The design of ultra-high-speed miniature centrifugal compressors

Authors

M.V. Casey - PCA Engineers Limited, Lincoln, United Kingdom and University of Stuttgart, Germany
D. Krähenbuhl, C. Zwyssig - Celeroton AG, Zurich, Switzerland

Abstract

This paper describes recent experience in the development and application of several ultrahigh-speed miniature centrifugal compressors with an impeller diameter less than 30 mm and using high speed electric motors to provide rotational speeds between 200,000 and 600,000 rpm. In a growing number of applications at low flow rates such micro-compressors can be successfully used to replace much larger positive displacement devices or to replace larger centrifugal compressors operating at lower rotational speeds. A range of applications for heat pumps, fans and general air supply are considered in which the typical features of the stages developed are the low size, very low mass flows and high speeds. Dimensional analysis is used to show how the scaling laws for the compressor match those of the motor. These also show that a range of designs of different design styles are required; from low flow coefficient stages with two-dimensional geometry to high flow coefficient mixed flow stages. In addition to a description of the applications, and the stages developed for these, some information is provided on the design strategy, design tools and performance prediction methods used in the design process. Test data from a range of devices demonstrates that that an overall efficiency around 65% can be achieved. The measured performance is shown to agree well with the predicted performance of the stages to validate the design techniques used.