Baffles longitudinal

The longitudinal baffle (9J perforins the same function as the cake baffle disc but in form Is a rectangular plate fitted, by welding, between two adjacent 

While this device is simple and easy to fit. it can be difficult to u.se. Reing longitudinally fitted, it can cause unwanted paddling of the bowl contents, which interferes with the hydraulic equilibrium In I he bowl. For easy applications mechanical simplicity outweighs practical difliculties. 

A form of this baffle has been used which is hinged. The idea behind this is to have fiLilomalic adjustment of gap height to cope with varying solids loads. This format may have problems with sealing of the sides, and very negative ponds, as it could allow washout. 

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A solid longitudinal baffle is provided to form a two-pass shell (Fig. 11-35F). It may be insulated to improve thermal efficiency. (See further discussion on baffles). A two-pass shell can improve thermal effectiveness at a cost lower than for two shells in series. 

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. 

In spht-flow shells the longitudinal baffle may be installed without a positive seal at the edges if design conditions are not seriously affected by a hmited amount of bypassing. 

Longitudinal baffles force the shell-side fluid to make more than one pass through an e.xchangci. With no longilurlinal baffle, such as in Figure... 

L the shell-side fluid makes one pass from inlet to outlet. With a longitudinal baffle, and with the nozzles placed 180° around the shell, the shell-side fluid would be forced to enter at the left, flow to the right to get around the baffle, and flow to the left to reach the exit nozzle. This would be required to approximate true counter-current flow, which was assumed in the heat transfer equations of Chapter 2. 

Shell Flange—Rear Head End 30. Longitudinal Baffle... 

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. 

Longitudinal baffles must also be compatible with the shell-side fluid, so they normally will be of the same material as tubes or baffles. This baffle never extends the full inside length of the shell, because fluid must flow by its fer end for the return pass in reaching the exchanger oudet. 

Figure 10-22D. Longitudinal baffle, sliding slot detail.

The length of the tubes should not be selected more than 4.5-5.5 times the shell diameter. This performance may be increased by placing two inlets in the bottom and two vapor outlets in the top, and at the same time adding shell-side longitudinal baffling to split the flow into four paths upon entrance. The paths recombine before leaving. 

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)...

The critical feature of this exchanger is the longitudinal baffle, which extends down the length of the shell. The baffle is fitted directly to, and thus becomes physically part of, the tube bundle. The function of the baffle is to force the shell-side fluid to flow down the entire length of the... 

The reason illustrates the true nature of the shell-and-tube heat exchanger. It is a compromise between an ideal heat-transfer configuration and practical mechanical limitations. In this case, the difficulty is preventing leakage around the longitudinal baffle. Such leaks permit the shell-side fluid to short-circuit the tube bundle that is, a percentage of the inlet flow, may flow directly to the outlet nozzle. In extremely serious cases, I have seen the bell head (shown in Fig. 19.8) 100°F colder than the shell-side outlet temperature. 

Figure 19.9 Detail illustrating how a modem longitudinal baffle seals up against the inside of the exchanger shell.

Two shell passes are obtained with a longitudinal baffle, type F in Figures 8.11(a) or 8.3(c). More than two shell passes normally are not provided in a single shell, but a 4-8 arrangement is thermally equivalent to two 2-4 shells in series, and higher combinations are obtained with more shells in series. 

A common basis for the design of settlers is an assumed droplet size of 150 ftm, which is the basis of the standard API design method for oil-water separators. Stokes law is applied to find the settling time. In open vessels, residence times of 30-60 min or superficial velocities of 0.5-1.5ft/min commonly are provided. Longitudinal baffles can cut the residence time to 5-10 min. Coalescence with packing or wire mesh or electrically cut these... 

Divided shell, with longitudinal baffle, in/out opposite side in middle... 

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