Stack exit velocity distribution for higher effective stack height

Abstract

The effective height of a smoke stack can be increased by better preserving the temperature and velocity of the flue gases, which in turn, can be achieved by minimizing the entrainment of the cold ambient air into the plume. Based on the entrainment hypothesis, the optimal velocity distribution at the stack exit and the optimal size of the stack exit for minimum ambient entrainment are derived. Laboratory experiments were performed to compare the ability of rising across an inversion by a plume from a conventional stack and by a plume from a stack designed according to the new theory. The qualitative experiments showed that under identical atmospheric conditions, while the plume from the conventional stack would be trapped by the inversion, the plume from the new stack penetrated across the inversion. Based on the theory, devices may be built and installed on the top of industrial chimneys to eject the effluents to a higher altitude. The present study is for a neutral and calm atmosphere only. Parallel studies on two-dimensional plumes are also made.