Numerical investigation of a double twisted tube heat exchanger in different configurations

Abstract

This study investigates the thermal and hydraulic performance of three configurations of double twisted tube heat exchangers (DTTHEs): circular (DCTTHE), elliptical (DETTHE) and square (DSTTHE) tubes, all with a twist ratio of 5. Numerical simulations were performed using Ansys Fluent with the k-ε turbulence model at Reynolds numbers ranging from 5000 to 25 000 to analyse heat transfer enhancement mechanisms. The working fluids were hot water and cold water, with varied inlet mass flow rates. Key performance parameters, such as the Nusselt number, overall heat transfer coefficient, pressure drop and effectiveness, were computed. Results demonstrate that DETTHE outperforms the other configurations, achieving superior heat transfer efficiency due to intensified secondary flows and vortices that enhance fluid mixing and disrupt thermal boundary layers. DETTHE exhibited the highest overall heat transfer coefficient, Nusselt number and effectiveness, with a maximum improvement in overall performance factor of approximately 74% and 300%, compared to DCTTHE and DSTTHE, respectively. However, this enhancement came at the cost of higher pressure drops. Temperature contours revealed uniform thermal distribution and improved heat exchange in DETTHE, particularly at the outlet region. Enhanced turbulence, secondary flow generation and stronger mixing near the tube walls contributed to these improvements. The study highlights the trade-off between thermal performance and hydraulic losses. The findings from this comparative analysis provide insights into the relative performance of different double twisted tube designs. Among the designs, DETTHE achieved the highest performance factor, making it a promising solution for compact and high-efficiency industrial heat exchangers.