DEVELOPMENT AND EVALUATION OF POLYMER BASED PHASE CHANGE MATERIALS (PCMs) FOR THERMAL ENERGY STORAGE APPLICATIONS

Abstract

Energy and environment conservation are the two major issues that the human beings are facing nowadays. Rapid industrial developments and population boom in the past few centuries have resulted in an enormous increase in energy demand. We are preeminently surviving on the mercy of fossil fuels that on average, account for almost 80% of the total energy production. However, the burning of fossil fuels brought the largest environmental issue ever, which is climate change caused by CO2 emissions. According to the report of BP statistical review 2020, primary global energy requirements are derived from the consumption of energy resources in an increasing order as: Oil > Coal > Natural Gas > Hydroelectric > Nuclear etc. On contrary, Indian energy consumption is mainly driven by coal as fuel source which is followed by oil. Also, our home turf is expected to witness the highest energy consumption growth rate of 129 % among major economies across the world by 2035. Among various forms of energies being considered, thermal energy is also an important concern topic of interest and therefore it necessitates the need of an effective energy storage and conservation systems to store the energy whenever it is available, which can be utilized especially over viewing the diverse climatic conditions and population blast existing in the Indian subcontinent. Developing Thermal Energy Storage (TES) systems by effective utilization of Phase Change Materials (PCMs) has proved to be the key technology in energy systems for conserving energy and increasing energy efficiency. Various studies have been carried out for tailoring out new PCMs with prime attention towards inorganic PCMs or organic ones especially paraffins-fossil fuel product. iv Renewable initiative can be a game changer in field of energy science because the demand for energy is constantly increasing as some of the possible sources like fossil fuels, coal and nuclear are decreasing. In this research work, efforts have been made in the direction for the development of new PCMs derived from non-paraffin origin compounds belonging to organic genre of PCMs family mainly composed of renewable resource material; fatty acids (caprylic acid, undecylenic acid, capric acid) and polyethylene glycols (PEG600, PEG1500, PEG20000) in combination of polymeric materials to successfully manufacture latent heat thermal energy storage products in the form of encapsulated (micro and nano dimensions) and form-stable configurations. Furthermore, lab-synthesized metal oxide nanoparticles have been incorporated to PEG based PCMs in order to optimize their characteristics; and subsequent effect of the presence of nano-size filler on the latent heat storage characteristics, resistance towards thermal and ultraviolet exposure and flame-retardant properties has been studied. Fourier Transform Infrared (FTIR) analysis confirmed the successful confinement of the fatty acids inside the polymers used for encapsulation as a core-sheath assembly in the resultant micro- and nanoencapsulated PCMs. Morphological studies suggested that the PCM microcapsules and nanofibrous PCMs were formed successfully with average diameter found to be 4 μm and 56.4 nm respectively. Differential Scanning Calorimetry (DSC) data vouched the capability of the both prepared encapsulated PCMs as efficient latent heat thermal energy storage (LHTES) material systems with latent heats of fusion values deduced as 98.7 J/g and 55.68 J/g respectively for the microencapsulated and the nanoencapsulated PCMs. They also possessed favourable thermal energy storage/release potential and thermal cycling stability. Form-stable PCMs, prepared as thin nanocomposite films derived from PEG1500 and PEG600 as active latent heat storage components supported by hydrophilic polymer matrix duly v reinforced with titanium dioxide nanoparticles (NTO) have fabricated through solvent casting method. It was observed that the latent heat density tends to increase with increased concentration of PEGs in the PVA matrix. The incorporation of metal oxide nanoparticles lead to notable enhancement in the phase change properties, thermal stability, ultraviolet irradiation resistance and flame retardant characteristics of the resultant nanocomposite PCMs. It was concluded that the shifting of phase change temperatures, along with surge in latent heat values and control over degree of supercooling were found to vary linearly with the increasing dosage of the added nanoparticles. Thermogravimetric analysis (TGA) also suggested the improvement in thermal stabilities of PEG based form-stable PCMs at higher temperatures, after the introduction of the nanoparticles in proportional loadings. The presence of nanoparticles also altered the latent heat energy storage and release characteristics within the prepared PCMs. The presence of metal oxide nanoparticles in the formulated nanocomposite films resulted in efficient ameliorating of the UV resistance and flame-retardant nature of the produced PEG based form-stable PCMs. In addition, the polyurethane (PU) based PCMs have been prepared containing capric acid as working PCM confined into the macromolecular framework of PU matrix. They undergo melting and crystallization transitions at 28.8 °C and 26.1 °C with accompanying latent heat capacities of 30.7 J/g and 31.9 J/g, respectively. The obtained PCMs also found to exhibit decent thermal reliability behaviour post 100 thermal cycles experience. The incorporation of fatty acid has resulted into significant change in the topographical arrangement of formed polyurethane based PCMs.