Numerical simulation of a nebulizer with multiple orifices

Abstract

A vibrating mesh nebulizer is a medical device that can break liquid medication into an aerosol of tiny droplets so that patients can inhale them to treat diseases. The volumetric flow rate of this kind of nebulizer is determined by many factors, including the orifice geometry, the vibration amplitude and the vibration mode shape. Thus, many experiments were designed to assess the effects of these different variables on flow rate and to find the optimal set of device parameters that maximizes the flow rate. However, it can be very expensive to perform such physical experimentation with physical prototypes, which needs different orifice geometries to be fabricated for different test regimes. The orifice sizes are microscopic with diameters typically between 3 µm and 5 µm, thus, they are difficult to be fabricated with the exact shape and diameter that are required. Therefore, virtual prototyping by means of numerical simulation models are required as the orifice geometries and other factors can be easily changed in the simulation models. This study aims to provide a numerical simulation model that is experimentally validated. By comparing the simulated flow rates with the experimentally obtained flow rates, and the simulated droplet diameters with the experimentally obtained droplet diameters, it was found that the errors are all less than 10 % which demonstrates this numerical simulation model is adequately validated by experiment. Thus, instead of carrying out expensive experiments, this simulation model can be used for predicting the volumetric flow rates for different prescribed orifice geometries. Furthermore, this paper also simulates the effects of viscosity and surface tension on the flow rate, where either viscosity or surface tension increases, the flow rate will decrease.