C3 - Properties of Pure Substances (Thermo)

saturation line

division on phase diagram between liquid & vapor

triple line

point where solid, liquid & gas coexist

supercritical fluids

fluid @ high compression which shares properties of liquids & gases

quality

x = m_vapor/v_total

phase mixture

• v_avg = xv_g + (1-x)v_f = v_f + xv_fg

  • v_fg = v_g - v_f

• y_avg = y_f + xy_fg

  • y = v, h, or u

superheated vapor

P & V become independent properties

subcooled liquid

y ≈ y_{f @ T}

• h ≈ (h_{f @ T})(P - P_sat)V_{f @ T}

ideal gas equation

Pv = RT

compressibility constant

Z = Pv/RT = v_actual/v_ideal

• v_ideal = RT/P

principle of corresponding states

@ P_r & T_r, Z is approximately constant across substances

• P_r = P/P_cr

generalized compressibility chart

1. ideal @ very low pressures

2. ideal @ high temperature & moderate pressure

3. deviation greatest around CP

pseudo-reduced specific volume

v_R = v_actual/(RT_cr/P_cr)

other equations of state

• van der waals

• Beattie-Bridgeman Equation of State

• Benedict-Webb-Rubin Equation of State

• Virial Equation of State