Experimental investigation of TiO 2 /Water nanofluid effects on heat transfer characteristics of a vertical annulus with non-uniform heat flux in non-radiation environment Yasser Abbassi a,⇑ , Mansour Talebi b , Amir Saeed Shirani a , Jamshid Khorsandi b a Department of Engineering, University of Shahid Beheshti, Iran b Nuclear Science & Technology Research Institute, Iran article info Article history: Received 25 May 2013 Received in revised form 3 January 2014 Accepted 10 January 2014 Available online 18 February 2014 Keywords: Experiment TiO 2 /Water nanofluid Vertical annuli Cosine heat flux Non-radiation environment abstract In this paper, an experimental study carried out to investigate the heat transfer performance of a 10 nm TiO 2 /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 nano- particles 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 num- ber and low nanoparticles concentrations. It is observed that by increasing Reynolds number or nanopar- ticles 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 concen- trations (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 trans- fer parameters are independent of pressure and entrance temperature in our experiment ranges. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Ordinary heat transfer fluids such as water, oil and EG are widely used to prevent the overheating or to enhance heat transfer rate of different systems used in microelectronics, industry, trans- portation, electronic, nuclear engineering and etc. But, the poor heat transfer properties of these coolants compared with those of most solids are the primary obstacle of high compactness and the efficiency of the heat transfer systems. Therefore, many researchers have centralized their works on improvement of high performance heat transfer fluids in last decades. In the early re- searches, suspension and dispersion of millimeter or micrometer- sized particles were employed. However, heat transfer fluids containing suspended particles of micro/millimeter sizes had ma- jor disadvantages like erosions of the components by abrasive reactions, clogging in small passages, sedimentation of particles and increased pressure drop. Nanofluid is a new class of fluid for improving both thermal conductivity and suspension stability in the various industrial fields. It is consisting of uniformly dispersed and suspended nanometer-sized particles which were first pio- neered by Choi and Eastman (1996) in 1995. Compared with sus- pensions of micro/millimeter sized particles, the heat transfer rate and stability of nanoparticles suspension is improved. Nanofl- uids have developed as a new class of heat transfer fluids and have grown tremendously in the past few years. Researchers are being challenged to figure out many unanticipated thermophysical fea- tures of these fluids, to propose new models to explain their behav- ior. A plenary summary of the previous studies on the properties of nanofluids is rendered recently by Duangthongsuk and Wongwises (2009). Sajadi and Kazemi (2011) investigated turbulent heat transfer characteristics of TiO 2 /Water nanofluid in a circular pipe for max- imum nanoparticles volume concentration of 0.25%. The results indicated that addition of small amounts of nanoparticles to the base fluid considerably augmented heat transfer, while Nusselt numbers are approximately the same for all nanoparticles volume concentration. Recently Abbasian Arani and Amani (2012, 2013) http://dx.doi.org/10.1016/j.anucene.2014.01.033 0306-4549/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Address: Department of Engineering, University of Shahid Beheshti, Evin, GC, P.O.Box: 1983963113, Tehran, Iran. Tel.: +98 09386714575. E-mail address: yasser.abbassi@gmail.com (Y. Abbassi). Annals of Nuclear Energy 69 (2014) 7–13 Contents lists available at ScienceDirect Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene