Determination of the Polytropic Exponent in a Hermetic Scroll Compressor under Variable Operating Conditions
Enio P. BANDARRA FILHO, Mouhammad EL HASSAN, Zeeshan RANA, Jose Alberto dos Reis PARISE
Abstract. This work presents an experimental study on the polytropic exponent of a hermetic scroll compressor. The objective was to measure how the following factors influence the overall polytropic exponent: (i) discharge-to-suction pressure ratio; (ii) electric motor angular velocity; and (iii) frequency and refrigerant composition. Experimental data from an existing apparatus, previously published by the authors, included pressure and temperature at both compressor suction and discharge sides, along with the electric motor input power frequency. In this study, the polytropic exponent was calculated using the power-law equation that characterizes a thermodynamically polytropic process and the corresponding refrigerant equation of state. Prior results from different compressors operating with air, R12, R22, and two binary mixtures showed relatively constant values for each compressor. All these compressors were of the open type. In contrast to earlier tests with open compressors, a single hermetic scroll compressor exhibited a linear increase in the discharge-to-suction pressure ratio and a non-linear relationship with input power frequency. A statistical curve fit model was developed using the collected data to represent mathematically the compression process of a scroll-type compressor running with various refrigerants. This model accurately predicts the compressor’s discharge temperature within a maximum difference of 3 K. Overall, a satisfactory agreement was observed between the model predictions and the experimental data.
Keywords
Polytropic Exponent, Refrigeration System, R410A, R32, R452B, R454B
Published online 4/25/2026, 8 pages
Copyright © 2026 by the author(s)
Published under license by Materials Research Forum LLC., Millersville PA, USA
Citation: Enio P. BANDARRA FILHO, Mouhammad EL HASSAN, Zeeshan RANA, Jose Alberto dos Reis PARISE, Determination of the Polytropic Exponent in a Hermetic Scroll Compressor under Variable Operating Conditions, Materials Research Proceedings, Vol. 64, pp 943-950, 2026
DOI: https://doi.org/10.21741/9781644904091-117
The article was published as article 117 of the book Energy Futures
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 license. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
References
[1] PARISE, José A.R. Simulation of vapour-compression heat pumps. Simulation, v. 46, n. 2, p. 71-76, 1986. https://doi.org/10.1177/003754978604600206
[2] MAXWELL, James C. Theory-of-Heat. London, 1904.
[3] PEREIRA, R.H.; MOTTA, S.Y.; PARISE, J.A.R. A Study on the Polytropic Exponent. Part I: Open Reciprocating Compressors. In: , 1995, São Paulo. III Congreso Ibero Americano de Aire Acondicionado e Refrigeracion, CIAR-CONBRAVA. São Paulo 1995.
[4] BECERRA, Elizabet Vera et al. A study on the polytropic exponent of reciprocating semi-hermetic compressors. In: , 2008, Curitiba, Parana. International Congress of Refrigeration, Air Conditioning Ventilation and Heating of Mercosul. Curitiba, Brazil, 2008.
[5] PANATO, Victor Hugo. Análise experimental de fluidos refrigerantes alternativos ao R410A em sistemas de ar condionado. PhD Thesis, Brazil, 2020.
[6] PANATO, Victor H.; PICO, David Fernando Marcucci; FILHO, Enio Pedone Bandarra. Experimental evaluation of R32, R452B and R454B as alternative refrigerants for R410A in a refrigeration system. International Journal of Refrigeration, 2022. https://doi.org/10.1016/j.ijrefrig.2021.12.003
[7] BELL, Ian H. et al. Pure and pseudo-pure fluid thermophysical property evaluation and the open-source thermophysical property library coolprop. Industrial and Engineering Chemistry Research, v. 53, n. 6, p. 2498-2508, 2014. https://doi.org/10.1021/ie4033999
[8] ÜÇER A.S.; BENSON, R.S. Simulation of single and double stage reciprocating compressor systems with allowance for frictional effects and heat transfer. Israel Journal of Technology, v. 15, p. 196-208, 1977.
[9] CUI, Michael M; SAULS, Jack. Impact of Power Frequency on the Performance of a Scroll Compressor. In: , 2008, West Lafaye, IN, USA. International Compressor Engineering Conference. West Lafaye, IN, USA: Purdue University, 2008. p. Paper 1903.
[10] GROLL, E. Modeling of Compressors, USNC/IIR Short Course on “Simulation Tools for Vapor Compression Systems and Component Analysis. In: , 2004. International Refrigeration Conference at Purdue, 2004.
[11] DARDENNE, Laurent et al. Semi-empirical modelling of a variable speed scroll compressor with vapour injection. International Journal of Refrigeration, v. 54, p. 76-87, 2015. Disponível em. https://doi.org/10.1016/j.ijrefrig.2015.03.004
[12] BURT, Charles M. et al. Electric Motor Efficiency under Variable Frequencies and Loads. Journal of Irrigation and Drainage Engineering, v. 134, n. 2, p. 129-136, 2008. https://doi.org/10.1061/(ASCE)0733-9437(2008)134:2(129)
[13] GUO, Weihua et al. R32 Compressor for Air conditioning and Refrigeration applications in China. In: , 2012, West Lafayette, Indiana, USA. International Compressor Engineering Conference. West Lafayette, Indiana, USA: Purdue University, 2012. p. 2098.
[14] TSUJII, Hideki. TEST REPORT # 15 System Drop-In Test of Refrigerant R-32 in a VRF Multi-split Heat Pump., 2013.
