Latent Heat and Steam Formation - Continued.

Phase 2 (B to C)

In this phase we add latent heat to the water. The x-axis shows that we add a lot of heat from point B to point C. But the temperature on the y-axis shows no increase (the temperature stays at 212 deg F). We expected that, we know that at the saturation temperature, water needs latent heat to start converting itself into steam. Unless all of it is converted into steam, the temperature of the water/steam mixture stays at 212 deg F.

How much heat did we add in this phase? We can calculate that by using the following formula:

Latent Heat Added = (Latent Heat of Vaporization) x Mass

In our case we have the following:

Latent heat of vaporization for water is 970 BTU per pound

Mass = 1 lb.

Therefore, Latent Heat Added = 970 x 1 = 970 BTU