Low specific speed turbo-compressor

The present contribution describes a new class of turbocompressor developed at Imperial College London based on recent turbomachine innovations, which is suitable for efficient operation at low specific speed. At low specific speed (that is, high pressure ratio, low shaft speed and low mass flow), positive displacement machines are typically used. These have been found to be large, expensive and require high-maintenance. The innovative turbocompressor described is a fraction of the size and weight of a positive displacement machine, delivering oil-free compressed gases reliably. The design is simple enough to be manufactured at low cost and may be arranged in a multistage configuration similar to a standard industrial turbocompressor, in order to achieve the required pressure ratio. For a single stage, a pressure ratio of 1.62 at an efficiency of over 60% has been predicted by CFD, and is being validated by experimental work. Intercooling may be employed in a multi-stage arrangement to achieve improved performance. A multi-stage demonstrator, which is being built to investigate stage interactions, is described. For low mass flow applications (60 krpm, 10 g/s air, and with atmospheric inlet conditions) a high speed permanent magnet motor may be used to drive the turbocompressor. For medium flow/ medium speed applications (20krpm, 90 g/s air, at atmospheric inlet) this new turbocompressor design may be driven by a readily available, low cost, geared or belt driven motor. The new turbocompressor innovation may be employed in applications as diverse as fuel gas compression for microturbines (50- 750 kW), gas pressure boosting for medium sized gas turbines (1-5 MW), fuel cell gas compression, automotive super-charging, oil-free air compression, and many other industrial gas compression applications. (C) IMechE 2003.