Heat transfer enhancement in a double-pipe helical heat exchanger using spring wire insert and nanofluid

Double-pipe helical heat exchangers (DPHHXs) are widely used for cooling and heating applications. In this study, a combination of two methods is used to enhance the performance of DPHHX. The thermal-hydraulic performance is investigated using a nanofluid of silicon dioxide and water (SiO2/water) as well as spring wire insert (SWI) experimentally and numerically. The numerical model is validated with the experimental results. The parameters such as Nusselt number, pressure drop, exergy efficiency, and thermal-hydraulic enhancement factor are investigated for Reynolds number range from 4500 to 7000. The results show the Nusselt number is enhanced with nanofluid employment and SWI. Nusselt number increases by 34% when 0.1% volume concentration of nanofluid is used and by 43.5% when spring wire is only used compared to base water. The configuration with a 0.3% volume concentration and SWI achieves the highest Nusselt number enhancement ratio, exhibiting a 174% increase compared to other configurations. In the same case, the pressure drop ratio reaches its peak at 157%. The exergy efficiency improves with an increase in nanoparticle volume concentration, with the 0.3% concentration with SWI showing the highest values, ranging from 54 to 65%. Among different concentrations, the SiO2/water nanofluid with a 0.2% volume concentration with SWI demonstrates the highest thermal-hydraulic enhancement factor, making it the optimal choice. The results prove that spring wire inert is more effective than nanofluid in the DPHHX. The contours, streamlines, and vectors of the temperature, velocity, and pressure distributions give more understanding for the heat transfer and fluid flow.