Buoyancy Effects in the Entrance Region of an Inclined Multirectangular-Channel Solar Collector

Abstract

A numerical procedure is presented for the entrance region of an inclined multirectangular-channel solar collector with significant buoyancy effects. The upper wall heat flux is taken to be uniform, while the lower wall is assumed to be insulated. The heat flux distribution on the side wall of the rectangular channel is obtained by coupling a heat-conduction numerical procedure in the metallic region surrounding the channel to the main numerical procedure which solves the hydrodynamic and energy equations of the flow inside the channel. Numerical results are presented for water flowing in a multirectangular-channel solar collector with an aspect ratio AR = 4 inclined at an angle α = 30 deg to the horizontal. The resulting variable heat flux distribution on the side wall enhances the intensity of the secondary flow. The effects of the nonuniform heat flux distribution and the spacing between the rectangular channels on the variation of Nusselt number in the entrance region are presented for different values of Rayleigh number. At a value of Ra = 5 × 105 , Nusselt number is more than 300 percent above the constant property prediction.