1、An analytical and numerical study of solar chimney use for room natural ventilation Ramadan Bassiouny *, Nader S.A. KouraDepartment of Mechanical Power Engineering and Energy, Minia University, Minia 61111, EgyptAbstract The solar chimney concept used for improving room natural ventilation was analy
2、tically and numerically studied. The study considered some geometrical parameters such as chimney inlet size and width, which are believed to have a significant effect on space ventilation. The numerical analysis was intended to predict the flow pattern in the room as well as in the chimney. This wo
3、uld help optimizing design parameters. The results were compared with available published experimental and theoretical data. There was an acceptable trend match between the present analytical results and the published data for the room air change per hour, ACH. Further, it was noticed that the chimn
4、ey width has a more significant effect on ACH compared to the chimney inlet size. The results showed that the absorber average temperature could be correlated to the intensity as:(Tw = 3.51I0.461) with an accepted range of approximation error. In addition the average air exit velocity was found to v
5、ary with the intensity as :(nex = 0.013I0.4).Keywords: Solar chimney; Natural ventilation; ACH; CFD1. Introduction Efficient air ventilation and thermal comfort are of great importance in rural areas and hot climate conditions. Ventilation is the intentional supply of fresh outdoor air to a space to
6、 dilute and remove indoor air contaminants. Ventilation, whether naturally or mechanically, is a very urgent need in many residential and industrial zones. Natural ventilationoccurs due to two causes: aeromotive or wind driving force, or buoyancy driving force (stack effect) due to temperature diffe
7、rence between indoor and outdoor air temperatures. A significant temperature difference should be existed for the thermal driving force or stack effect to be appreciated. Use of solar energy can create such a large temperature difference, and hence improve the stack effect for space natural ventilat
8、ion. The solar chimney is an effective practical way to enhance space natural ventilation. In most tropical countries, where it is almost very difficult for the majority to have an air conditioner, people rely on natural ventilation, instead, to achieve comfort through opening windows. However, in s
9、ome climates, where the wind effect is not significant, just opening windows cannot effectively move the air inside the space to help diluting contaminants, odors, and satisfying the comfort feeling. This is due to the small pressure difference between the indoor and outdoor air. The solar chimney d
10、esign and construction allow storing an amount of solar energy into a surface, then releasing this energy to an adjacent column of air raising its temperature, and accordingly it flows upward entraining an outdoor fresh air into the space. This will create an air breeze inside the space.The main dri
11、ving force in moving the air upward in the chimney is the buoyancy force due to the absorbed energy. Generally, solar energy with high intensity is available in the Middle East countries. Egypt in general has rich sunny and clear skies. These conditions encourage adopting such a concept to enhance b
12、uilding natural ventilation and save energy. Hence this was the motivation behind the present study.2. Previous studies The solar chimney is an attractive idea for many researchers in different fields. Some previous studies have been seen in the literature that investigates the use of solar chimney,
13、 with different configurations, in ventilation improvement. Some researchers have been interested in analyzing the vertical chimney, while others have been studying the inclined chimney. Bansal et al. 1 are the pioneers to study solar chimney configurations and performance. They developed a mathemat
14、ical model to study the effect of using solar chimneys on thermal-induced ventilation in buildings. A theoretical and experimental study was carried out by Mathur et al. 2 to evaluate the possibility of making use of solar radiation to induce room ventilation in hot climates. The theoretical results
15、 of the proposed model were in a good agreement with the experimental ones. They found out that air flow increases linearly with the increase in solar radiation or the air gap between absorber and the glass cover. Macias et al. 3 presented a practical approach to improve the passive night ventilatio
16、n in social housing by applying the solar chimney concept. Instead of using fan forced ventilation, they used an accessible high thermal mass in building construction to collect solar energy during the afternoon in their concrete walls (50). For every flat there was a separate chimney with a swinging flap at top, and while collecting energy the flap was closed. Then, during night when the ambient temperature drops to abou
