Geometric shape of smoke flow

Smoke from the chimney. Named for its feathery appearance. Emissions are usually expressed by emission rate (kg/h or g/s); The distribution of emissions in the downwind direction is generally expressed by the average concentration (mg/m3) during the emission period. By tracing the diffusion experiment or actual observation of smoke plume, it can be seen that the shape of smoke plume is closely related to weather and atmospheric turbulence.

If the atmospheric stability is roughly divided into unstable, neutral and stable, the geometric shape of the plume can be summarized as A, B, C, D and e5 as shown in the figure. On the right side of the figure, the average concentration profile perpendicular to the center of the plume axis at a cross section of the downwind direction of the pollution source is drawn qualitatively, showing the relationship between the geometry of the plume and the concentration distribution in the vertical direction. Under the condition that the atmospheric turbulence intensity is approximately uniform, the concentration distribution curve is symmetrical about the plume and conforms to the normal distribution (see Figures A, B and C). On the contrary, it is non-normal distribution (see Figure D and E).

A. Chain shape: This kind of plume twists and turns into a chain shape, swings violently in the horizontal and vertical directions, and is easy to split and dissipate, and with the increase of the distance from the chimney, the pollutant concentration decreases rapidly. This plume mostly appears in the afternoon when the lower atmosphere is unstable and the turbulence develops strongly, and it is common in sunny summer afternoons.

Cone B: This plume is shaped like a cone with a horizontal axis, and the shape of the plume is very clear. Cone plumes mostly appear on cloudy days, when the wind speed is high, when the lower atmosphere is in neutral equilibrium, or at the transition moment of atmospheric temperature stratification in the morning and evening (from stable to unstable, or from unstable to stable). At this time, the plume in the near-surface gas layer often flows along the dominant wind direction and spreads in a cone shape. The distance from the chimney to the ground of conical plume is longer than that of chain plume.

C. Fan shape: Looking down at this feather, it has a fan shape. Fan-shaped plumes mostly appear in sunny nights or mornings, when the wind in the lower layer is low, the temperature rises from bottom to top, and the atmosphere is in a stable state. In this case, the plume can only slowly spread to both sides in a stable gas layer. The pollutant concentration in the fan plume is very high. When encountering mountains, hills or tall buildings, pollutants will sink and cause ground pollution.

D. Diffuse smoke (smoked smoke): Diffuse smoke plume mostly appears when the radiation inversion is destroyed after sunrise. At this time, there is an inversion layer above the smoke shaft, and the air layer between the smoke shaft and the ground is unstable, so the smoke flow is blocked by the inversion layer when it rises and diffuses to a certain extent, so that the vertical diffusion space is limited from the ground to the bottom of the inversion layer. In this case, if the low-altitude wind is small, the dilution ability of the atmosphere will be lower, and the high-concentration smoke plume will spread to the ground quickly, causing serious pollution on the ground. Most smog accidents happen in this situation.

E. Roof shape (ascending shape): This kind of smoke plume mostly appears in the evening. When the gas layer between the smoke shaft and the ground is stable and the gas layer above the smoke shaft is unstable, the smoke flow flows in the upper unstable gas layer along the dominant wind direction and spreads like a roof. The lower edge of the roof-shaped plume is clear and the smoke is dense; The upper part of the plume is sparse and even discontinuous fragments appear.