Mollier Diagram (h-s Chart) and Steam Tables
1 / 10
Using steam tables, the enthalpy of superheated steam at 10 bar and 250°C is 2937.6 kJ/kg. The enthalpy change when cooled isobarically to dry saturated steam at 10 bar (h_g = 2778.1 kJ/kg) is:
-159.5 kJ/kg
159.5 kJ/kg
2937.6 kJ/kg
-2778.1 kJ/kg
 Enthalpy change Δh = h_final – h_initial = 2778.1 – 2937.6 = -159.5 kJ/kg, as the steam is cooled from 250°C to the saturation temperature at 10 bar (~179.9°C).
2 / 10
Steam at 20 bar and 400°C (h = 3247.6 kJ/kg, s = 7.127 kJ/kg·K) is throttled to 2 bar. Throttling is an isenthalpic process. Using steam tables at 2 bar (hf = 504.7 kJ/kg, h_g = 2707.0 kJ/kg), the final state is:
Wet steam
Dry saturated steam
Superheated steam
Saturated liquid
Throttling is isenthalpic (h_initial = h_final = 3247.6 kJ/kg). At 2 bar, h_f = 504.7 kJ/kg, h_g = 2707.0 kJ/kg. Since h = 3247.6 kJ/kg > h_g, the steam is superheated (enthalpy exceeds that of dry saturated steam).
3 / 10
On a Mollier diagram, the quality (dryness fraction) of steam can be determined:
In the superheated region
In the saturated liquid region
Along the critical point line
In the wet steam region
The Mollier diagram shows constant quality lines in the wet steam region (below the saturation curve), allowing the dryness fraction to be determined directly for wet steam.
4 / 10
Using steam tables, the entropy of saturated liquid at 5 bar is 1.860 kJ/kg·K, and the entropy of dry saturated steam is 6.821 kJ/kg·K. The entropy of wet steam with a dryness fraction of 0.85 at 5 bar is:
5.998 kJ/kg·K
6.821 kJ/kg·K
4.224 kJ/kg·K
1.860 kJ/kg·K
For wet steam, s = sf + x (sg – sf). Given x = 0.85, sf = 1.860 kJ/kg·K, sg = 6.821 kJ/kg·K:
s = 1.860 + 0.85 × (6.821 – 1.860) = 1.860 + 0.85 × 4.961 = 1.860 + 4.21685 = 5.998 kJ/kg·K.
5 / 10
The specific volume of superheated steam at 8 bar and 300°C is 0.2938 m³/kg (from steam tables). Compared to dry saturated steam at 8 bar (v_g = 0.2404 m³/kg), the specific volume is:
Lower
Higher
Equal
Cannot be determined
 Superheated steam at 300°C has a higher temperature than the saturation temperature at 8 bar (~170.4°C), leading to a larger specific volume (0.2938 m³/kg > 0.2404 m³/kg).
6 / 10
Steam at 15 bar and 350°C undergoes isentropic expansion to 1 bar. Using steam tables (h = 3074.5 kJ/kg, s = 7.223 kJ/kg·K at 15 bar, 350°C; at 1 bar, sf = 1.302 kJ/kg·K, sg = 7.359 kJ/kg·K), the quality of the final state is:
0.978
0.892
0.786
1.0
For isentropic expansion, s_initial = s_final = 7.223 kJ/kg·K. At 1 bar, sf = 1.302 kJ/kg·K, sg = 7.359 kJ/kg·K. Since sf < 7.223 < sg, the steam is wet. Dryness fraction x = (s – sf)/(sg – s_) = (7.223 – 1.302)/(7.359 – 1.302) = 5.921/6.057 ≈ 0.892.
7 / 10
On a Mollier diagram, an isentropic process is represented by:
A horizontal line
A vertical line
A curved line
A diagonal line
 An isentropic process has constant entropy (s). On the Mollier diagram (h-s chart), this is represented by a vertical line, as entropy remains constant while enthalpy changes.
8 / 10
Using steam tables, the enthalpy of dry saturated steam at 10 bar is 2778.1 kJ/kg, and the enthalpy of saturated liquid is 762.8 kJ/kg. The enthalpy of wet steam at 10 bar with a dryness fraction of 0.9 is:
2537.63 kJ/kg
2778.1 kJ/kg
2015.3 kJ/kg
2286.95 kJ/kg
For wet steam, h = hf + x (hg – hf). Given x = 0.9, hf = 762.8 kJ/kg, hg = 2778.1 kJ/kg:
h = 762.8 + 0.9 × (2778.1 – 762.8) = 762.8 + 0.9 × 2015.3 = 762.8 + 1813.77 = 2537.63 kJ/kg.
9 / 10
On a Mollier diagram, the constant pressure lines for superheated steam:
Are horizontal
Are vertical
Diverge as entropy increases
Converge as entropy increases
On the Mollier diagram, constant pressure lines for superheated steam slope upward and diverge as entropy increases, reflecting the increase in enthalpy with temperature at constant pressure
10 / 10
The Mollier diagram is a plot of:
Pressure vs. volume
Temperature vs. entropy
Enthalpy vs. entropy
Temperature vs. pressure
 The Mollier diagram is a graphical representation of steam properties, plotting enthalpy (h) on the y-axis against entropy (s) on the x-axis, used to analyze steam processes and determine properties like quality and enthalpy.
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