| Summary: | 博士 === 國立中正大學 === 機械工程所 === 95 === New methods are proposed to evaluate the inter-rotor clearance and leakage of twin-screw compressors and vacuum pumps. The proposed methods are based on the iso-clearance contour diagram (ICCD), the maximum sphere method and the minimum cross-section method. Two new rotor profiles are also proposed, analyzed by these methods, and tested by the experiment on performance to show the validations of these leakage evaluation methods.
The efficiency of twin-screw compressors or pumps depends mainly on the inter-rotor leakage, and the inter-rotor leakage is determined primarily by the rotor profiles. However, the inter-rotor leakage is unavoidable for twin-screw compressors and vacuum pumps. In the past, the length of a theoretical sealing line (instant contact line) and the size of a blowhole area obtained by the tooth contact analysis (TCA) are the criteria to evaluate the possible leakage paths of a twin-screw compressor. But the rotor profiles of a twin-screw vacuum pump might not be conjugate, and the wrap angle of a twin-screw vacuum pump is several times of a conventional twin-screw compressor. Therefore, the leakage paths are not the same, and the theoretical sealing line (instant contact line) might not exist, and the blowhole area is not clearly defined for a twin-screw vacuum pump.
In this thesis, the ICCD and the maximum sphere method are developed to completely describe the size and shape of the cavity in an overlapped portion between two rotors, the distribution of the inter-rotor clearance and all the possible leakage paths. These methods can be applied to calculate the inter-rotor clearance, and the evaluation results can be used for further analysis such as the cutting tool design, the optimum programming, and the thermodynamic analysis. The tooth profiles of the two mating rotors are not necessarily conjugate to each other by utilizing these methods. As for the minimum cross-section method, this method determines the sizes and shapes of all the possible leakage paths and indicates the critical leakage paths.
The results of the proposed leakage evaluation methods increase more flexibility in geometric designing and help to evaluate the performance for the conjugate twin-screw compressors and non-conjugate vacuum pumps. And the results of this thesis can be used as a basis for further research on the optimization, the thermodynamic analysis, and the vacuum system design.
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