Equivalent Evaporation — “From and At 100°C” Definition The term “equivalent evaporation from and at 100°C” is defined as the amount of water evaporated from feedwater at __________ into dry saturated steam at 100°C at normal atmospheric pressure (1.013 bar). Select the correct feedwater temperature.

Introduction / Context:
Boiler performance is compared using a common reference called “equivalent evaporation from and at 100°C.” This normalizes different steam conditions and feedwater temperatures to a standard basis so that efficiencies and steaming capacities can be compared meaningfully across plants and fuels.

Given Data / Assumptions:

• Reference pressure is atmospheric (approximately 1.013 bar).
• Reference steam state is dry saturated steam at 100°C.
• Reference feedwater temperature is also at the saturation temperature of 100°C.

Concept / Approach:
“From and at 100°C” literally means the water begins at 100°C and is evaporated to dry saturated steam at 100°C. On this basis, the latent heat of vaporization used for comparison is the standard value at 100°C. Real boilers seldom operate exactly at these conditions; the definition provides a calculation method to convert the actual heat absorbed by feedwater into an equivalent mass that would have been evaporated under the standard reference condition.

Step-by-Step Solution:
Define the reference latent heat: h_fg at 100°C.Compute actual heat added to water/steam in the boiler per kilogram under operating conditions.Divide actual heat added by h_fg at 100°C to obtain equivalent kilograms evaporated “from and at” 100°C.Hence, the feedwater reference temperature in the definition is 100°C.

Verification / Alternative check:
Textbook boiler trials convert the measured enthalpy rise of feedwater to this standard using the factor of evaporation, which is based on the same 100°C reference.

Why Other Options Are Wrong:

• 0°C, 40°C, 60°C: These are common feedwater temperatures in practice, but they are not the reference for the standardized “from and at 100°C” definition.

Common Pitfalls:
Confusing “equivalent evaporation” with actual mass flow; it is a normalized reference for comparison, not necessarily the real evaporated mass at operating conditions.

Final Answer:
100°C