Stratification, thermal

Fig. 5. Typical thermal stratification of a lake, reservoir, or poorly mixed estuary in summer which, because of density differences, estabUshes discrete 2ones...

Pasquill (11) advocated the use of fluctuation measurements for dispersion estimates but provided a scheme "for use in the likely absence of special measurements of wind structure, there was clearly a need for broad estimates" of dispersion "in terms of routine meteorological data" (p. 367). The first element is a scheme which includes the important effects of thermal stratification to yield broad categories of stability. The necessary parameters for the scheme consist of wind speed, insolation, and cloudiness, which are basically obtainable from routine observations (Table 19-3). 

Example 7.5.5 Point Source In a Room with Thermal Stratification... 

FIGURE 7.78 The cylinder of Example 7.5.4 in a room with thermal stratification. 

If the room has a certain amount ol heat surplus, this will lead to thermal stratification. Ihe thermal stratification will attenuate the rotation, and eventually lead to a flow pattern as showm in Fig. 8.22,... 

The dimensioning of displacement ventilation is shown in the example in Section 7.5.4. That given above is an example of displacement ventilation with weak thermal stratification. Even though the stratification is weak, the contamination in the lower, cleaner zone is normally on the order ol onc-rhird of the contamination in the upper zone. 

Figure 8.30 shows an example of displacement ventilation in a silicon carbide furnace room. Ihe thermal stratification is very strong, as indicated in the graph on the right-hand side of the figure. 

FIGURE S.47 Thermal stratification should be taken into account when locating the exhaust openings. 

If a significant thermal stratification is expected inside the booth, the pressure difference between the inside and the outside ot the booth, which increases with height has to be taken into account during the design prtKcss. Appropriate design features include efficient capture devices in the ceiling o( the booth and an overall dense structure of the booth. 

Additional calculations are necessary if significant heat loads inside the booth cause thermal stratification. A capture system in the ceiling would be advantageous in this case. A check of the pressure in the booth is necessary to avoid spilling of contaminated air near the top of face opening due to the thermal pressure. The height-dependent inflow or spilling velocity due to pressure differences can be calculated as... 

The major reasons for the beluu ior of vertical temperature in water bodies are the low thermal condnctii ity and the absorption of heat in the first few meters. As tlie surface waters begin to heat, transfer to low er layers is reduced and a stability condition develops. The prediction of thermal behavior in lakes and reser oirs is an important power plant siting consideration and also is a major factor in preienting e.xcessive thermal effects on sensitive ecosystems. Furthermore, the extent of thermal stratification influences the vertical dissolved ox)gen (DO) profiles where reduced DO often results from minimal exchiuige with aerated water. ... 

Fig. 14-5 Typical distribution of P and temperature in a temperate lake in summer. Thermal stratification restricts exchange between surface and deep wafers. Phosphorus is depleted in the surface waters by the sinking of biologically produced particles.

As cooling occurs in the late fall and early winter, the thermal stratification breaks down, permitting mixing of the deep and surface layers. This allows the surface layers to be replenished with P. During the winter months, biological productivity in a temperate lake is limited by the availability of light rather than nutrients. 

Also, the alterations can be classified depending on their intensity. The more intense or frequent the intensity, the easier to predict the consequences. When the alterations are slighter or less frequent, it may occur that the natural factors are more important than the alteration itself [3]. The effect produced by the reservoirs depends on different factors, like the size of the reservoir, the residence time, the stability of the thermal stratification and the withdrawal depth. Moreover, there is a certain interannual variability in the magnitude as well as in the timing of the alterations [4]. Among these factors, the most important one is the depth at which water is released. 

Like many other reservoirs in the temperate regions, Mequinensa is monomictic. The thermal stratification begins in spring, intensifies and attains its maximum in summer. In the autumn the water column mixes and water temperature is uniform in the vertical dimension in winter. The summer stratification is more intense close to the dam [39]. In this area, during the stratification period the surface temperatures can attain 24-27°C, while at the bottom remain around 14—16°C [36-39]. 

Thermal stratification in reservoirs ( lake-type versus river-type )... 

Ghosh, A., Weidenschilling, S. J., McSween, H. Y. and Rubin, A. (2006) Asteroid heating and thermal stratification of the asteroid belt. In Meteorites and the Early Solar System II, eds. Lauretta, D. S. and McSween, H. Y., Jr. Tucson University of Arizona Press, pp. 555-566. 

Orig. CO2 Amount of total carbon dioxide which was not affected by the activity of organisms after the thermal stratification had been established and thus existed originally. In this paper, the amount was assumed to be the average value of the total carbon dioxide in surface water layers which are almost saturated with air. 

Figure 8. Downward areal flux (sediment-trap-measured) of phosphorus at 29 m during the period of thermal stratification.

A net loss of approximately 230 mg of P/m2 occurred in the water column (nepheloid zone excluded) from the onset of thermal stratification to late October. Measured trap fluxes of 122 mg of P/m2 over this period were almost identical with the measured water-column loss of particulate P (Figure 1). Loadings and fluxes are balanced by regeneration of filtrable P in the nepheloid region. 

Particle-bound Hg concentrations of sediment trap material exhibited strong seasonal response and accounted for the differences between the Hg flux and mass and carbon fluxes late in the summer. Particle-bound HgT content in spring and early summer was below 200 ng/g, but during late summer stratification it reached levels between 200 and 400 ng/g. Levels were highest following breakdown of thermal stratification and remained high throughout the fall (>350 ng/g). The elevated HgT levels after overturn most likely represented a shift from dissolved to particle-bound Hg. 

The surface area of Lake Greifen is 8.5 X 10 m2, and the volume is 150 X 106 m3 its average depth is 17.7 m, with a maximum of 32.2 m. The residence time of water is 1.1 years. Thermal stratification lasts about from May to December, and lake overturn usually takes place in December-January. An anoxic hypolimnion develops during summer stagnation from about June to December. 

Figure 4. The longitudinal vortex. A longitudinal vortex showing laminar flow about the central axis. The coldest water filaments are always closest to the central axis of flow. Thermal stratification occurs even with minimal differences in water temperature. The central core water is subjected to the least turbulence and acclerates ahead, drawing the rest of the water body in its wake.

Korty RL, Schneider T (2007) A climatology of the tropospheric thermal stratification using saturation potential vorticity. J Climate (in press)... 

Schneider T (2007) The thermal stratification of the extratropical troposphere. In The Global Circulation of the Atmosphere. Schneider T, Sobel AH (eds) Princeton University Press, Princeton, NJ 47-77 Spicer RA, Harris NBW, Widdowson M, Herman AB, Guo S, Valdes PJ, Wolfe JA, Kelley SP (2003) Constant elevation of southern Tibet over the past 15 million years. Nature 421 622-624 Spicer RA, Herman A, Kennedy EM (2005) The sensitivity of CLAMP to taphonomic loss of foliar physiognomic characters. Palaios 20 429-438... 

Twiss, M. R., J. C. Auclair, and M. N. Charlton. 2000. An investigation into iron-stimulated phytoplankton productivity in epipelagic Lake Erie during thermal stratification using trace metal clean techniques. Canadian Journal of Fisheries and Aquatic Sciences 57 86-95. 

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