The arguments in favor of using nanofluids in thermal applications are increasing substantially since last few decades. Nanofluids provide improved performance in heat transfer compared to their base fluids due to their superior thermal properties. Even though nanofluids exhibit better thermal properties, their usage has been limited due to their stability issues. The stability of the nanofluid greatly affects its thermal properties over a period of time. The stability and thermal properties of nanofluids can be affected by parameters like surfactants used and their quantity, and materials used for the preparation of nanofluids. While exploring the effects of process parameters on the stability and thermal properties of the nanofluids, the full factorial design is not always necessary or possible, and statistical methods like the Taguchi method can be used for the design of experiments. In this study, the Taguchi method is used and the L4 orthogonal array is formed to prepare nanofluid samples using different combinations of the process parameters. In the Taguchi method, the effect of process parameters on characteristics of output is calculated in the form of Signal to Noise ratio (SNR). In this study, surfactant material, surfactant concentration, and nanoparticle material are selected as process parameters. For each process parameter two levels are selected. For surfactant material, the levels are cetyl trimethyl ammonium bromide (CTAB) and Sodium Lauryl Sulfate (SLS). For surfactant concentration ratios the levels are selected as 1:1 and 4:1 to the nanoparticle weight, and for nanoparticle material the levels are CuO and Fe3O4. The nanofluid samples as per parameters in the L4 orthogonal array are prepared with 0.1% weight of nanoparticles and their stability and properties are studied.

For studying stability zeta potential, hydrodynamic diameter, Polydispersity index (PDI) and turbidity of the samples is measured. The effect of the process parameters on the zeta potential of the sample and hydrodynamic diameter of the particles has been calculated in the form of SNR.  As a higher value of zeta potential is desired, SNR for zeta potential is calculated using larger the better approach and as lower values of hydrodynamic diameters are desired hence smaller the better approach is used. The values of PDI and turbidity are measured and studied to confirm the stable nature of the solution. The feasibility of turbidity as a potential stability indicator is also studied. The viscosity and thermal conductivity of each nanofluid sample is measured with the change in temperature (20, 25, 30, 35 and 40^0^C) is measured. The transient line heat source method and rotational viscometry principles are used for these measurements, respectively. The results are compared with each other and the effect of process parameters on these properties is calculated. As the wetting characteristics of nanofluids also play an important role in heat transfer from surfaces, the contact angle of the nanofluids with a copper surface is also measured. The axisymmetric drop shape analysis of a sessile drop is conducted for the measurement. The values of the contact angle are calculated using ImageJ software and are compared with the base fluid i.e. water.   

The results show that the surfactant plays a dominant role in the stability of nanofluids, the zeta potential and hydrodynamic characteristics are largely dependent on the surfactant material. It is also found that the nanoparticle material has a dominant effect on the thermal conductivity of the nanofluids. The results also show that the turbidity measurement can give first-hand information about the stability of nanofluids but it cannot act as a definitive index for stability.


Effect of Surfactants and Nanoparticle Materials on the Stability and Properties of Cuo-Water and Fe3o4-Water Nanofluids

Division / Sponsors: 
Heat Transfer Division (HTD), Fluids Engineering Division (FED)

Heat Transfer Summer Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2020/volume/83709

18th International Conference on Nanochannels, Microchannels, and Minichannels
Paper Proceedings: https://asmedigitalcollection.asme.org/ICNMM/ICNMM2020/volume/83693

Fluids Engineering Division Summer Meeting
Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2020/volume/83716

HT-ICNMM2020 - Virtual Conference, SHTC - Virtual Conference, FEDSM2020 - Virtual Conference

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