Flow nets drawing

Although many groundwater hydrologists customarily employ computerized techniques for analyzing groundwater flow problems, it is valuable for the student of groundwater transport to be able to draw and interpret flow nets. To draw a flow net, the following rules must be observed ... 

Students routinely record experimental data and plot graphs in laboratory notebooks, and in this instance the completed flow net handouts are also glued in. The experimental work and most of the data analysis and flow net sketching are completed within the three hour laboratory class. Students are then asked to draw brief conclusions and to present their notebooks for marking three days later. If resourees permitted, this group of exercises would be very suitable for writing up as a fuller report or technieal note, an activity that would help to develop the student s writing skills. 

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

The first technique is to draw an envelope with the reactor effluent as the inlet stream and the product flows as the outlet streams. Stream.s from other units must be included. The flow rates and compositions of the entering and leaving streams are then totaled. The net is the rciictor effluent. This is the method practiced by most refiners. 

The water which thus traverses the scrubber, and becomes partly saturated with tar, ammoniacsl matter, and naphtha, flows off from the base by a pipe into a tank, net exhibited in tha drawing, but which may be designated by z, Fig. 40. After passing through the first scrubbers,... 

Step 8. Pass each eluting agent through the resin column at flow of 5 mL per minute. Collect sequential 5-ml fractions of each eluent and measure the radio-iodine net count rate in each eluent fraction. Draw curve of net radioiodine count rate vs. eluted volume. Select the eluting solution that removes radio-iodine from the resin column most effectively, i.e., in the smallest volume. 

In an electrochemical reaction (O + ne o R), both forward and backward reactions can occur simultaneously. At equilibrium, no net current flows out of or draws into the system, and the current density of the forward reaction equals the current density of the backward reaction. This current density is called the exchange current density, as described above in Equations 1.34 to 1.37. The exchange current density is a kinetic parameter that depends on the reaction and on the electrode surface upon which the electrochemical reaction occurs. 

Similarly, one may consider the material balance across the side-draw stage too. Since the side-draw product stream is not terminated by a reboiler or a condenser, there is no exact value that the net flow in either CS3 or CS5 is required to be. Thus, just like the CSs across the feed stage, there are multiple flow directions that may exist across the side-draw stage. These are depicted in Figure 7.11a d. 

In a similar way to which feasible flow directions at the side-draw and feed stages were determined, a summary of the net flow directions at the bottommost thermally coupled point is given in Figure 7.12. By simple symmetry, the topmost thermally... 

It is interesting to note that for all FPs other than FP3, the net flows in the CSs above and below the side-draw stage (CS3 and CS5) are in the same direction. This means that both these CSs will have the same sign for the net flow as well as reflux. This does not seem to be a problem on flkce value, but one needs to consider how the refluxes in these CSs come about and what their roles are. It can be shown that... 

Through Equations 7.11 7.14 we now have formal conditions which dictate when changes in the global FP will occur. Notice that each of these equations is a linear function in terms of v and d> and depend only on the reflux in the topmost (reference) CS (Fai), the Distillate, Feed, and Side-draw flowrates (D, F, and S, respectively). Recall, however, that for a fixed feed flowrate, the quantities D and S are dependent on the specified product compositions one wishes to achieve. Interestingly, these net flow boundaries are independent of the feed quality or whether the side-draw is removed as a vapor or liquid product. Thus, for an arbitrary choice of product compositions and Fai> we can represent the transition from one FP to the next in a d>y versus 4> diagram, as shown in Figure 7.14. 

Typical difference point placements for each of the FPs are shown in Figure 7.18a e. These were generated by collectively looking at the four mass balances (around the feed, side-draw product, and both thermally coupled sections at the top and bottom). Each of the dotted lines represents each of these mass balances, adhering to the net flow direction of the CSs as shown in Figure 5.12. It is remarkable to note that the nonsymmetric FPs (FPj, FP2, FP4, FP5) force either X 2 negative composition space, meaning that these FPs may... 

Since the reflux ratios are, by definition, dependent on the net flow of a particular CS, the same arguments put forward in Sections 7.3.2 wiU hold for reflux ratios with regard to net FPs. For instance, choosing a FP that will lead to CS2 having a negative net flow will cause the value of R 2 to also be negative in this CS. However, because is defined as the ratio of liquid flowrate to the net flowrate in a particular CS, the actual value of in a particular CS depends on the quality of the feed, and whether the side-draw product is liquid or vapor. Just as we have conveniently represented net flow patterns in >-space, we can also then construct lines of constant reflux in the >-space, which will ultimately allow us to hone in on feasible designs, as will be illustrated in Section 7.4. In order to do this, it is necessary to write all our reflux equations in terms of v and as shown in the equations below... 

E. (a) Capillary electrophoresis was conducted at pH 9, at which electroosmotic velocity is greater than electrophoretic velocity for a particular anion. Draw a picture of the capillary, showing the anode, cathode, injector, and detector. Show the directions of electroosmotic and electrophoretic flow of a cation and an anion. Show the direction of net flow for each ion. 

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