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The absorption air-conditioning system is a low-power-consumption and low-noise system and is also good at balancing the electricity peak-valley system. It can be driven by low-grade energy, such as solar energy and industrial exhaust heat. The nanofluids, which possess the superior thermophysical properties, exhibit a great potential in enhancing heat and mass transfer. In this paper, nanofluids of H2O/LiBr with Fe3O4 nanoparticles were introduced into absorption air conditioning system. The effects of critical parameters, such as the flow rate of H2O/LiBr nanofluids, nanoparticle size and mass fraction, on the falling film absorption were investigated. The H2O/LiBr nanofluids with Fe3O4 nanoparticle mass fractions of 0.01 wt %, 0.05 wt % and 0.1 wt %, and nanoparticle sizes of 20 nm, 50 nm and 100 nm were tested. The results imply that the vapor absorption rate could be improved by adding the nanoparticles to H2O/LiBr solution. The smaller the nanoparticle size, the greater the enhancement of the heat and mass transfer. The absorption enhancement ratio increases sharply at first by increasing the nanoparticle mass fraction within a range of relatively low mass fraction and then exhibits a slow growing even reducing trends with increasing the mass fraction further. For Fe3O4 nanoparticle mass fraction of 0.05 wt % and nanoparticle size of 20 nm, the maximum mass transfer enhancement ratio is achieved about 2.28 at the flow rate of 100 L h-1. Meanwhile, a fitting formula of mass transfer enhancement ratio for Fe3O4 nanofluids has been improved. [ABSTRACT FROM AUTHOR]