Performance analysis of non-metallic dry running scroll compressors

Manufacturing cost of high precision scroll compressor parts remains a dominating factor in determining the overall production cost. Traditionally scroll compressors are made of metallic parts which require high tolerances to avoid leakage. Precision is even more important when the compressor is designed for oil-free operation and metal to metal contact can potentially be detrimental to the overall performance. With implementation of non-metallic compressor parts such as plastics, various avenues such as injection molding can be taken to reduce production cost. In addition, various polymer blends can be chosen to alleviate the danger of contact through the use of self-lubricating materials. A particular oil-free air compressor has been chosen for an investigation as to the practicality of conversion to a plastic design. In order to better understand the processes involved in the investigated compressor, a comprehensive mathematical model has been developed. The model uses derived analytic equations for the geometry with application to a wide range of compressor designs stemming from various involute curves. The geometry has been numerically validated for accuracy and includes volume, surface area and centroid locations for the compression pockets, as well as wall length and thickness for variably wall scroll compressors. Differential equations governing the temperature and specific volume of the pockets have been derived as well as relations for resulting forces and overturning moments. An adaptive RK4 solver has been implemented to solve the system of equations. The compressor model has been validated against experimental data for the investigated compressor and a parametric study has been performed. Different wrap combinations as well as discharge port locations have been studied for the investigated compressor. In addition, how variable wall thickness can impact various aspects of compressor leakage has been investigated. With results from the parametric study a new compressor concept has been designed and built from both plastic and metallic materials. Performance test have been conducted on the compressor concept and comparison between plastic and metallic compressor performance have been made. Final model validation with use of plastic has been performed