Experimental study on natural convection of MWCNT-water nanofluids in a square enclosure

One of the methods to improve the efficiency of a wide range of energy systems is to enhance the performance of the heat transfer fluids. Nanofluids consisting of multi-walled carbon nanotubes in water base were studied experimentally in a square cavity with differentially heated side walls. The investigation was carried out for particle volume concentrations of 0 to 1% at Ra number 10(8). The thermal conductivities and viscosities for the nanofluids were experimentally determined. However, it was observed that the available correlations from literature did not agree well with the experimental data. The nondimensional Nusselt number characterised the heat transfer performance. Thermal conductivity was measured for the range of volume concentration 0-1% and maximum enhancement of 6% was found to be at 1%. Viscosity was measured and observed to increase by 58% over the 0-1% particle volume concentration range tested. The experimental results on natural convection yielded a maximum enhancement in heat transfer performance of 45% at volume concentration of 0.1%. This research supports the idea that "for nanofluids with effective thermal conductivity greater than the thermal conductivity of the base fluid, there may exist an optimum concentration which maximizes the heat transfer."