Phase Change Materials (PCMs)

• PCM stands for Phase Change Material
• PCMs are substances that can absorb and release thermal energy during the process of melting and freezing
• This process occurs at a relatively constant temperature
• PCMs are used in a variety of applications for thermal energy storage and temperature regulation

Phase Transition

• PCMs work on the principle of phase transition
• Phase transition involves changing from one state of matter to another (e.g., solid to liquid, liquid to gas)
• The most commonly utilized phase transition for PCMs is solid-liquid due to the smaller volume change and ease of handling
• During melting, a PCM absorbs heat as it changes from a solid to a liquid
• During freezing, a PCM releases heat as it changes from a liquid to a solid
• The temperature at which this phase change occurs remains nearly constant, which is a key characteristic of PCMs

Types of PCMs

• PCMs can be broadly classified into organic, inorganic, and eutectic PCMs
• Organic PCMs include paraffin waxes, fatty acids, sugar alcohols, and polymers
• Paraffin waxes are readily available, inexpensive, non-corrosive, and exhibit congruent melting and freezing
• Fatty acids possess sharp melting points and are chemically stable, but they can be more expensive and may be corrosive
• Sugar alcohols are non-toxic and exhibit little to no subcooling, but have low thermal conductivity
• Polymers are available in a wide range of properties, but can be expensive and may have complex phase change behavior
• Inorganic PCMs include salt hydrates and metallic PCMs
• Salt hydrates have high latent heat per unit volume and can be inexpensive, but they can exhibit supercooling and phase segregation
• Metallic PCMs possess high thermal conductivity and are non-flammable, but they are heavy and can be expensive
• Eutectic PCMs are mixtures of two or more components that solidify or liquefy at a single temperature
• Eutectic PCMs can be tailored to achieve specific melting temperatures and can offer improved thermal properties

Key Properties of PCMs

• Melting Temperature is the temperature at which the PCM changes from a solid to a liquid
• Freezing Temperature is the temperature at which the PCM changes from a liquid to a solid
• Latent Heat is the amount of heat absorbed or released during the phase change process
• Thermal Conductivity is the ability of the PCM to conduct heat
• Specific Heat Capacity is the amount of heat required to raise the temperature of the PCM by a certain amount
• Density is the mass per unit volume of the PCM
• Stability refers to the PCM's ability to maintain its thermal properties over repeated cycling
• Congruency ensures that the PCM melts and freezes uniformly without phase segregation
• Non-Corrosivity ensures that the PCM does not react with the surrounding materials
• Safety involves that the PCM should be non-toxic and non-flammable

Encapsulation of PCMs

• Encapsulation is a technique used to contain the PCM within a protective shell
• Encapsulation prevents leakage, protects the PCM from the environment, and improves heat transfer
• Microencapsulation involves encapsulating the PCM in small capsules (typically 1-1000 μm in diameter)
• Macroencapsulation involves encapsulating the PCM in larger containers (typically >1 mm in diameter)
• Common encapsulation materials include polymers, metals, and ceramics

Applications of PCMs

• PCMs are used in Building thermal management
• PCMs can be incorporated into walls, roofs, and floors to absorb and release heat, reducing temperature swings and energy consumption
• PCMs are used in Solar thermal energy storage
• PCMs can store thermal energy from solar collectors for later use in heating, cooling, or electricity generation
• PCMs are used in Electronic device cooling
• PCMs can absorb heat generated by electronic components, preventing overheating and improving performance
• PCMs are used in Thermal packaging
• PCMs can maintain a constant temperature inside shipping containers, protecting temperature-sensitive goods
• PCMs are used in Textiles
• PCMs can be incorporated into clothing and bedding to regulate body temperature and improve comfort
• PCMs are used in Automotive industry
• PCMs can be used to manage battery temperature in electric vehicles, improving performance and lifespan

Advantages of PCMs

• PCMs offer high energy storage density compared to sensible heat storage materials
• PCMs operate at a nearly constant temperature during charging and discharging
• PCMs can be used in a wide range of applications
• PCMs are relatively simple to integrate into existing systems

Disadvantages of PCMs

• PCMs can have low thermal conductivity, which can limit heat transfer rates
• PCMs can exhibit supercooling, which can reduce the effectiveness of the material
• PCMs can be expensive, especially for certain types of materials
• PCMs can undergo phase segregation, which can reduce the performance of the material over time

Performance Enhancement Techniques

• The thermal conductivity of PCMs can be enhanced by adding conductive additives such as metal particles, carbon nanotubes, or graphite
• Supercooling can be reduced by adding nucleating agents to the PCM
• Phase segregation can be prevented by using encapsulation techniques or by selecting PCMs with congruent melting behavior
• Heat transfer rates can be improved by using heat exchangers or by increasing the surface area of the PCM

Future Trends

• Development of new PCM materials with improved thermal properties and stability
• Reduction in the cost of PCM materials
• Development of new encapsulation techniques
• Integration of PCMs into a wider range of applications
• Research on advanced PCM-based energy storage systems