Advantages And Disadvantages Of Paraffins

2.8. Phase change material 2.8.1. Definition

Is a substance with a high heat of fusion which, melting and solidifying at a certain temperature, is capable of storing and releasing large amounts of energy. Heat is absorbed or released when the material changes from solid to liquid and vice versa; thus, PCMs are classified as latent heat storage (LHS) units.

2.8.2. Characteristics and Classification

PCMs latent heat storage can be achieved through solid-liquid, solid-gas and liquid-gas phase change. However, the only phase change used for PCMs is the solid-liquid change.

Solid–gas and liquid–gas transformations are generally not employed for energy storage in spite of their highest latent heats, since gases occupy large volumes. Large changes in volume make the system large, complex and impractical. In solid–solid transitions, heat stored as the

 Paraffins have no tendencies to super cool.

 Paraffins are chemically stable.

 Paraffin waxes show high heats of fusion.

 Paraffin waxes don’t segregate

 Paraffin waxes are safe

 Paraffins are non-corrosive. Disadvantages

 Low thermal conductivity

 High volume change between the solid and liquid phases

 Commercial paraffins do not have sharp exact melting points.

 Paraffins are flammable

 Pure paraffins are expensive

 Technical grade paraffins (which has properties worse than pure paraffins) is commonly used as PCMs for thermal energy storage because it is cheaper than pure paraffins.

 Noncompatible with the plastic containers

Organic materials include congruent melting, self-nucleation and usually non-corrosiveness to the container material. Commonly used organic PCMs for heating and cooling in buildings falling in the range of 20–32ºC with their melting point and latent heat of fusion are listed in Table2.1.

Table2. 2: Organic substances with potential use as