Overall (thermal) efficiency wording “The ratio of work delivered at the turbine shaft to the heat supplied is called the overall thermal efficiency of the turbine.” Evaluate this statement.

Introduction / Context:
Overall (thermal) efficiency broadly compares useful output (shaft work) with the thermal energy input available from fuel or steam. Although exact wording varies by textbook, the spirit is to measure how effectively supplied heat becomes shaft power in the cycle or turbine system considered.

Given Data / Assumptions:

• “Heat supplied” refers to the thermal input associated with the working fluid entering the turbine or, in cycle terms, the boiler heat input.
• “Work delivered” refers to net turbine shaft work after mechanical losses, if the definition is plant-wide.
• Focus is on a macroscopic efficiency measure, not component-level aerodynamic efficiency.

Concept / Approach:

In many curricula, overall thermal efficiency η_th is defined as η_th = W_out / Q_in, where W_out is the useful shaft work and Q_in is the heat supplied from fuel (in a plant sense) or to the working fluid (cycle sense). The phrasing “of the turbine” is informal; rigorously, overall thermal efficiency usually applies to the cycle, but the ratio concept remains valid as a measure of heat-to-work conversion effectiveness. Hence the statement is accepted as true in the context of common exam terminology.

Step-by-Step Solution:

Verification / Alternative check:

Standard Rankine-cycle analyses compute η_th by dividing net cycle work by boiler heat input; component wording varies but the ratio mirrors the definition given.

Why Other Options Are Wrong:

Mechanical efficiency deals with internal power vs. shaft power, not heat-to-work conversion.Limiting to impulse turbines is unnecessary; definition is general.

Common Pitfalls:

Confusing internal (isentropic) efficiency with overall thermal efficiency; the former uses ideal enthalpy drops, the latter uses boiler heat input.

Final Answer:

True