Types, methods, techniques, and applications for microencapsulated phase change materials (MPCM): A review

Abstract

Phase Change Materials (PCM) can be employed in many fields because of their capacity to absorb and release energy when it is necessary. Nowadays, the number of studies about these materials is increasing because of their benefits in energy systems. This paper reviews the previous researches and developments on microencapsulated phase change materials (MPCM) in thermal energy storage (TES) systems, focusing on the different methods of encapsulations and also the different applications of these materials. This review aims to be a useful guide for the researchers in this area, because it explains the different types of phase change core materials, the different shells, the methods to microencapsulate these PCM, the most used techniques to characterize these microencapsulated phase change materials, and a revision of the main applications.Storage these type of materials to store energy, and release it when the systems needed, for example, the chilly bins studied by Oró et al. [15] to enhance the thermal performance. Also, it is possible to use phase change materials in cold storage needs, as Oró et al. [16] evaluate, studying the compatibility of PCM with metallic materials, but a common problem in PCM cooling applications is the subcooling, which happens when a material is cooled and the crystallization does not start below the freezing temperature [17].Another very significant application of PCM is the one in the building sector [18], in passive applications like floors [19], walls [20-23] (for example conventional and alveolar brick [24]), and ceiling studies. There is another case, which is in active systems in domestic applications as heating [25] and hot water [26][27][28][29].Since PCM undergo the solid-liquid states, they need to be encapsulated for their inclusion in the final system. Due to the leakage in the liquid state when mixing the PCM with other materials, such as building construction materials [30], and because of the corrosion and the thermal reliability, the possibility to make a polymeric container for PCM, in small vessels, using the encapsulation technology and producing capsules calling them encapsulated Phase Change Material for energy storage [31] has been investigated. Encapsulation techniques vary from macroencapsulation in slabs, panels, etc. to microencapsulation [32,33]. When the sizes of these capsules are micrometers, these are called Microencapsulated Phase Change Material (MPCM), which consisted on a polymeric shell and a core made of the storage material. The microencapsulation is a process of enclosing micron-sized particles of solids or droplets of liquids or gases in an inert shell, which in turn isolates and protects them from the external environment. The captivity of waxes into the microcapsules allows to increase the heat transfer[3] and to control de volume changes when the phase change is happening. Microencapsulation methodology for PCM still needs to be improved because the microcapsules can break easily when they collide with other microcapsules when they are used in...

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