Thermal study of a cistern's dome (the case of Motamed cistern in Lar, Iran)

• Cisterns can keep water in low temperatures for long time due to passive ventilation.
• Effective passive ventilation is owed to the dome shape, windcatchers and openings.
• Forced convection heat transfer mechanism is much effective than natural one.
• Interior surfaces do not experience temperature variations unlike exterior ones.

In this study thermal behavior of an active cistern is investigated experimentally and numerically for both wind and “no wind” conditions. The cistern is modeled using three-dimensional Finite Volume Method and quasi-steady state condition by considering variations of ambient temperature and intensity and direction of solar radiation. Temperature distributions on the outer surface of the dome and windcatchers are compared with thermography measurements for different hours of a day. Furthermore, natural ventilation caused by the heated dome is calculated by a two-dimensional quasi-steady modeling. The streamlines, velocity vectors, natural plume generated over the dome and temperature distributions are computed for different times during a day. The plume as well as the air motion inside the cistern is determined for different times during a typical day. Natural ventilation through the cistern opening and different wind-catchers are also calculated. Ventilation enhances convection heat transfer which is found non-uniform on the dome. Convection heat transfer coefficient changes between 2–10 W/m2K and 12–37 W/m2K for no-wind and wind-blowing conditions, respectively. The modeling shows that cisterns are appropriate system for storing cool water in hot arid regions.