Circular Fins Improve Exhaust Heat Recovery in Aviation

This study explores adding circular fins to an annular tube bundle in an aircraft engine exhaust heat exchanger to recover more waste heat. Using 3D computational fluid dynamics, the researchers examined local flow and heat-transfer behavior in a finned evaporator design.

Results indicate the finned tube bundle achieves an overall fin effectiveness of 10, which substantially increases the heat transferred compared with a non-finned tube bundle. The work uses the Water-Enhanced Turbofan (WET) concept as a development platform and highlights the potential of such heat-exchanger measures for future propulsion concepts aimed at reducing emissions by 2050.

What the study examined

The paper looks at adding circular fins to an annular finned tube bundle placed in the exhaust flow of an aero engine evaporator. The broader aim is to examine waste heat recovery as part of innovative propulsion concepts such as the Water-Enhanced Turbofan (WET), which uses an evaporator in the exhaust to recover heat by evaporating water.

The research focuses on the thermal resistance on the exhaust side of the evaporator, which the authors identify as the limiting factor for heat transfer. To address that limitation, the study models an annular finned tube bundle and evaluates how the fins change local flow and heat transfer patterns.

Key findings

• Three-dimensional computational fluid dynamics (CFD) simulations were used to compute local heat transfer and flow behavior for the finned configuration.
• The finned tube bundle configuration was found to produce an overall fin effectiveness of 10, indicating a substantial increase in transferred heat compared with a non-finned tube bundle.
• The analysis shows how adding fins reduces the thermal resistance on the exhaust side, which in turn increases the amount of heat that can be moved into the evaporator.

Why it matters

Waste heat recovery in aero engines is of interest because it could help future propulsion concepts meet emissions goals set for mid-century. The WET concept serves here as a test case: even though industry attention to WET has decreased, it provides a useful platform to study how heat exchangers interact with engine components.

By demonstrating, through CFD modeling, that a finned tube bundle can markedly boost heat transfer in an evaporator, this work highlights a design option for reclaiming exhaust energy. Such improvements in heat-exchanger performance may inform further development of propulsion technologies that aim to make better use of available thermal energy.