Parametric investigation of internal Y-shaped fin configurations under natural convection in a concentric annulus

Abstract

Natural convection heat transfer inside concentric annular enclosures has been well researched for decades. Such enclosures have been employed as intermediate layers between fluid streams in heat exchangers, particularly in latent heat thermal energy storage applications. Convection heat transfer coefficients originating from natural convection are relatively low, which drives the need for heat transfer enhancements by using extended surfaces (e.g., fins, heat sinks). In this study, numerical simulations are performed to investigate the natural convection heat transfer inside a concentric annulus in the presence of Y-shaped fins. Each Y-shaped fin has four important geometric parameters: (i) length of the fin base a, (ii) length of the fin branches b (i.e., the V-section), (iii) primary fin spacing angle θ, and (iv) secondary fin angle or branch angle α. Steady-state simulations are conducted using COMSOL Multiphysics® with constant temperature boundary conditions to generate the laminar natural convection profiles in the enclosure filled with air. The average Nusselt numbers, calculated at both the inner and outer walls of the enclosure, are used to gauge the heat transfer. The model is built with thin layer approximated fins first and subsequently compared to a modified model with fins with finite thickness. The optimized case using the thick fin model is found to yield a percent increase in Nu of 358.8% compared to the case with no fins. Lastly, the entropy generation is considered to determine the second law efficiency of the system, which is approximately 91%.