Experimental investigation on flow condensation of R141b with CuO nanoparticles in a vertical circular tube

An experimental investigation was conducted on the flow condensation of R141b with CuO nanoparticles inside a vertical smooth tube. The test section was with inner diameter of 4 mm and length of 350 mm. Superheated vapor was mixed with the spherical CuO nanoparticles with mean diameter of 40 nm. The experiments were performed at various mass fluxes and two different super degree of 4 K and 10 K. The migration mass of nanoparticles and the average nanoparticle concentration were defined. The heat transfer enhancement ratio was utilized to exhibit the effect of nanoparticles on heat transfer coefficient. It was found that the migration mass of nanoparticles increased with the mass flux of vapor and the initial mass of nanoparticles as well as decreased with the superheat degree. The average nanoparticle concentration increased with the initial mass of nanoparticles and decreased with mass flux and superheat degree of vapor. In all cases, the heat transfer coefficient increased with the increase of nanoparticle concentration and superheat degree, but the enhancement of heat transfer was more announced at low mass flux. For 1% mass fraction, the maximum heat transfer enhancement of up to 39.68% was achieved as compared with pure refrigerant case.