Abstract:

In the present study, convective heat transfer coefficient and pressure drop of Al2O3/water nanofluid in laminar flow regime under constant inlet temperature conditions inside a circular finned-tube with a typical twisted tape was experimentally investigated. For this purpose, Al2O3 nanoparticles of 20 nm size were synthesized, characterized and dispersed in distilled water to formulate Al2O3/water nanofluid containing 3 and 5% volume concentration of nanoparticles. The thermophysical properties like thermal conductivity and viscosity of Al2O3 nanofluid is determined through experiments at different volume concentrations and validated. Experiments are conducted in the Reynolds number range of (678–2033) with tape of twist ratio (H/D = 1.85). The effect of different volume concentrations on convective heat transfer coefficient and friction factor was studied. The results emphasize that increasing of particle volume concentration leads to enhance convective heat transfer coefficient. Measurements show the average heat transfer coefficient enhanced about 21-51 % with 5% volume concentration and increased about 19-38 % with 3% volume concentration compared to distilled water. In addition, the average ratio of (fnf/fbf) was about 2.3 for 5% volume concentration. Therefore, there is a significant increase in friction factor for nanofluids. A generalized regression equation is developed for the estimation of Nusselt number and friction factor valid for nanofluid. 

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