CFD analysis of spray nozzle arrangements for multi effect desalination evaporator

Solid cone spray nozzles are commonly used in Multi-Effect Desalination (MED) falling film evaporators due to their inherent advantage of uniform flow distribution over tube bundles. This is accomplished by setting minimum 30% overlap of spray streams in order to avoid dry patches, fouling and non-uniformity of liquid load. Considering such factors, the present work focuses on the analysis of horizontal falling film evaporator with tube bundle of 30 columns having triangular 60⁰ pitch and a tube diameter of one inch. Effect of key parameters like solid cone angle, number of nozzles, spacing, height and seawater mass flow rate on velocity distribution, spray overlapping and liquid load were studied for MED. For this purpose, a comprehensive numerical simulation for different configurations was carried out using Computational Fluid Dynamics (CFD) tool ANSYS Fluent v18. Results show that the number of nozzles can be reduced by selecting optimum cone angle, height from nozzles to 1^st row of tube bundle and nozzle spacing. The liquid load in the 1^st row was found to be higher than the 2^nd row due to the triangular pitch configuration that may result in fouling due to very low liquid load on the bottom rows. This can be avoided by choosing higher pitch or rectangular configuration with additional cost for the same surface area. Our analysis provides a better guideline to achieve efficient heat transfer by avoiding fouling for proper operation of evaporators.