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Modeling Nasal Passages is Nothing to Sneeze At

FLOW-3D CFD simulation of a nasal passage positioned in the head
Don't cut off your nose to spite your face.

Nasal drug delivery system, a promising non-invasive means of administrating drugs, poses numerous design challenges. If the spray particles are too large they tend to deposit in the anterior portion of the nasal cavity which reduces the effectiveness of the drug. If the particles are too small, a majority of the particles could pass directly to the lungs wasting most of the dose. For some drugs it is desirable to target a specific region of the nasal cavity like the olfactory region, which has a potential of delivering drugs directly to the brain. Designing a successful nasal drug delivery system requires optimizing various factors such as drug particle size, particle speed, spray angle, and nozzle insertion depth. Using FLOW-3D, the effects of the various design parameters on the system can be easily studied by running a series of simulations.

The animation shows the trajectory of spray particles through the nasal cavity. Particles are colored by size, where red indicates the largest particles and blue the smallest. The simulation shows that the smaller the particles are, the deeper they penetrate into the nasal cavity. The smallest particles then exit the nasal cavity and go further into the respiratory system.

Simulation Setup

Uniform velocity boundary condition was imposed at the nostrils, velocity was set to zero at walls (no-slip condition) and a particle model was used to model the transport of particles in the air-stream. The wall of the nasal passage is usually wet so the particles stick (i.e., they form a deposit) once they hit the wall. To model this sticking effect it is assumed that particles stick to the wall as soon they come in contact with wall.

Spray particles sometimes carry electrostatic charge which can affect their motion. This phenomenon can also be simulated using FLOW-3D. However, in this case, it was assumed that there is no electrostatic charge on the particles.

Using the FAVOR™ Technique

It is likely that respiratory airflow, shape and size of the nasal cavity will vary from person to person, whereas the particle size will most likely be fixed for a particular device. It would therefore be important to test the design for a range of nasal cavities. FLOW-3D incorporates a special technique, known as the FAVOR™ (Fractional Area Volume Obstacle Representation) method, which is used to define general geometric regions within the rectangular grid. The FAVOR™ technique simplifies the meshing process making it easier to test the device design for a range of nasal cavities.

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