A review on heat transfer enhancement techniques during natural convection in vertical annular geometry

Heat transfer enhancement caught the attention of researchers owing to the need for compact size heat exchangers. This is because of the development of micro-devices due to advancements in electronics. The heat transfer through natural convection in vertical annular geometry has many benefits and, if designed efficiently, will result in energy saving due to no/less moving parts. This paper reports the review of techniques used by researchers for heat transfer enhancement during natural convection flow in vertical annular geometry. Several techniques that have a significant impact on the design and performance are discussed here in detail viz. use of nanofluids, use of the magnetic field, use of cylinder wall rotation, use of discrete wall heating, use of porous material, use of boiling, use of rings, etc. The implementation of each technique along with its advantages and drawbacks are also discussed. The authors also suggested their recommendation of techniques to be used for heat transfer enhancement. The study highlights research gaps and weak points that have not received the researchers' attention so far. This article outlines areas that needed the most attention in the future.