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    Öğe
    Heat transfer and flow characteristics in a sinusoidally curved converging-diverging channel
    (Elsevier France-Editions Scientifiques Medicales Elsevier, 2020) Kurtulmus, Nazim; Zontul, Harun; Sahin, Besir
    The objective of this work is to present the thermal performance characteristics and to examine the hydrodynamic structure of the fluid which improves the rate of heat transfer in parallel with the penalty of pressure drop by means of the time-averaged streamlines topology, , streamwise velocity distribution, , vorticity concentration, and turbulent Reynolds stress, (u'v') over bar /U-2 for the sinusoidal wavy channel. A wide range of experiments were performed for Reynolds numbers, Re ranging from 4 x 10(3) to 1 x 10(4) in order to determine the heat transfer rate and the friction factor, f with varying the channel height expansion/contraction ratio, M = H-min/H-max such as 0.5, 0.35 and 0.28. The results revealed that a significant heat transfer enhancement was achieved with a considerable penalty of pressure drop. The highest thermal performance factor, TPF was obtained as 1.46 for M = 0.5. Numerical simulations were conducted to confirm the experimental results for the same parameters. The Shear Stress Transport k-w (SST k-w) turbulence model was used to perform numerical analyses. After ensuring the consistency of experimental thermal performance results with numerical predictions, the Particle image velocimetry (PIV) system was utilized for investigating the flow physics in the sinusoidally curved converging-diverging channel for all M values at Re = 4 x 10(3) where the TPF is maximum.
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    Öğe
    Investigation of convective heat transfer and flow hydrodynamics in rectangular grooved channels
    (Pergamon-Elsevier Science Ltd, 2021) Zontul, Harun; Hamzah, Hudhaifah; Kurtulmus, Nazim; Sahin, Besir
    An experimental and numerical investigation is conducted for convective heat transfer and flow characteristics in a channel with rectangular grooved top and bottom walls. The study is performed between 2 x 103and 6.5 x 103 of Reynolds numbers. Heat transfer experiments are conducted by applying constant heat flux to the channel upper and lower walls. The averaged Nusselt number, Nu, is presented as an indicator of heat transfer. In the experiments, 1.9-2.4 times larger Nu values were obtained by using grooved channels instead of straight channels. Pressure measurements show that the corrugated channel causes an increase in pressure loss. The Particle Image Velocimetry, PIV method is employed to reveal the flow hydrodynamics and its relation with convective heat transfer. Using the ability of the PIV method to provide instantaneous flow data, interactions between the recirculation flow bubbles in the grooves and the mainstream are observed. In the numerical part of the study, the k-epsilon turbulence model is used, and predicted results are found to be consistent with experiments. The validated numerical method is used to investigate the effect of groove aspect ratio on heat transfer and pressure drop.