Experimental study exploring the heat transfer increase in double tube evaporator of vapor compression unit using nanorefrigerants is investigated. Aluminum oxide Al₂O₃ and copper oxide CuO nanoparticles are dispersed into refrigerants R134a, to form nanorefrigerant. Aluminum oxide nanorefrigerant void fraction is ranged from 0.1% to 0.70% whereas copper oxide nanorefrigerant void fraction is ranged from 0.06% to 0.16%. Nanorefrigerant absorbs its latent
heat of evaporation from hot water flowing in the annular space of the evaporator. The effect of nanorefrigerant void fraction, heat flux, and the hot water flow rate and its temperature at the evaporator inlet on flow boiling heat transfer is illustrated. The results showed that higher values of heat transfer coefficient (h.t.c) are attained in case of using R134a. Also, a maximum value of the htc at void fraction of 0.09% CuO nanoparticle and 0.5% of Al2O3 nanoparticles for R134a is noticed. Empirical correlation equations for the htc in terms of the operating parameter are obtained.