What is latent heat and how is it used in process calculations?

Latent heat is the energy absorbed or released during phase change at constant temperature. Latent heat of vaporization: energy to convert liquid to vapor (e.g., water ~2257 kJ/kg at 100C). Latent heat of fusion: energy to convert solid to liquid. Latent heat of sublimation: solid to vapor directly. In process calculations: sizing evaporators and condensers, calculating steam requirements, evaluating refrigeration cycles, and drying operations. Latent heat varies with temperature, typically decreasing as temperature approaches critical point (zero at Tc).