Experimental Investigation of Screw Compressor Clearance Monitoring Techniques

The aim of this study is to propose new methods to monitor operational clearances in oil-free screw compressors. The motivation has been to support research into leakage flows through generating data on clearance variations, and thus to develop systems that can be used for condition monitoring and control in industrial machines. By reviewing some monitoring applications in API 619 screw compressor packages, it was found that a substantial number of sensors were employed to optimise and protect assets but that a considerable number of failures could also arise as a result of the additional system components. Although Eddy-current probes and optical fibre bundles are already used in turbomachinery to measure clearance gaps, they are experimentally investigated in static conditions. They were both found to be sensitive to the change in distance to a female and male screw compressor rotor, and further investigation in dynamic conditions could further support the advantage they show for the application. Additionally, fibre Bragg grating sensors were bonded to the external casing of a Roots blower to measure the cyclic temperature change. The linear response achieved emphasises the advantage of the approach and supports the interest in further developing such a system to measure temperatures and strains inside screw compressors.

 

The measurement of clearances in an oil-free screw compressor could provide experimental data of their variations during operation. This could be a key parameter in understanding the role that leakage flows play in the energy transfers inside the machine, and inevitably the impact on performance. While this data could be used to validate modelling tools, measurement techniques which are developed in this research could be employed as condition monitoring and control systems in industrial packages.