Abstract In this study, the effect of the passive heat transfer improvement method of ammonia/water couple with alumina (Al2O3) particles in nano-size were examined in diffusion absorption coolers regarding to the heat performance of the system. Adding nanoparticles into fluid leads to significant improvement in heat transfer since the surface area and heat capacity of the fluid increase due to nanoparticles. Therefore, in this study cooling/absorption fluid mixtures with Al2O3 nanoparticles and their impact on system performance were assessed. The results of experiments indicated that the system with nanoparticles provided better absorption of heat from the generator and faster evaporation of the cooler from the cooling/absorption fluid. The connection units of the heat transfer in the system were investigated considering the effect of fluids containing nanoparticles. It was observed that the operation time of the system was reduced due to shorter heat transfer periods. Consequently, it resulted in obtaining desired temperature faster.