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

parameters on the heat transfer and pressure drop characteristics of packed bed
solar energy storage system with large sized elements as a storage material of five
different shapes. It was clear from the experimental results that the spherical shape
has the highest heat transfer coefficient and the second lowest friction factor
coefficient amongst the other five shapes.
Standish and Drinkwater [122] reported that the element shape is a significant
variable in gas liquid flooding in packed column. Gauvin and Katta [123] emphasized
that the major operating cost in packed bed system is directly related to the pressure
drop in the bed, which can not be predicted with reliability when the elements in the
bed depart from the spherical shape. Barba and Spiga [124] analyzed the behavior
of encapsulated salt hydrates, used as latent energy storage in a domestic hot water
tank. The discharge process of the (PCM) was analyzed for three different
geometrical configurations, i.e. considering the PCM encapsulated in slab, cylindrical
or spherical polyethylene containers. The influence of the geometry and the Jacob
number which is defined as:
Ja c T
T
H
(2.3)
s m pcm1
where T pcm1 is the wall temperature of the cooled PCM cell surface, on the ending
time of solidification were investigated. Spherical capsules, operating with high
Jacob numbers (not too high to compromise the efficiency of the latent heat storage
system) exhibited the largest energy density and the most rapid charge and release
times as shown in figure (2.3).
2.8 Desalination with humidification-dehumidification technique
Basin type solar stills exhibit two main draw backs. The first is the combined loss of
evaporation, convection and radiation energy received by the condenser, which
accounts for most of the energy lost to the surroundings. Partial recovery of this heat
for feed preheating or to be stored for extending plant the production after sun-set
has been an essential approach for enhancing the performance of solar distillers.
Practically full recovery is almost impossible due to thermodynamic irreversibilities.
The technical and economical viability of the energy recovery system should be
justified with the additional yield gain.
The second drawback is the transient trend of water production and long idleness of
the plant after sunset and during cloudy periods when the ambient temperature is
low and the heat sink is promising (i.e. cooling seawater temperature in the
condenser is low). The limited heat capacities of these distillation systems can not
support the plant operation during night or cloud periods. This drawback can be
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