Numerical Investigation of Solid–Liquid Dissolution for Nutrient Mixing Improvement in a Thin-Layer Cascade System

Maintaining an optimal concentration of nutrients in photobioreactors (PBRs) is a key issue for their optimal design and operation. In this study, a numerical investigation was conducted to quantify the dissolution of KNO₃ and Na₂HPO₄ inside a thin-layer cascade (TLC) reactor and determine its consequential effect on the reactor performance for algal cultivation. A computational fluid dynamics (CFD) model based on Euler–Euler approach was used to investigate nutrient mixing in TLC and evaluate the effect of flow and geometric properties of the reactor. A wide range of pertinent parameters such as channel width, channel depth, mass flow rate and nutrient particle size were considered. Nutrient concentration plots, nutrient mixing in terms of mass transfer coefficient, and solid hold-up in the reactor were established. The nutrient dissolution improved in the reactor with small dimensions operating at high mass flow rates and was inversely related to the nutrient particle size; that is, small particle results in increased nutrient mixing due to the enlarged interfacial area.