Impact of Heat Transfer on Centrifugal Compressors of Micro Turbines

Micro turbines are small, high-speed gas turbine engines. When designed for a power output of 5 to 15 kW, micro turbines could provide the power for a household or a small set of units, serve as a range extender for hybrid electrical vehicles, or an auxiliary power unit to meet anti-idling requirements for heavy-duty diesel truck engines. The smaller the gas turbine, the harder it however is to achieve a competitive efficiency. At the considered power level, manufacturing limitations become significant and heat transfer and fluid leaks start to dominate. Significant development in material science has enabled higher temperatures to be sustained, so that reasonable efficiencies could be obtained. Achieving these efficiencies however depends critically on limiting the effect of inter component heat transfer. In this paper the impact of heat losses on the performance of small centrifugal compressors are investigated. The paper presents the adaptation of a 1D design and performance analysis code to accommodate heat transfer effects. The modifications made to the code to account for heat transfer will be discussed and a validation of the adapted code will be given. After that the performance of several non-adiabatic compressor impellers will be discussed in detail. Design modifications will be presented that reduce the impact of heat transfer for the investigated compressors. The impact on heat transfer on the compressor maps will also be detailed.