An evaluation model for wall heat transfer effects on micro centrifugal compressors and its application in aerodynamic design

In micro gas turbine generators, the significant temperature difference within close proximity of the hot and cold components induces a substantial heat influx into the micro centrifugal compressor. This heat influx profoundly modifies the aerodynamic characteristics of the compressor. Ensuring a precise evaluation of the performance decline attributable to wall heat transfer effects and systematically integrating these impacts into the aerodynamic design process assumes paramount importance. Previous evaluation models, which involved unnecessary simplifications, suffered from limitations in accuracy. This paper presented a novel evaluation model for the diabatic isentropic efficiency through entropy analysis of the diabatic ideal compression process and the actual compression process. The rigorous theoretical derivation without any simplification empowers this model to faithfully mirror the authentic aerodynamic performance of diabatic compressors. The experimental and numerical verification results indicate that the proposed model is more reliable than the previous 'preheating-adiabatic compression' model when evaluating performance degradation stemming from wall heat transfer. The new model exhibits an error of approximately 3.7% at the design point and a mean absolute error of about 6% along the characteristic line of the design speed. Both deviations are deemed acceptable within the purview of engineering assessments. Furthermore, this paper illustrated an instance of the novel model's application in the aerodynamic design process. A prototype compressor, impeccably designed under adiabatic conditions but falling short of performance benchmarks during the performance test, was redesigned using the proposed method. The experimental results show that through the incorporation of wall heat transfer effects, the redesigned compressor aligns perfectly with design requirements, yielding an efficiency enhancement of roughly 1.5%.