chapter 2 Properties of Pure Substances

2-1 Pure Substance 2-1-1 Definition of Pure Substance A homogeneous substance is pure substance 2-1-2 Phases of Pure Substance Solid Liquid Gas Plasma

2-2 Phase Change Process of Pure Substance 2-2-1 Constant Pressure Process of Water

T=constant vapor solid p Triple line Solid+Vapor T Critical point 1” 2” 3” 4” 5” c c 1’ 2’ 3’ 4’ 5’ 5 5” 1” 2” 3” 4” 5’ 1’ 2’ 3’ 4’ 1 2 3 4 1 2 3 4 5 vapor Liquid +Vapor Critical point Liquid Liquid +solid Solid+Vapor solid p T Triple line

2-2-1 Properties of Water 1.One point： Critical point C 2.Two lines： Saturated water line, Saturated vapor line 3.Three Regions: Compressed water region, Saturated mixture region, superheated vapor region 4.Five states: Compressed water, Saturated water, Saturated mixture, Saturated vapor, superheat vapor

2-3 P-v-T surface and P-T diagram

Extract on freezing 2-3-2 p-T diagram Melting line Expand on freezing Critical point Expand on freezing P liquid Vaporization Solid Vapor Sublimation T

2-4 Property Tables 2-4-1 Saturated Liquid and Vapor One property is enough to Calculate other properties. t ℃ P, MPa v’ v” h’ h” s’ s” 100 0.1013 0.00104 1.6738 419.06 2676.3 1.3069 7.3564 200 1.5551 0.00116 0.12714 352.4 2791.4 2.3307 6.4289 Enthalpy ---- the combination property: H=U+PV Or, per unit mass h=u+Pv

2-4-2 Saturated Mixture One property to calculate saturated properties, but how to determine the properties of saturated mixture? One special property to calculate the fraction of liquid and vapor, the quality

2-4-3 Superheated Vapor Two independent properties are used to Calculate other properties T ℃ P=0.1 MPa v, m3/kg h, kJ/kg s, kJ/kg.K 100 1.6958 2676.2 7.3628 150 1.9364 2776.4 7.5438

2-4-4 Reference state and reference value Water: Saturated liquid at 0.01 ℃ is taken as the reference state, where u=0 s=0 R-12: Saturated liquid at -40 ℃ is taken as the reference state, where u=0 s=0 Notice: The reference state differ with different tables

2-5 The Ideal-Gas Equation of State The molecules of ideal-gas have no volume There are no attraction among molecules of ideal-gas 2-5-2 The Ideal-Gas Equation of State (1). pV = mRT pv=RT R------The gas constant (2) pVm = μRμT pvm=RμT Rμ-----The universal gas constant = 8.314kJ/kmol.K

2-6 Real Gases 2-6-1 Compressibility Factor Pv=RT can only be employed for the gas under high temperature or low pressure For real gas, from pv=RT : z------- Compressibility Factor: a measure of deviation from ideal-gas behavior z=1: Ideal-Gas z>1 or z<1: Real-Gas

2-6-2 Van der Waals Equation of State (1)consider the volume occupied by the molecules themselves from pv=RT : Since the smaller space for the molecules flying will lead to more chance of hit on its container ,the pressure of the gas will increase then . Correct this by replacing v as v-b

The contraction should be in proportion to ρ2 which can be write as 1/v2. ‘a’ is proportional coefficient decided by experiment (2) consider contraction among the molecules The contraction will lead to a decrease on pressure, so correct the equation as following:

2-6-3 Other Equations of State (1) Beattie-Bridgeman Equation (2) Martin-Hou Equation (3) Virial Equation

The end of This Chapter Thank you