Application of morphed non-linear phase oscillators for representing rolling piston compressor performance

Abstract

Rolling piston compressors are small capacity volumetric machines used mainly in household refrigerator and heat-pump units. One of the main characteristics of the compressor is the way how the pressure builds up within the cylinder. This information can be used in more complex models for further investigations, e.g. to analyse the mechanical and thermal stresses of the compressor components. Modelling methods to resemble the pressurisation process of the rolling piston compressor with non-linear oscillators is presented in this paper. The mathematical description of the non-linear oscillators can be used to produce a continuous signal resembling the pressure fluctuations within the cylinder. For the definition of the necessary functions, the main characteristics of the typical rolling piston pressurisation diagram were identified. At first the pressurisation process was approximated by using the mathematical formula of the common Van der Pol oscillator. The oscillator was modified and extended with a linear second order differential equation to improve the resemblance between the target and model functions. To achieve better agreement with the target diagrams, Morphed non-linear oscillators were established. Polynomial and constructive incremental learning method was used to achieve adequate data fitting and the results of both methods were compared. The results show acceptable conformity and proved to be adequate to provide input data for further investigations i.e. for parametric studies of the compressor design. Besides modelling rolling piston compressors, this method can be applied for other volumetric compressors with cyclic pressurization sequence.

A Review on Sliding Vane and Rolling Piston Compressors

“…The semi-empirical model formulated by Molinaroli et al [83] only required eight input parameters and had a performance prediction accuracy of ±5%. Another novel method of reproducing the cyclic pressure variation in the compressor was presented by Farkas et al [84] and used mathematical functions for non-linear oscillators to curve-fit the pressure profile.…”