Fig. 8(a)–(c) shows the effects of fiber porosity on the average
value and the distribution of the superficial air velocity and the
physical air velocity along the length. Both superficial and physical
velocities are generated by FADS with an equivalent diameter
of 282 m under the supply air flow rate of 0.134 m3/s. As can be
seen, the porosity greatly affects the average physical air velocity and distributionof superficial andphysical velocity along the length
direction, yet it does not affect the average value of superficial
air velocity much. The uniformity of the distribution of superfi-
cial air velocity along the length direction becomes worse with
the increasing porosity (in Fig. 8(a)). However, the corresponding
average superficial velocity almost remains a constant value (in
Fig. 8(c)). For example, the superficial air velocity along the length
direction decreases by 2.8% when the porosity is 0.5, and the corresponding
value is up to 6.3% and 14.2% when the porosity is 0.7 and
0.8 respectively. It also can be seen that the average physical air velocity decreases with the increasing porosity (in Fig. 8(b)) and its
distribution uniformity along the length direction becomes worse
(in Fig. 8(c)). For instance, the physical air velocity first decreases
and then rapidly increases against the distance away from the inlet
when the porosity is 0.9. The physical air velocity along the length
direction increases by 2.5% as the porosity is 0.5, but the corresponding
value rises up to 12.4% when the porosity grows up to 0.8.
The reason is that physical air velocity equals the ratio of superficial
air velocity to fiber porosity [20], so its average value is influenced
by fiber porosity. While the superficial air velocity refers to the
average air velocity on the total discharging area and it equals the
ratio of supply air flow rate to total air discharge area, i.e. the area
of surface of half cylindrical fiber, so its average value has nothing
with fiber porosity. However, both the distribution of superficial
air velocity and physical air velocity along the length direction is
related with the static pressure inside FADS, which is influenced by
the fiber porosity.