Experimental study of natural heat transfer from finned heat exchanger fixed in variable shape of duct

The work was an experimental study of natural heat transfer from heated cylinders fixed in variable shape air duct, made from Pyrex glass. Two finned cylinders made from mild iron, outer diameter (12) mm, inner diameter (10) mm, rectangle fins dimensions (70*40) mm. The angle of two walls from the duct was changed to five angles α:(0°,3°,5°,10°,15°) with vertical to make converge shape. The cylinders were fixed inside the duct at top, centre and bottom. The cylinders were heated by supply variable power of constant heat flux (88,177,390 and 680) W/m2. The study was done with Rayleigh numbers (15x103 to 14x104). The heat was carried by free convection by atmosphere air. The results of experimental found for top location, the value of Nusselt number increased by 7.8% at ԛ•= 88 W/ m2 when increase the value of angle from 0° to 5°, and increased by 20% at ԛ•= 680 W/ m2 when increased the value of angle from 0° to 15°.For centre location, the value of Nusselt number increased by 25 % at ԛ•= 88 W/ m2 when increase the value of angle from 0° to 3°, and increase by 21 % at ԛ•= 680 W/ m2 when increase the value of angle from 0° to 10°.For bottom location, the value of Nusselt number increased by 35 % at ԛ•= 88 W/ m2 when increase the value of angle from 0° to 3°,and increased by 30 % at ԛ•= 680 W/ m2 when increasing the value of angle from 0° to 10°.The best location for the heat exchanger was at the bottom, and the best angle was 15°.