Advanced Thermal Management of High Temperature Fuel Cells via Active Flow Control

Abstract

The ultimate objective of this research is to investigate the effectiveness of cathode gas (air) recirculation for the thermal management of a solid oxide fuel cell (SOFC) stack. SOFCs conventionally operate at high temperatures (>600o C); and recovering heat from stack exhaust is critical to improving the stack and system performance. Prevalent approaches implement bulky and expensive high temperature gas-to-gas heat exchangers. Also, ejectors are being investigated for recirculation of the air; however, an ejector with typically large velocity gradients would incur large viscous losses. An alternative recirculation approach is being developed for distributed entrainment via active flow control. The entrainment would allow recuperative thermal mixing to occur that may be more effective than the preceding two approaches. The ultimate goal of this research thrust is to reduce, or even exclude, the need of an air preheater in a SOFC system. The cathode air preheat contributes to a large portion of the cost of a SOFC system. Verifying and demonstrating the efficacy of the Coand and #259; effect has been the initial focus, and positive results have been demonstrated in a test environment from a fluid mechanics standpoint. This has been based upon three stages of experimental development, inclusive of cross-sectional area and activated blowing degrees-of-freedom. Seed thermal testing of the system has demonstrated legitimate thermal mixing capabilities. EES thermodynamic modeling developments confirm that the approach can reduce or even exclude the air preheat. It is concluded that recuperative thermal mixing with this recirculation approach is indeed feasible and has the potential to greatly reduce the cost and efficiency of the SOFC system.