Mollier Chart Water English

Overview

Engineering reference data for Mollier Chart Water English 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

Interpreting the Mollier Chart

The Mollier chart (enthalpy-entropy diagram) is a visual tool for analyzing the thermodynamic properties of water and steam. Key lines and regions on the chart include:

• Constant Pressure Lines (Isobars): Appear as nearly vertical lines that curve across the chart. They are labeled with pressure values (e.g., psia).
• Constant Temperature Lines (Isotherms): In the superheated steam region, these lines are slightly curved. In the two-phase (wet steam) region, they are horizontal lines corresponding to saturation temperatures at given pressures.
• Constant Moisture Content Lines (Constant Quality or Dryness Fraction): In the two-phase region, these lines indicate the percentage of steam (by mass) in a wet mixture. A line labeled "90" means the mixture is 90% steam and 10% liquid water.
• Saturated Vapor Curve (Dome): The boundary separating the two-phase region (left/underneath) from the superheated steam region (right/above). Points on this curve represent 100% dry, saturated steam.
• Saturated Liquid Curve: The left boundary of the two-phase region, representing saturated water.

Key Properties Read from the Chart

Using the chart, you can determine multiple properties for a single point:

• Enthalpy (h): Read vertically from the enthalpy scale (BTU/lb).
• Entropy (s): Read horizontally from the entropy scale (BTU/lb·°R).
• Temperature (T): Follow the constant temperature line passing through the point.
• Pressure (P): Follow the constant pressure line passing through the point.
• Quality (x) or Moisture: For points inside the dome, follow the constant moisture line to the right edge to find the dryness fraction.

Common Engineering Applications

The Mollier chart is used to quickly visualize and calculate processes without complex equations:

• Steam Turbines: Plotting the expansion of steam through turbine stages to determine work output and exit conditions.
• Throttling Valves: Represented as a constant-enthalpy process (vertical drop) to find the resulting temperature and quality.
• Heat Exchangers: Determining heat transfer rates by finding enthalpy changes for the steam or water stream.
• Mixing Processes: Combining streams by adding mass-weighted enthalpies.

Note on English Units

This chart uses English (Imperial) units. Key scales are:

• Enthalpy (h): BTU per pound mass (BTU/lb)
• Entropy (s): BTU per pound mass per degree Rankine (BTU/lb·°R)
• Temperature (T): Degrees Fahrenheit (°F)
• Pressure (P): Pounds per square inch absolute (psia)

For reference, the digital version of this chart is available at: chemicalogic.com/download/mollier_chart_english.pdf

References

• Original Source