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A. Bhattacharya
also desirable to maintain the integrity of the system. The foam material and PCM
combination should also have high wettability to prevent formation of air pockets
due to shrinkage of PCM during solidification.
11.3.2 Thermo-physical Properties of PCM
The most important property of PCM is high latent heat of fusion as this is the critical
factor which governs the total energy storage capacity of the system. PCM should
also have relatively high thermal conductivity for better heat transfer to the interior
regions and high specific heat for better sensible heat storage. As mentioned before,
PCM should also have high wettability with the metal foam structure. Another important property is the change in density during solidification and melting. Typically,
PCMs undergo shrinkage due to volume contraction during solidification. Ideally,
shrinkage should be as minimum as possible. Shrinkage can be very detrimental
to the performance of energy storage system as it can lead to the formation of air
pockets between the metal foam and PCM thus drastically reducing the effective
thermal conductivity of the system. Other important properties of PCM are chemical
inertness and stability. Initial filling up of the metal foam with PCM also requires
the PCM to have lower viscosity.
11.3.3 Foam Porosity
The overall porosity of the metal foam has to be carefully chosen based on detailed
analysis. Lower porosity results in higher heat transfer rates leading to faster charging
and discharging of energy. On the other hand, higher porosity, leads to larger volume
fraction of PCM leading to higher overall energy storage capacity. The sensible heat
capacity of the metal foam and PCM needs to be considered to calculate the required
porosity of the system.
11.3.4 Foam Structure
The structure of the metal foam plays an important role in the performance of a
metal foam-PCM energy storage system. It has been shown that foams with lower
pore size and higher pore density have higher heat transfer rates due to the more
intricate network of metal structure (Lafdi et al. 2007; Ren et al. 2017; Dinesh and
Bhattacharya 2019). Also, open cell foams with high porosity enables significant
convective heat transfer which contributes towards the overall heat transfer rate. On
the other hand, closed foams or nearly closed foam structures have conduction as
the dominant heat transfer mechanism. Foams with regular structure and irregular
structure may also have different heat transfer characteristics.
A. Bhattacharya
also desirable to maintain the integrity of the system. The foam material and PCM
combination should also have high wettability to prevent formation of air pockets
due to shrinkage of PCM during solidification.
11.3.2 Thermo-physical Properties of PCM
The most important property of PCM is high latent heat of fusion as this is the critical
factor which governs the total energy storage capacity of the system. PCM should
also have relatively high thermal conductivity for better heat transfer to the interior
regions and high specific heat for better sensible heat storage. As mentioned before,
PCM should also have high wettability with the metal foam structure. Another important property is the change in density during solidification and melting. Typically,
PCMs undergo shrinkage due to volume contraction during solidification. Ideally,
shrinkage should be as minimum as possible. Shrinkage can be very detrimental
to the performance of energy storage system as it can lead to the formation of air
pockets between the metal foam and PCM thus drastically reducing the effective
thermal conductivity of the system. Other important properties of PCM are chemical
inertness and stability. Initial filling up of the metal foam with PCM also requires
the PCM to have lower viscosity.
11.3.3 Foam Porosity
The overall porosity of the metal foam has to be carefully chosen based on detailed
analysis. Lower porosity results in higher heat transfer rates leading to faster charging
and discharging of energy. On the other hand, higher porosity, leads to larger volume
fraction of PCM leading to higher overall energy storage capacity. The sensible heat
capacity of the metal foam and PCM needs to be considered to calculate the required
porosity of the system.
11.3.4 Foam Structure
The structure of the metal foam plays an important role in the performance of a
metal foam-PCM energy storage system. It has been shown that foams with lower
pore size and higher pore density have higher heat transfer rates due to the more
intricate network of metal structure (Lafdi et al. 2007; Ren et al. 2017; Dinesh and
Bhattacharya 2019). Also, open cell foams with high porosity enables significant
convective heat transfer which contributes towards the overall heat transfer rate. On
the other hand, closed foams or nearly closed foam structures have conduction as
the dominant heat transfer mechanism. Foams with regular structure and irregular
structure may also have different heat transfer characteristics.