Thermodynamic Analysis of Two-stage Vapour Compression Refrigeration Systems Using Eco-friendly Refrigerants

As Nigeria continues to expand its industrial, commercial, and residential cooling needs, the demand for efficient and environmentally sustainable refrigeration systems is growing. However, the environmental impact of conventional refrigerants has raised concerns due to their high global warming potential and ozone depletion potential. This study presents a thermodynamic analysis of two-stage vapour compression refrigeration systems in Nigeria, utilizing eco-friendly refrigerants which offer low global warming potential and zero ozone depletion potential. The refrigeration system comprises a high-pressure stage compressor and a low-pressure stage compressor with the inter stage pressure taken to be the ideal inter stage pressure. Performance analysis of R-717, R-600, R-600a and R-290 two-stage vapour compression refrigeration systems were made using seven parameters. The effect of the variation of five operating/design parameters (evaporating temperature, condensing temperature, superheating temperature, sub cooling temperature and refrigerant mass flow rate) on Coefficient of Performance (COP) of two-stage vapour compression system was analysed using engineering equation solver software. The results showed that as evaporating temperature decreases from 0oC to -50oC, COP decreased for all the four refrigerants considered. R-717 gave the highest COP value of 7.636 at evaporating temperature of 0oC while R-600a gave the lowest value of 4.009 at the same temperature. The results also showed that the COP of all the four refrigerants increased with increase in sub cooling temperature and Superheating Temperature, whereas it decreased with increase in condensing temperature. The study revealed that, except for the mass flow rate, all other operating parameters significantly affect the COP of refrigeration systems considered.