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Define saturation pressure, saturated liquid, etc.; sketch

Short answer

Saturation pressure is the pressure at which a pure substance boils at a given temperature. Saturated liquid is liquid at its saturation temperature, with quality x=0. Quality is the mass fraction of vapour in a saturated mixture. Superheated vapour is vapour at a temperature above its saturation temperature. Isotherms on a P-v diagram are horizontal inside the two-phase dome and curved outside.

Define saturation pressure, saturated liquid, quality and superheated vapor. Also sketch the isotherm lines on the P-V (saturation curve) diagram.

  • Saturation pressure: the pressure at which a pure substance boils (changes phase) at a given temperature. For water at 100 °C it is 101.3 kPa.
  • Saturated liquid: liquid at the saturation temperature for its pressure; if any heat is added, some of it starts to vaporise (x = 0, v = v_f).
  • Quality (dryness fraction), x: the mass of vapour divided by the total mass of a saturated mixture; x = m_g/(m_f + m_g), varying from 0 to 1.
  • Superheated vapour: vapour at a temperature higher than the saturation temperature at its pressure; it is a single phase. Degree of superheat = T − T_sat.

Isotherms on P-v (saturation curve) diagram

 P|            CP (critical point)
  |          .-*-.   T > Tc
  |         /     \_______
  | liquid /  wet   \____  T2 (isotherm)
  |  x=0  |  mixture  | x=1   superheated
  |  ||   |-----------|------ T1 (horizontal
  |  ||   |           |        in wet region)
  +------------------------------- v
  • Below the critical temperature (T₁, T₂), an isotherm falls as a curve in the liquid region, then becomes horizontal inside the dome (boiling at constant P = P_sat(T)), then falls as a hyperbola-like curve in the superheated region.
  • The critical isotherm (T = T_c) touches the top of the dome at the critical point with a point of inflection (horizontal tangent).
  • Above T_c, the isotherm is a smooth curve with no phase change.

✓ Answer checked by Claude Opus 5.5 (high effort)

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