In this paper, a simple positive displacement mechanism is investigated, which comprises two counter-rotating meshing rotors within a casing. Although considered for various applications more than a century ago, the basic geometry of this mechanism has not been further explored or adapted to modern gas compressor technology. As a fully balanced rotational mechanism operating at uniform angular velocity, potential applications range from pumps to expanders, from slow large displacement to high-speed devices; nonetheless, this research focuses on high-performance oil-less gas compressors as an ideal application. During one complete cycle, the main rotor compresses and discharges the fluid, whilst the secondary rotor seals the compression chamber. Important features of this mechanism are the circular profiles of the rotors, the potential to accommodate large ports for reduced flow losses, and ease of cooling. The simple geometry facilitates a cost-effective means of achieving tight operating clearances between rotors and casing for enhanced sealing without the need for liquid lubricants such as oil. This study and preliminary tests indicate that pressure ratios suitable for standard industrial applications can be obtained over a broad speed range, whilst minimizing friction and flow losses, a major drawback of current technologies. Moreover, two-phase compression and injection of liquids prior to compression have been studied and identified as a means to further improve efficiency and cooling.

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