Experimental investigation of TiO2/Water nanofluid effects on heat transfer characteristics of a vertical annulus with non-uniform heat flux in non-radiation environment

In this paper, an experimental study carried out to investigate the heat transfer performance of a 10 nm TiO2/Water nanofluid (deionized water) in a vertical annulus with non-uniform heat flux at its inner tube. The experimental apparatus is a vertical annulus which is designed to simulate flow over nuclear fuel rods in non-radiation environment. Electrically produced heat flux has cosine shape. The effects of nanoparticles volume concentration (0.25%, 0.5%, 1% and 1.5%) and different flow rates on wall temperature profile, maximum wall temperature, local and averaged heat transfer coefficient and local and averaged Nusselt number is studied by this experiment. Experiments were conducted in different Reynolds number and low nanoparticles concentrations. It is observed that by increasing Reynolds number or nanoparticles volume fractions, inner wall temperature (cladding temperature) decreases and its profile shape flattens. The heat transfer coefficient for nanofluid is found to be higher than that for pure water and it increases with increasing volume concentrations. Results also indicate that at very low volume concentrations (less than 0.005) nanofluids has no major impact on heat transfer parameters. Effect of pressure and entrance temperature on heat transfer parameters is also considered. It is understood that heat transfer parameters are independent of pressure and entrance temperature in our experiment ranges.