Surface area, effect velocity, average

Let us designate the average volume flux density of water across area A3 of component j by 7y, which is the average velocity of the water movement (Chapter 2, Section 2.4F). A7 can be the root surface area, the effective cross-sectional area of the xylem, or the area of one side of the leaves. In the steady state, the product J v A7 is essentially constant, because nearly all of the water taken up by the root is lost by transpiration that is, the same volume of water moves across each component along the pathway per unit time. We will represent the drop in water potential across component j by AT7 defining the resistance of component j ( ) as follows ... 

During injection, the effectiveness of the spray against elemental iodine vapor is chiefly determined by the rate at which fresh solution surface area is introduced into the containment building atmosphere. The rate of solution surface created per unit gas volume in the containment atmosphere may be estimated as (6F/VD), where F is the volume flow rate of the spray pump, V is the containment building net free volume, and D is the mass-mean diameter of the spray drops. The first-order removal coefficient by spray, A., may be taken to he = 6 T FfV D, where A g is the gas-phase mass-transfer coefficient, and T is the time of fall of the drops, which may be estimated by the ratio of the average fall height to the terminal velocity of the mass-mean drop (Reference...). 

This is indeed the expression (4.106) for the reaction-rate constant of hard spheres impinging on a surface, is the average velocity of the atoms perpendicular to the surface and nd is the effective surface area of an adsorbed atom (5 = A max ... 

In general the net macroscopic pressure tensor is determined by two different molecular effects One pressure tensor component associated with the pressure and a second one associated with the viscous stresses. For a fluid at rest, the system is in an equilibrium static state containing no velocity or pressure gradients so the average pressure equals the static pressure everywhere in the system. The static pressure is thus always acting normal to any control volume surface area in the fluid independent of its orientation. For a compressible fluid at rest, the static pressure may be identified with the pressure of classical thermodynamics as may be derived from the diagonal elements of the pressure tensor expression (2.189) when the equilibrium distribution function is known. On the assumption that there is local thermodynamic equilibrium even when the fluid is in motion this concept of stress is retained at the macroscopic level. For an incompressible fluid the thermodynamic, or more correctly thermostatic, pressure cannot be deflned except as the limit of pressure in a sequence of compressible fluids. In this case the pressure has to be taken as an independent dynamical variable [2] (Sects. 5.13-5.24). 

By considering the gas impact, the velocity effect on the current density, averaged over the area of the electrode surface, is also examined under different cell voltages as illustrated in Figure 12.16. A higher average current density for a faster electrolyte flow rate is observed as the latter reduces both concentration and ohmic overpotentials. 

---