Crossflow tower

Another type of crossflow cooling tower is the wet-dry tower, which consists of a normal crossflow tower over which a few air coils are placed. The hot water is first cooled by an air cooled heat exchanger and then drops to the wet cooling tower where more cooling is obtained by the evaporative mechanism. Figures 5 and 6 provide examples. In contrast, deck-filled towers contain tiers of splash bars or decks to aid in the breakup of water drops to increase the total water surface and, subsequently, the evaporation rate. 

Hot water basins are used to distribute water in crossflow towers. Here, water is pumped to an open pan over the wet deck fill. The bottom of the pan has holes through which water is distributed. Manufacturers will fit specially shaped plastic drip orifices into the holes to give the water an umbrella shape for more uniform distribution. Different size orifices are used for different flow rates. Ideally, the basin will be almost full at maximum flow. This way, sufficient depth is retained for good water distribution as turn down occurs. The turn down ratio can be extended by the addition of hot water basin weirs- a pattern of baffles perhaps 2... 

Basin The area at the bottom of the tower for collecting cold water. Crossflow towers have a hot water distribution basin at the top and, in some cases, a water basin between the top and bottom basins. 

Diffusion (Redistribution) Deck A device below the hot water distribution basin of a crossflow tower to break up the water going through the orifices before it goes through the fill. 

Distribution System Mechanical method of passing hot water over the fill uniformly. Low-pressure spray-through piping and nozzles are usually used in counterflow towers gravity drop is normally utilized in crossflow towers. 

Park, J. E. and Vance, J. M. Chem. Eng. Progr., 67 (1971) 55. Computer model of crossflow towers PlCOOTTl, M. Hydrocarbon Process., 56(6) (1977) 163. Design quench water towers. 

The gravity distribution basin located at the top of a crossflow tower is left open to the atmosphere. Water gravitates through orifices to the tower packing below, thus providing a splash-type pattern. 

The maximum L G ratio corresponds to the case of minimum air rate. For a given temperature this occurs when the tower s operating line (line CA in Figure 6.1) intersects the saturation curve. For this case the driving force is zero and Ntu becomes infinite. The point of zero driving force may occur at the outlet point. Figure 6.2 shows the effect of varying L G for a crossflow tower. 

A low air rate requires a large tower, while a high air rate in a smaller tower requires greater fan power. Limitations in air velocities are typically 300-500 fpm in counterflow towers, and 350-650 fpm in crossflow towers. 

Higher velocities are obtainable in crossflow towers because of larger air inlet and greater eliminator area. Also, the discharging air does not pass through the water distribution system. 

Stop valves are used on both counterflow and crossflow towers to regulate the water flow, particularly between cells on multicell towers, and to shut off the water for maintenance or other purposes. In regions in which freezing temperatures are not encountered, conventional stop valves may be replaced on crossflow towers with flow control valves that... 

Flow control valves are used on crossflow towers to equalize water flow between tower cells and cell basins. Flow control valves, if properly designed, may also be used as stop valves under certain climatic conditions. 

Fig. 1.3 (a) Natural draft, hyperbolic, counterflow tower (b) Natural draft, hyperbolic crossflow tower (c) Induced draft, crossflow tower (d) Induced draft, counterflow tower (e) Forced draft, galvanized, evaporative condenser (f) Induced draft, FRP, bottle tower. 

In crossflow towers, the plenum area occupies the center of the tower, usually in a V shape, from the base of the tower to the fan. In counterflow towers, the plenum area occupies the entire top third plan area of the tower. 

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