(183an) Effect of Material and Geometry of Nanofillers on Thermal Conductivity of Nanofluids

Nanofluids are colloid dispersions of solid nanofillers in conventional heat transfer fluids like water, ethylene glycol etc. Thermal conductivity of nanofluids are highly enhanced than its parent base fluid and it is efficiently capable of handling the high heat flux of modern optoelectronic instruments. Effect of different parameters on the enhancement in thermal conductivity of nanofluids is the widely researched topic from the beginning. However, report on the effect of geometry of the fillers of different materials is very sparse. In this study, firstly we have prepared several ethylene glycol (EG) based stable nanofluids with wide ranges of nanofillers with different material and geometry. Material of nanofillers includes highly conducting metal like copper, moderately conducting tungsten disulfide, zinc oxide, titanium dioxide and poorly conducting non-metal like bentonite clay and geometry includes different 1D, 2D and 3D nanostructures like nanorods, nanowires, nanoplates, nanosheets, nanospheres etc. Those fillers have been thoroughly characterized under FESEM, TEM, and XRD to confirm their morphology and phase purity. Then, enhancement in thermal conductivity of the nanofluids has been studied systematically to understand the synergistic effect of both the parameters. Thermal properties analyzer (KD2 Pro, Decagon Devices, Inc., USA) has been used for measurement of the thermal conductivity at room temperature (25 °C). Repeated experiments on EG-based nanofluid confirm that the error for the measurement is below ±1% and it is highly reproducible with this setup. Enhancement is highly dependent on the thermal conductivity of the material and hence copper yields a significant enhancement with respect to other metal oxides and non-metals. Whereas, enhancement is reasonably very high with a very low loading of elongated nanostructures and percolated path through the structures are supposed to be responsible for such behavior. Interestingly, 2D elongated structures like nanoplate and nanosheet lead to the best result irrespective of the thermal conductivity of the fillers.