DG-FEM based simulation of laminar convection in an annulus with triangular fins of different heights

This work presents numerical simulation of laminar forced convection in the fully developed flow through the finned annulus of a double-pipe with triangular fins of different heights. The flow is subjected to the boundary condition of constant heat transfer rate per unit axial length with uniform peripheral temperature distribution. The aim is to investigate the effects of employing fins in two groups of unequal heights for different values of other parameters determining the configuration of the finned annulus, on the thermal performance of the finned duct. The governing partial differential equations of the convection problem are numerically solved by employing the discontinuous Galerkin finite element method (DG-FEM). The hydraulic and thermal characteristics like the friction factor, the Nusselt number and the j-factor are studied against various geometric design parameters. It has been observed that using the fins in two groups of different heights, the velocity and temperature distributions can be significantly altered to have more favourable flow and thermal characteristics. The maximum values of the coefficients of friction and heat transfer, and the j-factor do not necessarily lie on equal heights of the two fin groups. An arrangement of one group of fins being at its maximum height and the other one at its minimum height, has shown very fascinating performance in comparison with all the fins being at their maximum equal height. Upto 63 times more gain in the Nusselt number and 61 times more gain in the j-factor than the corresponding increase in the friction factor has been achieved by such an arrangement. The present study recommends the use of the fins with unequal heights for reducing the cost, weight and pressure loss with their thermal performance being better or at least comparable with that of the equal fins.