The Effect of Baffles on the Temperature Distribution and Heat-Transfer Coefficients of Finned Cylinders

An investigation was made to determine the effect of baffles on the temperature distribution and the heat-transfer coefficient of finned cylinders. The tests were conducted in a 30-inch wind tunnel on electrically heated cylinders with fins of 0.25- and 0.31-inch pitch.

Four types of baffles, were tested: Plates mounted at various positions around the cylinder and at various angles with respect to the air stream; streamline baffles mounted near the rear of the cylinder; shell baffles with variously shaped openings mounted around the test cylinder symmetrically with respect to a plane through the axis of the cylinder and parallel to the air stream and integral baffles composed of strips welded to the tips of the fins of the test cylinder to form passages between the fins through which the air could flow to the rear of the cylinder.

The results of these tests showed that the use of integral baffles gave a reduction of 31.9 percent in the rear-wall temperature and an increase of 54.2 percent in the heat-transfer
coefficient a compared with a cylinder without baffles.

Although the effect of the shell baffles were not equal to those of the integral baffles, they gave a large reduction in rear-wall temperatures and a large increase in the heat-transfer coefficient. The best results were obtained with the shell baffles mounted in contact with the fins, when the intake opening was equal to the arc subtended by an angle of approximately 145°, when the extensions were S inches or more in length, and when the ratio of exit area to area between fins was approximately 1.6. The heat-transfer coefficient with the best shell baffles varied as the air speed to the 0.85 power.