Civil Engineering Reference
In-Depth Information
change temperature (Cabeza
2012
). Usually, the solid/liquid phase change is
studied. The amount of heat stored can be calculated by:
Q
¼
m
Dh
ð
1
Þ
where Dh is the phase-change enthalpy, also called melting enthalpy or heat of
fusion, and m is the mass of storage material.
2 Materials
2.1 Phase-Change Materials
Phase-change materials must have a large latent heat and high thermal conduc-
tivity, but the most important selection parameter is that the melting temperature
of the materials lies in the practical range of operation. Other parameters are
congruent melting, minimum subcooling, chemical stability, low in cost, non-
toxicity and non-corrosivity. Materials that have been studied are paraffin waxes,
fatty acids, and eutectics of organic and non-organic compounds (Farid et al.
2004
;
Sharma et al.
2009
). Tables
1
and
2
show a comparison between organic and
inorganic PCM (Mehling and Cabeza
2008
; Rathod and Banerjee
2013
; Zalba
et al.
2003
).
According to Kenisarin and Mahkamov (
2007
), the following phase-change
material (PCM) properties to be used for latent heat storage were highlighted as
desirable:
• a high value of the heat of fusion and specific heat per unit volume and weight,
• a melting point which matches the application,
• a low vapour pressure (\1 bar) at the operational temperature,
• a chemical stability and non-corrosiveness,
• not to be hazardous, highly inflammable or poisonous,
• a reproducible crystallisation without degradation,
• a small subcooling degree and high rate of crystal growth,
Table 1 Comparison of organic and inorganic materials for heat storage (Mehling and Cabeza
2008
; Zalba et al.
2003
)
Organic
Inorganic
Advantages
No corrosives
Greater phase-change enthalpy
Low or none subcooling
Chemical stability
Disadvantages
Lower phase-change enthalpy
Subcooling
Low thermal conductivity
Corrosion
Flammability
Phase separation
Phase segregation, lack of thermal stability
