The bulk storage system of encapsulation consists of using tank
heat exchangers for PCM which are similar in design to the existing
tanks used for TES, but with some differences [13]. The problem of
PCM bulk systems is the need for an extensive heat transfer area
between the PCM and the HTF. This limitation has been extensively
addressed by inserting fins or using high conductivity particles,
metal structures, or fibers in the PCM side or direct contact heat
exchangers.
Microencapsulation system, spherical or rod-shaped particles
are made using a thin and high molecular weight polymeric film.
The results presented by Roy and Avanic [59] showed that the heat
transfer characteristics for PCM emulsions are similar to those of
microencapsulated PCM suspensions, thus confirming that the
microcapsule walls do not affect the heat transfer process
significantly.
If the PCM modules can be so small that could be part of the
HTF, then the main part of the heat stored will be transferred out
of the storage. In this case, the heat storage and heat transfer medium
become one fluid which is always liquid and has a component
that stores latent heat. This type of component is known as phase
change slurry. Yamagishi et al. [32] and Kumano et al. [41,42] have
been working in the enhancement of the slurry systems.