Heat Transfer and Natural Ventilation Airflow Rates from Single-sided Heated Solar Chimney for Buildings

摘要

Heat transfer process and natural ventilation driven by a solar chimney attached to a sidewall of building are investigated with CFD technique (MITFLOW) in detail. In this paper, conditions and parameters studied in the modelling study are the cavity width of the solar chimney, the wall temperature, the height and breadth of the solar chimney, the ratio of outlet area to inlet area as well as the outlet location of the solar chimney. The ranges of calculation parameters focused on a solar chimney with single-sided solar collector (single-sided heated wall) cover following conditions: solar chimney length L = 0.5m～5.0m, breadth B=0.1m～0.5m, height H=2.0m~5.0m, and B/H=0.05～0.25. Heated wall surface temperature Tw is changed in the range of 30℃～70℃; the ratio of the outlet area to inlet area A_r is changed in the range of 0.6～1.0. It is found that for given building geometry and inlet areas, there is an optimum cavity width at which a maximum airflow rate can be achieved. Based on the prediction, the airflow rate reaches maximum when B/H is approximately 1/10. It is also found that for given chimney geometry, solar chimney ventilation flow rate can be increased with the enhancement of chimney height only the cross sectional area no more than the critical area, because cross section area has a strong effect on the transitional and/or turbulent convective heat transfer in an enclosure. From the view of economy technology, the optimized height of a solar chimney can be determined according to the optimized section ratio of breadth to height and available breadth in practice. On the analysis of CFD prediction, it is noted that optimized ventilation flow rate can be obtained when the outlet area takes the same area as the inlet area. Generally, there is good agreement among the numerical results, available experimental data from literature and theoretical analysis of natural ventilation from the solar chimney.