Fig. 10(a)–(c) displays the effect of equivalent diameter on the
superficial and physical air velocity generated by a FADS with
a porosity of 0.64 under the supply air flow rate of 0.134 m3/s.
It can be seen that the equivalent diameter greatly impacts the distribution of superficial air velocity and physical air velocity along
the length direction. But it does not change the average air super-
ficial air velocity and physical air velocity a lot. The uniformity
of both the distribution of superficial air and physical air velocity
along the length direction becomes worse with the increase of
the equivalent diameter. For example, both superficial air velocity
and physical air velocity along the length direction increase by
0.4% and 8.9% when the equivalent diameter is 100 m and 400 m,
respectively. The corresponding value increases up to 15.4% when
the equivalent diameter is 500 m. For the average air velocity,
the superficial velocity and physical velocity remain almost constant
at 0.07 m/s and 0.112 m/s, respectively, which satisfies the
Dupuit–Forchheimer relation, i.e. U = ε u, where the porosity ε is
0.64. The main reason is that, for a given fiber, the larger the equivalent
diameter is,the sparser the fiber is,therefore, airflow in cavity
of FADS is similar to the jetted flow, that is, static pressure at the
inlet is lower and the corresponding value is higher at the end. As a
result, most of airflow is discharge outfrom the end, and air velocity
is also distributed accordingly along the length direction as shown
in Fig. 10(a) and (b).
Th