الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Enhancement of the convective heat transfer coefficient of air is a challenging problem due to the poor thermal characteristics of air as well as the high thermal resistance caused by the boundary layer. There are many ways to enhance thermal convection like using extended surface and porous media. An innovative method to improve the convective heat transfer of cross airflow over a circular cylinder by the application of secondary air jet is introduced in this study.
The proposed method aims to suppress the boundary layer and thus reduce thermal resistance. A two-dimensional numerical model is developed which consists of a hollow circular cylinder made of copper, with a 5 cm outside diameter and 1 cm inside diameter. The cylinder is in the middle of an air channel 2 m long and rectangular cross-section. A heat flux of 6 W/cm2 is applied on the inner surface of the cylinder. A secondary air jet was applied, from a 5 mm circular opening on the upper wall of the air channel, with different angles (theta) of 25° to 155°. The position of the air jet also varied from above the stagnation point to other positions downstream (S). This distance of the applied jet relative to the diameter of the cylinder (S/D) varied from 0 to 1.2. The height of the air channel relative to the diameter of the cylinder (H/D) was changed from 2 to 8. At constant H/D, the total mass flow rate of air is kept constant in both cases, with and without the jet having the same channel height. An experimental study was performed for H/D = 2,4,6, and 8 with three jets of inclination angles θ = 55°, 65°, 90°, 115° and 125° located at S/D = 0, 0.5, and 1.
A comparison between the average Nusselt number in all cases and the case where there is no air jet was carried out. Results show that there is an enhancement of the average heat transfer coefficient of up to six times the case with no jet.