Experimental and Numerical Analysis of a PCM-Supported ...

includes the determination of liquid holdup both below and above the loading point.
This model will be shortly described to the extent that is only needed for
determination of liquid and gas holdups as closure relationships, while calculation
procedures for estimation of the pressure drop are presented in Appendix (B).
Holdup measurements for eight different types of packing have been correlated by
Stichlmair et al [29] as follows:
h
l
(4.42)
l
1 3
0.555Frl
Where h l (or ε l in energy and mass balance equations) is a function of Froude
number, which is defined as:
Fr
a
g
2
l
vl,sup
(4.43)
4.65
where v l , sup is the superficial liquid velocity. The gas fraction can be determined as:
(4.44)
g
l
Where in conventional particle bed, the specific packing area per unit volume a is
directly related to the porosity ε through the following equation:
6(1 )
a (4.45)
dp
It is interesting to mention that although the Brinkman equation can be used to
model the flow field, Stichlmair et al [29] model will be used for determination of the
liquid and gas holdup (which are fundamental parameters for modeling heat and
mass transfer) and can also be used for calculation of pressure drop along the
packed bed under forced draft where the influence of buoyant forces can be
neglected.
4.2.3.4 Interfacial areas
Generalized methods for predicting the mass-transfer performance of larger-scale
packed distillation columns have been reviewed by Kister [32]. For random packing,
only four methods have been thought to be general and reliable enough to merit
serious consideration for commercial design [40]. Namely, Cornell et al. [42], Onda
et al. [35], Bolles and Fair [44], and Bravo and Fair [43]. Additionally, based on the
integrative approach to the pressure drop and liquid holdup model of Stichlmair et al
[29], Wagner et al. [40] developed a new model to provide a correlation for effective
interfacial area in randomly packed columns.
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