Investigation of the Effects of Flow Swirl on Heat Transfer Inside a Cylindrical Cavity

Experiments were conducted to determine local heat transfer coefficients on the inside surfaces of a cylindrical cavity that is cooled by a swirling air flow. Temperature-sensitive liquid crystals were used as temperature sensors. Five blowing (cooling) modes were tested: three with swirl numbers of 0.36, 0.84, and 1.73; a fourth with no swirl (axial flow), and a fifth that was similar to the fourth but had the flow direction reversed. Flow visualization and static pressure measurements were performed to improve understanding of the situation. The smoke-wire technique was successfully used to picture the flow patterns. Plots of local Nusselt number along the cavity surfaces were obtained for the five blowing modes and for three different Reynolds numbers. The swirling cases had similar flow fields with higher heat transfer rates near the cavity top and lower rates near the cavity bottom (the opposite of the nonswirling cases). A tornadolike structure on the cavity bottom was observed in the swirling cases. This structure became stronger and more violent as the degree of swirl and the Reynolds number were increased. The Nusselt number curves for the two nonswirling cases were of similar shape, although the flow direction was reversed.