Research on power consumption distribution characteristics of a water-lubricated twin-screw air compressor for fuel cell applications

Abstract

The water-lubricated twin-screw air compressor is very suitable for applications in high-pressure PEMFCs in distributed power generation, for it can provide absolutely oil-free air. Power consumption distribution is a significant characteristic for clarifying the influence mechanism of water injection and lubrication, which could provide the optimizing direction for performance enhancement. Hence, a mathematical model is constructed in this paper, aiming to analyze the power consumption distribution in different positions of the compressor at different rotating speed, including indicated power of dry air, water vapor and liquid water, friction power in the rotor chamber, friction power of radial journal bearings, thrust bearings and the lip seal. Results show that thrust bearings account for the largest amount of total power loss by over 52%, followed by indicated power of liquid water, radial journal bearings, while the indicated power of water vapor, friction powers in the rotor chamber and of the lip seal are minor power losses. This is very different from the common oil-injected twin-screw compressors, in which the friction power in the rotor chamber is also the dominant power loss. It illustrates the advantage of the low friction coefficient of water for sealing clearances in the water-lubricated twin-screw air compressor.