Abstract
Abstract Buildings contribute to 40% of total global energy consumption, which is responsible to 38% of greenhouse gas emissions. It is critical to enhance the energy efficiency of buildings to mitigate global warming. In the last decade, advances in thermal energy storage (TES) techniques using phase change material (PCM) have gained much attention among researchers, mainly to reduce energy consumption and to promote the use of renewable energy sources such as solar energy. PCM technology is one of the most promising technologies available for the development of high performance and energy-efficient buildings and, therefore, considered as one of the most effective and on-going fields of research. The main limitation of PCM is its leakage problem which limits its potential use in building construction and other applications such as TES and textiles, which can be overcome by employing nano-/micro-encapsulation technologies. This paper comprehensively overviews the nano-/micro-encapsulation technologies, which are mainly classified into three categories including physical, physiochemical and chemical methods, and the properties of microcapsules prepared. Among all encapsulation technologies available, the chemical method is commonly used since it offers the best technological approach in terms of encapsulation efficiency and better structural integrity of core material. There is a need to develop a method for the synthesis of nano-encapsulated PCMs to achieve enhanced structural stability and better fracture resistance and, thus, longer service life. The accumulated database of properties/performance of PCMs and synthesised nano-/micro-capsules from various techniques presented in the paper should serve as the most useful information for the production of nano-/micro-capsules with desirable characteristics for building construction application and further innovation of PCM technology.
Highlights
Phase change materials (PCMs) are a group of functional materials that support the same purpose as a function of temperature with intrinsic capability of absorbing, storing and releasing thermal energy in form of latent heat known as enthalpy of fusion [1,2,3], during phase transition cycles at their operating temperatures under isothermal conditions
Literature reports that solid–solid PCMs have one major advantage over solid–liquid PCMs [32], i.e. they require no encapsulation since no fluid gets generated during the phase transition process; so, the overall cost will be reduced because nano-/microencapsulation technology will not be required
Current study has extensively reviewed the specifications of PCMs, encapsulation technology/methods, and provided a summary of properties of nano-/micro-capsules fabricated in previous studies
Summary
Phase change materials (PCMs) are a group of functional materials that support the same purpose as a function of temperature with intrinsic capability of absorbing, storing and releasing thermal energy in form of latent heat known as enthalpy of fusion [1,2,3], during phase transition cycles at their operating temperatures under isothermal conditions. Availability of PCMs in a wide range of melting points [7] is the main reason why they are extensively utilised in several different real-world applications including the following: (1) developing smart thermal microgrids; (2) portable thermal batteries; (3) indoor thermal management systems; (4) thermoregulating textiles, (5) warm supplies thermal protection; (6) in solar-driven cookers, (7) in solar heating systems; (8) water heaters; (9) refrigerators; (10) air-conditioning; (11) for cooling; (12) for the enhancement of thermal comfort in buildings; (13) thermal performance of building materials; (14) for the fabrication of energysaving equipment, (15) in healthcare; and (16) food preservation [8,9,10] Overall, they are highly beneficial in any application that relies on controlled and efficient thermal energy storage (TES) and releases, commonly achieved by exploiting their melting and crystallisation behaviour. Inorganic PCMs do have number of benefits such as high energy density, relatively high thermal conductivity and low cost, but their applications are hindered significantly due to the following two serious drawbacks they exhibit: (1) phase separation/segregation and (2) sub-cooling/ supercooling behaviours [28]
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