How is thermal efficiency defined in relation to power boilers?

Thermal efficiency in relation to power boilers is defined as the measure of how effectively a boiler converts fuel energy into thermal energy. This concept pertains to the performance of the boiler in utilizing the energy content of the fuel to produce useful heat. High thermal efficiency indicates that most of the energy from the fuel is being transformed into heat, which can then be used for generating steam or for heating purposes.

This definition underscores the importance of the energy conversion process within the boiler. Factors that affect thermal efficiency include the design of the boiler, the type and quality of the fuel used, and operational conditions such as temperature and pressure. Boilers that operate at higher thermal efficiency minimize energy losses, which ultimately leads to reduced fuel consumption and lower operational costs.

In contrast, the other options do not accurately represent thermal efficiency. The ratio of water temperature to steam temperature is more related to the energy transfer within the boiler rather than its overall efficiency in converting fuel to thermal energy. The total heat output of the boiler does not account for the energy content of the fuel consumed, and the volume of steam produced per hour is a measure of the output capacity of the boiler rather than its efficiency in energy conversion.