How is a steam turbine’s heat rate related to its efficiency?

In the context of steam turbines, the heat rate and efficiency are inversely related: the lower the heat rate, the better the turbine's efficiency.1

The heat rate represents the amount of heat energy that must be supplied to the feedwater to produce a specific amount of generator power output. Because a lower heat rate indicates that less thermal energy is required to generate the same amount of electricity, it signifies a more efficient conversion process.1

Several factors influence this relationship, including:
* Operational conditions: Higher steam generator exit temperatures and pressures generally improve efficiency and decrease the heat rate.1
* Energy losses: The heat rate is impacted by mechanical and bearing losses, generator losses, exhaust losses, and the turbine's inherent efficiency in converting the thermal energy of steam into work.1
* Load: Operating at part-load results in a loss of efficiency, which consequently leads to a higher heat rate.1

Ultimately, improving efficiency is a primary goal in mechanical engineering to minimize the waste heat that must be exhausted into the environment, as dictated by the second law of thermodynamics.2