Once the voidage distribution along the bed is known, the gas
pressure drop along the height of the bed can be obtained from Eq. (7)
Δpg =
ugρsg
vt
∫h
0
ϕ
ð1−ϕÞn dz ð7Þ
For the fluidization process, Eq. (3) can be rewritten as:
uc
vt
=
∫h
0 ϕe−Jzdz
∫h
0
ϕ
ð1−ϕÞn e−Jzdz
: ð8Þ
where J=(4/Dh)μj, and uc is the critical gas velocity (maximum
interstitial gas velocity of undisturbed particles) The particle
concentration (or voidage) was assumed to be equal to the particle
concentration at the end of the defluidization process
ϕðzÞ = ϕðzÞ jug =0.
Eqs. (4)–(8) suggest that hysteresis and overpressure will be
observed due to wall effects in fluidized beds with small diameters, as
observed in previous studies [38–40]. For instance, wall effects were
observed by Srivastava and Sundaresan [38] and Loezos et al. [39], who
studied fluidized particles in cylindrical bedswith internal diameters of
10 and 50 mm. In addition, wall effects were also observed by Liu et al.
[40] , who used microfluidized beds with internal diameters ranging
from12 and 32 mm. Alternatively, in the present study, Jackson's model
was adjusted to the experimental data obtained in a 2D bed.
In this way, the value of the coefficient n was fitted to the experimental
data using the methodology of Srivastava and Sundaresan [38]
and Loezos et al. [39]. The value of ϕmin was assumed to be equal to the
average particle concentration under minimum fluidization conditions,
ϕmf, which was estimated by measuring the mass of the particles
in the bed and the fixed bed height. According to the work of
Srivastava and Sundaresan [38] and Loezos et al. [39], two different J
values were used in the present study. Namely, Jdf, was used for the
defluidizaton curve, and Jf was used for the fluidization process. The
value of Jf was obtained was obtained from Eq. (8), where uc is known,
and Jdf and ϕmax were optimized to fit the experimental data. Table 4
summarizes the values of the parameters for each experiment, and
Fig. 6 shows the experimental data and the theoretical results of
Jackson's model. As shown in the figure, hysteresis was observed
during the fluidization process.