Moving layer

In turbulent flow there is mixing of the moving layers and the fluid resists distortion to a greater degree than in laminar flow, therefore the viscosity is greater. For turbulent flow, Eq. (6.4) becomes ... 

Like a hydroplaning tractor trailer (viewed in very slow motion), the upper fault block glides until it rans into something. When the thrust sheet runs into something that resists its forward motion, the detachment fault turns into a ramp, leading up to the surface. The moving layer of upper crast is pushed up the ramp-like fault, and the front of the fault block rises out of the ground. The mountains thrown up where the thrast fault reaches the surface are one kind of fault block mountains. The... 

Heat Transfer to the Wall A number of investigations of heat-transfer coefficients at the wall in fluidized beds have been reported, and in all cases the values found for h, were considerably larger than those for an empty tube at the same fluid velocity. Presumably this is because the motion of solid particles near the wall tends to prevent the development of a slow-moving layer or film of gas, and the heat-carrying capacity of the particles themselves as they move between the center and the wall of the reactor is significant. 

VISCOSITY AND MOMENTUM FLUX. Although Eq. (3.3) serves to define the viscosity of a fluid, it can also be interpreted in terms of momentum flux. The moving fluid just above plane C in Fig. 3.1 has slightly more momentum in the X direction than the fluid just below this plane. By molecular collisions momentum is transferred from one layer to the other, tending to speed up the slower moving layer and to slow down the faster moving one. Thus, momentum passes across plane C to the fluid in the layer below this layer transfers momentum to the next lower layer, and so on. Hence x-direction momentum is transferred in the y direction all the way to the wall bounding the fluid, where = 0, and is delivered to the wall as wall shear. Shear stress at the wall is denoted by t ,. 

Even under turbulent conditions there remains near the fluid/solid interface a slow moving layer (usually referred to as the viscous sub-layer) resulting from the "drag" between the fluid and the solid surface. 

The resistance that a liquid offers to flow, caused by internal friction between adjacent moving layers, is known as its viscosity. For a pure liquid, Newton defined the coefficient of viscosity as follows. Consider two parallel, adjacent planes in a liquid, of area A, distant x m. apart, moving relative to one another with a velocity v m.sec.-L The frictional force per unit area, F/A, is then given by — F/A = rj dv/dx,... 

Viscous resistance has not the same origin in liquids and in gases. In the latter it depends upon the transfer of momentum from faster to slower moving layers (p. 20), and increases with temperature as the thermal exchange becomes more lively. In liquids it falls. The inverse of the viscosity, the fluidity, increases with temperature according to the law, ... 

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