Liquid-Vapour Mixtures

Definitions

Saturated Liquid
Liquid on the point on vapourisation.
Saturated Vapour
Vapour on the point on condensation.
Triple Point
Vapour, liquid and solid states can exist in thermodynamic equilibrium. Occurs at low pressures.
Critical Point
Volume increase at vapourisation is zero. Occurs at high pressures.
Compressed Liquid
Liquid at a temperature lower than saturation temperature.
Superheated Vapour
Vapour at a temperature higher than saturation temperature. Not on the point of condensation.

Ideal gas law does not apply. Internal energy and enthalpy change definitions also do not apply. Isentropic relations do not apply.

Quality, Dryness Fraction

$$ x = \frac{m_{vapour}}{m_{total}} = \frac{m_{g}}{m_{tot}} $$

Properties of liquid-vapour mixtures can be interpolated from their mass ratios and respective properties, either given or from data tables.

Heat Transfer

$$ Q = m C_{p} \Delta T = \Delta H = m \Delta h = m (h_2 - h_1) $$

Interpolated Properties for Mixtures

$$ y_{AV} = y_{f} + x ( y_g - y_f ) $$

Can apply to any consistent and inherent property ( \(v \), \( h \), \( s \) ...)

Where \( y _f \) is the fluid property, \( y_g \) is the gaseous property, \( x \) is the quality and \( y _{AV} \) is the average, or interpolated property.