Diffusion
Diffusion is a physical process that refers to a movement of species that spread out in a region with different properties.
For example, when the concentration of a diffusing species in fluid is low, that species is considered negligible and this is called a passive scalar. Specify a diffusion coefficient since passive scalar diffuses in fluid, and no other material property settings nor setting fluid as a mixture of substances are necessary.
Figure 1: A room with an aroma diffuser placed by a wall
This shows a case study of diffusion analysis of an aromatic oil in a room. Figure 2 shows a mesh distribution around an aromatic diffuser. The total number of elements of the analysis region is approximately 420 thousand. Considering the aromatic oil to be a passive scalar, the diffusion coefficient is 10－4 m2/s. The flow rate from the aromatic diffuser is 300mL/h.
Figure 2: Mesh distribution
A transient analysis is initiated for an hour (3600s) real time. A restart calculation is performed in this case to shorten calculation time. As shown in Figure3, from 0s to 60s the time increment is 0.01s and from 60s to 3600s the time increment is 1s. After the restart calculation, the flow is considered constant and only diffusion is calculated. This process can make the calculation 1000 times shorter than without it.
Figure 3: Transient analysis
Figure 4 shows a velocity vector around the diffuser and a time-varying volume rendering depicting concentration (1ppm) up to 60s. (30x recording speed). The flow becomes constant after 60s and the aromatic oil diffuses around the diffuser. Figure 5 shows a time-varying volume rendering depicting concentration (1ppm) in a room up to an hour (600x recording speed). The aromatic oil is diffused in the entire room after an hour.
Figure 4: Diffusion analysis of an aromatic oil (1)
Figure 5: Diffusion analysis of an aromatic oil (2)