How collector entrance influences the solar chimney performance: experimental assessment

The collector in the solar chimney, in addition to absorbing solar energy, is responsible for collecting air and directing it to the chimney. Heat transfer occurs naturally and slowly through most of the chimney height which results in the formation of secondary flows that reverse the flow and cause losses in the entrance. In the present study, it will be shown that one of the most important parameters responsible for the formation of secondary flows is the collector inlet height. To comprehensively assess this issue, two indoor experimental setups for a solar chimney with different collector geometries are fabricated and several tests with various collector entrance heights are performed. The effects of collector entrance height on heat transfer and airflow velocity and temperature within the chimney are evaluated. Based on the obtained results, for the conventional geometry of solar chimney, decreasing the collector entrance height from 20 to 10 cm (one quarter) improves the outlet velocity and the rate of energy transfer factor by 17% and 62%, respectively; whereas, for the other geometry, decreasing the collector entrance height from 16 to 8 cm (one half) results in 13% and 37% improvement in the mentioned parameters. The effects of collector entrance height are also investigated for three other geometries of solar chimneys available in the literature.