Water movements, convective

The problem of estimating the diffusion layer thickness therefore reduces to that of estimating u and We have considered three possible mechanisms for the movement of phytoplankton through the water gravitational sinking, convective water movements and the swimming of flagellates. 

Gravitational sinking. Phytoplankton cells are generally denser than the surrounding sea water and therefore sink unless kept in suspension by convective water movements (35). ( for... 

American Journal of Science, Vol. 291, pp. 109-176 Haszeldine, R.S., Samson, I.M. and C. Cornford, 1984. Quartz diagenesis and convective fluid movement Beatrice oilfield, UK North Sea. Clay Minerals, 19, pp. 391-402 Hedberg, H.D., 1980. Methane generation and petroleum migration. In Roberts III, W.H. and R.J. Cordell (eds.), 1980. Problems of petroleum migration. The American Association of Petroleum Geologists Studies in Geology, no. 10, pp.179-206 Hem, J.D., 1985. Study and interpretation of the chemical characteristics of natural water. 

Convective gas phase transport in natural unsaturated soil systems may be induced by variations in temperature, air pressure and groundwater, by wind pressure or by seepage water movement after rain events. All these processes are of minor importance in lab column experiments and have not been implemented in DiffModV. The only convective movement in the gaseous phase considered in DiffMod is the ground air recharge due to gas volume decrease caused by oxygen consumption. The effects of this type of convection have to be taken into consideration as they result in an increase of the initial oxygen penetration depth or the thickness of the pyrite oxidation zone and thus induce an increase of the total pyrite decomposition rate on the column by 10 to 15 %. 

The so-called free or natural convection processes will continue to drive water movement and therefore the magnitude of MTCs when external or forced convection influences, such as wind, are absent. Some fundamentals of both the thermal gradient and the concentration gradient driven free convection process are presented in Section 2.5.7. 

A second mechanism of heat transport is illustrated by a pot of water set to boil on a stove - hotter water closest to the flame will rise to mix with cooler water near the top of the pot. Convection involves the bodily movement of the more energetic molecules in a liquid or gas. The third way, that heat energy can be transferred from one body to another, is by radiation this is the way that the sun warms the earth. The radiation flows from the sun to the earth, where some of it is absorbed, heating the surface. 

Both pH and the availability of nutrient ions in soil play important roles in rhizo-sphere dynamics and are often dependent on one another. Nutrient ions move in soil toward plant roots either by mass flow with the soil water or by diffusion. Mass flow is the result of bulk convective movements of the soil solution toward roots, whereas diffusion occurs in response to a concentration gradient for a particular ion, which results from its absorption by the root and depletion from the... 

Any material that provides adequate protection against water should at least limit convective soil gas movement. Properly applied waterproofing materials should help block pressure-driven entry of soil gas. 

In the literature we can now find several papers which establish a widely accepted scenario of the benefits and effects of an ultrasound field in an electrochemical process [13-15]. Most of this work has been focused on low frequency and high power ultrasound fields. Its propagation in a fluid such as water is quite complex, where the acoustic streaming and especially the cavitation are the two most important phenomena. In addition, other effects derived from the cavitation such as microjetting and shock waves have been related with other benefits reported for this coupling. For example, shock waves induced in the liquid cause not only an enhanced convective movement of material but also a possible surface damage. Micro jets of liquid, with speeds of up to 100 ms-1, result from the asymmetric collapse of cavitation bubbles at the solid surface [16] and contribute to the enhancement of the mass transport of material to the solid surface of the electrode. Therefore, depassivation [17], reaction mechanism modification [18], surface activation [19], adsorption phenomena decrease [20] and the mass transport enhancement [21] are effects derived from the presence of an ultrasound field on electrode processes. We have only listed the main phenomena referring to the reader to the specific reviews [22, 23] and reference therein. 

The movement of synthetic pyrethroids in soil and sediment is basically controlled by diffusion, convection, and dispersion. When entering a water-sediment system... 

Convection The transport of heat as a result of the physical movement of a carrier, such as air, water, or magma. Convection occurs spontaneously due to density differences. 

Convection In addition to the double-headed arrow labeled Diffusion, the center oval in Figure 4.3 contains a downward arrow labeled Precipitation and an upward arrow labeled Evapotranspiration. Both these latter terms refer to movement of the water within the soil. They form the major drivers of convection within the soil. In fact Phelan and Webb list three key conclusions concerning transport of the subject molecules within the soil [1, p. 42] ... 

From an engineering perspective, deep-fat frying can be defined as a unit operation where heat and mass transport phenomena occur simultaneously. Convective heat is transferred from the frying media to the surface of the product, which is thereafter conducted within the food. Mass transfer is characterized by the loss of water from the food as water vapor and the movement of oil into the food (Singh, 1995). 

There are two types of convection in an air boundary layer (1) forced convection created by air movement across the water body and (2) free convection created by a difference in density between the air in contact with the water surface and the ambient air. If the water body is warmer than the surrounding air, free convection will occur. The combination of these two processes is illustrated in Figure 8.15. 

This model bears the imprint of its own limitations as a good model should. It is assumed that there is no movement, yet algae are growing in the upper layers of the water and presumably making the medium more dense. This suggest that sedimentation or convective roll-over should be considered. We shall not go into such generalizations here, but merely leave this example with the comment that the same equations turn up in the theory of a continuous reactor in which a belt of material is to be impregnated with a solution, whose solute is immobilized on sites in the belt. 

In this problem, a standard pan is used as shown in Fig. 11-6. The mean wind movement is measured 6 in above the pan rim, and water-evaporation rates are measured with the pan placed on the ground (land pan) or in a body of water (floating pan). For the land pan and with a convectively stable atmosphere, the evaporation rate has been correlated experimentally [13] as... 

Solute movement through soil is a complex process. It depends on convective-dispersive properties as influenced by pore size, shape, continuity, and a number of physicochemical reactions such as sorption-desorption, diffusion, exclusion, stagnant and/or double-layer water, interlayer water, activation energies, kinetics, equilibrium constants, and dissolution-precipitation. Miscible displacement is one of the best approaches for determining the factors in a given soil responsible for the transport behavior of any given solute. 

---