Viscosity of nanofluids

Figure 14 shows the effective viscosity of all three nanofluids with different volume concentrations of particles, measured at temperatures between 20°C and 50°C. The viscosity of nanofluids increased dramatically with an increase in particle concentration and decreased with temperature, following the trend of the viscosity for pure water, for low particle concentrations. 

S.M.S. Murshed, K.C. Leong and C. Yang, Investigations of thermal conductivity and viscosity of nanofluids, International Journal of Thermal Sciences, 47(5), 560-568 (2008). 

Abstract. In this study we report a literature review on the research and development work concerning thermal conductivity of nanofluids as well as their viscosity. Different techniques used for the measurement of thermal conductivity of nanofluids are explained, especially the 3co method which was used in our measurements. The models used to predict the thermal conductivity of nanofluids are presented. Our experimental results on the effective thermal conductivity by using 3co method and effective viscosity by vibro-viscometer for Si02-water, Ti02-water and A Os-water nanofluids at different particle concentrations and temperatures are presented. Measured results showed that the effective thermal conductivity of nanofluids increase as the concentration of the particles increase but not anomalously as indicated in the some publications and this enhancement is very close to Hamilton-Crosser model, also this increase is independent of the temperature. The effective viscosities of these nanofluids increased by the increasing particle concentration and decrease by the increase in temperature, and cannot be predicted by Einstein model. 

The measurements of effective viscosity of Si02-water, Ti02-water and Al203-water nanofluids at different particle volimie concentrations were performed using Vibro Viscometer SV-10. To be use of the accuracy of the measurement the viscosity of water was measured before and after each experiment. The results of the measurements performed at room temperature are shown in Figs. 11-14. 

Figure 11. Relative viscosity of Si02-water nanofluids as a function of nanoparticle volume fraction compared with the models.

Figure 12. Experimental results of relative viscosity of Si02 nanofluids, compared to selected literature data.

Figure 14. Comparison of effective viscosity of water based nanofluids with as a function of temperature.

The viscosity and thermal conductivity of nanofluids containing MWNT stabilised by CHT were investigated. The MWNT fluid was stabilised with a CHT solution. The investigations showed that the thermal conductivity enhancements obtained were significantly higher than those predicted by Maxwell s theory. It was also observed that dispersing CHT into deionised water significantly increased the viscosity of the nanofluid, which explains its non-Newtonian behaviour. 

A. Turgut, I. Tavman, M. Chirtoc, H. P. Schuchmaim, C. Sauter and S. Tavman, Thermal conductivity and viscosity measurements of water-based Ti02 nanofluids, Int J Thermophys, 30, 1213-1226 (2009). 

J. Avsec and M. Oblak, The calculation of thermal conductivity, viscosity and thermodynamic properties for nanofluids on the basis of statistical nanomechanics, International Journal of Heat and Mass Transfer, 50, 4331-4341 (2007). 

Here, is the nanofluid density, /tnf is the nanofluid viscosity, Cp f is the specific heat capacity, p is the volume fraction, Cpp is the particle specific heat capacity, and Cpf is the specific heat capacity of the base fluid. 

Concentration/separation of sample solutes is one of most important functions in micro- and nanofluidic systems. TGF has proved to be a promising technique that can achieve concentration and separation in microfiuidic devices. However, so far very limited experimental and theoretical investigations have been reported. Experimentally, it is highly desirable to develop various microfiuidic structures that can be utilized by the TGF technique to cmicentrate different samples. Furthermore, more experiments should be carried out to characterize the thermoelectrical properties of buffers and samples so as to obtain the temperature-dependent electroosmotic mobility and electrophoretic mobility, as well as buffer conductivity, viscosity, and dielectric permittivity for each individual sample and buffer solution. In addition, the development of reliable, accurate, high-resolution, experimental techniques for measuring fiow, temperature, and sample solute concentration fields in microfiuidic channels is needed. Theoretically, the model development of TGF is still in its infancy. The models presented in this study assume the dilute solute sample and linear mass flux-driving forces correlations. However, when the concentrations of the sample solute and the buffer solution are comparable, the aforementioned assumptions break down. Moreover, the channel wall zeta potential in this situation may become nonconstant. More comprehensive models should be developed to incorporate the solute-buffer and solute-channel wall... 

In order to investigate the heat transfer characteristics of a nanofluid in the trapezoidal microchannel, we employed a CuO-water combination as the working fluid. Clearly, the thermal fluid properties of the nanofluid have to be updated. Thus, in the governing Eqs. (5) and (6), the following expressions were introduced, replacing the previous ptf and parameters. T)fpically, for a very dilute suspension, the effective viscosity, density and specific heat capacity have the following forms ... 

MicroChannel heat sink (MCHS) performance using copper-water and carbon nanotube-water nanofluids as coolants was analyzed by Tsai and Chein [28], The microchamiel heat sink was modeled as a porous medium. The MCHS performance was characterized by the thermal resistance which was divided into the conductive thermal resistance and convective thermal resistance. When employing a nanofluid as the coolant, the convective thermal resistance was found to increase due to the increase in viscosity and decrease in thermal capacity. The reduction of the total thermal resistance was contributed to the reduced temperature difference between the MCHS bottom wall and bulk pure fluid or nanofluids which pro-... 

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