Ideal Specific Work of Rotary Compressors: A New Approach

The paper deals with the analysis of the compression stroke in rotary displacement compressors, following an innovative approach. Both a theoretical study and an experimental activity have been carried out to achieve the results. The rotary compressors are positive displacement machines in which compression and displacement are affected by the positive action of rotating elements. Currently, these machines are successfully employed in many applications, such as refrigeration, heat pumps and supercharged automotive engines. The first step of the activity presented in this paper has been the analysis (also in terms of bibliographical research) of the well-known theory behind the operation of the rotary compressors, in order to clarify the correct ideal working process. The main finding has been the evaluation that the use of the classical “pV representation” to calculate the ideal specific work leads to a numerical error in the result. In order to overcome the miscalculation, the authors have proposed a different representation of the process, introducing a new approach and a consistent model. Starting from the new pV representation, a more detailed equation has been achieved to calculate a more exact value of the ideal specific work. After the theoretical analysis, a test bench has been set up, in order to compare the developed model with experimental data: particularly, the machine object of test has been a scroll compressor. The specific work has been evaluated for the scroll compressor, tested under different working conditions, (for example, at different compression ratios): the values have been successfully compared with the theoretical ones, previously calculated by the new equation. An optimistic conclusion is represented by the good agreement of the new proposed model with the experimental data, while it is still simple, adaptable, and theoretically strict.