Numerical Analysis of a High-Speed Centrifugal Compressor using HFC-134a

• Main Authors: Chien-Chang Wu, 吳建成
• Other Authors: Sheam-Chyun Lin
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/94yzr5

碩士 === 國立臺灣科技大學 === 機械工程系 === 105 === Due to the longtime operation characteristics, the static pressure, noise, efficiency, and life time become the crucial evaluation indices for selecting the proper refrigeration and air-conditioning equipment. And the demand on designing a high-efficiency compressor motivates this thesis aiming to establishing an effective and reliable simulation scheme for accelerating the compressor design. Incorporated with the commercial CFD codes Fluent, a new two-step calculation procedure is proposed here to speed up the lengthy convergence procedure encountered in utilizing the built-in NIST (National Institute of Standards and Technology) database. Note that the database in NIST is recognized as the most accepted property source for the coolant HFC-134a. Nevertheless, using NIST data leads to the time-consuming, high-grid-quality and hard-to-converging problem, which enables the comprehensive parametric study on the high-speed compressor using HFC-134a almost impossible to carry out within a reasonable time interval. To solve this difficulty, this work firstly chooses the famous Soave-Redlich-Kwong (SRK) equation to execute the simulation associated with compressor to obtain the first-order calculation spending 1/4 CPU time of that needed in the regular simulation. Thereafter, with the first result as the initial condition, the final tune-up simulation is performed normally in Fluent with NIST database. As a result, not only 1% deviation between the normal and two-step solutions is found, but also more than 50% reduction on CPU time and a better stable convergence are observed in this new approach at the 50%-loading operation point. Afterward, with this new approach, the performance enhancement on centrifugal compressor is executed numerically in two parts aiming at the impeller and the housing in sequence. At first, with the aids of CFD visualization on the corresponding flow phenomenon, variations on meridional contour, number, and inlet/outlet angle of the blade are analyzed systematically to identify the appropriate parameter setting on this compressor rotor. Later, the cross-section of spiral housing, the cut-off clearance, and the diameter of diffuser are adjusted for finding out the proper settings to yield a superior compressor design. Accordingly, at the 60%-loading operation, the optimized impeller design yields a 74.8% static efficiency, which is 5% higher than the original design’s. Also, no significant changes on the maximum static pressure and the volume flow rate are observed over the entire operating range. On the other hand, at medium- to high-loading conditions, the velocity distribution at the fan discharge becomes more uniform, which may result in a noise reduction usually. In conclusion, this research successfully establishes a systematic and reliable simulation scheme to improve the aerodynamic performance of a high-speed centrifugal compressor. Also, the new two-step calculation procedure enables the design process to complete in a realistic time for meeting the engineer’s practical need.