Optimal Placement of Non-Intrusive Waste Heat Recovery Devices in Exhaust Ducts

The Secretary of the Navy has ordered the U.S. Navy and Marine Corps to reduce energy usage. This study explores how to optimize placement and size of a non-intrusive waste heat recovery device for energy recovery in exhaust ducts. Additionally, it explores the effect that a device has on the exhaust infrared signature by analyzing the change in the bulk temperature at the exhaust outlet. Optimal device placement and size is dependent on duct geometry, external heat transfer coefficient, and flow characteristics, namely Reynolds number. Infrared signature intensity reductions of 1 14 are only achievable with unpractically long thermoelectric generator devices and high external heat transfer coefficients. Doubling the external heat transfer coefficient increases heat recovery by 15 30 for low Reynolds number flows 104 and 75 90 for high Reynolds number flows 105106. In low Reynolds number flows 104, device position can account for a 75 change in energy recovery whereas high Reynolds number flows 106 have unexpected areas of higher heat transfer. Position changes can increase heat recovery 10 70, while increasing device size may only marginally improve results. Identifying local maxima for heat transfer, especially in high Reynolds number flows 106, is counterintuitive because of unexpected recirculation zone effects.