Influence factors on thermal conductivity of ammonia-water nanofluids

Abstract

In order to investigate the mechanism of nanoparticles enhancing the heat and mass transfer of the ammonia-water absorption process, several types of binary nanofluids were prepared by mixing Al₂O₃ nanoparticles with polyacrylic acid (PAA), TiO₂ with polyethylene glycol (PEG 1000), and TiN, SiC, hydroxyapatite (noodle-like) with PEG 10000 to ammonia-water solution, respectively. The thermal conductivities were measured by using a KD2 Pro thermal properties analyzer. The influences of surfactant and ammonia on the dispersion stabilities of the binary nanofluids were investigated by the light absorbency ratio index methods. The results show that the type, content and size of nanoparticles, the temperature as well as the dispersion stability are the key parameters that affect the thermal conductivity of nanofluids. For the given nanoparticle material and the base fluid, the thermal conductivity ratio of the nanofluid to the ammonia-water liquid increases as the nanoparticle content and the temperature are increased, and the diameter of nanoparticle is decreased. Furthermore, the thermal conductivity ratio increases significantly by improving the stabilities of nanofluids, which is achieved by adding surfactants or performing the proper ammonia content in the fluid.

Keywords

binary nanofluids / ammonia-water / thermal conductivity / size effect / dispersion stability

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