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This paper examined the thermal conductivity of poly-alpha-olefin (PAO) based nanofluids using three transient methods including the transient plane source (TPS) technique. They also explored how temperature, shape, and nanoparticle concentration affect thermal conductivity. The thermal properties of aluminum oxide/PAO and multi-walled carbon nanotubes (MWCNT)/PAO were tested, and results showed that nanoparticle concentration increases thermal conductivity more than expected.
This paper focused on determining the thermal conductivity of multiwalled carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs) that were dispersed throughout n-octadecane as phase change materials (PCMs). The Thermal Constants Analyzer TPS measured the thermal conductivity of the n-octadecane samples at solid and liquid phases using the transient plane source (TPS) method. Results showed that the thermal conductivity of the solid phase n¬-octadecane/MWCNTs samples increased with nanotube concentration. The solid and liquid phase PCMs followed a similar decreasing trend as temperature rose, but overall, thermal conductivity values were much lower in the liquid phase. These results give reason to believe that CNFs and MWCNTs may be used as energy storage composites in the future.
Many conventional fluids have low thermal conductivities. Adding thermally conductive nanometer-sized particles to these fluids transforms them into thermally conductive nanofluids. In this study, the thermal conductivity of aqueous alumina and multi-walled carbon nanotube (MWCNT) nanofluids was measured using the transient plane source (TPS) method with a thermal constants analyzer TPS. During each trial, 0.015 W of power were administered to each sample for two seconds. Results of the experiment showed that thermal conductivity increased with the nanofluid concentration. The alumina nanofluid would be an effective heat transfer medium because it enhances the thermal conductivity of the nanofluid while maintaining viscosity. Alternatively, MWCNT/water nanofluids become more viscous with the addition of nanofluids, which decreases the thermal conductivity of the solution. It was also discovered that the thermal conductivity of the alumina nanofluid was reduced by 7.0% after 55 days, likely due to eventual aggregations of the nanoparticles, which would increase the viscosity of the liquid.
Many conventional fluids have low thermal conductivities. Adding thermally conductive nanometer-sized particles to these fluids transforms them into thermally conductive nanofluids that can be used for refrigeration and air conditioning systems. In this paper, the transient plane source (TPS) method is used to explore the thermal conductivity of multi-walled carbon nanotube (MWCNT) nanofluids in a helically coiled, double-pipe heat exchanger. The thermal conductivities of the MWCNT nanofluids were measured using the thermal constants analyser. Although each sample had different concentrations of MWCNT nanotubes, the nanofluids performed similarly in the TPS tests. Therefore, the helically coiled tube had an insignificant effect on the thermal conductivity of the nanofluids. Although adding MWCNT increased thermal conductivity, the high viscosity of the fluid caused a loss of heat transfer, which cancelled out the effect of the carbon nanotubes, forming an inefficient cooling medium.
Multi walled carbon nanotubes (MWCNTs) and carbonized resorcinol-formaldehyde (RF) resin were used to create a conducting aerogel with a high electrical conductivity and Seebeck coefficient but a low thermal conductivity. The addition of the MWCNTs caused the figure of merit (ZT) for the aerogel to increase by two orders of magnitude. The researchers determined that it was possibly to control the electrical conductivity, thermal conductivity, and Seebeck coefficient independently of each other due to the unique structure present in the aerogel.
