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There are three main alternatives for the improvement of heat transfer in phase change materials (PCM) such as the use of additives, support matrices and customized designs for heat exchangers. The first two alternatives imply incurring additional material costs, as well as a decrease in the specific heat storage capacity by using components that remain solid during the process. The present work therefore sought to study the effect of the use of a coil shell heat exchanger with a square cross section on natural convection during the melting process of hydrogenated palm stearin. Three different sections of the profile called square profile, U-profile, and L-profile and two types of material, copper, and stainless steel, were studied. A test bench was built with a capacity of 5 kg of this PCM, implementing a hot water recirculation system with flow and temperature measurement and including 9 temperature sensors inside the PCM. The melting process was conducted by recirculating water with a temperature of 75° C and a flow rate of 2 L/min. The results show a marked effect of natural convection on the melting process, presenting characteristic profiles for this phenomenon. It was found that the highest temperatures are recorded in the upper part of the PCM and that the heat transfer in the solid material is appreciably low. The results allow us to identify for each profile, the zones in which heat transfer is relatively high because of natural convection and those zones that require the use of additives or support matrices. It is therefore expected to contribute to the design of more efficient and lower commercial cost configurations. [ABSTRACT FROM AUTHOR]

The search for new phase change materials (PCM) of renewable origin and low cost, as an alternative to the use of paraffin wax, contributes to the environmental resilience of solar thermal energy systems. An important source of PCMs of renewable origin are vegetable oils and fats, especially those with established agro-industrial chains. Globally, palm oil has positioned as an indispensable product in many industrial sectors. One of the main by-products of palm oil refining is palm stearin, which can be hydrogenated to improve its thermal properties. This paper presents the results of the performance of a Solar thermal energy storage system (STESS) located in a Colombian paramo area with an altitude of 3,200 m.a.s.l. The system store heat in 550 kg of Hydrogenated Palm Stearin (HPS), contained in a rectangular vessel, which allow to supply hot water and space heating for a country house. The average ambient temperature is 12°C during the day and 7°C at night. This experimental station implements a robust measurement and control system including 39 PT-100 type temperature sensors, and different actuators connected to a control system based on Arduino and Raspberry Pi devices. This configuration permit also to implement a remote monitoring system. The constructed STESS employs 140 collector tubes, running at a maximum temperature of 95°C. According to the energy load tests during a period of 7 hours of operation, approximately 40.0 MJ were stored as heat in the hydrogenated palm stearin. For the same period, the heat transfer fluid received approximately 170 MJ of energy. In subsequent discharge tests, the heat stored in the HPS allowed the ambient temperature inside the room to be maintained 8°C above the external ambient temperature for up to 8 hours during the night, demonstrating the technical feasibility of using this new PCM from renewable sources. [ABSTRACT FROM AUTHOR]

In order to mitigate the effects of climate change, contribute to energy autarky and improve the quality of life of the population, Colombia has adopted the energy transition to renewable energy as a state policy. In this context, the use of solar thermal energy, which is abundant in the tropical zone, should be considered as one of the alternatives to be prioritised. A solar thermal energy storage system (STESS) has been developed for the supply of hot water and heating in paramo areas. The system is capable of storing energy in the form of latent heat using a renewable phase change material (PCM). The PCM reaches a maximum temperature of 70° C, allowing enough energy to be stored to take several hot showers and maintain a comfortable temperature in a room. This paper evaluates the performance of the developed STESS from a financial point of view, analysing the associated capital and operational costs. It is also compared with alternative technologies available in the area based on electric heaters and propane gas heaters. The operating cost analysis concludes that the performance of the STESS allows savings of variable operation cost up to 90 % compared to electric energy-based systems. These results become even more relevant considering that many of these areas are not connected to the national electricity grid and almost none of them have a reliable supply of propane gas. Regarding capital costs, although STESS requires an initial investment up to 20 times the value of alternative systems, its long lifetime, low operating costs and reliability make it an attractive alternative in this scenario. [ABSTRACT FROM AUTHOR]

Many energies management and storage technologies use phase change materials (PCM) to increase process efficiency. Technologies such as solar thermal energy storage, passive temperature management in buildings, even the development of high-performance sportswear employ various types of PCM. Phase change materials can be classified according to the working temperature, their nature or the phase transition, highlighting the use of materials of renewable origin. There are different methodologies to modify the properties of PCM, among which the preparation of eutectic mixtures stands out. This is a technique that allows obtaining PCM with a lower melting temperature than that of the initial components. Considering the above, this work presents the thermal characterization of mixtures of palm stearin, hydrogenated palm stearin, beeswax, and paraffin wax in order to evaluate the heat storage potential of the resulting products. Mixing ratios of 80:20, 65:35, 50:50, 35:65 and 20:80 were evaluated. Melting and crystallisation temperatures and enthalpies and their solid and liquid heat capacities were measured by differential scanning calorimetry. The thermal stability of the mixtures was also determined by thermogravimetric analysis. From the results obtained, the PCM obtained by mixing beeswax and hydrogenated palm stearin, which presents its eutectic melting point for the mixture ratio of 50:50 with a temperature of 56 °C and an enthalpy of fusion of 264 kJ/kg, stands out. [ABSTRACT FROM AUTHOR]

Palm stearin is the heavy fraction obtained during palm oil refining. It consists mainly of saturated fatty acids and is often an unwanted by-product that reduces the economic efficiency of the processes. Although it is currently used in the manufacture of margarine or industrial vegetable fats, the increase in palm oil production will lead to higher production of palm stearin. The composition, low cost and physicochemical characteristics of palm stearin make it an ideal raw material for obtaining phase change materials for thermal energy storage in solar thermal energy systems. This work explores the esterification of hydrogenated palm stearin (HPS) for obtaining phase change materials with suitable properties for application. The esterification conditions were studied using low and high molecular weight alcohols, like ethanol, butanol and cetyl alcohol, according to Fischer's esterification principles. The esters formation was characterized by attenuated total reflectance infrared spectroscopy. For both HPS and products obtained, melting and solidification temperatures and enthalpies, and heat capacity were determined by DSC according to ASTME793-06(2018) and ASTME1269-11(2018). A crude wax was obtained by esterification of the fatty acids present in palm stearin in all cases. Among the esters produced, the one obtained by using cetyl alcohol, which has a melting temperature of 55.9 °C and an enthalpy of fusion of 257.26 kJ/kg, stands out. This novel PCM is presumed to have an optimal performance for heat storage applications in low temperature solar thermal systems (50°C - 90°C), for hot water supply and space conditioning. [ABSTRACT FROM AUTHOR]