Role of obstructing block on enhanced heat transfer in a concentric annulus
Abhinav Saha, Aranyak Chakravarty, Koushik Ghosh, Nirmalendu Biswas, Nirmal K. Manna
Abstract
The scope of this work is to investigate the influence of an obstruction size and its location on the buoyancy-driven convection in a concentric annulus. The inner cylinder of an annulus is maintained at higher temperature than the outer cylinder. An obstructing adiabatic block is placed in the space between the annulus. To explore the impact of the obstruction on the thermo-fluid flow structure, the block size and its position are varied. The annular region between the cylinders is assumed to be filled with air. The governing differential equations are solved numerically via the finite volume technique-based solver. The simulations are carried out for a controlling range of Rayleigh numbers (Ra = 103–105). The effect of the block size (d¯ = 0–0.8) and its positions (Φ=0−360°) on the heat transfer features are extensively examined. It is observed that the heat transfer is maximum for a particular Rayleigh number, block size, and its position. There exist a critical Rayleigh number (Racr) for the enhanced heat transfer. Depending on the block size and its position and Racr, the flow structure exhibits multi-cellular formation, which dictates the heat transfer markedly. The average heat transfer rate improves markedly up to a certain block size and convection regime, after which thermal behavior deteriorates. The local heat transfer attains a peak value near the location, where multi-cells are formed. The heat transfer enhancement parameter is approximately equal to 10% for the optimum block size. The findings of this study will be very helpful for the designing of the thermal system pertaining to efficient heat exchanging devices and other technological applications.Highlights The influence of location and size of an obstructing adiabatic block on buoyant convection in an annulus of the differentially heated concentric cylinder is investigated.Thermo-fluid flow behavior is markedly influenced by the obstructing block size and its position. The optimum block size and position are determined for the maximum heat transfer in an annulus for various Rayleigh numbers.The critical Rayleigh number for the optimum heat transfer is evaluated.The heat transfer parameter is approximately 10% for the optimum block size.