الفهرس 
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Abstract
In the present work, turbulent flow and heat transfer for steady and fully developed flow for an incompressible Newtonian fluid inside a rectangular duct was investigated. The effects of changing the duct aspect ratio on the flow and heat transfer characteristics were studied.
Predictions are obtained, using the nonlinear k-ε model for turbulent flows; namely, flow in stationary ducts of rectangular cross section with various aspect ratios. Calculations have been made for fully turbulent steady flows Results include local distributions of velocities, kinetic energy, Reynolds stresses, wall shear stress, and stream functions etc., together with the overall parameters of the flow. Wherever possible, detailed comparison of the results obtained with experimental data and other numerical model results has been performed. In general, the agreements observed were good.
Previous investigations showed that increasing the duct aspect ratio had lead to decrease the effect of secondary flow near the corner (mainly the turbulence driven secondary flow). The present work investigated the effect of secondary flow from a square duct to ducts with aspect ratio up to 100:1,which can be considered as a flat plate.
Experimental investigations for the flow and heat transfer over a flat plate were also performed using open circuit wind tunnel (300-mm 300-mm) with free-stream turbulence intensity is about 0.2 to 0.3% over the opening velocity range of 10 to 30m/s.
Experimental setup included the wind tunnel, the flat plate test section and the traverse mechanism constructed mainly for the present work.
For the flat plate heating surface, a series of experiments was carried out at different flow velocities. A new correlation obtained for the average heat transfer coefficient. Correlations given by previous investigators for the smooth plate were compared with the present results. The comparisons showed good agreement.
The present study for turbulent flow characteristics such as main flow and secondary flows showed a very good agreement when compared with available previously published results.
Numerical results of convective heat transfer inside the rectangular ducts was good agreement especially with small aspect ratio (AR<5:1),while with aspect ratio less than 5:1, less agreement were found. The lack of available data for the last may be the reason. Finally the effect of heat convection over a flat plate that is experimentally tested observed that as increasing the aspect ratio the behavior of flat plate characteristics was prompted.