A Numerical Investigation on Natural Convection Heat Transfer in Annular-Finned Concentric Horizontal Annulus Using Nanofluids: A Parametric Study

Abstract

Natural convection heat transfer in a concentric horizontal annulus with annular fins is numerically studied. Due to the low thermal conductivity of water, CuO-water and Al₂O₃-water nanofluids were used as heat transfer fluids. The effect of three different parameters, including fin spacing, fin eccentricity, and fin thickness at different fin diameters and Rayleigh number range of 10⁴ to 9 $\times$ 10⁵, were studied. The obtained results revealed that Al₂O₃-water nanofluid has the highest heat transfer rate. The calculated heat transfer rates for Al₂O₃-water nanofluid for Rayleigh numbers of 9 $\times$ 10⁵, 10⁵, and 10⁴ were respectively up to 12.1%, 26.2%, and 31.6% higher than the heat transfer rate obtained for water. The best heat transfer rate occurred at the fin spacing range of 2 to 3 mm at Rayleigh number of 9 $\times$ 10⁵. Moreover, it was observed that by decreasing the Rayleigh number, the maximum heat transfer rate took place at higher fin spacing. It was concluded that fin eccentricity improves the heat transfer rate, especially for low fin spacing. Furthermore, it was demonstrated that fin eccentricity could improve the heat transfer rate by up to 50.2%. Simulation results indicated that fins with low thickness have higher heat transfer rates than those with higher thickness at lower fin spacing. However, fins with high thickness have higher heat transfer rates than those with lower thickness at higher fin spacing.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors would like to express their gratitude to the Sharif University of Technology for their financial support via the quality grant program.

Notes on contributors

Mahyar Ashouri

Mahyar Ashouri received his master's degree in Mechanical Engineering from the Sharif University of Technology, Iran, in 2017, and his BSc degree in Mechanical Engineering from the AmirKabir University, Iran, in 2015. His research interests include heat transfer, fluid mechanics, computational fluid dynamics, thermal energy storage, and heat pumps.

Mohammad Mehdi Zarei

Mohammadmehdi Zarei received his master's degree in Mechanical Engineering from the Sharif University of Technology, Iran, in 2019, and his BSc degree in Mechanical Engineering from the AmirKabir University, Iran, in 2016. His research interests include heat transfer, fluid mechanics, optimization techniques, and computational fluid dynamics.

Ali Hakkaki-Fard

Ali Hakkaki-Fard is an Associate Professor of the School of Mechanical Engineering at the Sharif University of Technology (SUT). He is also the head of the Renewable and Sustainable Energy Systems lab at the SUT. He received his PhD from McGill University, Montreal, Canada, in 2011. He then joined CanmetENERGY as a postdoctoral researcher and then as a research scientist until Dec. 2015. He joined the Sharif University of Technology in Dec. 2015. His research interests include renewable energies, optimization of thermal systems, and inverse heat transfer.