NUMERICAL STUDY OF NATURAL CONVECTIVE HEAT TRANSFER WITHIN M-SHAPED ROOFS

Abstract

Natural convective heat transfer in M-shaped roofs has been investigated using CFD approach with the aim of determining the flowfield and thermal characteristics of the attic when heated through the ceiling for pitch angles 14^o, 20^o, 25^o and 35^o and Rayleigh number between 10⁶ and 10⁷. The results show that the ‘M’ shape of the roof has strong influence on the airflow pattern and heat transfer. For all the roof pitches, counterrotating cells with varying intensities and thermal plumes are obtained. The air velocity variation laterally across the attic forms a sequence that mimics the flowfield thus enabling the relative size of a cell and its intensity at a position in an attic of a particular pitch to be predicted. The size of the twin vortices at the central area is found to increase by 4% with the roof pitch. As the pitch increases, the thermal plumes get thicker while their number reduces and heat transfer rate decreases.