Understanding Equivalent Evaporation in Boilers

The question asks for the specific term that defines the amount of dry saturated steam produced from feed water at 100°C under normal atmospheric pressure. This is a standard measure used in boiler performance analysis.

What is Equivalent Evaporation?

Equivalent evaporation is a standard way to compare the performance of different boilers. It is defined as the amount of dry saturated steam generated from feed water supplied at a temperature of 100°C, when converted into steam at a pressure of normal atmospheric pressure (1.01325 bar or 101.325 kPa).

This specific definition provides a baseline, allowing engineers to compare the steam-generating capacity of boilers operating under vastly different actual conditions (different feed water temperatures and steam pressures). By converting the actual steam production to this standard condition, a fair comparison can be made. The heat required under this standard condition is the latent heat of vaporization at 100°C, which is approximately 2257 kJ/kg.

Why Other Options Are Incorrect

• Degree of superheat: This term refers to the temperature difference between the superheated steam and the saturation temperature of steam at the same pressure. It describes the state of steam beyond the saturation point, not the amount generated under standard conditions.
• Boiler thermal efficiency: This is the ratio of the useful heat absorbed by the working fluid (water/steam) to the heat supplied by the fuel. It is a measure of how efficiently the boiler converts fuel energy into steam energy, not the amount of steam generated under a specific standard condition.
• Dryness fraction: This term is used for wet steam and represents the proportion of the mass of dry steam in a mixture of dry steam and water particles. It describes the quality of wet steam, not the total amount of steam generated under standard conditions.

Therefore, the definition provided in the question precisely matches the definition of Equivalent Evaporation.