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

Q m H
c
( T T1)
c ( T 2 T
)
(2.2)
m
s
m
l
m
where ΔH m is the latent heat of melting and c s and c l the are specific heats of the solid
and liquid phase, respectively.
2.5.2 Advantages of LHES
The main advantages of LHES over other storage systems may be summarized in
the following:
a) Higher energy density per unit mass and per unit volume, resulting in
reduction of mass and volume of the storage unit. It has been reported [86]
that phase change materials store 5 to 14 times more heat per unit volume
than sensible heat storages such as water, masonry, or rock.
b) The PCM temperature remains nearly constant during the phase change,
which is useful for smoothing temperature variations, then keeping the subject
at uniform temperature. In other words, heat extraction and storage take place
at (nominally) constant temperature corresponding to the phase change
temperature.
c) Lower storage temperatures, which reduce the heat loss.
Latent heat energy storage media are confined in three basic forms; solid-solid,
solid-liquid, and solid-liquid-vapour phase change.
2.5.3 Solid-Solid Phase Change Storages
The challenges to widespread use of PCM are their packaging or capsulation, high
cost, and lake of technical knowledge among potential customers and users. For
solid-solid phase transformation the need for encapsulation of phase change
material is eliminated. This enables the high capacity properties of phase change to
be exploited without the additional thermal resistance and the associated costs due
to the encapsulation. In solid-solid transitions, heat is stored when the material is
transformed from one crystalline structure to another. Generally, the latent heat of
transformation for this transition is smaller than that of the solid-liquid phase change
materials. However, there are some of them having high capacity, form-stable, that
can be used as direct contact thermal storage systems in many applications in
industry and in commercial and residential heating. Some of the most promising
materials for solid-solid PCM are the commercially available vinyl silane graft
copolymer, a polysiloxane [88], and organic solid solution of pentaerythritol,
pentaglycerine, Li 2 SO 4 , and KHF 2 [92].
Some investigations that have dealt with the Polysiloxane, as a promising formstable
candidate for thermal energy storage proved that it has high latent heat of
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