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2 Review of Literature: Motorcycle helmet
2.13.1.1 Organic PCM (Paraffins and Fatty Acids)
This class of PCM includes paraffins (C n H 2n+2 ) and fatty acids (CH 3 (CH 2 ) 2n COOH).
Of these two materials, paraffins are widely used as PCM. Carl Reichenbach discovered paraffin [derived from the Latin parum (=barely) + affinis (=lacking affinity
or reactivity)], which is the common name given to a group of alkane hydrocarbons
with the general formula C n H 2n+2 , where n is greater than about 20. The alkane series
with more than 15 carbon atoms per molecule is waxy solids at room temperature
and is known as paraffin wax. Although in general, paraffin is a technical name
for an alkane, in most cases, it refers specifically to a linear chain or normal alkane,
whereas branched or isoalkanes are called iso-paraffins. These PCM are straight chain
hydrocarbons with 2-methyl branching groups near the end of the chains [146].
The paraffins with an even number of carbon atoms are generally preferred, as
these are cheap, more stable and more abundant. The heat of fusion and melting
points of paraffins increase with the increase in molecular weight. The paraffins can
be classified into two main groups: even-chained (n-paraffin) and odd-chained (isoparaffin). The classification of paraffins into even-chained or odd-chained groups
depends on the content of alkanes within the substance (ranging from 75 to 100%)
[147]. Kaygusuz and Sari [148] investigated the thermal performance and phase
change stability of palmitic and stearic acids as a latent heat energy storage material.
They found better stability of the stearic and palmitic acids, which was accomplished
at low inlet water temperature when compared with the high inlet water temperature.
The paraffins absorb much more heat than normal materials during the melting
process. Use of paraffinic PCM in textiles substantially increases the heat storage
capacities of the textiles. The temperature remains constant during the melting and
crystallisation processes of paraffin, thus making it a good source of heat storage for
textile applications. These paraffins are enclosed in very small spheres with diameters
of only a few micrometres. The microencapsulated paraffins are not only permanently
locked in the fibres but also coated onto the surface of a textile structure. Some of
the paraffins are readily available for textile applications at lower cost, have a wide
range of melting temperatures and are thermally reliable even after a large number
of thermal cycles [149, 150].
Fatty acids are organic compounds having melting ranges and heat of fusion values
similar to organic paraffins. Only a limited number of fatty acids have melting and
freezing points in the range of 20–40 °C [151]. Therefore, fatty acids have limited
applications in textiles as energy storage materials. Another disadvantage of fatty
acids is their availability in only narrow temperature ranges. Feldman and Shapiro
[152] found fatty acids and their binary mixtures are attractive candidates for latent
heat thermal energy storage in space heating applications. They observed the melting
point and latent heat of transition of the fatty acids range from 30 °C to 65 °C and
153 kJ/kg to 182 kJ/kg, respectively.
Paraffins are the ideal candidate for PCM applications due to their large temperature range and their availability in various forms and structures. The storage capacity
of paraffins is high as compared to other compounds, and these materials can be
frozen without supercooling. The paraffins possess a wide range of melting points
2 Review of Literature: Motorcycle helmet
2.13.1.1 Organic PCM (Paraffins and Fatty Acids)
This class of PCM includes paraffins (C n H 2n+2 ) and fatty acids (CH 3 (CH 2 ) 2n COOH).
Of these two materials, paraffins are widely used as PCM. Carl Reichenbach discovered paraffin [derived from the Latin parum (=barely) + affinis (=lacking affinity
or reactivity)], which is the common name given to a group of alkane hydrocarbons
with the general formula C n H 2n+2 , where n is greater than about 20. The alkane series
with more than 15 carbon atoms per molecule is waxy solids at room temperature
and is known as paraffin wax. Although in general, paraffin is a technical name
for an alkane, in most cases, it refers specifically to a linear chain or normal alkane,
whereas branched or isoalkanes are called iso-paraffins. These PCM are straight chain
hydrocarbons with 2-methyl branching groups near the end of the chains [146].
The paraffins with an even number of carbon atoms are generally preferred, as
these are cheap, more stable and more abundant. The heat of fusion and melting
points of paraffins increase with the increase in molecular weight. The paraffins can
be classified into two main groups: even-chained (n-paraffin) and odd-chained (isoparaffin). The classification of paraffins into even-chained or odd-chained groups
depends on the content of alkanes within the substance (ranging from 75 to 100%)
[147]. Kaygusuz and Sari [148] investigated the thermal performance and phase
change stability of palmitic and stearic acids as a latent heat energy storage material.
They found better stability of the stearic and palmitic acids, which was accomplished
at low inlet water temperature when compared with the high inlet water temperature.
The paraffins absorb much more heat than normal materials during the melting
process. Use of paraffinic PCM in textiles substantially increases the heat storage
capacities of the textiles. The temperature remains constant during the melting and
crystallisation processes of paraffin, thus making it a good source of heat storage for
textile applications. These paraffins are enclosed in very small spheres with diameters
of only a few micrometres. The microencapsulated paraffins are not only permanently
locked in the fibres but also coated onto the surface of a textile structure. Some of
the paraffins are readily available for textile applications at lower cost, have a wide
range of melting temperatures and are thermally reliable even after a large number
of thermal cycles [149, 150].
Fatty acids are organic compounds having melting ranges and heat of fusion values
similar to organic paraffins. Only a limited number of fatty acids have melting and
freezing points in the range of 20–40 °C [151]. Therefore, fatty acids have limited
applications in textiles as energy storage materials. Another disadvantage of fatty
acids is their availability in only narrow temperature ranges. Feldman and Shapiro
[152] found fatty acids and their binary mixtures are attractive candidates for latent
heat thermal energy storage in space heating applications. They observed the melting
point and latent heat of transition of the fatty acids range from 30 °C to 65 °C and
153 kJ/kg to 182 kJ/kg, respectively.
Paraffins are the ideal candidate for PCM applications due to their large temperature range and their availability in various forms and structures. The storage capacity
of paraffins is high as compared to other compounds, and these materials can be
frozen without supercooling. The paraffins possess a wide range of melting points