Split flow

B) U-tiihe exchanger with honnet-type stationary head, split-flow shed, 483-mm (19-in) inside diameter with tubes 21-m (7-ft) straight length. SIZE 19-84 TYPE GBU. 

For split flow (Fig. 11-35G), the longitudinal baffle may be solid or perforated. The latter feature is used with condensing vapors. 

A double-split-flow design is shown in Fig. 11-35H. The longitudinal baffles may be solid or perforated. 

Nonisotnermal Operation Some degree of temperature control of a reaction may be necessary. Figures 23-1 and 23-2 show some of the ways that may be applicable to homogeneous liquids. More complex modes of temperature control employ internal surfaces, recycles, split flows, cold shots, and so on. Each of these, of course, requires an individual design effort. 

G is a split flow. The fluid comes in and goes both way.s around the longitudinal baffle and then exits. H is very rare a double split flow. J is a divided flow. K is a kettle type reboiler, which is a special type and is best explained by looking at the example AKT in Figure 3-9. Kettle types are common where there is a boiling liquid or where gas is liberated from shell fluid as it is heated. The weir controls the liquid, making sure the tubes are always immersed in liquid. Gas that flashes from the liquid can exit the top nozzle. 

Split flow Liquid flow across the tray is split into two or more flow paths. 

Double pass A split-flow tray with two liquid flowpaths on each tray. Each path handles half of the total liquid flow. 

Figure 10-34J. MTD correction factor, split flow shell, 2 tube passes.

These units normally do not have a disengaging space but allow the vapor-liquid mixture to enter the distillation unit or other similar item of equipment. Feed is from the bottom with a split flow on the shell side by means of a shell-side baffle in the center being open at each end. 

Unfortunately, the preset split flow ratio is only an approximate indication of the sample split ratio. The latter depends in a complex way on many parameters, including the range of sample volatilities, sample solvent, volume of sample injected. 

The divided flow and split-flow arrangements (G and J shells) are used to reduce the shell-side pressure drop where pressure drop, rather than heat transfer, is the controlling factor in the design. 

Figure 12.12. Shell types (pass arrangements), (a) One-pass shell (E shell) (b) Split flow (G shell) (c) Divided flow (J shell) (d) Two-pass shell with longitudinal baffle (F shell) (e) Double split flow (H shell)...

Thus, the column diameters chosen for the two dimensions are determined by the amount of sample available and will dictate the flow rate ranges available to use. In split-flow systems, where only a portion of the first-dimension effluent is injected into the second dimension, the choice of column size is unlimited and the two methods can be developed independently. In comprehensive systems where the entire sample from the first dimension is injected into the second dimension, the flow rates are generally lower in the first dimension to accommodate the lower injection volumes into the second dimension. For example, for a 1-mm ID column in the first dimension with a flow rate of 50 (tL/min and a sampling rate of 1 min, 50 pL could be injected onto the second dimension. A 50-(lL injection onto a4.6-mm ID column flowing at 1 mL/min should be accommodated fairly well based upon its composition. In Chapter 6, the first dimension column diameters are estimated based upon the injection volume and sampling rate into the second dimension. 

FIGURE 14.18 Flow diagram of split flow capillary LC system. 1. Solvent reservoirs. 2. Model 5000 syringe pump (Varian, Walnut Creek, California). 3. Static mixer. 4. Injection port. 5. Column. 6. Detector. 7. Pressure transducer. 8. Pulse dampener. 9. Purge valve. 10. U-flow controlling device. 11. Waste. 

Many commercial split flow capillary LC systems incorporate a nano flow sensor mounted online to the capillary channel. The split flow system can be easily modified from a conventional system and performs satisfactorily for capillary LC applications. However, the split flow system may require thermal control and the LC solvent requires continuous degassing. In addition, the system may not work reliably at a high flow split ratios and at pressures above 6000 psi due to technical limitations of the fused silica thermal conductivity flow sensor. The split flow system based on conventional check valve design may not be compatible with splitless nano LC applications. The conventional ball-and-seat check valve is not capable of delivering nano flow rates and is not reliable for 7/24 operation at low flow. 

Two modes of operation are to be studied (a) All of the feed goes to the inlet, (b) Half of the feed goes to the inlet and the other half to the middle of the reactor. The reactor is of sufficient size to give 50% conversion when all of the material is charged at the inlet. What conversion is obtained by the split flow arrangement x = fraction of A that is converted nt = nl+na+nb+nd = 1 5naO+na = na0(2.5-x)... 

Equations (2) and (1) together with the appropriate temperature equation, (3) or (4) or (5), are solved by POLYMATH. The full flow and the split flow operations give the same conversion in the same size reactors. At half flowrate, the values are x2 = 0.5 and T2 = 1521 at the midpoint, the same as the final values of the full stream. 

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