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ABSTRACT
Solar energy is one of the most important renewable energy sources, but it is not available every time and every season. Thus, storing of solar energy is important. One of the popular methods of heat storage is use of phase change materials (PCMs) which have large thermal energy storage capacity. In this study, the heat storage tank in a domestic solar water heating system was chosen as control volume. The experiments were performed in the province of Elazıg, Turkey, in November when solar radiation was weak due to cloudy sky. The heat storage tank of the system was modified to fill PCM between insulation and hot water part. A few PCMs which are Potassium Fluoride, Lithium Metaborate Dihydrate, Strontium Hydroxide Octahydrate, Barium Hydroxide Octahydrate, Aluminum Ammonium Sulfate, and Sodium Hydrogen Phosphate were analyzed to proper operating conditions using a Differential Scanning Calorimeter (DSC) and the best PCM was obtained with the Aluminum Ammonium Sulfate and Sodium Hydrogen Phosphate mixture. Thus, eutectic PCM was obtained and used in a heat storage tank of the solar water heating system. Energy and exergy analysis of heat storage tank was performed with and without the PCM. Energy and exergy analysis has shown that the heat storage tank with the PCM is more efficient than without the PCM and the maximum exergy efficiency was obtained as 22% with the heat storage tank with the PCM.
Funding
This study is carried out in scope of 108M420 numbered research project supported by The Scientific and Technological Research Council of Turkey (TÜBİTAK). The authors would like to thank TÜBITAK for financial support.
Nomenclature
| A | = | area, m2 |
| Cp | = | specific heat, J/kg K |
| = | rate of exergy transfer, W | |
| h | = | enthalpy, J/kg |
| k | = | heat transfer coefficient, W/m2K |
| ke | = | kinetic energy, J/kg |
| = | mass flow rate, kg/s | |
| pe | = | potential energy, J/kg |
| W | = | power of circulation pump, W |
| P | = | pressure, kPa |
| R | = | universal gas constant (kJ/kmol K) |
| = | rate of heat transfer, W | |
| T | = | temperature, K |
| = | volumetric flow rate, m3/s | |
| = | flow exergy, kJ/kg | |
| = | density, kg/m3 | |
| = | efficiency, % |
Subscripts
| a | = | ambient |
| b | = | bottom |
| cv | = | control volume |
| ex | = | exergy |
| i | = | inlet |
| l | = | loss |
| ls | = | lateral surface |
| m | = | mass |
| ms | = | metal sheet |
| o | = | outlet |
| PCM | = | phase change material |
| s | = | storage |
| t | = | time |
| u | = | upside |
Superscripts
| ph | = | physical |
| ch | = | chemical |