Process Intensification of Nanoemulsion Production Using Orifice-Based Hydrodynamic Cavitation: Influence of Flow Area on Cavitational Yield and Emulsification Performance

Abstract

Hydrodynamic cavitation (HC) has emerged as a sustainable, energy-efficient technology for intensifying the production of pharmaceutical- and food-grade oil-in-water nanoemulsions. This study investigates the influence of orifice flow area, characterized by β-values (orifice-to-pipe area ratios) of 0.01, 0.02, and 0.04, on emulsification under operating pressures ranging from 2 to 24 bar(g) at different recirculation passes. While HC process optimization is conventionally based on achieving the minimum droplet size, orifice devices often operate at relatively moderate pressures and require multiple recirculation passes. Thus, cavitational yield was introduced as a performance metric to evaluate process efficiency and identify optimum operating conditions. The results demonstrated that the target droplet size could be achieved under relatively mild cavitation conditions (cavitation number, Cv = 0.22) rather than excessively intense cavitation conditions (Cv ≤ 0.1) when using a high β-value device. The highest cavitational yield (0.190 m2/J) with a droplet size of 245 nm was obtained at 20 passes using the β = 0.04 orifice, indicating superior energy utilization and emulsification efficiency. Analysis of Cv and hydraulic energy density (ε) showed that efficient droplet disruption depends on the combined effects of cavitation intensity and cumulative energy input, not cavitation intensity alone. We developed an empirical correlation based on Cv and ε that showed good agreement with the experimental data. The influence of cavitation on droplet breakup diminished with increasing numbers of recirculation passes, while the effectiveness of additional energy input progressively decreased at lower β-values, indicating diminishing returns in emulsification performance. Furthermore, the nanoemulsions exhibited excellent storage stability, maintaining mean droplet sizes below 200 nm under refrigerated, ambient, and 60 °C storage conditions for 30 days, with only moderate growth observed at 80 °C. These findings show that optimizing orifice geometry using cavitational yield is an effective strategy to improve the energy efficiency and performance of HC-assisted nanoemulsion production.