Performance Analysis of Brayton and Rankine Cycle Microsystems for Portable Power Generation

The presented work analyses the design space and performance potential of microfabricated Brayton cycle and Rankine cycle devices, accounting for lower component efficiencies, temperatures limited by the material properties and system implementation constraints imposed by silicon microfabrication and miniaturization. By exploring the design space of such microsystems, their potential thermal efficiency and power density are defined. Results for both types of devices are shown graphically and design challenges and guidelines are determined and found to be different from their large-scale counterparts. Similar analysis was performed for Brayton and Rankine cycle devices, with more complete assessment of the latter by including, windage, generator, conductive and heat sink losses. In contrast to the Brayton cycle, the compression work of the Rankine cycle is minimal and the pump efficiency is not critical. The investigation suggests a higher potential for Rankine cycle devices than for Brayton cycle devices.