Plume rise from a chimney with an elongated exit cross section

The effect of using a nozzle with an elongated exit cross section as a passive device for increasing jet penetration into cross flow was studied experimentally in a wind tunnel. It was found that the smoke plume dispersion and jet penetration are governed not only by the ratio of flow velocities in the pipe and in the cross flour, but also by the shape of the exit cross section and its orientation with respect to the cross flow. An elongated exit cross section may be particularly effective whenever only a narrow wedge of wind directions leads to air pollution of populated areas. It was found that when such a nozzle is oriented along the wind direction, the chimney effective height is increased as compared to a circular exit cross section, in spite of the fact that the velocity ratio in our experiments was higher for the circular exit. Possible physical reasons for the advantage of the elongated over the circular section shape at the exit are discussed.