Buoyant Plumes

In addition to short-term emission estimates, normally for hourly periods, the meteorological data include hourly wind direction, wind speed, and Pasquill stability class. Although of secondary importance, the hourly data also include temperature (only important if buoyant plume rise needs to be calculated from any sources) and mixing height. 

Buoyancy-induced dispersion, which is caused near the source due to the rapid expansion of the plume during the rapid rise of the thermally buoyant plume after its release from the point of discharge, should also be included for buoyant releases (15). The effective vertical dispersion cr is found from... 

Since in the initial growth phases of a buoyant plume the plume is nearly symmetrical about its centerline, the buoyancy-induced dispersion in the crosswind (horizontal) direction is assumed to be equal to that in the vertical. Thus, the effective horizontal dispersion is found from... 

Vertical temperature gradient The lapse rate (rate of decrease in temperature with increases in height) must be taken into account because it affects the final height to which a buoyant plume rises. 

A particularly difficult aspect of the problem of diffusion of atmospheric pollution is the determination of the height to which a buoyant plume with an initial exit velocity will rise. Plume rise, which is defined as the distance between the top of the stack and the axis of the centroid of the pollutant distribution, has been found to depend on ... 

Concawe Ah = 5.53Qh /U Regression formula best suited for large buoyant plumes... 

These effective stack parameters are somewhat arbitrary, but the resulting buoyancy flux estimate is expected to give reasonable final plume rise estimates for flares. However, since building downwash estimates depend on transitional momentum plume rise and transitional buoyant plume rise calculations, the selection of effective stack parameters could influence the estimates. Therefore, building downwash estimates should be used with extra caution for flare releases. 

BUOYANT PLUME RISES INTO ZONE WHERE RETURN LAND BREEZE DOMINATES wno PATTERN THIS BEHAVIOR WILL BE DtURNALLY VARYIND AND VERY DIFFICULT TO PREDICT. 

Basically a regression equation. Suited more to large buoyant plume ai icatioos. 

It does not calculate source emission rates. While it handles jets, it does so simply and docs not calculate the details of the jet motions and thermodynamics. It should not be used for strongly buoyant plumes. The error diagnostics are limited to checking the consistency of input parameters. Run time error diagnostics are missing but are rarely needed due to its robustness. 

Airborne contaminant movement in the building depends upon the type of heat and contaminant sources, which can be classified as (1) buoyant (e.g., heat) sources, (2) nonbuoyant (diffusion) sources, and (d) dynamic sources.- With the first type of sources, contaminants move in the space primarily due to the heat energy as buoyant plumes over the heated surfaces. The second type of sources is characterized by cimtaminant diffusion in the room in all directions due to the concentration gradient in all directions (e.g., in the case of emission from painted surfaces). The emission rare in this case is significantly affected by the intensity of the ambient air turbulence and air velocity, dhe third type of sources is characterized by contaminant movement in the space with an air jet (e.g., linear jet over the tank with a push-pull ventilation), or particle flow (e.g., from a grinding wheel). In some cases, the above factors influencing contaminant distribution in the room are combined. 

FIGURE 7.80 CDF-predicted values of maximum velocity V, temperature differential, ( C), and airflow, q (Us), in the horizontal cross-section of the buoyant plume above the heated cube (0.66 m x 0.66 m X 0.66 m, 22SW).i ... 

FIGURE 10.84 Practical application to control highly buoyant plume. Supply airflow rate is 2.34 m s exhaust flow rate is 12.48 s". ... 

The model is a straightforward extension of a pool-fire model developed by Steward (1964), and is, of course, a drastic simplification of reality. Figure 5.4 illustrates the model, consisting of a two-dimensional, turbulent-flame front propagating at a given, constant velocity S into a stagnant mixture of depth d. The flame base of width W is dependent on the combustion process in the buoyant plume above the flame base. This fire plume is fed by an unbumt mixture that flows in with velocity Mq. The model assumes that the combustion process is fully convection-controlled, and therefore, fully determined by entrainment of air into the buoyant fire plume. 

Kung, H.C. and Stavrianidis, R, Buoyant plumes of large - combustion scale pool fires, Proc. Comb. Inst., 1982, 19, pp. 905-12. 

The mechanism of turbulent mixing which brings air into the buoyant plume is called entrainment. It has been described empirically by relating the momentum of the induced air proportionally to the vertical momentum (mean or centerline),... 

We will derive the governing equations for a buoyant plume with heat added just at its source, approximated here as a point. For a two-dimensional planar plume, this is a line. Either could ideally represent a cigarette tip, electrical resistor, a small fire or the plume far from a big fire where the details of the source are no longer important. We list the following assumptions ... 

Hasemi, Y. and Tokunaga, T., Flame geometry effects on the buoyant plumes from turbulent diffusion flames, Combust. Sci. Technol., 1984, 40, 1-17. 

The fate of dissolved Fe from MOR vents has been investigated at the Rainbow plume from the mid-Atlantic Ridge. Plume particles were sampled from the buoyant part of the Rainbow plume, proximal to the vent, as well as particles from neutrally buoyant portions of the plume that were more distal from the vent (Severmann et al. 2003). Particles from the buoyant part of the plume have positive 5 Fe values (up to +1.2%o), whereas in the neutrally buoyant sections of the plume, the particles have a near-constant 8 Fe value of -0.2%o that matches the Fe isotope composition of the vent fluid. The high 5 Fe values of plume particles that were proximal to the vent probably reflect oxidation processes. In the neutrally-buoyant plume, all aqueous Fe(ll) had been oxidized and it appears that there was no net loss in Fe because the neutrally buoyant plume particles have the same isotopic composition as the vent fluid. Moreover, metalliferous sediments sampled below the plume match the isotopic composition of the plume particles. The implication of these data is that for at least one plume, the Fe isotope composition of the vent fluid matches that of the plume particles. The Rainbow vent fluid, however, has an unusually high Fe to S ratio and hence it is uncertain if these results can be extrapolated to other plumes that originated fi om vent fluids that had lower Fe to S ratios. 

Several laboratory studies have contributed to our understanding of turbulent chemical plumes and the effects of various flow configurations. Fackrell and Robins [25] released an isokinetic neutrally buoyant plume in a wind tunnel at elevated and bed-level locations. Bara et al. [26], Yee et al. [27], Crimaldi and Koseff [28], and Crimaldi et al. [29] studied plumes released in water channels from bed-level and elevated positions. Airborne plumes in atmospheric boundary layers also have been studied in the field by Murlis and Jones [30], Jones [31], Murlis [32], Hanna and Insley [33], Mylne [34, 35], and Yee et al. [36, 37], In addition, aqueous plumes in coastal environments have been studied by Stacey et al. [38] and Fong and Stacey [39], The combined information of these and other studies reveals that the plume structure is influenced by several factors including the bulk velocity, fluid environment, release conditions, bed conditions, flow meander, and surface waves. 

The rate of heat release of a fire is the driving force for a buoyant plume. When the plume hits the ceiling, it turns into a ceiling jet whose characteristics determine when heat detectors respond4 or when sprinklers are activated.5... 

Baum, H.R. and Rehm, R.G. Calculations of three dimensional buoyant plumes in enclosures. Combustion Science and Technology, 1984. 40, 55-77. 

An obvious physical effect of oceanic mantle plume volcanism is to raise sea level by lava extrusion onto the ocean floor through the buoyant plume head uplifting the oceanic lithosphere and... 

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