Turning vanes in exhaust duct flow: study for energy efficiency, optimization and pressure drop mitigation

Abstract

This thesis presents a computational fluid dynamics (CFD) study on the effects of turning vanes and their placement in an exhaust duct with a sharp bend of ninety degrees and the application toward waste heat recovery devices. CFD models were implemented in ANSYS/CFX to handle flow in both laminar and turbulent regimes. Applying the principles from the Reynolds-averaging Navier-Stokes governing equations as well as the k-ε turbulent model, accurate simulations were performed to explore the behavior of exhaust gas flow field, pressure drops and recirculation zone sizes for various flow Reynolds (Re) numbers. The effects of turning vane location, vane setting angle, and number of vanes were evaluated. Flow visualization was used as a means of determining ideal locations for future installation of WHR devices. Results for 5000<Re<2x105 showed significant improvement in pressure drop across the 90-degree duct with a single turning vane, showing ranges of 50–70% reduction in overall pressure drop across the duct. This pressure reduction could yield significant fuel savings compared to an engine or generator without a turning vane. Increasing the number of vanes neither reduced the pressure drop further, nor did it reduce the size of the primary recirculation zone.