Purpose – This paper aims to numerically investigate the heat transfer and entropy generation characteristics
of water-based hybrid nanofluid in natural convection flow inside a concentric horizontal annulus.
Design/methodology/approach – The hybrid nanofluid
is prepared by suspending
tetramethylammonium hydroxide-coated Fe3O4 (magnetite) nanoparticles and gum arabic (GA)-coated
carbon nanotubes (CNTs) in water. The effects of nanoparticle volume concentration and Rayleigh number on
the streamlines, isotherms, average Nusselt number and the thermal, frictional and total entropy generation
rates are investigated comprehensively.
Findings – Results show the advantageous effect of hybrid nanofluid on the average Nusselt number.
Furthermore, the study of entropy generation shows the increment of both frictional and thermal entropy
generation rates by increasing Fe3O4 and CNT concentrations at various Rayleigh numbers. Increasing
Rayleigh number from 103 to 105, at Fe3O4 concentration of 0.9 per cent and CNT concentration of 1.35 per
cent, increases the average Nusselt number, thermal entropy generation rate and frictional entropy generation
rate by 224.95, 224.65 and 155.25 per cent, respectively. Moreover, increasing the Fe3O4 concentration from 0.5
to 0.9 per cent, at Rayleigh number of 105 and CNT concentration of 1.35 per cent, intensifies the average
Nusselt number, thermal entropy generation rate and frictional entropy generation rate by 18.36, 22.78 and
72.7 per cent, respectively.
Originality/value – To the best knowledge of the authors, there are not any archival publications
considering the detailed behaviour of the natural convective heat transfer and entropy generation of hybrid
nanofluid in a concentric annulus.