This paper was dedicated to the study of small-scale solar chimneys by analyzing the influence of geometric parameters on the flow conditions and annual average exergetic efficiency. A mathematical model was developed to estimate the mass flow rate, the outlet and ground temperatures, based on an energy balance and empirical correlations from the literature. The geometry of a prototype built in the city of Belo Horizonte/Brazil was used as standard reference default. The parametric analysis showed that the most important parameters are the diameter of the tower and diameter of the collector and the height of the tower, since they promote larger changes in the airflow conditions and in the annual average exergetic efficiency.
Solar chimneys are devices that use solar energy to generate a hot airflow that can be used for power production, the drying of agricultural products, and/or water desalination. The performance of a small-scale solar chimney is studied numerically. The computational domain includes the solar chimney, the ground, and the atmosphere. The turbulent airflow is simulated using the commercial CFD code Ansys Fluent. The only boundary conditions required for the simulation are the wind speed, the ambient temperature, and the absorbed energy from the ground, determined by an energy balance in the system. The system was simulated for one day in the summer in the city of Belo Horizonte, Brazil. The ambient crosswind plays an important role in the velocity and temperature. The velocity inside the solar chimney increased with the wind speed, increasing the heat transfer and decreasing the airflow temperature. When the wind speed increased from 0 to 10 m/s, the outlet velocity increased from 1 to 4 m/s, and the outlet temperature decreased from 313 to 304 K.
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