Clausius-Clapyeron equation

A certain amount of energy will be required to raise the molecules to a level of kinetic energy where they will escape. In the special case of a liquid passing to the vapor state, the energy put into the system to cause volatilization is the latent heat of vaporization. The property is characteristic for a given chemical and may vary with temperature. The temperature relationship of the latent heat of vaporization may be calculated by the Clausius-Clapyeron equation. 

Over a small temperature range, the enthalpy of vaporization is essentially constant. Thus, we may use the Clausius-Clapyeron equation. Equation 3.2.32, to express the vapor pressure of water as a function of temperature. Next, calculate the mole fraction of water in the exit air using Equation 3.2.28, where p2,is, is the vapor pressure of water at the exit-air temperature. We assimie that heat capacity of air and water vapor is constant over the temperature range of interest. Using data taken from Reid et al. [2], calculate the heat capacities at 100 "F (37.8 °C). Thus, Cp, = 8.2 Btu/lbmol-"F (34.3 kJ/kg mol-K) and Cpz = 7.2 Btu/lbmol-°F (30.1 kJ/kg mol-K). The heat capacity of water, 18.0 Btu/lbmol- F (75.4 kJ/kg mol-K), is also assumed constant. We select 32.0 "F as the reference temperature, tR, to correspond to the steam tables. Thus, Equations 37 to 42 in Table 3.2.2 are the pure conqronent enthalpies of all the components. 

The rate of change of the temperature of equilibrium between two phases with change in pressure is given by the Clausius-Clapyeron equation. 

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