A Critical Review of Phase Change Materials for Cold Thermal Energy Storage Applications: Conventional Materials and Bio-Based Alternatives

A Critical Review of Phase Change Materials for Cold Thermal Energy Storage Applications: Conventional Materials and Bio-Based Alternatives

Modern cold chains are critical to global food security but come with significant environmental costs. The refrigeration sector consumes immense amounts of electricity—up to 281 TWh annually—resulting in approximately 261 million tonnes of CO₂ emissions. Of these, 60% are indirect emissions from electricity, while 22% come from refrigerant leakage, and another 18% from diesel use. Power production alone contributes to 42.2% of global GHG emissions, highlighting the urgent need to reduce cold storage's dependence on fossil-fuel-derived energy.

Despite widespread refrigeration deployment, food waste persists. Over 1.05 billion tonnes of food are wasted annually, with a major share attributed to spoilage during storage and transport. This juxtaposition—technological advancement and persistent inefficiency—demands a new approach to cold storage.

Fig 1. (a) Electricity production by source between 1985 and 2022. (b) Distribution of electricity production by sources for the year 2022. (c) Greenhouse emissions for different sectors between 2019 and 2022. (d) Greenhouse emissions for different sectors for the year 2022. (Ouaouja Z., et al., 2025)

Thermal Science of Phase Change Materials (PCMs)

Phase Change Materials operate by absorbing or releasing latent heat during their phase transitions. Unlike traditional thermal storage that relies on sensible heat, PCMs undergo a physical transformation—typically solid-to-liquid or vice versa—storing or releasing large amounts of thermal energy at near-constant temperatures.

The total energy storage capacity of PCMs is calculated as: QPCM = Qs(l) + QL + Qs(s)

This equation includes sensible energy in the liquid (Qs(l)) and solid states (Qs(s)), and latent energy (QL). The latent heat makes PCMs especially valuable for cold thermal energy storage (CTES) because it stabilizes temperature with minimal energy loss.

Categories and Characteristics of Conventional PCMs

• Organic PCMs: Derived from petroleum, paraffin waxes are widely used due to their availability, chemical stability, and tunable melting points. However, they are flammable and pose long-term environmental concerns.
• Inorganic PCMs: Hydrated salts and metallics offer high thermal conductivity and storage capacity but suffer from phase segregation, corrosiveness, and supercooling effects.
• Eutectics: Eutectic mixtures—combinations of organic and inorganic compounds—allow for precise control of melting points and are adaptable across a wide temperature spectrum, from -70°C to 15°C.
• Commercial Availability: Market-dominant PCMs include hydrated salts and paraffin. For instance, salt solutions have melting points between -86°C and -1.6°C, with latent heats ranging from 116–314 J/g. Paraffins typically range from -52°C to 5°C, with latent heats between 155–300 J/g.

Overcoming Performance Barriers

• Low Thermal Conductivity: To boost performance, nano- and micro-scale additives—like carbon nanotubes and aluminum oxide—have been used to enhance conductivity by up to 248%. However, this often comes at the cost of reduced latent heat capacity.
• Supercooling and Phase Segregation: Hydrated salts are particularly susceptible. The use of nucleating agents such as sodium alginate or structured porous supports has shown promise in stabilizing phase transitions.
• Encapsulation Techniques: Macroencapsulation (e.g., metal shells), microencapsulation (polymer shells), and nanoencapsulation are strategies employed to manage PCM containment, enhance heat exchange, and prevent leakage or degradation.
• Material Compatibility: Stainless steel exhibits the highest compatibility across PCM types, minimizing corrosion risks, especially with aggressive salt hydrates.

Applications in Refrigeration and Cold Chain Systems

• Thermal Shielding
  PCMs can be embedded in the walls of walk-in freezers or containers to act as thermal buffers. Field tests demonstrated a reduction of peak heat flux by up to 8.57%, and a delay in peak load by 4.5 hours, enhancing thermal stability with minimal energy input.
• Cold Thermal Energy Storage (CTES)
  PCMs allow excess cold energy to be stored during off-peak hours and released when needed. Full-storage systems can achieve energy savings between 18–86.7%, while partial storage systems offer demand flattening and peak shaving benefits up to 60% in COP enhancement.
• Compressor Efficiency and Runtime Reduction
  PCMs installed near evaporators reduced daily compressor operating time by 30–39%, allowing compressors to shut down for extended periods without temperature rise.
• Effects on Temperature Regulation
  PCMs stabilize air temperature during defrost cycles and door openings, reducing fluctuations by as much as 3°C. During power outages, PCMs can maintain storage temperatures for up to 11 hours longer compared to non-PCM systems.
• Enhancing Heat Exchangers
  When integrated into condensers and evaporators, PCMs reduce thermal stress and temperature volatility. Studies show improvements in COP between 17.6–27% and energy savings up to 21%.
• Influence of Design Parameters
  PCM thickness: Optimal range is between 2.5 and 6 mm; beyond this, compressor runtime increases.
  Encapsulation material: Copper outperforms steel and aluminum in conductivity.
  Fins: Structured fins improve energy efficiency by up to 9.56%.
  Orientation and placement: Horizontal or hybrid configurations yield more uniform temperature distribution than vertical orientations.

Impacts on Food Preservation

PCMs protect food quality by reducing ice crystal formation, minimizing drip loss, and maintaining relative humidity. For example:

• Meat drip loss reduced from 17% to 10%
• Mushroom weight loss reduced from 79% to 13%
• Strawberry rotting rates reduced by 58%
• Ice crystal size in frozen desserts halved from 80 µm to 40 µm

Environmental and Economic Benefits

Emissions Reduction

PCM integration in European refrigeration systems could reduce CO₂ emissions by 15.6–75.4 kt annually. In cold chain transport, emissions can drop by 78.5%, with operational cost savings of over 91%.

Energy Cost Management

By storing cooling during off-peak electricity pricing periods, PCM-equipped systems offer both financial and load-balancing advantages, especially when coupled with solar or off-grid power sources.

Bio-Based PCMs: Sustainable Thermal Alternatives

Current Limitations and Research Priorities

• Low latent heat in many bio-based PCMs necessitates higher volumes or hybrid formulations.
• Limited field trials mean that most bio-based PCM applications remain at the proof-of-concept stage.
• Encapsulation challenges need scalable, cost-effective solutions.
• Lifecycle Assessment (LCA) data is scarce. Preliminary studies suggest palm oil derivatives and used cooking oil PCMs are viable, but production impacts must be carefully weighed.

Future Directions

Conclusion

Phase Change Materials—particularly bio-based variants—represent a transformative opportunity for the cold chain industry. They enable energy savings, improve temperature regulation, reduce spoilage, and offer a clear pathway to sustainable refrigeration. As food security and climate mitigation converge into a shared priority, the integration of PCM technology stands poised to redefine how the world preserves, transports, and consumes perishable goods. The next frontier of cold storage is not more power—it's smarter materials.

If you are interested in our services and products, please contact us for more information.

This article is for research use only and cannot be used for any clinical purposes.