Experimental Study on the Enhancement of Mass Transfer Utilizing Fe_3O_4 Nanofluids

摘要

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 H_2O/LiBr with Fe_3O_4 nanoparticles were introduced into absorption air conditioning system. The effects of critical parameters, such as the flow rate of H_2O/LiBr nanofluids, nanoparticle size and mass fraction, on the falling film absorption were investigated. The H_2O/LiBr nanofluids with Fe_3O_4 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 H_2O/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 Fe_3O_4 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 100L h~(-1). Meanwhile, a fitting formula of mass transfer enhancement ratio for Fe_3O_4 nanofluids has been improved.