Effect of Temperature and Nanoparticle Concentration on Free Convective Heat Transfer of Nanofluids

Janusz T. Cieśliński, Slawomir Smolen and Dorota Sawicka
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Janusz T. Cieśliński: Faculty of Mechanical Engineering and Ship Technology, Institute of Energy, Gdansk University of Technology, Narutowicza 11/12, 80233 Gdańsk, Poland
Slawomir Smolen: Faculty of Nature and Engineering, J.R. Mayer–Institute for Energy Engineering, City University of Applied Sciences Bremen, Neustadtswall 30, 28199 Bremen, Germany
Dorota Sawicka: Faculty of Nature and Engineering, J.R. Mayer–Institute for Energy Engineering, City University of Applied Sciences Bremen, Neustadtswall 30, 28199 Bremen, Germany

Energies, 2021, vol. 14, issue 12, 1-19

Abstract: A theoretical analysis of the influence of temperature and nanoparticle concentration on free convection heat transfer from a horizontal tube immersed in an unbounded nanofluid was presented. The Nusselt (Nu) number and heat transfer coefficient were parameters of the intensity of the convective heat transfer. For free convection, the Nu number was a function of the Rayleigh (Ra) number and Prandtl (Pr) number. The Rayleigh (Ra) number and Prandtl (Pr) number were functions of the thermophysical properties of nanofluids. The thermophysical properties of nanofluids varied with temperature and nanoparticle concentration. Therefore, an analysis was conducted to evaluate the effects on the performance of nanofluids due to variations of thermal conductivity, viscosity, thermal expansion, density, and specific heat, which are functions of nanoparticle concentration and temperature. Water- and ethylene glycol (EG)-based nanofluids with dispersed alumina (Al 2 O 3 ) nanoparticles at mass concentrations of 0.01%, 0.1%, and 1% were considered. Calculated Nu numbers and heat transfer coefficients were compared with experimental values taken from the published literature.

Keywords: nanofluids; thermophysical properties; free convective heat transfer; horizontal cylinder (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
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