Enhancement of thermal stratification by combining differenttypes of insulation materials in cylindrical hot water storagetanks

The energy storage systems used today can be examined in two basic categories as the storage of electrical energy and thermal energy. With energy storage systems, electrical energy and thermal energy are stored in conditions where there is extra energy production or energy production is less costly and reused when needed. Hot water storage tanks have an important place among thermal energy storage methods. To benefit from the thermal energy in the hot water tanks more efficiently and for a longer time, providing thermal stratification in the tank is one of the commonly used methods. Thermal stratification is a structure formed as a result of preventing the mixture of hot and cold water that occurs with cooling. In the literature, there are many experimental and numerical studies examining the effects of hot water tank design and positioning on thermal stratification. In this study, unlike the literature studies, the effect of insulation geometry, tank dimensions, and insulation layers consisting of different materials on thermal stratification was investigated numerically. In this thesis, numerical analyzes were carried out for different tank aspect ratios, insulation step ratios, insulation types, and insulation thicknesses. Considering its thermal conductivity and usability, glass wool, polyurethane foam and aerogel were preferred as insulation materials. Numerical analyzes were evaluated in terms of temperature distribution in the tank, fluid movements, first and second laws of thermodynamics. The results of the analysis revealed that the thermal stratification increased with the reduction of the tank aspect ratio and the use of stepped insulation geometry. Different combinations of insulation materials were used and it was determined that the highest thermal stratification occurred in the glass wool-airgel insulation pair. The highest temperature difference in the tank was obtained as 15.313 °C for the use of glass wool-aerogel and 7.9 °C for the use of glass wool insulation only. In addition, energy and exergy analyses were carried out to determine the feasibility of the used tank geometry and insulation layers. With the use of gradual insulation and different insulation combinations, a reasonable decrease occurred in the energy and exergy efficiency of hot water. These results showed that the use of stepped insulation geometry and layered insulation structure in hot water tanks is practically applicable.