Oxygen convective flow

For the well-mixed continuous-flow liquid phase shown in Fig. 1, the balance equations for oxygen and substrate must account for the supply of each component both by convective flow and by gas-liquid transfer, as well as by the diffusion rate into the biofilm. 

Along with electronic transport improvements must come attention to substrate transport in such porous structures. As discussed above, introduction of gas-phase diffusion or liquid-phase convection of reactants is a feasible approach to enabling high-current-density operation in electrodes of thicknesses exceeding 100 jxm. Such a solution is application specific, in the sense that neither gas-phase reactants nor convection can be introduced in a subclass of applications, such as devices implanted in human, animal, or plant tissue. In the context of physiologically implanted devices, the choice becomes either milliwatt to watt scale devices implanted in a blood vessel, where velocities of up to 10 cm/s can be present, or microwatt-scale devices implanted in tissue. Ex vivo applications are more flexible, partially because gas-phase oxygen from ambient air will almost always be utilized on the cathode side, but also because pumps can be used to provide convective flow of any substrate. However, power requirements for pump operation must be minimized to prevent substantial lowering of net power output. 

The last two terms in each equation represent the oxygen transported in the capillary by the convective flow of blood. The terms... 

Figure 25-13. Oxygen measuring device with a solid-electrolyte cell in flue gas transported by an aspirator and by a convective flow in consequence of temperature differences (64].

Solubilization of respiratory carbon dioxide in solutions around the plant can mediate convective flows in several plants, including deepwater rice (Raskin and Kende, 1985), Carex (Kon-calova et al., 1988), and young mangrove plants (Curran et al., 1986). Raskin and Kende (1985) provided evidence that convective flow of oxygen in deepwater rice is driven by solubilization of... 

The relative importance of each of the processes described above is difficult to ascertain because all the processes function simultaneously and independently, and various interactive factors regulate each process. Humidity-induced pressurization is usually the most dominant process, regulating convective flows in many wetland plants. Species with cylindrical culms and linear leaves usually have internal pressurization potential (Brix et al., 1992) and may be able to grow in deeper water than species dependent on root oxygenation due to diffusion only (Brix et al., 1992). 

Acting on temperature appears as a more simple, efficient and reactive way to control /evap- Figure 15.7 shows an illustration of the temperature dependence of the convective flows. In this experiment, the substrate temperature was used to control the evaporation rate /evap- Experiments were carried on using 500 nm diameter PS particles suspended in water. The assembly was performed on oxidized PDMS surfaces treated with oxygen plasma. 

Figure 15.7 Influence of the evaporation rate on the convective flow involved in convective assembly. Experiment was performed on an oxygen plasma-treated PDMS surface [500 nm PS particles, 0.2% solid content].

Due to convective flow in the melt, transport in the GaAs melt should be quick enough so that concentration differences in the melt can be neglected. Assuming a planar solid/liquid interface the balance of carbon and oxygen in liquid GaAs can be expressed by the respectively extended well known SCHEIL... 

Equation (9.73) can be used to explain the burning behavior with respect to the roles of flame radiation and convection. It can also explain the effects of oxygen and the addition of external radiant heat flux. These effects are vividly shown by the correlation offered from data of Tew arson and Pion [18] of irradiated horizontal small square sheets of burning PMMA in flows of varying oxygen mole fractions. The set of results for steady burning are described by a linear correlation in q" and Xq2 for L= 1.62 kJ/g in Figure 9.16. This follows from Equation (9.73) ... 

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