Performance and reliability of exhaust gas waste heat recovery units

Abstract

This thesis presents the effect of exhaust tube length-to-diameter (L/d) ratio, jacket-to-tube diameter (D/d) ratio, coolant inlet and outlet placements, exhaust gas swirling conditions, and tube materials (steel, copper, Inconel, and ceramic) on heat recovery performance, exhaust side pressure drop, and temperature profile in the exhaust gas Waste Heat Recovery Unit (WHRU). Non-dimensional parametric studies of a selected counter-flow Water Jacket WHRU was conducted using analytical and Computational Fluid Dynamic (CFD) models. Exhaust gas Reynolds numbers between 20,000 and 400,000, representative of exhaust gas flow in the exhaust stacks of U.S.Marine Corps’ MEP803A diesel generators and the U.S.Navy's 501-K17 gas turbine generators, were used. Results indicate heat recovery increases with higher L/d, D/d, and swirling exhaust gases conditions but with a severe pressure drop penalty. Addition of a solid heat spreader at the exhaust gas inlet and the use of suitable tube materials were also found to influence temperature profiles in the WHRU and mitigate adverse temperature gradients to some extent without any additional pressure drop penalty. Optimal laterally shifted placement of coolant inlet and outlet was found to improve heat recovery by up to 19% and was very effective at mitigating adverse temperature profiles, which improves the reliability of exhaust gas WHRU.