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Modeling and Conceptual Design of Solar Water Desalination System with Ground Condenser

Asgari, Behrad | 2022

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 55691 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Kazemzadeh Hannani, Siamak; Hakkaki Fard, Ali
  7. Abstract:
  8. Providing fresh water for domestic and agricultural purposes has become one of the most pressing issues of the present century. Due to the dependency of conventional desalination on fossil fuels, these methods are associated with carbon dioxide and other greenhouse gas emissions. Therefore, renewable energy-based desalination systems have come to the fore. This study scrutinizes the performance of the solar Humidification-Dehumidification (HDH) desalination systems with subsurface condensers. In this system, solar energy evaporates water, and subsurface condensers condense water vapor into fresh water. Therefore, this system uses two renewable solar and geothermal energy. Due to the lack of an accurate numerical model in the previous researches, a comprehensive 3D transient computational fluid dynamics model of the system is developed in the present study. Moreover, to reduce computational costs, the hybrid analytical-numerical model of the system is formulated based on thermodynamic analysis and the conservation of mass and energy. Despite previous researches that ignore the ground temperature changes due to the heat transfer between the subsurface condenser and the surrounding soil, the hybrid analytical-numerical model is proposed based on Duhamel’s theorem, infinite line source method, and superposition principle, to accurately apply changes in soil temperature. Moreover, since no experimental study concentrates on the thermal performance of the subsurface condenser, an experimental setup of the subsurface condenser is built and used to verify the developed model of the subsurface condenser. The developed models are used to evaluate the system performance, parametric studies, and optimization. The Design of Experiments (DOE) methodology is adopted to determine simulated cases. The Response Surface Model is also applied for sensitivity analysis and parametric study, and the non-dominated sorting genetic algorithm II optimization algorithm is used to determine optimum design parameters. Moreover, to improve the performance of solar humidifier, the use of the baffle turbulator in the solar humidifier is proposed and investigated. In addition, the long-term performance of several configurations of the solar HDH desalination system with the subsurface condenser, including open-loop system, closed-loop system, closed-loop system with an air-cooled condenser, closed-loop system with internal heat exchanger and closed-loop system with an air-cooled condenser and internal heat exchanger is evaluated. The results show that the developed models accurately predict the experimental results. It is demonstrated that since the average daily water yield and GOR of the closed-loop system are 115% and 127% higher than the open-loop system, respectively, the closed-loop system is recommended for a solar HDH desalination system with the subsurface condenser. Moreover, the accumulated heat in the ground significantly degrades the long-term system performance, especially in the closed-loop design. The increase in the ground temperature after ten years of the closed-loop system operation is four degrees Celsius more than the open-loop system; therefore, ground thermal recovery is inevitable, especially if the system is used in subsurface irrigation where the ground temperature should not increase too much. By using the internal heat exchanger and air-cooled condenser before the subsurface condenser, in addition to increasing the daily water yield and GOR by 10.8% compared to the closed loop system, the ground temperature can be prevented from rising too much, i.e., one degree Celsius increase in the ground temperature after ten years of system operation
  9. Keywords:
  10. Solar Desalination ; Humidification-Dehumidification ; Evaporative Condenser ; Subsurface Condenser ; Solar Still ; Renewable Energy Resources

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