256
R. Saxena et al.
example is lead acetate batteries however, long term stability of these storage is still
a topic of research. The advantage of these materials is high storage density near
ambient temperature; thus, losses are greatly subsided.
This study however, deals with PCMs for application in Indian climatic conditions.
13.3 PCM Properties and Methods of Characterization
13.3.1 Desired PCM Properties and Their Inherent Problems
The PCM selection for a particular application is to be made judiciously, with the
help of the following parameters (Mehling and Cabeza 2008):
• Suitable phase change temperature and high latent heat; specifically, temperature
must be determined with high accuracy (as melting and solidification temperature
plays a critical role in storage and release of heat at required temperature which is
a pre-requisite for any thermal energy storage system);
• Other thermophysical properties: large heat capacity, low volume change ratio,
large density and thermal conductivity, no phase segregation and lower supercooling;
• Chemical parameters: high chemical stability, no corrosion, low toxicity, noninflammable, compatible and non-polluting;
• Economic parameters: good recyclability, proper availability and cheap.
PCMs also possess certain inherent problems that should to be addressed before
their application. Some of the major issues are as follows:
• Super-cooling (also referred as sub-cooling). It is the difference in melting
and solidification temperature; PCMs are to be cooled below their solidification onset temperature to initiate nucleation which is followed by crystallization/solidification. For inorganic PCMs, sub-cooling is significantly higher.
• Phase segregation. PCMs (generally hydrated salts and eutectic mixtures) generally exhibit phase segregation. They separate out during melting thus making it
inhomogeneous.
• Low thermal conductivity. It is problem for most of the PCMs. For organic PCMs
the thermal conductivity is below 0.5 W/m K. For inorganic PCMs it is generally
below 1 W/m K.
To overcome the above disadvantages the foremost priority is to assess the PCM
properties with high accuracy and precision as there is divergence in data or data mismatch in the available literature followed by measures to enhance the PCM properties
as per their specific field of application.
R. Saxena et al.
example is lead acetate batteries however, long term stability of these storage is still
a topic of research. The advantage of these materials is high storage density near
ambient temperature; thus, losses are greatly subsided.
This study however, deals with PCMs for application in Indian climatic conditions.
13.3 PCM Properties and Methods of Characterization
13.3.1 Desired PCM Properties and Their Inherent Problems
The PCM selection for a particular application is to be made judiciously, with the
help of the following parameters (Mehling and Cabeza 2008):
• Suitable phase change temperature and high latent heat; specifically, temperature
must be determined with high accuracy (as melting and solidification temperature
plays a critical role in storage and release of heat at required temperature which is
a pre-requisite for any thermal energy storage system);
• Other thermophysical properties: large heat capacity, low volume change ratio,
large density and thermal conductivity, no phase segregation and lower supercooling;
• Chemical parameters: high chemical stability, no corrosion, low toxicity, noninflammable, compatible and non-polluting;
• Economic parameters: good recyclability, proper availability and cheap.
PCMs also possess certain inherent problems that should to be addressed before
their application. Some of the major issues are as follows:
• Super-cooling (also referred as sub-cooling). It is the difference in melting
and solidification temperature; PCMs are to be cooled below their solidification onset temperature to initiate nucleation which is followed by crystallization/solidification. For inorganic PCMs, sub-cooling is significantly higher.
• Phase segregation. PCMs (generally hydrated salts and eutectic mixtures) generally exhibit phase segregation. They separate out during melting thus making it
inhomogeneous.
• Low thermal conductivity. It is problem for most of the PCMs. For organic PCMs
the thermal conductivity is below 0.5 W/m K. For inorganic PCMs it is generally
below 1 W/m K.
To overcome the above disadvantages the foremost priority is to assess the PCM
properties with high accuracy and precision as there is divergence in data or data mismatch in the available literature followed by measures to enhance the PCM properties
as per their specific field of application.