An in-depth numerical and experimental analysis of wire coil inserts: enhancing thermal performance and fluid flow characteristics in double pipe heat exchangers

Abstract

This study investigates the heat transfer, thermal hydraulic performance, and entropy generation of turbulent flow in a horizontal double pipe heat exchanger. The heat exchanger is integrated with wire coil inserts, featuring various combinations of pitch ratios (P/Dc) and wire diameters (d), using numerical analysis. The RNG k-ε model and the finite volume technique have been utilized to solve the equations, and experimental data from published studies have been used to validate three-dimensional simulations. The computational findings have been obtained for a range of Reynolds numbers (Re) 5500 ≤ Re ≤ 11,500 using three different types of wire diameter (d = 1 mm, d = 1.5, and d = 2 mm) and pitch ratios P/Dc in the range of (3.125–0.625) for a heat flux of 5000 W m^-2. The effect of these parameters on the Nusselt number, friction factor (ƒ), entropy generation number, and thermal performance factor (TPF) are investigated and compared with those of plain pipe under similar conditions. The incorporation of wire coil inserts significantly improves fluid mixing by creating a swirling flow pattern. The Nusselt number showed its highest enhancement at 111.11%, coupled with a substantial 347.8% increase in friction factor penalty with P/Dc = 0.625 and d = 2 mm at the highest Re as compared to plain tube. The highest value of the TPF recorded during the investigation was 1.36, observed at P/Dc = 0.625 and d = 2 mm, with a Re of 5500. This study also compares numerical results with experimental findings, revealing variations within a range of ± 10%.