Numerical investigation of thermo-hydraulic performance in an annular heat exchanger with sinusoidal vortex generators

Abstract

This study investigates thermal performance enhancement by utilizing vortex generators (VGs). VGs come in many designs, and this paper proposes optimizations for the sinusoidal vortex generator (SVG) when used in an annular conduit to improve heat transfer with minimal pressure drop. Two vital parameters of the SVG are analyzed, namely, blockage ratios (BRs) (0.1 and 0.2) and attack angles (α) (0–90°). The investigated fluid regime is turbulent, with the Reynolds number (Re) ranging from 5973 to 11,947. Three rows of SVGs are fitted on the surface of the inner pipe, where constant heat flux is applied, while the outer pipe wall is entirely insulated. The results indicate that the highest Nusselt number is enhanced by 20.4% over the smooth pipe when the case with BR = 0.2 and α = 90° is used at Re = 5973. However, the friction factor increases by 56.5% for the same case. Two types of transverse vortices are identified, where one type has its rotational axis normal to the inner pipe surface, and the other has its rotational axis parallel to the inner pipe surface. Those vortices with the axis perpendicular to the pipe surface merge with the fluid above the SVG to develop longitudinal vortices in different BRs and α. The case with BR = 0.2 and α = 15° yields the greatest average performance evaluation criterion (PEC) compared to other tested cases with a value of 1.054. This study finds that SVGs can contribute to a more efficient annular pipe-based heat transfer system.