Performance improvement of vapour compression refrigerant system using graphene and multi-walled carbon nanotube nano-lubricants

The use of Vapour Compression Refrigerant (VCR) systems is very common in households and industries. Owing to the system's widespread utilisation, an analysis of the vapour compression refrigeration system's performance is required. Consequently, it has been discovered that the system's electricity consumption remained extremely high and that the output was incompatible with the input, which reduced its efficiency. To solve this issue, more research is needed to produce higher system performance, such as using nanoparticles as additional ingredients in pure compressor oil to yield higher performance. In the VCR systems, different results can be achieved depending on the type of nanoparticle selected and the concentration of the nano-lubricant. Among the nanoparticles with suitable characteristics are graphene and Multi-Walled Carbon Nanotubes (MWCNT). Therefore, this research aims to determine the optimal concentration of graphene and MWCNT in Polyolester (POE) oil and the impact of using nano-lubricants in the R134a system, such as reducing compressor work and exergy destructions, as well as improving the Coefficient of Performance (COP) system. The initial method was to characterise each graphene sample (0.1-0.3 g/L) and MWCNT (0.5-0.7 g/L) to eliminate the unstable concentrations. The characterization findings revealed that the three most optimal concentrations of each nano-lubricant are 0.1, 0.15, and 0.2 g/L for graphene and 0.5, 0.55, and 0.65 g/L for MWCNT nano-lubricant. The following step was to inject nano-lubricant into the compressor part. Among other graphene nano-lubricant concentrations, working with 0.2 g/L showed the highest reduction of compressor work and total exergy destruction, as well as improvement of COPheating. The value of each parameter was 30%, 30%, and 16.94%, respectively. The same thing also happened in the system when using MWCNT nano-lubricant with 0.65 g/L as the most stable concentration compared to other concentrations. The value of each parameter was 39.33%, 40.42%, and 50.26%, respectively. By comparing the result, the best performance of VCR system was achieved by using 0.65 g/L MWCNT nano-lubricant. In conclusion, replacing pure POE oil with nano-lubricants indicated higher system performance by increasing the COP value, saving more energy in the compressor part and minimising energy loss in the system.

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