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Phase change materials

Phase change materials are substances that absorb and release heat energy when they change phase (known as latent heat). When a material melts, it changes from a solid phase to a liquid phase. During the phase transition, many materials are able to absorb a significant amount of heat energy. The opposite is true when the material freezes and solidifies: the material will give out the heat that it absorbed when it melted. Different materials will melt and solidify at different temperatures and are able to absorb different amount of heat energy. 

Phase change materials are useful because they melt and solidify at specific, defined temperatures, making them suitable to control the temperature in range of diverse applications. Materials that melt to absorb heat are much more efficient at absorbing heat energy compared to sensible heat energy materials. This means that it takes a much smaller amount of a material to store heat energy phase change material than using a material that does not change phase. 
Temperature controlled packaging using pcms for food or medical items

Phase change materials

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CrodaTherm ME Wax

Microencapsulation

Learn about Croda's microencapsulation technology for PCMs

Understanding the different between sensible heat and latent heat

 
glass of water showing use of PCM

Sensible heat capacity

When matter is heated and no change of phase occurs, its internal temperature increases. An example of this is a glass of water that heats up in the sun. As the sun shines onto the glass, the water increases in energy and the water molecules get more energetic. The water increases in temperature. This is known as sensible heat. 

Sensible heat capacity is the ability of a material to absorb heat energy as it increases in temperature (warms up).

 
Ice water showing Latent heat capacity

Latent heat capacity

If a glass of ice cubes is placed in sunlight, the ice will also start to heat up sensibly. One the ice gets to its phase transition temperature (0°C), it will start to melt. 

If you measured the temperature of the ice as it melts, you will find that until all the ice has melted, it will remain at 0°C. This is because when a PCM such as ice changes phase, the temperature will remain constant until all the material has melted. This is known as latent heat.
 
Latent heat capacity is the ability of a material to absorb or release heat energy as it melts or freezes without increasing in temperature.

Comparing sensible heat and latent heat of water/ice

It takes a large amount of energy to melt ice into water.

Property Value  Explanation
Specific heat of ice (sensible heat) 2.1 kJ/ kg/ ºC Heat capacity of ice. This is the amount of energy needed to raise the temperature of 1kg of ice by 1ºC
Latent heat of melting ice 334 kJ/ kg  Energy needed to melt 1kg of ice into water, at 0ºC
Specific heat of water (sensible heat) 4.1/ kJ/ kg/ ºC Heat capacity of water. This is the amount of energy needed to raise the temperature of 1kg of water by 1ºC
  • the energy needed to melt 1kg of ice at 0ºC could heat 1kg of liquid water from 0ºC to 81.5ºC! (334kJ/ 4.1kJ = 81.5ºC);
  • the inverse is also true: It takes 334kJ of energy to freeze 1kg of water at its freezing temperature (0ºC) into ice; and
  • this demonstrates the powerful effect of using a phase change material to store heat energy latently rather than using sensible heat capacity.

The difference between sensible heat and latent heat

Graph showing the the effect of phase change materials

To begin with, when the ice is in its frozen state, it must be heated up sensibly before it will get to its phase transition temperature. Once the ice has reached its melting temperature, it stops increasing in temperature as it melts.

Once all the ice has melted, it starts to increase in temperature again. The inverse happens when water is frozen back into ice.

Why are phase change materials useful?

Capturing and storing energy is difficult. Phase change materials (PCMs) are ideal for use in any application where a storage and release of thermal energy is desired. PCMs act like a battery for heat energy because they absorb heat energy as they melt and can be “recharged” by cooling them until they crystallise and give the stored energy back the environment. They can store and release heat energy thousands of times without change in thermal properties.

Water has a high latent heat capacity; why can’t I just use water?

Water does have a high latent heat capacity, but it melts and freezes at 0ºC. This means that for many applications, the melting temperature is too low or too high. 

We offer CrodaTherm™ bio-based phase change materials at a wide range of melting temperatures with high latent heat capacities. This means you can choose the best melting temperature for your application.

What makes CrodaTherm phase change materials different?

High performance products: CrodaTherm PCMs have high latent heat capacities, making them efficient in use.

Green chemistry: CrodaTherm materials are up to 100% USDA Certified bio-based & our sites have RSPO sustainable palm oil certification.

Low flammability: CrodaTherm PCMs are not classified as flammable and have higher flash points than competing materials.

Good material compatibility: CrodaTherm materials have good long-term compatibility with multiple material types.

Long-term stability: CrodaTherm PCMs are stable & have consistent performance for a minimum of 7000 cycles for long term reliability and performance.

Minimal evaporation: CrodaTherm PCMs have a low rate of loss due to evaporation even at elevated temperatures.

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