Morphological optimization of butterfly-shaped inserts for heat transfer enhancement in tubular heat exchangers: a numerical study

Abstract

Single-phase heat transfer enhancement in heat exchangers represents a crucial issue for effective thermal treatment in many industrial applications, especially when highly viscous fluids or gases are processed. Increase of heat transfer capabilities might be obtained by passive techniques, such as tube corrugations or static inserts promoting boundary layers disruption at the fluid-wall interface. Different inserts have been proposed for tubular heat exchangers over the past decades, including twisted tapes, wired coils, conical rings and butterfly-shaped geometries. However, the literature lacks optimal geometries definitions. The aim of the present work is to achieve a morphological optimization of a butterfly insert through an adjoint approach to maximize heat transfer over pressure losses in heat exchangers tubes. In the present investigation, conjugate conduction-convection heat transfer in the computational domain is solved through a steady RANS approach. Turbulence is treated by means of the Realizable k-ε model with enhanced wall function. The model is successfully validated against experimental data. The optimization results suggest a reduction of the opening angle of the butterfly inserts of about 22°. The reported remarks can be used as guidelines for fabrication of optimized designs in tubular heat exchangers applications.