Parallel-flow trays

Figure 6.19 Linde tray arrangements (a) multiple downspouts (b) parallel-flow tray.

Further, because of the nature of sohds-gas contacting, which is usually by parallel flow and rarely by through circulation, heat transfer and mass transfer are comparatively inefficient. For this reason, use of tray and compartment equipment is restricted primarily to ordinaiy drying and heat-treating operations. Despite these harsh hmitations, when the listed situations do exist, economical alternatives are difficult to develop. 

Figure 17.11. Types of contactors for reacting gases with liquids many of these also are suitable for reacting immiscible liquids. Tanks (a) with a gas entraining impeller (b) with baffled impellers (c) with a draft tube (d) with gas input through a rotating hollow shaft, (e) Venturi mixer for rapid reactions, (f) Self-priming turbine pump as a mixer-reactor, (g) Multispray chamber. Towers (h) parallel flow falling film (i) spray tower with gas as continuous phase (j) parallel flow packed tower (k) counter flow tray tower. (1) A doublepipe heat exchanger used as a tubular reactor.

Cross-flow tray with half stamped out slots. The flap opening acts as a nozzle. The vapor jet forms parallel to the tray and forces the liquid to flow across the tray to the downcomer. To avoid draining of the tray a minimum vapor velocity is required. 

For drying in a compartment or tray dryer where the air passes in parallel flow over the surface of the tray, the air conditions do not remain constant. Heat and material balances similar to those for through circulation must be made to determine the exit-gas temperature and humidity. 

The whole string of trueks is periodically advanced through the tunnel until these are removed at the other end of the tunnel. Air movement, circulation, and heating methods vary in tunnel dryers. Three different arrangements, namely, counterflow, parallel flow, and combined flow, are shown in Figure 21.8. These dryers are simple and versatile in comparison with other types of dryers. Food pieces of any shape and size can be handled. If solid trays are incorporated, fluids can also be dried. 

FIG. 23-25 Typ es of industrial gas/Hqiiid reactors, (a) Tray tower, (h) Packed, counter current, (c) Packed, parallel current, (d) Falling liquid film, (e) Spray tower, if) Bubble tower, (g) Venturi mixer, h) Static in line mixer, ( ) Tubular flow, (j) Stirred tank, (A,) Centrifugal pump, (/) Two-phase flow in horizontal tubes. 

Figure 11.3d shows a process where the manipulated variable affects the two controlled variables and in parallel. An important example is in distilla tion column control where reflux flow aSecte both distillate composition and a tray temperature. The process has a parallel structure and this leads to a parallel cascade control system. 

To provide this finished water quality, a system incorporating flocculation, settling, and mixed-media filtration is used. Fig. 6 schematically illustrates the flow of the system used. After flocculation, the coagulated water is processed through a shallow-depth sedimentation basin using tube settlers. Tube settlers provide efficient sedimentation in greatly reduced detention times. The tube settlers are essentially a honeycomb of 1-in. trays operating in parallel. The... 

Figure 9.6. Tray dryer arrangements, batch and continuous. Performance data are in Table 9.5. (a) Air flow across the surfaces of the trays, (b) Air circulation forced through the beds on the trays (Proctor and Schwartz Inc.), (c) Continuous drying of trays mounted on trucks that move through the tunnel air flow may be in parallel or countercurrent (P.W. Kilpatrick, E. Lowe, and W.B. Van Arsdel, Advances in Food Research, Academic, New York, 1955, Vol. VI, p. 342).

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