Forced, natural and mixed-convection heat transfer and fluid flow in annulus: A review

The enhancement of the thermal performance of heat exchanging equipment transport energy at low financial cost by various techniques is presented in this review. Heat transfer is classified into three forms, namely, conduction, convection, and radiation. Convection is one of the major modes of heat transfer that can be qualified in terms of being natural, forced, gravitational, granular, or thermomagnetic. In the past decade, several studies on convection heat transfer in annular pipes with nanofluids have been reported. The effect of eccentricity in horizontal, inclined and vertical directions on heat transfer rate in most numerical and experimental investigations for horizontal, inclined and vertical annular tubes is studied. The effects of heater length, as well as the Darcy, Prandtl, Reynolds, Grashof and Rayleigh numbers on heat transfer in concentric and eccentric annular tubes are also investigated. This paper reviews various researches on fluid flow and heat transfer behavior in an annulus. A basic description of the convection heat transfer is given. Numerical and experimental investigations are conducted according to the concentric and eccentric annuli. Finally, conclusions and important summaries are presented according to the collected data.