40
2 Review of Literature: Motorcycle helmet
2.13.4 Selection of Suitable PCM
While selecting an appropriate PCM for thermo-regulating action, many factors
are taken into consideration such as cost, availability, toxicity, colour, heat storage
capacity and durability. The selection of PCM for various applications mainly
depends on the temperature range needed for the application. However, for textiles,
the main criterion for selection is the temperature at which the PCM will function
(i.e. the phase change temperature of the PCM) to keep the wearer comfortable. For
textile applications, the PCM with melting temperatures of 20–40 °C (i.e. close to
body temperature) are selected [176, 195].
In addition to this, the viability of producing the different types of micro-PCM and
the production costs also should be taken into account. PCM can be used either in a
pure form or as a mixture. For applications with wide temperature ranges, mixtures
are more efficient than single chemicals. The temperature at which the solid/liquid
transition takes place depends on the number of carbon atoms on the chain backbone.
The quantity of PCM in a fabric is constrained by the weight and/or the duration for
which it performs its function of cooling and the reverse process of heating. Further
research is being carried out to enhance the performance of PCM and also to reduce
the weight of the fabrics. In active sports, for cooling in a stationary position where
weight is not an important criterion, the PCM can be enclosed as a gel in sealed
capsules placed in pockets of the clothing.
The appropriate melting temperature of PCM is selected according to the final
applications, and it should lie within the practical range of operation, i.e. it should
melt congruently with minimum sub-cooling and should be chemically stable. Materials with melting temperatures below 15 °C are used for storing coolness in airconditioning applications, and materials with melting temperatures above 90 °C
are used for absorption refrigeration. All other materials with melting temperatures
between these two temperature ranges can be used in solar heating and for heat
load levelling applications. Paraffin waxes are one of the best materials suitable for
PCM applications because of their low cost, non-toxicity, eco-friendliness and easy
process of application by microencapsulation. The quantity of the material used for
phase change effect determines the thermal insulation value.
Shape-stabilised or form-stable composite PCM are one of the new developments
in PCM technology, classified as solid–solid PCM and solid–liquid PCM [206–
209]. Paraffin/high-density polyethylene (HDPE) composites form a stable solidliquid PCM mixture for thermal energy storage for textile applications [210]. In the
composite, the mass percentage of paraffins could go up to a maximum of 76%
without any seepage of the paraffins in the melted state [211].
2 Review of Literature: Motorcycle helmet
2.13.4 Selection of Suitable PCM
While selecting an appropriate PCM for thermo-regulating action, many factors
are taken into consideration such as cost, availability, toxicity, colour, heat storage
capacity and durability. The selection of PCM for various applications mainly
depends on the temperature range needed for the application. However, for textiles,
the main criterion for selection is the temperature at which the PCM will function
(i.e. the phase change temperature of the PCM) to keep the wearer comfortable. For
textile applications, the PCM with melting temperatures of 20–40 °C (i.e. close to
body temperature) are selected [176, 195].
In addition to this, the viability of producing the different types of micro-PCM and
the production costs also should be taken into account. PCM can be used either in a
pure form or as a mixture. For applications with wide temperature ranges, mixtures
are more efficient than single chemicals. The temperature at which the solid/liquid
transition takes place depends on the number of carbon atoms on the chain backbone.
The quantity of PCM in a fabric is constrained by the weight and/or the duration for
which it performs its function of cooling and the reverse process of heating. Further
research is being carried out to enhance the performance of PCM and also to reduce
the weight of the fabrics. In active sports, for cooling in a stationary position where
weight is not an important criterion, the PCM can be enclosed as a gel in sealed
capsules placed in pockets of the clothing.
The appropriate melting temperature of PCM is selected according to the final
applications, and it should lie within the practical range of operation, i.e. it should
melt congruently with minimum sub-cooling and should be chemically stable. Materials with melting temperatures below 15 °C are used for storing coolness in airconditioning applications, and materials with melting temperatures above 90 °C
are used for absorption refrigeration. All other materials with melting temperatures
between these two temperature ranges can be used in solar heating and for heat
load levelling applications. Paraffin waxes are one of the best materials suitable for
PCM applications because of their low cost, non-toxicity, eco-friendliness and easy
process of application by microencapsulation. The quantity of the material used for
phase change effect determines the thermal insulation value.
Shape-stabilised or form-stable composite PCM are one of the new developments
in PCM technology, classified as solid–solid PCM and solid–liquid PCM [206–
209]. Paraffin/high-density polyethylene (HDPE) composites form a stable solidliquid PCM mixture for thermal energy storage for textile applications [210]. In the
composite, the mass percentage of paraffins could go up to a maximum of 76%
without any seepage of the paraffins in the melted state [211].