Introducing, design and thermohydraulic analysis of an innovative thermally enhanced lamella heat exchanger for waste heat recovery

Growing demand for sustainable energy and decarbonization highlights waste hot-air streams as a major source of thermal losses and an opportunity for improved efficiency and emission reduction. This study proposes, designs, and comprehensively analyzes an innovative lamella heat exchanger that induces beneficial swirl and boundary-layer disruption to enhance heat transfer while maintaining low frictional losses, thereby addressing key limitations of conventional designs. The design further incorporates a relocated shell-side outlet and circular inlet/outlet sections, improving flow distribution and enabling seamless integration into exhaust ducts, HVAC systems, and process piping. Four twisted geometric configurations 90° twisted, modified 90° twisted, 180° twisted, and a hybrid arrangement combining straight and 180° twisted lamellae are systematically evaluated against a conventional straight design. A validated three-dimensional CFD framework based on Reynolds-Averaged Navier-Stokes (RANS) equations with the SST k-ω turbulence model is employed to accurately capture complex flow behavior and thermal transport. The results demonstrate that geometric modification significantly enhances heat transfer through improved mixing and boundary-layer disruption. The hybrid configuration delivers the best overall performance, with Nusselt number enhancements of 36.0% on the shell side and 137.1% on the tube side at the highest shell-side velocity (with the shell-side enhancement reaching 90.5% at the lowest velocity), together with a maximum effectiveness improvement of approximately 20.3% and goodness-factor ( j / f ) improvements of up to about 63% relative to the straight design at a shell-side inlet velocity of 1 m/s. Despite increased velocity leading to higher frictional losses, the hybrid design achieves the optimal balance between heat transfer enhancement and pressure drop, as reflected by the performance evaluation criterion. Overall, the proposed configuration offers a highly effective and practical solution for advanced air-to-air waste heat recovery applications.