The usefulness of PCM for refrigeration

Phase change materials attract a growing interest in the cold sector, too. How they can be used is the research subject of a team of the University of Salerno

We like Phase Change Materials (PCM) more and more. According to Markets and Markets, the global market is expected in neat growth, rising from 477 million dollars in 2021 to over 1 billion dollars within 2026. The interest is connected with the properties of materials themselves, able to absorb, to store and to release a big quantity of heat at a relatively constant temperature, changing their physical state. Refrigeration has shown attention to PCM for a long time now, too. However, how can we use them and what benefits can they offer? These questions are answered by the research carried out by the team of scientists of the laboratory of Cold Technique of the University of Salerno, of which is member the professor Angelo Maiorino, CSO of the innovative ARES (Advanced Refrigeration and Energy Systems) startup, belonging to the incubator of Salerno University’s spinoffs, whose CEO is the professor Ciro Aprea.
«The PCM project was born even before the pandemic, aware of the importance of PCM in ensuring the right preliminary conditions to the cold chain in the refrigerated transport», Maiorino introduces.
The project was conceived precisely to understand the potentialities of PCM inside refrigerating machines at temperatures that can range from 0 °C and slightly more, up to -30 °C.
Simple initial tests to approach the topic have confirmed its complexity from the technical point of view. The starting application was subjected to an experimentation addressing a refrigerating plant at -30 °C, filled with bags containing water, the most elementary existing PCM element.

The research work on PCM
«Our strategy is identifying the right phase change material in terms of correct temperature of phase changes to grant its efficacy. The starting idea is ensuring cold in machines to meet a couple of requirements the market is asking for: the first is wondering whether the PCM applicability can be a strategy also aimed at the energy saving and concerning this there is not a great opportunity. The reason is elementary: to make the used PCM store the right quantity of refrigerating energy, to be released in a successive phase, it requires, upstream, some energy (generally electric) needed to enable the operation of the refrigeration plant dedicated to the “solidification” of the PCM itself. The second requirement is asking for electric energy outside when available, or intervening when convenient from the economic point of view». Concerning the latter aspect, we started from the awareness that the electric energy market and its contractual terms are linked with time slots in which there are peaks (generated by renewable source plants) and at consequent more favourable energy costs. Therefore, the potentially winning idea is thinking of a PCM applicability when convenient, in terms of energy cost.
«Moreover, we might also think of an environmental convenience, provided by the opportunity of relying on a particularly rich temporary energy production from renewables, free from CO2 emissions – the professor of the University of Salerno specifies in person –. By systematizing this information, concerning this the PCM can be beneficial in the cold chain, also in the field of the refrigerated transport».
Why adopting the PCM? Because it allows exploiting the latent heat, that is to say that quantity of exchanged energy (under form of heat) during the execution of a phase change. The benefit consists in exploiting the fact that in a narrow space it is possible to cumulate a notable quantity of energy (refrigerating or thermal, according to the application’s requirements). Therefore, having a low mass quantity for an important storage is a concept of notable importance.

Where the research on PCM leads
The scientific world is strongly interested in the combination between PCM and nanomaterials, for instance. The specific research focuses on the materials that can arouse interest also in terms of weight, since it becomes a considerable factor in the refrigerated transport.
«From the experimental point of view, we have adopted a strategy connected with the use of PCM positioned in a determinate way, place and quantity inside an already existing refrigerated compartment (for instance, in case of a machine retrofit). Then, “transferring” energy at the most appropriate time becomes an interesting possibility».
The optimization is studied by the startup ARES through the ”packaging” of the PCM for storage and successive cold release. «We work at the data collection and management, on fluid-dynamics, using more than one workstation to simulate this technique, by modelling bi- and three-dimensional ambits. By means of all these factors, we are optimizing the mass of PCM that can be used for the application, especially in transport», Maiorino further specifies.
One of the most interesting situations in experimental terms is linked with the rapidity of the PCM freezing, sometimes stumbling into the super-cooling phenomenon that allows us to drop under the melting point of a substance without it starts solidifying. It is a very changeable thermodynamic instability.

Study prospects
The research opens to interesting prospects. «The primary is devising the most possible autonomous systems. The experimentation has also highlighted interesting records, with the maintenance of an acceptable temperature inside the compartment for some days, too. Passing from food to biomedical, things change precisely due to the need of avoiding temperature oscillations: however, also in this case PCM are precious allies, keeping the temperature constant and also homogeneous at space level».
The research interest, oriented to water, is now focused on the opportunity of optimizing, reducing its necessary mass and improving the release performance. «There is a strong interest also in systems of passive type for the refrigerated transport, also in the cold maintenance, especially in developing Countries where the energy provisioning is difficult and scarce», Maiorino ends.