High temperature heat exchangers and microscale combustion systems: applications to thermal system miniaturization

The objective of traditional research and development on heat exchangers (HEs) has been to improve the performance and/or reduce the size and cost of the HE. Traditional research in power conversion has focused primarily on efficiency issues. However, rapidly developing applications in high temperature power and propulsion, pollution control/heat recovery, and high density power electronics has introduced new opportunities and challenges in developing cost-effective high performance, high temperature heat exchangers (HTHE) and microscale power systems. In this article the focus is placed on HTHEs for power/propulsion and thermal incineration/heat recovery applications, and on enabling technologies for microscale combustion systems. First a brief review of the growing need for HTHEs and microscale combustors and the state-of-the-art materials and fabrication technologies is presented. Next, various heat transfer augmentation techniques and their potential applicability to performance enhancement of HTHEs are discussed. Selected results of a case study involving a carbon fiber HE enhanced with an active heat transfer augmentation technique are presented. Issues associated with microscale combustion systems are presented, and technology enabling their development, namely, catalytic combustion and electrohydrodynamic (EHD) reaction rate augmentation techniques are discussed.