An Effectiveness--Number of Transfer Units Relationship for Evaporators With Non-negligible Boiling Point Elevation Increases

Abstract

An effectiveness number of transfer units (ε–NTU) model is developed for use in evaporators where the evaporating stream: (1) comprises a volatile solvent and nonvolatile solute(s) and (2) undergoes a significant, but linear change in boiling point elevation (BPE) with increasing solute molality. The model is applicable to evaporators driven by an isothermal stream (e.g., steam-driven or refrigerant-driven) in parallel flow, counterflow, and crossflow configurations where the evaporating stream is mixed. The model is of use in a variety of process engineering applications as well as the sizing and rating of evaporators in high-salinity desalination systems.