11 PCM-Metal Foam Composite Systems for Solar Energy Storage
209
is present in Pielichowska and Pielichowski (2014), Zalba et al. (2003) and Nazir
et al. (2019). The main factor for the selection of storage medium is the operating
temperature of the system. PCM based energy storage systems have been discussed
in details in Sharma et al. (2009), Kenisarin and Mahkamov (2007), Farid et al.
(2004), Agyenim et al. (2010) and Xu et al. (2015).
11.1.3 Thermal Enhancement of Latent Heat Energy Storage
Systems
Among all the energy storage media, PCMs, in particular organic PCMs, have been
studied and used most widely. PCMs have high latent heat of fusion and thus can
store large quantities of energy in a limited size. However, PCMs typically have low
thermal conductivities. As a result, the full storage potential of a system cannot be
used if the operating time cycle is of short duration as the entire PCM cannot be
melted in that time. Various mechanisms for increasing the heat transfer in the PCM
has been proposed such as the use of high thermal conductivity fins, use of flow
channels, use of filler materials, nanoparticles, encapsulated PCM distributed in the
heat transfer fluid and porous metal matrix structures such as metal foam. Extensive
discussion about various thermal enhancement mechanisms have been presented in
Fan and Khodadadi (2011), Liu et al. (2016), Ibrahim et al. (2017), Qureshi et al.
(2018) and Lin et al. (2018).
11.2 PCM-Metal Foam Hybrid System
11.2.1 Concept
The main concept of thermal enhancement of PCM based LHES systems involves
the use of a high thermal conductivity secondary material whose main function is
to distribute the heat quickly to different parts of the energy storage unit. Increasing
the amount of this material increases the overall heat transfer rate of the system but
at the cost of reduced energy storage due to the reduced amount of PCM present
in the system. Another important parameter for designing these systems is the area
of contact between the PCM and the high thermal conductivity material. Based on
these criteria, metal foam structures are among the best mechanisms for thermal
conductivity enhancement of PCM based energy storage systems.
Metal foams are metallic structures with high porosity. As a result, they have low
weight but very high surface area. Metal foam structures with different geometries can
be produced such as structures with regular geometries consisting of arranged array
of cells or irregular geometries with randomly distributed pores. At lower porosity,
the foam structure may consist of large number of pores embedded within a metallic
209
is present in Pielichowska and Pielichowski (2014), Zalba et al. (2003) and Nazir
et al. (2019). The main factor for the selection of storage medium is the operating
temperature of the system. PCM based energy storage systems have been discussed
in details in Sharma et al. (2009), Kenisarin and Mahkamov (2007), Farid et al.
(2004), Agyenim et al. (2010) and Xu et al. (2015).
11.1.3 Thermal Enhancement of Latent Heat Energy Storage
Systems
Among all the energy storage media, PCMs, in particular organic PCMs, have been
studied and used most widely. PCMs have high latent heat of fusion and thus can
store large quantities of energy in a limited size. However, PCMs typically have low
thermal conductivities. As a result, the full storage potential of a system cannot be
used if the operating time cycle is of short duration as the entire PCM cannot be
melted in that time. Various mechanisms for increasing the heat transfer in the PCM
has been proposed such as the use of high thermal conductivity fins, use of flow
channels, use of filler materials, nanoparticles, encapsulated PCM distributed in the
heat transfer fluid and porous metal matrix structures such as metal foam. Extensive
discussion about various thermal enhancement mechanisms have been presented in
Fan and Khodadadi (2011), Liu et al. (2016), Ibrahim et al. (2017), Qureshi et al.
(2018) and Lin et al. (2018).
11.2 PCM-Metal Foam Hybrid System
11.2.1 Concept
The main concept of thermal enhancement of PCM based LHES systems involves
the use of a high thermal conductivity secondary material whose main function is
to distribute the heat quickly to different parts of the energy storage unit. Increasing
the amount of this material increases the overall heat transfer rate of the system but
at the cost of reduced energy storage due to the reduced amount of PCM present
in the system. Another important parameter for designing these systems is the area
of contact between the PCM and the high thermal conductivity material. Based on
these criteria, metal foam structures are among the best mechanisms for thermal
conductivity enhancement of PCM based energy storage systems.
Metal foams are metallic structures with high porosity. As a result, they have low
weight but very high surface area. Metal foam structures with different geometries can
be produced such as structures with regular geometries consisting of arranged array
of cells or irregular geometries with randomly distributed pores. At lower porosity,
the foam structure may consist of large number of pores embedded within a metallic