Importance of cloud motion and two-way momentum coupling in the transport of pharmaceutical nasal sprays

Abstract Nasal sprays, which produce relatively large pharmaceutical droplets with sizes mostly higher than 10 μm, are primarily used to deliver locally acting drugs to the nasal mucosa. Due to the large spray droplet size and high spray velocity, these droplets carry significant momentum, which can influence the surrounding gas field (i.e., two-way coupling) and strongly influence the transport mechanics and droplet deposition profile. The objective of this study was to determine if two-way momentum coupling leading to cloud motion is an important factor in simulating pharmaceutical nasal sprays, and if so, to develop a computationally efficient method to capture this effect. In this study, the effects of two-way momentum exchange between the nasal spray droplets and the surrounding air were analyzed using Computational Fluid Dynamics (CFD) simulations of sprays from two pharmaceutical nasal spray pumps. The computational spray transport was modeled using different modeling approaches including one-way coupled and two-way coupled Euler-Lagrange framework and Euler-Euler framework. Detailed comparisons of the computational simulation results and in vitro spray transport measurements were performed to establish which approach is more accurate for predicting the nasal spray transport. The simulation results indicated that the coupling effect of the spray momentum exchange with the air molecules created an air-jet velocity profile, which in turn led to a cloud-like motion of the smaller droplets. The airflow created by the cloud of droplets as a whole imparts significant momentum on the smaller droplets and transports them further into the flow field. The comparison study of simulation results and the in vitro measurements demonstrated that the two-way coupled Euler-Lagrange approach is more effective in accurately capturing the nasal spray transport. The spray modeling results indicated that the effects of two-way momentum exchange between the nasal spray droplets and the surrounding air was significant and influenced the spray droplet transport. Calculating the two-way coupling effects was computational resource intensive and time-consuming. Hence, reduced-time and resource modeling approaches including a quasi two-way coupled approach and momentum transfer approach were introduced to simplify the calculation.