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

Several models and approaches for mass transfer coefficients on both the gas and
liquid sides are presented by Wagner et al. [40]. Various approaches and models for
determination of the wetted and effective interfacial areas for mass transfer
presented by Kister [32] and Gandhidasan [41] were preliminary examined and
compared against each other.
One particular problem to address here is the significant discrepancies between the
predicted values of mass transfer coefficients between various approaches and
models. It is observed that many researchers have used Onda et al. [35] model to
describe the liquid-gas interfacial areas and mass transfer coefficient in distillation
columns. Klausner et al. [45] have already developed a detailed heat and mass
transfer analysis for a HDH system called the diffusion driven desalination (DDD)
process. They extensively tested Onda et al. [35] correlations and used it to evaluate
the mass transfer coefficients on the liquid and gas sides. They reported that
excellent results were obtained against experimentation measurements [47]; thus
the same approach will be applied here.
Nevertheless, Klausner and Mei [45-46] modified Onda et al. [35] model described
by equations (4.46-4.47) by introducing a constant of 2.2 instead of 1.45 for
calculating the wetted interfacial area in the (DDD) system. They argued that the
model underestimates the wetted surface area of the packing and this was the
reason behind this modification in equation (4.47). The model is based on the
concept of wetted packing area as a geometric parameter in determining the
Reynolds number for the liquid as opposed to the interfacial area.
a
a
e
c
exp 1.45
l
0.75
0.1 0.2 0.
05
1 Rel
Wel
Frl
(4.46)
a
w
a
c
exp
2.2
L
0.75
0.5 0.2 0.
05
1 Re
LA
WeL
Fr
L
(4.47)
Therefore, this modification could be even more crucial for the present analysis due
to the existence of conductive packing media or a solid phase in the energy and
mass balances. However, their predicted performance using this modified correlation
is always higher than their experimental measurements in terms of the outlet air
humidity content, outlet water temperature, and outlet air temperature.
In the original model, Onda et al. [35] assumed the wetted area was equal to the
effective interfacial area. The total wetted surface area in the irrigated column is
expected to be greater than the effective area for mass transfer due to existence of
static liquid holdup which contributes little to heat and mass transfer. This finding has
been ascertained during the course of preliminary calculations of the effective
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