Design of a Microfabricated Rankine Cycle Steam Turbine for Power Generation

This paper presents the system-level and component design of a micro steam turbine power plant-on-a-chip which implements the Rankine cycle for micro power generation. The microfabricated device consists of a steam turbine that drives an integrated micropump and generator. Two-phase flow heat exchangers are also integrated on-chip with the rotating components to form a complete micro heat engine unit, converting heat to electricity. The system-level design includes cycle analysis and overall performance predictions, accounting for the expected performance of miniaturized components, thermal and structural integrity of the microsystem, and system-level trade-offs for optimal overall performance. Operating principles and design studies are also presented for the core component, with emphasis on a multistage, planar, radial microturbine and a spiral groove viscous pump. Design consideration for two-phase flow heat exchangers, microbearings, seals and micro-generators are also presented. Expected power levels range from 1–12 W per chip with energy conversion efficiency in the range of 1–11%. This suggests power density of up to 12 kW/kg for this technology, which is an order of magnitude greater than competing technologies, such as thermoelectrics. This study suggests the viability of a micro Rankine power plant-on-a-chip, but also identifies critical engineering challenges that must be met for practical implementation.