Experimental investigation of key aerothermal phenomena in micro-scale radial turbocompressors

Novel conceptions of miniaturized sustainable energy systems have been a remarkable driver for boosting the design and development of micro-scale turbomachinery. This is particularly the case of radial turbocompressors, whose miniaturization down to the millimeter size entails great challenges arising not only from manufacturing aspects but also from an aerothermal point of view. The aim of this paper is to experimentally characterize some of these key adverse aerothermal effects present in miniaturized turbocompressors and to assess their impact on the off-design performance. To do so, a specifically designed closed-loop test rig has been developed for the experimental investigation of a micro-scale turbocompressor, which allows testing different gases varying the inlet pressurization rate. Hence, low Reynolds-number effects can be identified at different boundary conditions as well as a clear non-adiabatic behavior. In terms of methods, a double-check procedure for the assessment of the internal efficiency is highlighted as a key contribution. Experimental results show the off-design low-Reynolds-number effects on efficiency and validate the prediction methods and results raised in previous analytical and numerical works.