Analysis of variance of nanofluid heat transfer data for forced convection in horizontal spirally coiled tubes

In the present study, an experimental study is carried out to investigate the effect of adding Al and Cu nanoparticles to the base fluid (water) on the heat transfer rate in a spirally coiled tube. The spirally coiled tube is fabricated from the straight copper tube with the inner and outer coil diameters of 100 and 420 mm, respectively. The experiments have been done for water and two types of nanofluids with different concentrations and at various operational conditions. The Thermal conductivities of these fluids have been measured experimentally. The results show that thermal conductivity of Cu-water nanofluid is about 18 % more than Al-water nanofluid at 2.23 vol. %. The forced convective heat transfer has been studied by changing the wall temperature, concentration, Gz number, and nanofluid type. The Results indicate that nanofluids have significant positive effect on convective heat transfer coefficient. Also, the Nusselt number increases with an increase in the Gz number. The most important effective parameters on the heat transfer are found to be the Gz number based on the analysis of variance (ANOVA) method. Based on the statistical analysis, a new correlation for the Nusselt number is introduced.