Mollier Diagram Water

Overview

Engineering reference data for Mollier Diagram Water in steam condensate.

Key Formulas

Steam Quality

$x = \frac{m_v}{m_{total}}$

Mass fraction of vapor in two-phase mixture.

Enthalpy of Wet Steam

$h = h_f + x \cdot h_{fg}$

Specific enthalpy of wet steam.

Flash Steam

$m_{flash} = m_{liquid} \frac{h_f - h_{f2}}{h_{fg2}}$

Steam generated when condensate flashes to lower pressure.

Condensate Load

$m_c = \frac{Q}{h_{fg}}$

Condensate generated by heat transfer.

Variables

Dryness Fraction

The dryness fraction (also called quality) represents the proportion of saturated vapor in a unit mass of wet vapor. It is a dimensionless quantity denoted by $x$.

$x = \frac{m_v}{m_v + m_l}$

Where:

• $m_v$ = mass of vapor (kg)
• $m_l$ = mass of liquid (kg)

The dryness fraction ranges from:

• $x = 0$ for saturated liquid (all liquid, no vapor)
• $x = 1$ for saturated vapor (all vapor, no liquid)

For wet steam, the specific enthalpy can be calculated using:

$h = h_f + x \cdot h_{fg}$

Where:

• $h_f$ = specific enthalpy of saturated liquid (kJ/kg)
• h_{fg = latent heat of vaporization (kJ/kg)

Unit Conversions

Practical Applications

The Mollier diagram is particularly useful for analyzing adiabatic steady-flow processes in:

• Nozzles — converting pressure energy to kinetic energy
• Diffusers — converting kinetic energy to pressure energy
• Turbines — extracting work from expanding steam
• Compressors — increasing fluid pressure through work input

Example: Reading Enthalpy from the Diagram

For saturated steam ($x = 1$, indicated by the bold red line on the diagram) at a pressure of 10 bar:

$h \approx 2770 \text{ kJ/kg}$

This value can be verified using steam tables for water/steam properties.

References

• Original Source