This systematic study aims to provide an extensive review of the experimental and numerical studies conducted on natural convection heat transfer and fluid flow in a vertical annulus.

Natural convection in vertical annular geometry has wide applications, such as in the design of the nuclear reactor, electronic equipment cooling, insulation of aircraft cabin, and control of heating and ventilation in building design, etc.

Parameters with significant impact on the design and performance are discussed in detail. This includes viz. the effect of operating and geometrical parameters, the effect of cylinder rotation, the effect of magnetic field, effects of using porous media, effects of discrete heating, conjugate analysis, boiling flow, use of Nano-fluids and some miscellaneous. Furthermore, the study highlights weak points and important research gaps such as the lack of experimental studies, 3D studies, etc. Following this, some directions for future research to address these research gaps are provided.