تقصي استعمال البارافين كمادة متغيرة الطور مع الماء في أنظمة تسخين الماء بالطاقة الشمسية

Investigation of use of the Paraffin as a Phase Change Material with Water in Solar Water Heating Systems

Solar energy is one of the most important sources of renewable energy used to reduce the effects of pollution and global warming as a result of burning fossil fuels; however, this energy is intermittent and available during daytime only. This research aims to experimentally and numerically study the possibility of improving the heat storage capacity of a solar water heating system by using phase change materials (PCMs). A PCM solar water heating system was designed and manufactured at the University of Kerbala under the climatic conditions of the City of Karbala in Iraq, and the system was experimentally tested for the period between 20 March to 20 April in 2019. Two main heat sources are used in this work; the first one is a flat plate solar collector connected directly to a water tank, and the second heat source was an electric heater element.
For flat plate solar collector configuration, the cases without PCM (the tank contains water only) and with 31% PCM (PCM containers were incorporated within the water tank) was experimentally tested under variable flow rates (1, 3, 5) L/min. The second heat source (an electric heater element ) is used to avoid the effect of fluctuating in solar intensity on the PCM behaviour, and a similar scenario was repeated for the cases of without and with PCM. Paraffin wax which dissolves in range of (52 ± 2) ᵒC was used as a PCM material and packed in cylindrical aluminium containers which immersed inside the water tank. Furthermore, numerical modelling using ANSYS Fluent was carried out (including the processes of melting and solidification of paraffin wax) to highlight the behaviour of the PCM material during the charging/discharging heat processes.
Results showed that integrating PCM materials with solar water heating systems is practical and useful as PCM materials can store an extra amount of heat to be provided at night. Experimental results showed that the proposed PCM solar heating system could achieve a water temperature of about 9.3 °C higher than that of without using PCM and the improvement in hot water temperature due to the use of PCM reached up to 23 %. In contrast, the maximum improvement in heat storage due to the use of PCM is about 14 %. Also, results showed that adding copper mesh reduces the melting time by up to 12.5%; however, it affects the amount of heat storage negatively as a result of reducing the amount of paraffin wax. Finally, experimental and numerical data were validated, and a good agreements are achieved with an average deviation of about 5.17%.