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

the air pressure drop ∆P per unit bed height through a porous bed with relative
uniform porosity:
2
2
g
(1
) vg
g
(1
) vg
P 150 1.75
(4.10)
2 3
3
d
d
p
p
Where d P is the diameter of particles, and v g is the superficial gas velocity.
4.2.3 Two phase flow in dual phase change regenerators
Modeling two phase flow in dual phase change regenerators is rarely presented in
the literature for the condenser [17], but not a single analysis has been reported for
the evaporator up to the best knowledge of the author. The underlying heat and
mass transfer processes are complex and require the solution of highly nonlinear
coupled partial differential equations for space and time varying flow characteristics
and tracking the moving boundaries. Derivation of the governing equations to
describe steady state and dynamic characteristics of multi-phase multi-component
dual phase change regenerators of the evaporator and condenser is expected to be
more complicated and should be clearly formulated on rational basis and supported
by experimental validation.
4.2.2.1 Flow in the evaporator
Figure (4.4) shows a schematic of the evaporator chamber with its flow pattern and
operation features. Warm salt water from the external PCM storage tank is gently
sprayed in tiny droplets at the top of the evaporation tower and trickles downward by
gravity where heat and mass transfer take place between sprayed droplets and a
countercurrent dehumidified air leaving bottom of the condenser chamber.
Countercurrent air stream is heated and humidified in contact with the hot water film
while hot water is cooled down and partly evaporated. On the other side, another
binary heat transfer between solid PCM beads and both liquid water film and humid
air (gas mixture) take place simultaneously. This is due to non-fully wetted surface
area of packing elements.
The binary interactions between solid phase and both fluid phases are dependent on
the interfacial areas and flow characteristics. The evaporated water leaves behind
salts and other contaminations resulting in concentrated brine with lower
temperature at the bottom of the evaporator. A mutual interdependency between
heat and mass transfer and flow fields couples between hydrodynamics and
thermodynamics.
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