Development of experimental setup and testing of a cross vane expander-compressor unit in a refrigeration system

• Main Author: Khoo, Zhong Xun
• Other Authors: Ooi Kim Tiow
• Format: Final Year Project
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/60954
• Institution: Nanyang Technological University

With the discovery of the two daunting concerns that the Earth is facing, which are the depletion of ozone layer and global warming, there is a need to develop environmental friendly refrigeration and air conditioning systems. Since then, carbon dioxide has been proposed as an alternative solution for the synthetic refrigerants. However, due to the large expansion loss during the expansion process, the efficiency of the transcritical carbon dioxide refrigeration cycle is very low. Hence to overcome this limitation, the conventional expansion valve is replaced by an expander for work recovery. In this study, a new type of expander-compressor unit named as the cross vane expander-compressor unit is presented and its working principles are demonstrated. This type of expander-compressor unit performs the expansion and compression processes simultaneously and utilizes the recovered energy for the compression process. An experimental test bed is developed next to prove that the expander-compressor prototype is able to perform accordingly to the theoretical design. The equipment and the measurement devices required and selected for the experiment are discussed and presented. The equipment consists of the evaporator, condenser and motor. The measurement devices include the flow meters, thermocouples, torque meter, pressure transducers, and DAQ system. Before the pressure transducers are installed on the experimental setup for measurement purposes, they are calibrated first. The calibration results of the pressure transducers have showed that they exhibit high linearity with a R2 value of 1.00. Lastly, to avoid the prototype from failure due to the exposure to high pressure refrigerant or high tangential force, numerical stress analyses for the various critical components have been performed. These components comprise the vane, inner cylinder body, outer cylinder, housing, and the shaft. Based on the simulation results, these components are able to withstand the stresses that arise due to the pressure difference. However, this is not the case for the maximum deformation that the components will experience. The maximum deformations of the housing and the shaft are either close to the maximum acceptable clearance limit or have exceeded the limit. Hence, this can pose a problem to the operation of the prototype and may eventually lead to the failure of the prototype. On the other hand, the deformations of the vane are found to have negligible effect on the thermodynamic properties of the refrigerant as well.