Thermodynamics of phase change UPM（热力学相变芬欧蓝）.pdf

THERMODYNAMICS OF PHASE CHANGE Phase changes 1 Phase rule 2 Clapeyron equation 2 Discontinuities in the phase change. Vapour fraction 5 Closed system evolutions 7 Open system evolutions 8 Metastable states 9 Vaporization kinetics 11 Exergy 13 Type of problems 14 PHASE CHANGES We said in Chapter 4: Thermodynamic Potentials and Properties, that when a system reaches an unstable state it splits itself into different phases with different properties but in equilibrium with each other. Chapter 5: Control Volume, was just a halt to change our view-point and see how the balance equations change when we let mass flows through the frontier of our system. Now we proceed with the thermodynamics of simple compressible system, and we analyse phase changes in a pure chemical substance, as already introduced in Chapter 4. Only phase changes in pure small-molecule substances are considered (i.e. usual gases, water and other simple inorganic liquids, small-chain hydrocarbons, metals and other inorganic solids), but not glasses, polymers and composites. It is interesting, however, to look at how, for instance, honey (or milk, oil, wax) boils and solidifies, or at how wax melts (or paper, wood, teflon, concrete, and so on). Furthermore, we focus on the liquid/vapour phase change, covering other phase changes occasionally; solid/solid allotropic transformations are not mentioned at all. Glasses are substances (inorganic as silicates or organic as plastics) that solidify from a molten state into an amorphous solid (i.e. without crystalline order); see Thermal effects on materials. Phase changes in mixtures are also covered in Chapter 7: Mixtures and Solutions. It is also important to mention that although we only deal here with phase changes of aggregation in a pure substance (the first phase transitions discovered), other thermodynamic phase chan