Which factor most directly determines the Rankine cycle's thermal efficiency?

Which factor most directly determines the Rankine cycle's thermal efficiency?

• A. Steam conditions (temperature and pressure)
• B. Reactor fuel enrichment
• C. Shielding thickness
• D. Cooling tower humidity

Answer: (A)

The key idea is that the efficiency of a Rankine cycle is set by the energy balance of heat added and work extracted, which is driven most directly by the steam entering the turbine. When the steam is hotter and at higher pressure at turbine inlet, it carries more energy and can do more work as it expands in the turbine. This increases the turbine work more than the heat added, raising the net work output relative to heat input and thus boosting thermal efficiency. Material limits aside, higher steam temperature and pressure improve the cycle’s efficiency because they maximize the useful energy converted to mechanical work during expansion. The other factors don’t directly set the cycle’s thermodynamic efficiency. Reactor fuel enrichment affects how much energy the reactor can release, not how efficiently that energy is converted in the steam cycle. Shielding thickness changes radiation protection, not the steam cycle. Cooling tower humidity influences heat rejection performance, but the fundamental efficiency is still governed by the steam conditions at boiler and turbine, especially the turbine inlet state.

The key idea is that the efficiency of a Rankine cycle is set by the energy balance of heat added and work extracted, which is driven most directly by the steam entering the turbine. When the steam is hotter and at higher pressure at turbine inlet, it carries more energy and can do more work as it expands in the turbine. This increases the turbine work more than the heat added, raising the net work output relative to heat input and thus boosting thermal efficiency. Material limits aside, higher steam temperature and pressure improve the cycle’s efficiency because they maximize the useful energy converted to mechanical work during expansion.

The other factors don’t directly set the cycle’s thermodynamic efficiency. Reactor fuel enrichment affects how much energy the reactor can release, not how efficiently that energy is converted in the steam cycle. Shielding thickness changes radiation protection, not the steam cycle. Cooling tower humidity influences heat rejection performance, but the fundamental efficiency is still governed by the steam conditions at boiler and turbine, especially the turbine inlet state.