What diagram is used when the quality is above 50% and for superheated steam?

What diagram is used when the quality is above 50% and for superheated steam?

• A. Mollier Diagram
• B. P-V Diagram
• C. T-S Diagram
• D. H-X Diagram

Answer: (A)

When dealing steam that is mostly vapor or in the superheated region, you want a diagram that links both enthalpy and entropy and spans from the saturated mixture through to the superheated states. The Mollier diagram, which is a plot of enthalpy versus entropy, does exactly that. It includes the saturated liquid and saturated vapor limits as well as the two-phase region and the superheated region, with lines of constant pressure that let you read off how h and s change as heat is added or removed. In the two-phase region, you can connect the state to the saturated line at a given pressure to infer quality (the vapor fraction) via the enthalpy data, and as you move above the saturated vapor line you remain on the same chart to describe superheated states. This makes it particularly convenient when the quality is high (more than half vapor) and when the steam is superheated, because you can track energy and entropy changes in a single diagram without switching tools. Other diagrams have limitations here: P-V focuses on pressure–volume relationships and misses direct energy-entropy information; T-S is excellent for irreversibility and cycle analysis but doesn’t immediately show quality or enthalpy relationships across phase change; H-X is tailored to two-phase mixtures at a fixed pressure and isn’t as useful once you’re into the superheated region.

When dealing steam that is mostly vapor or in the superheated region, you want a diagram that links both enthalpy and entropy and spans from the saturated mixture through to the superheated states. The Mollier diagram, which is a plot of enthalpy versus entropy, does exactly that. It includes the saturated liquid and saturated vapor limits as well as the two-phase region and the superheated region, with lines of constant pressure that let you read off how h and s change as heat is added or removed.

In the two-phase region, you can connect the state to the saturated line at a given pressure to infer quality (the vapor fraction) via the enthalpy data, and as you move above the saturated vapor line you remain on the same chart to describe superheated states. This makes it particularly convenient when the quality is high (more than half vapor) and when the steam is superheated, because you can track energy and entropy changes in a single diagram without switching tools.

Other diagrams have limitations here: P-V focuses on pressure–volume relationships and misses direct energy-entropy information; T-S is excellent for irreversibility and cycle analysis but doesn’t immediately show quality or enthalpy relationships across phase change; H-X is tailored to two-phase mixtures at a fixed pressure and isn’t as useful once you’re into the superheated region.