Exhaust gas heat recovery using a double-pipe heat exchanger with helical fins, considering gas radiation effect; numerical investigation, performance analysis, and optimization

Recovering waste heat from industrial exhaust gases, including those from flare systems, offers a crucial opportunity to enhance energy efficiency and minimize environmental impact. This study investigates the thermal and hydrodynamic performance of a novel gas-to-gas double-pipe heat exchanger with helically baffled fins, specifically designed for heat recovery from flare exhaust gases in various industrial applications. A numerical approach using the finite element method analyzes the effects of helical pitch length, cold gas inlet velocity, and gas radiation absorption coefficients on heat transfer and pressure drop. The study considers pitch lengths from 25 to 100 mm, cold air velocities between 0.5 and 1.5 m/s, and absorption coefficients from 0 to 2 m⁻¹. The results demonstrate that reducing the pitch length enhances turbulence, leading to improved heat transfer but a significant increase in pressure drop. Gas radiation markedly boosts heat flux, particularly at higher absorption coefficients, with minimal influence on pressure drop. A multi-objective optimization approach, targeting maximum heat flux and minimal pressure drop, identifies the optimal configuration. The optimal design features a pitch length of 87.18 mm, an absorption coefficient of 1.88 m⁻¹, and a cold air inlet velocity of 0.63 m/s, achieving a heat flux of 828.45 W/m² and a pressure drop of 2.21 Pa.