A review of studies on forced, natural and mixed heat transfer to fluid and nanofluid flow in an annular passage

The enhancement of the thermal performance of heat exchanging equipment transport energy at low financial cost by various techniques is presented in this review. Various annular passage configurations have been used in the reviewed studies, namely circular, ellipse, rectangular, square, triangular, and rhombic annular channels with different fluid and boundary conditions. The effect of eccentricity in both horizontal and vertical directions on heat transfer rate in most numerical and experimental investigations for horizontal and vertical annular passages 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 passages are also investigated. In case of rotating the inner, outer or both cylinders of the annular cylinder arrangement, the generated secondary flow influences the heat transfer to fluid flow in an annular passage. The effect of nanofluid on the increased enhancement of heat transfer in an annular channel is presented. Related studies on curved, covered annular channels showed augmented heat transfer rate in comparison with straight annular channels. In this review, a good agreement is evident between experimental and numerical data, which could help researchers design thermal systems supported by annular passages with the goal of retarding energy consumption by equipment and machineries in applications that could ultimately contribute to appeasing the global energy crisis.