Performance enhancement of finned annulus using surface interruptions in double-pipe heat exchangers

Abstract

The present study investigates the thermo-fluid characteristics of a double pipe heat exchanger (DPHX) with split longitudinal fins (SLF) on the annulus side. The studied tubes with SLF are a modification of the conventional longitudinal finned tubes (LF) that allows for consecutive surface interruptions to break the boundary layer and provide an interrupted fluid passage along the flow length. The study is conducted using a high Prandtl number fluid (engine oil) with variable thermo-physical properties. Three-dimensional computational fluid dynamics (CFD) simulations are carried out under laminar flow conditions for configurations with a fin split interval between 0.333 and 0.166 m. A comparative analysis of the SLF configurations against the reference LF configuration is conducted based on fluid flow, heat transfer rate, and required pumping power. Furthermore, by evaluating integrated quantities such as the axially local heat transfer coefficient, total pressure, and bulk fluid temperature, it is noted that the main advantage of SLF is to repeat an entrance region-like effect along the flow length. The results demonstrate that the heat transfer rates in annulus equipped with SLF are higher than those with conventional LF by 31%–48% for the same pumping power and unit weight.