Bubble-flow horizontal

A common type of distillation contacting device used in refinery applications is the sieve tray. In the early 50 s and for many years before, the bubble cap tray was the mainstay of the distillation field. A sieve tray consists of a flat plate with regularly spaced holes, normally 1/2 to 1 inch in diameter. Liquid flows horizontally across the tray and into a channel, called a downcomer, which leads to the tray below. The sieve tray exhibits good capacity, excellent efficiency, low pressure drop, and good flexibility i.e., it will operate quite efficiently at tower loadings which are 1/2 to 1/3 of design values. 

Bubbly flow in horizontal pipes. High-velocity flow in horizontal pipes presents a minimum effect of the gravitational field and reduces one potential pa-... 

Wallis points out that, from continuity considerations and bubble dynamics, the cocurrent flow of uniformly dispersed bubbles as a discontinuous phase in a liquid can always be made to occur in any system and for any void volume. (This is not true for countercurrent flow.) Coalescence of bubbles may occur, of course, and if this coalescence is sufiiciently rapid, a developing type of flow is observed, usually from bubble to slug flow. Because of this behavior, the particular flow pattern observed in bubble flow is quite dependent on the previous history of the two-phase mixture. This would be true for both horizontal and vertical flow. 

The above equation was found to be inadequate and hence Wallis suggests the following dimensional empirical form for horizontal bubble flow,... 

Experiments carried out with accelerating horizontal bubble flow, that is, with variable quality, were correlated by similar but separate equations for f-in., -in., and -in. diameter pipe. For the -in. pipe,... 

Vertical separator. Fig. 2 is a schematic of a vertical separator. In this configuration inlet flow enters the vessel through the side. As in the horizontal separator, the inlet diverter does the initial gross separation. Liquid flows down to the liquid collection section of the vessel, then down to the liquid outlet. As liquid reaches equilibrium, gas bubbles flow counter to the direction of liquid flow and eventually migrate to the vapor space. The level controller and liquid dump valve operate in the same manner as in a horizontal separator. 

Fig. 5. Types of two-phase How in a horizontal pipeline (a) Stratified smooth flow where gas velocity is low. Liquid flows along bottom portion of pipelines with essentially a smooth surface, (b) Stratified flow with a wavy. surface, the waviness caused by increased gas flow velocity, (c) Liquid bridges the pipeline cross section, thus causing slugs or plugs of liquid, which move at a velocity approximately that of ihe flowing gas, (d) Annular flow, in which the liquid essentially flows as an annular film on the pipe wall while gas flows as in a centra) core of the pipe, (e) Dispersed bubble flow usually results when liquid flow rates are high and gas rates are low. Because of comparative density differences, most bubbles are found above the pipe center line. Conditions vary somewhat when the pipeline is in a vertical orientation. After Cindric, Gandhi, and Williams)...

Figure 6 shows the various flow patterns in horizontal flow, and similar patterns can be seen in vertical upflow or downflow. In general, bubble flow develops under high liquid-flow rates and low gas-flow rates annular flow develops under... 

For bubble flow and plug flow in horizontal tubes, the following correlation is proposed by Scott and Hayduk (S12) and Shah and Sharma (S16) ... 

Fig. 4.45 Flow patterns in a horizontal, unheated tube a bubble flow b plug flow c stratified flow d wavy flow e slug flow f annular flow g spray or drop flow...

In previous sections, two-phase gas-liquid flow was considered in vertical bubble columns and modified bubble columns. In these reactors, the desired regime of gas-Uquid flow is bubble flow, and therefore the column diameter is at least 150 mm. The superficial gas velocity usually varies from 10 to 500 nun/s and the superficial liquid velocity from 0.01 to 30 nun/s, with a liquid phase residence time from 10 min to a few days. In two-phase gas-liquid flows in horizontal pipes, the superficial gas and liquid velocities are in the range of 0.01 to 10 m/s and 0.1 to 5 m/s, respectively. For two-phase pipe-flow, the pipe diameter is usually up to 200 to 300 mm when used as a reactor. 

FIGURE 17.51 Flow patterns in tube bundles (a) spray flow, (b) bubbly flow (vertical and horizontal), (c) chugging flow (vertical), (d) stratified spray flow, (e) horizontal stratified flow as defined by Grant and reported in Ref. 69. 

Example 5.12 shows that as the velocity increases in horizontal flow, the pressure falls. The pressure decrease can cause the liquid to boil. Dramatic examples of this phenomenon occur in pumps, turbines, and ship s propellers. In these devices, the fluid is often speeded up to a velocity at which it forms a vapor bubble. Then the bubble flows to a region of higher pressure and collapses. The collapse can cause a sudden pressure pulse, and the pulses, occurring at high frequencies, can damage the pump, turbine, etc. The phenomenon of local boiling due to velocity increase is called cavitation, the study of which is an important part of modern research in fluid machines [5,6J. 

We have seen in Section 8.1.3 that multistage distillation is generally carried out in a vertical multiplate column in which each plate has crossflow. Vapor bubbles rise vertically through a liquid layer flowing horizontally in cross-flow over the plate (Section 8.1.3.5) the same two-phase flow scheme is employed in a plate for gas-liquid absorption stripping. We were introduced to the notion of stage efficiency, plate efficiency, tray efficiency, etc., in Section 8.I.3.4. We will introduce here the models used to... 

Conventional bubble-cap, perforated, and valve trays operate as crossflow contactors in which the liquid flows horizontally across the tray and contacts gas flowing vertically... 

In another somewhat similar design, a level of water several inches deep is maintained on each tray, and the bottom of each tray is perforated so that water jets flow downward to the tray below, entraining gas bubbles in the liquid on that tray. As in the previous design, the gas flows horizontally in the space between adjacent trays, then up through an opening at one end of the upper tray and back in the opposite direction in the next tray space. Plates of this type are sometimes referred to as shed or showor trays. 

Wet Oxidation Reactor Design. Several types of reactor designs have been employed for wet oxidation processes. Zimpro, the largest manufacturer of wet oxidation systems, typically uses a tower reactor system. The reactor is a bubble tower where air is introduced at the bottom to achieve plug flow with controlled back-mixing. Residence time is typically under one hour. A horizontal, stirred tank reactor system, known as the Wetox process, was initially developed by Barber-Cohnan, and is also offered by Zimpro. 

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