Abstract: The nano-refrigerants respectively of 0,0. 031%,0. 062%,0. 155% and 0. 248% ( volume fraction) Al₂O₃-R141b particles,were taken as the working fluids to perform flow boiling experiments in the aluminum-based rectangular microchannels of a hydraulic diameter of 1. 33mm,so as to reveal the influence of the nanoparticle concentrations on the surface energy of the microchannels after the experiments.The results show that ( 1) after adding a small amount of nanoparticles,a massive amount of activation nucleuses form on the wall surface,which brings forward the onset of nucleation boiling ( ONB) and then enhances the heat transfer; ( 2) the nanorefrigerant of 0. 062% Al₂O₃-R141b achieves the best effect in enhancing the heat transfer,and its heat transfer coefficient can be increased by a maximum of 48. 1% in comparison with that of pure R141b refrigerant; ( 3) when the nanoparticle concentration is greater than the optimal concentration of 0. 062%,the particle deposition on the surface becomes serious with the increase of the nanoparticle concentration,which causes the surface energy and heat flow resistance of microchannels to increase,but with a decrease in the heat transfer enhancement; and ( 4) the surface energy of the microchannels treated with the nano-refrigerants respectively of 0. 031%,0. 062%,0. 155%,0. 248% Al₂O₃-R141b particles,increases respectively by 0. 47,1. 39,1. 89 and 2. 14 times,in comparison with that of the original microchannels before the experiments.

Key words: microchannels, nano-refrigerant, heat transfer enhancement, surface energy