Experimental and numerical analysis of a salt gradient solar pond

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2018-9
Güven, Pelin
A salt gradient solar pond (SGSP) is a low-cost solar energy system, collects incoming solar radiation and then stores it in the form of thermal energy. SGSP has been developed recently and is considered as a large-scale energy collector for long-term use with no or little maintenance. It also has no environmental hazard. Most importantly, solar energy meets the energy demand in a clean and sustainable way; thus, SGSP can be though as a sustainable alternative for conventional energy systems. SGSP has three zones. The first zone, located right below the surface, is called Upper Convective Zone (UCZ), it has both the lowest temperature and density since it contains fresh water. The second zone is Lower Convective Zone (LCZ), this is where the solar radiation is stored, yielding the highest temperature and density. Finally, the third zone is Non-Convective Zone (NCZ), which is placed between LCZ and UCZ, including water with different concentrations of salt. Solar radiation is mostly absorbed in the LCZ, which results in increasing water temperature in this zone. To facilitate the working principle of SGSP and store energy, it is very important to create and maintain temperature and density gradients. Temperature gradient depends on several factors, such as solar radiation, wind speed, and ambient temperature as well as the diameter of SGSP, and depth of each zone. The aim of this thesis is to investigate the experimental and numerical analysis of a solar pond. In the experimental analyses, performance evaluation of the solar pond is conducted based on experimental data, which includes solar radiation, wind speed, and ambient temperature. Based on the experimental analyses, it can be concluded that solar insolation, wind speed, and ambient temperature have coupled effects on pond temperature. Besides, it is known that obtaining high LCZ temperature is the main purpose of SGSP mechanism and during the experimentation, the maximum LCZ temperature was recorded to be 46ºC. According to the results, GHI has a more significant impact on controlling the temperature of the layers than ambient temperature and wind speed. After that, a numerical model is developed using the finite element method to conduct the parametric analyses to investigate each effect of parameters individually on the layer temperatures. Based on numerical results, UCZ and NCZ temperatures increase with increasing insolation, whereas LCZ mostly protects its temperature. Additionally, wind speed only affects UCZ temperature, and it does not a have profound effect on both NCZ and LCZ temperatures. The numerical results indicate that variation in ambient temperature has the highest impact on pond temperature among other variables. Besides, it is maintained that the diameter of SGSP does not affect the pond temperature. As future work, a more detailed transient model is required to examine the effects of layer thicknesses on pond temperature. Additionally, using transparent cover materials over the surface of the pond can be examined in detail; thus, the amount of stored sustainable energy in the lower layer might increase, which can directly increase the overall efficiency of a SGSP.

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Citation Formats
P. Güven, “Experimental and numerical analysis of a salt gradient solar pond,” M.S. - Master of Science, Middle East Technical University, 2018.