ISSN Online: 2379-1748
ISBN Flash Drive: 978-1-56700-469-4
ISBN Online: 978-1-56700-470-0
Second Thermal and Fluids Engineering Conference
AN EFFECTIVENESS−NTU RELATIONSHIP FOR EVAPORATORS WITH NON-NEGLIGIBLE BOILING POINT ELEVATION INCREASES
Аннотация
In some evaporators, such as those used in the desalination of high-salinity produced waters, the rise in temperature
of the evaporating stream owing to boiling point elevation increase may be non-neglible. In such cases,
neither classical effectiveness−NTU relationships, which are valid for constant capacity rates, nor traditional
falling film evaporation analysis, which generally considers uniform vapor saturation temperature, are applicable.
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 non-volatile solute(s); and (2) undergoes a significant,
but linear change in boiling point elevation 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 reveals nonlinearities in the driving temperature difference for large changes in BPE, which can impact staging design and systemwide energy consumption. The broad applicability of the model is demonstrated by applications to high-salinity desalination systems and juice evaporators.