The ir-reversibility at the process of a vapour-compression refrigeration system (VCRS) with nanopartides in the working fluid was investigated experimentally. Mineral oil (MO) with 0.1 g L-1 TiO2 nanopartides mixture were used as the lubricant instead of Polyol-ester (POE) oil in the R134a, R436A (R290/R600a-56/44-wt.%) and R436B (R290/R600a-52/48-wt.%)VCRSs. The VCRS ir-reversibility at the process with the nanoparticles was investigated using second law of thermodynamics. The results indicate that R134a, R436A and R436B and MO with TiO2 nanoparticles work normally and safely in the VCRS. The VCRSs total ir-reversibility (529, 588 and 570 W) at different process was better than the R134a, R436A and R436B and POE oil system (777, 697 and 683 W). The same tests with Al2O3 nanoparticles showed that the different nanoparticles properties have little effect on the VCRS ir-reversibility. Thus, TiO2 nanoparticles can be used in VCRS with reciprocating compressor to considerably reduce irreversibility at the process. (C) 2012 Elsevier Ltd. All rights reserved.