Thermal plume rise

In many calculation methods, the momentum contributions to plume rise are considered negligible when compared to the thermal plume rise, and hence are ignored. 

The ASME method is one of the few calculation methods to consider emissions having relatively low exiting temperatures and relatively high exiting velocities. Under these conditions of release the momentum effects of the plume dominate over thermal, thus the momentum plume rise should be used in the GLC calculations. 

The use of a natural ventilation system assumes temperature stratification throughout the room height. Air close to heat sources is heated and rises as a thermal plume (Fig. 7.105). Part of this heated air is evacuated through air outlets in the upper zone, and part of it remains in the upper zone, in the so-called heat cushion. The separation level between the upper and lower zones is defined in terms of the equality of and G, which are the airflow rate in thermal plumes above heat sources and the airflow supplied to the occupied zone, respectively. It is assumed that the air temperature in the lower zone is equal to that in the occupied zone, and that the air temperature in the upper zone is equal to that of the evacuated air,... 

These results apply to plume rise in a tall open space of air at a uniform temperature. The results can be important for issues of fire detection and sprinkler response. Plume rise in a thermally stratified stable (dT /dz > 0) atmosphere will not continue indefinitely. Instead, it will slow and eventually stop and form a horizontal layer. It will stop where its momentum becomes zero, roughly when the plume temperature is equal to the local ambient temperature. 

Courtney R. and White R. (1986) Anomalous heat flow and geoid across the Cape Verde Rise evidence for dynamic support from a thermal plume in the mantle. Geophys, J. Roy. Astr. Soc. 87, 815 - 867. 

In this schlieren image of a girl, the rise of lighter, warmer air adjacent to her body indicates that hrnnans and warm-blooded animals are suirounded by thermal plumes of rising waim air. 

The usual thermal-elevation formulae can be used to perform a further evaluation of the height to which the radioactive release will be brought by the flame. The Stumke formula (see Equation 6.7) can be used to indicate a plume rise of more than 1000 m. 

Breakup Phase. It has been observed that plume rise continues after the thermal phase, progressing to a situation in which atmospheric turbulence begins to dominate the mixing. At this point there is a breakup of the plume into distinct parcels, with a nearly stepwise increase in plume diameter. The effect is more pronounced in strong turbulence. 

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... 

The layer is internally heated from its radioactive element content leading to a thermal expansion such that there is almost no density difference between the upper and deep mantle. This gives rise to a boundary between the upper mantle and deep mantle which is highly irregular. In places where dense lithospheric material descends the lower mantle layer is thin, and elsewhere, there are deep mantle upwellings which rise though the upper mantle, to produce "plume related" ocean island basalts (Fig. 3.34). 

We shall deal here with buoyant and forced plumes only. Our interest is in predicting the rise of both buoyant and forced plumes in calm and windy, thermally stratified atmospheres. 

Thermal Phase. In the thermal phase, mixing is due to self-generated turbulence. The plume retains a smooth shape and continues to show a moderate rise. The most dominant effect determining the path of the plume center-line is the total excess heat of the plume. 

If the pool height is 5 m, then the maximum driving pressure is about 15 Pa. This corresponds to a vertical flow velocity of 0.17 m/s. Suggesting that the rising plume has a diameter of 2 m, the mass flow is about 500 kg/s and the thermal flux is about 10.5 MW. 

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