Simulation of coupled heat transfers in a hollow tile with two vertical and three horizontal uniform rectangular cavities heated from below or above

•Coupled heat transfers in a hollow block heated vertically are studied numerically.•Results in terms of streamline and isotherms are presented and discussed.•The global heat transfer through the hollow block has almost linear behavior.•The appropriate overall thermal conductances U′ are calculated.•This kind of block permits a considerable reduction of heat in building roofs.

This paper presents a numerical study of the coupled heat transfers in hollow tile with two air cells deep in the vertical direction and three identical cavities in the horizontal one, uniformly heated from below or from above. The end vertical side walls of the structure are assumed to be adiabatic. The Boussinesq approximation is invoked and the flows are considered laminar and two-dimensional for the whole range of parameters considered. Conduction heat transfer in the solid partitions and radiation exchange between gray and diffuse surfaces are accounted for. The governing equations are solved by finite difference technique based on the control volume approach and the SIMPLE algorithm. Based on steady state simulation, the appropriate overall thermal conductances U′ are derived for the two considered situations (heating from below and from above). The results show that the hollow block with two air cells deep in vertical direction permits a considerable reduction of heat transfer between the inside and the outside of the building roofs.