thermal processes that its properties are of particular interest. First let us consider its density, or the reciprocal of density, which is called specific volume. Starting with ice, say at − 20C, and increasing the temperature, we find that ice expands, like most solids, until at 0C its specific volume is 1.091 17 cm³ gm⁻¹. Liquid water at 0C has a specific volume of 1.000 16, which decreases to a minimum value of 1.000 03* at 3.98C. Then it starts to expand, reaching its zero-degree value again at about 8C and expanding more and more rapidly to achieve a specific volume of 1.0435 at 100C, as shown in Figure 21.01(a). The density or specific volume of water vapor is of a different order altogether. It can be calculated with reasonable accuracy (and usefully) from its mass per mole.