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    ABSTRACT: Numerical simulations are performed to study the transition of the development of the thermal boundary layer of air along an isothermal heated plate in a large channel which is bounded by an adiabatic plate. In particular, the aim is to investigate the effects of the channel width (b) on the transition of the flow under various plate temperatures. Three different RANS based turbulent k–ε models namely standard, RNG and Realizable with an enhanced wall function are employed in the simulations. The channel width was varied from 0.04 m to 0.45 m and the numerical results of the maximum values of the flow velocity, turbulent kinetic energy were recorded along the vertical axis to examine the critical distance of the developing flow. The results show that the transition delays when the width is increased from 0.04 m to 0.08 m and particularly, the critical distance at b = 0.08 m reaches its maximum with the Grashof number of 2.8 × 1010. However, the critical distance drops when b is increased further from 0.08 m to 0.45 m, indicating an early transition of the flow. The transition remains unaffected by the adiabatic plate when b is greater than 0.45 m. Comparisons of selected numerical results are made with available experimental data of turbulent flow and a satisfied agreement is received.
    Full-text · Article · Nov 2014 · International Journal of Heat and Mass Transfer
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    ABSTRACT: Numerical simulations are performed to study the transition of the development of thermal boundary layer of air along isothermal heated plates in a large channel. In particular, the aim is to investigate the effects of the channel width on the transition of the flow under various plate temperatures. Realizable k–ε turbulence model with an enhanced wall function is employed to obtain the numerical simulations of flow and thermal fields in the channel. The channel width is varied from 0.04 m to 0.45 m and the numerical results of the maximum values of flow velocity, turbulent kinetic energy are recorded along the flow to examine the critical distance of the developing flow. Effects on the transition of the two different types of wall boundary conditions, isothermal and adiabatic, applied to the channel are also examined. The results particularly indicate that the flow transition in the isothermal cases takes later than that in the adiabatic cases.
    No preview · Article · Sep 2014 · International Journal of Heat and Mass Transfer
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    ABSTRACT: A numerical investigation has been carried out applying single phase approach on turbulent forced convection flow of water based Al2O3 and TiO2 nanofluids flowing through a horizontal circular pipe under uniform heat flux boundary condition applied to the wall. The effect of volume concentrations, Brownian motion and size diameter of nanoparticles on flow and heat transfer have been examined for Reynolds number, Re = 10 × 103 to 100 × 103, Prandtl number, Pr = 7.04 to 20.29, nanoparticle volume concentration, χ = 4% and 6% and nanoparticles size diameter, dp = 10, 20, 30 and 40 nm respectively. Results reveal that the small size of nanoparticles with their Brownian motion has the highest average shear stress ratio, heat transfer rate and thermal performance factor for χ = 6%. Besides, it is found that the heat transfer rate increases as the particle volume concentration and Reynolds number increase with a decrease of nanoparticles size diameter. Moreover, Al2O3 water nanofluid shows a higher heat transfer rate compared to that of TiO2–water nanofluid. Finally, a conclusion has been drawn from the present analysis that the heat transfer performance is more affected by the size diameter and Brownian motion of nanoparticles than the thermal conductivity of nanofluid. Results of the non-dimensional fully developed velocity and turbulent kinetic energy, frictional factor and average Nusselt number for pure fluid (water) as well as the result of average Nusselt number for Al2O3 and TiO2–water nanofluid have been validated with published experimental results as well as with available correlations where a reasonable good agreement has been achieved.
    No preview · Article · Aug 2014 · International Communications in Heat and Mass Transfer
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