Exact approximations for skin friction coefficient and convective heat transfer coefficient for a class of power law fluids flow over a semi-infinite plate: Results from similarity solutions

This paper investigates the flow and heat transfer of power-law fluids over a stretching sheet where the coupling dynamics influence of viscous sheet and ambient fluid is taken into account via the stress balance. A modified Fourier's law is introduced in which the effects of viscous dissipation are taken into account by assuming that the thermal conductivity is to be shear-dependent on the velocity gradient. The conditions for both velocity and thermal boundary layers admitting similarity solutions are found, and numerical solutions are computed by a Bvp4c program. The results show that the viscous sheet and rheological properties of ambient fluids have significantly influences on both velocity and temperature fields characteristics. The formation of sheet varies with the viscosity of fluid and draw ratio, which then strongly affects the relations of the local skin friction coefficient, the local Nusselt number, and the generalized Reynolds number. Moreover, for specified parameters, the flow and heat transfer behaviors are discussed in detail.

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Hybrid Al2O3-Cu/water nanofluid flow and heat transfer over vertical double forward-facing step

Thermal Science ◽

10.2298/tsci201130080t ◽

2021 ◽

pp. 80-80

Author(s):

Hussein Togun ◽

Raadz Homod ◽

T Tuqaabdulrazzaq

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Heat Transfer Coefficient ◽

Friction Coefficient ◽

Transfer Coefficient ◽

Skin Friction Coefficient ◽

Average Heat Transfer Coefficient ◽

Maximum Heat ◽

Average Heat ◽

Maximum Heat Transfer

Turbulent heat transfer and hybrid Al2O3-Cu/nanofluid over vertical double forward facing-stepis numerically conducted. K-? standard model based on finite volume method in two dimensional are applied to investigate the influences of Reynolds number, step height, volume fractions hybrid Al2O3-Cu/nanofluid on thermal performance. In this paper, different step heights for three cases of vertical double FFS are adopted by five different of volume fractions of hybrid (Al2O3-Cu/water) nanofluid varied for 0.1, 0.33, 0.75, 1, and 2, while the Reynolds number different between 10000 to 40000 with temperature is constant. The main findings revealed that rise in local heat transfer coefficients with raised Reynolds number and maximum heat transfer coefficient was noticed at Re=40000. Also rises in heat transfer coefficient detected with increased volume concentrations of hybrid (Al2O3-Cu/water) nanofluid and the maximum heat transfer coefficient found at hybrid Al2O3-Cu/water nanofluid of 2% in compared with others. It?s also found that rise in surface heat transfer coefficient at 1ststep-case 2 was greater than at 1ststep-case 1 and 3 while was higher at 2ndstep-case 3. Average heat transfer coefficient with Reynolds number for all cases are presented in this paper and found that the maximum average heat transfer coefficient was at case 2 compared with case 1 and 3. Gradually increases in skin friction coefficient remarked at 1stand 2ndsteps of the channel and drop in skin friction coefficient was obtained with increased of Reynolds number. Counter of velocity was presented to show the recirculation regions at first and second steps as clarified the enrichment in heat transfer rate. Furthermore, the counter of turbulence kinetic energy contour was displayed to provide demonstration for achieving thermal performance at second step for all cases.

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