Transient intrusion flow in a section-triangular attic

Natural convection in an attic between the roof and the ceiling plays a role in the thermal performance of buildings. The intrusion flow on the ceiling originated from the cooling inclined roof due to buoyancy, which often appears during winter- or night-time and determines heat transfer through the ceiling, is studied using scaling analysis and numerical simulation. Seven regimes and four scenarios of different heat transfer and dynamic of the transient intrusion flow are presented. Scaling relations of the intrusion flow of different regimes and critical times of the transition between those regimes dependent on Rayleigh number (Ra), Prandtl number (Pr) and aspect ratio (A) are obtained. Based on numerical simulation, the selected velocity scales are validated. Furthermore, the development of natural convection flows and heat transfer in the section-triangular attic are characterized.