Developing a demo environment on Phase Change Materials

Abstract

In order to meet the stricter climate and emissions targets that are being set around the world, the share of renewable energy sources in the energy production mix is being increased. The intermittent nature of most renewable energy sources poses a challenge for matching energy supply with energy demand. Energy storage is needed to store excess energy produced by the renewable energy sources when demand is low, and supply the energy at a later time when there is demand for it. Latent heat thermal energy storage using phase change materials is an efficient method for storing and releasing energy at almost constant temperature. The aim of this work was to create a demo environment on phase change materials that can be used in research and education. The thermophysical properties of phase change materials, such as the latent heat and the specific heat capacities, are central properties describing the amount of energy stored by the materials. A demo environment was built up based on the Temperature history (T-history) method, which can be used to determine the thermophyiscal properties of phase change materials. The T-history method is simple and affordable, and it is suitable to be used for educational purposes in a lab environment. Samples of phase change materials and a reference are heated up and cooled down in test tubes while the temperature of the samples and reference are measured. The method was tested on five different phase change materials. Four of these were different types of salt hydrates, which are inorganic phase change materials, and one was paraffin wax, which is an organic phase change material. The investigation of the five different phase change materials using the T-history method showed that the method did not function optimally according to instructions from literature. The values for the latent heat, the specific heat capacity and the total enthalpy of parallel samples had a rather large variation, which resulted in high standard deviations. Some of the thermophysical properties measured were consistent with literature values, while some differed. However, also the literature values for many properties of phase change materials tend to vary. The use of different methods and the lack of standards for determining the thermophysical properties of phase change materials may be the cause of this. One reason that the method did not function optimally can be that the convective heat transfer coefficient was too high. Another challenge was the supercooling property of the salt hydrates and that the temperature distribution was not uniform. Future studies could try to achieve better results by using a climate chamber for controlling the temperature, which is common in many recent studies that use the T-history method. Also, further studies could look at modifying the phase change materials by using various additives to adjust the properties of the materials and make them more viable options for energy storage.