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Theoretical analysis and experimental validation of working process of an oil-free twin screw expander.

Number: pap. L66

Author(s) : DIAO A., TAO J., FENG M., et al.

Summary

This article presents a mathematical model to predict the thermodynamic performance of an oil-free screw expander, which took such factors as leakage, flow resistance and mechanical friction into consideration. A test rig was built up to measure the output power of the expander as well as the total efficiency of the unit. The predicted data were compared with the test results, and the maximal deviation was less than 9.1% as the flow rate was larger than 5t/h. The total efficiency of the unit was analyzed and was found to be influenced significantly by the isentropic efficiency of the expander, which could be attributed to the gas leakage within the expander.

Research and development of power recovery system from low grade heat originated in the 1940s, which was mainly based on and hereinafter restricted by the turbine technology and also restricted by the limit of turbine[1]. In the 1970s, America set out to develop expander-generator technology followed by UK, Japan and Austria. Though screw expander is a later technology, it has many advantages over turbo-type and piston-type such as high efficiency, low cost, insensitivity to liquid, good adaptability to varied working conditions, start-up with load, low speed and etc. So, screw expander has acquired acceptance from more and more customers in industry. Up till now, valuable research has been done at City University, in which a twin screw expander was utilized in organic Rankine cycle [2-6]. Though Wu et al carried out theoretical analysis and prototype development of oil-free twin screw expander[7,8], validation of the prototype based on experiment data and further modification of theoretical model was not reported.

Methodology and experience gained from the screw compressor was borrowed by researchers as the screw expander was studied, and many new breakthroughs from technology of screw compressor can be directly applied to screw expander. Throughout the development period of twin screw compressor, one can easily realize that modeling of the working process is an effective approach to understanding of the compressor performance. Many famous screw compressor manufacturers have developed software package to simulate working process of the twin screw compressor, usually focusing on design of the rotor profile. With the software, the influence of parameters on the compressor performance can be investigated and the result can be applied for performance optimization by choosing proper designmeters[9,10]. Accordingly, a good thermodynamic model to predict the performance of the twin screw expander is worth developing.

The trend and requirements of screw expander in the market were considered, and good experience from modeling of screw compressor was combined, a thermodynamic model to predict performance of screw expander was developed. A test rig was built up to validate the model by comparing the experimental performance data with the simulated results.

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Pages: 10

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Details

  • Original title: Theoretical analysis and experimental validation of working process of an oil-free twin screw expander.
  • Record ID : 30022078
  • Languages: English
  • Source: 8th international conference on compressors and refrigeration, 2017.
  • Publication date: 2017/07/20

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