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Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Stability and rheology of dilute TiO2-water nanofluids | Penkavova et al. Nanoscale Research Letters 2011 6 273 http www.nanoscalereslett.eom content 6 1 273 o Nanoscale Research Letters a SpringerOpen Journal NANO EXPRESS Open Access Stability and rheology of dilute TiO2-water nanofluids Vera Penkavova Jaroslav Tihon and Ondrej Wein Abstract The apparent wall slip AWS effect accompanying the flow of colloidal dispersions in confined geometries can be an important factor for the applications of nanofluids in heat transfer and microfluidics. In this study a series of dilute TiO2 aqueous dispersions were prepared and tested for the possible presence of the AWS effect by means of a novel viscometric technique. The nanofluids prepared from TiO2 rutile or anatase nanopowders by ultrasonic dispersing in water were stabilized by adjusting the pH to the maximum zeta potential. The resulting stable nanofluid samples were dilute below 0.7 vol. . All the samples manifest Newtonian behavior with the fluidities almost unaffected by the presence of the dispersed phase. No case of important slip contribution was detected the Navier slip coefficient of approximately 2 mm Pa-1 s-1 would affect the apparent fluidity data in a 100- am gap by less than 1 . Background Bulk rheological properties of nanofluids shear viscosity 1 2 yield stress 3-7 and complex modulus 8 can be important factors for some applications e.g. convective heat transfer 9 10 and filtration 5 and can also provide some correlations with other properties such as volumetric particle concentration 1 2 thermal conductivity 11 12 or -potential 3-6 . On the other hand there are processes with a dominant microscopic length scale such as small Nernst diffusion thickness in heat mass transfer 13 small hydraulic radius in microfluidics 14-17 small pore diameter in filtration 5 etc. where the bulk rheology characteristics should be completed using another kind of information. In some cases two-scale description particle size or inter-particle distance vs. hydraulic radius is useful
