Flow nets stream tube

Assume the flow net shown in Fig. 3-8 was drawn for an aquifer 3 m thick with a hydraulic conductivity of 10 cm/sec and a porosity of 0.24. Calculate specific discharge in square B, discharge in each stream tube, and total aquifer discharge. What is the travel time for a dissolved chemical across square B From point x to point yl... 

According to the rules of flow nets, discharge is equal in each stream tube. Thus, total aquifer discharge is equal to the number of stream tubes multiplied by the discharge in each tube ... 

The flow net is a helpful tool for depicting the area of an aquifer from which a well captures water. It is essential to be able to delineate this area to avoid pulling contaminated groundwater into a well used for drinking water production areas of known contamination must lie outside the well s capture zone. Alternatively, if a well is to be used for groundwater remediation (removal of contaminated groundwater), the capture zone must enclose the contaminated areas. Capture curves, which are the boundaries of capture zones, may be drawn readily by inspection if a flow net is available the capture zone includes all stream tubes that terminate in the well. The following are two examples of capture curves. 

A stream tube, or stream filament, is a tube of small or large cross section and of any convenient cross-sectional shape that is entirely bounded by streamlines. A stream tube can be visualized as an imaginary pipe in the mass of flowing fluid through the walls of which no net flow is occurring. 

The shape of the coohng and warming curves in coiled-tube heat exchangers is affected by the pressure drop in both the tube and shell-sides of the heat exchanger. This is particularly important for two-phase flows of multicomponent systems. For example, an increase in pressure drop on the shellside causes boiling to occur at a higher temperature, while an increase in pressure drop on the tubeside will cause condensation to occur at a lower temperature. The net result is both a decrease in the effective temperature difference between the two streams and a requirement for additional heat transfer area to compensate for these losses. 

Experimental plug flow reactors may be small diameter tubes or packed beds with a larger ratio of diameter to length. The argument in favor of their employment is that they may simulate commercial units more closely. Rate data from pilot plant or commercial units also may need to be analyzed. A short packed bed may be operated with a high recycle ratio and will thus achieve substantially isothermal behavior and may have appreciable change in conversion between the net input and output streams. 

Fig. 7.2. Diagram of the PDS-1000/He, a stationary particle bombardment machine that is connected to a helium gas container. Controlled by adjustable valves, the gas stream (He) terminates in an acceleration tube, which is mounted on the top of a target chamber. This chamber is closed by a door and set under vacuum shortly before bombardment. When gas flows into the acceleration tube, the rupture disc bursts releasing the shock wave into the lower part of the tube. The gas pressure then accelerates the macrocarrier sheet containing the microprojectiles on its lower surface. The net-like stopping screen holds the macrocarrier sheet back and serves to block the shock wave, while the microprojectiles slip through the pores of the grid and continue on towards their final target.

The mole fraction xA1 is the vapor pressure of A divided by the total pressure provided that A and B form an ideal gas mixture and that the solubility of gas B in liquid A is negligible. A stream of gas mixture A-B of concentration xA2 flows slowly past the top of the tube, to maintain the mole fraction of A at xA2. The entire system is kept at constant temperature and pressure. There is a net flow of gas upward from the gas-liquid interface. The transport process is in the i-direction and at steady state with no convective mass transfer, and the reaction source is... 

Because the coefficients Ci and C are to be evaluated for the velocity distribution with zero net flow, (14.181) is as valid an approximation as (14.180). When feed is added to the enriched stream, as in a centrifuge with feed introduced by a tube at the axis, Eq. (14.181) is easier to use than (14.180). 

Under ideal conditions, seldom encountered, gas flowing through a straight tube would exhibit only laminar flow (the absence of all turbulence). In laminar flow, every molecule in the gas stream has only axial velocity and moves only in the direction of the bulk flow. Under conditions of complete turbulence, the gas molecules move in all directions, with no net flow. Flows encountered in practice exhibit some characteristics of both laminarity and turbulence (Fig. 21.3). Factors tending to favor... 

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