Design and development of the u-vane compressor

• Main Author: Lim, Yeu De
• Other Authors: Ooi Kim Tiow
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Mechanical engineering
• Online Access: https://hdl.handle.net/10356/136771
• Institution: Nanyang Technological University

This thesis presents the developmental work of a new positive displacement rotary compressor introduced by the author, namely U-Vane compressor (UVC), credited to the “U” like-shaped new vane bush component. The compressor is designed with the motivation of eliminating the vane tip friction of the rolling piston compressor and simultaneously reducing the unnecessarily large size of the cylinder and housing volume in the swing compressor. In the swing compressor, the vane is rigidly attached to the rotor, which eliminates the vane tip friction existing in the rolling piston compressor. However, the vane must be sufficiently long to prevent the possible operation jam and results in unnecessarily large size of the cylinder and hence increasing the housing volume in order to house the long vane. Thus, the newly introduced vane bush in UVC is made with two extended shoulders so that the vane can be made shorter as compared to that in swing compressor and subsequently reduces the size of the cylinder and housing volumes. With reference to Appendix A, it is anticipated that the size of the cylinder and housing volumes of UVC will be 30% smaller than that of the swing compressor. Mathematical models have been formulated to better understand the operational and performance characteristics of the UVC. The models take into consideration of energy, flow and heat transfer, mass conservation and momentum aspects of the compressor. Additionally, the mechanical losses, the dynamic aspect of the journal bearing, the internal leakage flows were also accounted for. The mathematical models were converted into a computational code using ForTran programming language and the 4th order Runge-Kutta method was used to integrate the simultaneous single order differential equations numerically. The working fluid was R-1234yf, the evaporating and condensing temperatures are 7.2 °C and 54.4 °C, respectively. The result shows that for a compressor with volumetric capacity of 32.5 cm3/rev, the mechanical efficiency is 75.71 % and the volumetric efficiency is 96.28 % when operating at 3000 rev/min. It is found that the largest frictional loss occurs at the vane sides, which contributes 47.8 % to the total frictional loss. The results also show that the leakages through radial clearance and rotor end-face clearance account for 49.9 % and 37.0 % of the total internal leakage, respectively. In order to further understand the operational behaviour of the compressor, the effects of several design and operational parameters on the compressor performance were also investigated. It is observed that lengthening the vane from 8.0 mm to 20.0 mm increases the mechanical efficiency by 8.7 %. By increasing the vane bush shoulder length from 4.0 mm to 12.0 mm, the mechanical efficiency improved by 3.3 %, mainly due to a reduction in the vane side friction. A similar magnitude of improvement in the mechanical efficiency can be obtained by thickening the rotor wall from 9.0 mm to 17.0 mm. However, increasing the operating speed from 1000 rev/min to 5000 rev/min reduces the mechanical efficiency by 10.7 %, due to higher frictional loss. For verification of the new design, a prototype machine with a volumetric displacement of 33.5 cm3/rev has been designed, fabricated, instrumented and measured experimentally with air as the working fluid. The prototype was tested from1200 rev/min to 2100 rev/min for discharge pressure of up to 5.27 bar (abs.), i.e. maximum pressure ratio of about 5.27. The maximum discrepancy between the predicted and measured power inputs was found to be 6.8 %. The measured mass flow rates are observed to be higher than the prediction when running at 1800 rev/min and 2100 rev/min and when the discharge pressure is below 5.0 bar, beyond which, the trend reverses. In addition, the volumetric efficiency of the prototype was measured to be from 43.4 % to 92.3 %. The variation of the instantaneous pressure in the working chamber was also measured, and the maximum and average mean discrepancies between the predicted and measured results are 8.3 % and 4.1 %, respectively.