Deck-filled towers

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. 

In an atmospheric spray tower the air movement - is dependent on atmospheric conditions and the aspirating effect of the spray nozzles. Natural-draft cooling tower operation depends on a chimney or stack to induce air movement. Mechanical-draft cboling towers utilize fans to move ambient air through the tower. Deck-filled towers contain tiers of splash bars or decks to assist in the breakup of water drops to increase the total water surface and subsequently the evaporation rate. Spray-filled towers depend only on spray nozzles for water breakup. Coil shed towers are comprised of a combination structure of a cooling tower installed on top of a substructure that contains atmospheric section coils. Hyperbolic natural-draft cooling towers are typically large-capacity systems. 

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... 

Cooling towers are classified according to the method by which air is introduced to the tower. The principal types are atmospheric spray, natural-draft, mechanical-draft, deck-filled, spray-filled, coil shed and hyperbolic towers. Most industrial cooling tower installations are field-erected units designed for specific thermal characteristics. 

Cooling Tower Technology—Wet Decking Fill Burger, Robert... 

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. 

The tower pressure losses are (1) tower packing or fill (70-80% of loss) (2) air inlet if induced draft (3) mist eliminators at top (4) air direction change losses and entrance to packing on forced draft units. These losses are a function of air velocity, number and spacing of packing decks, liquid rate and the relation between L and Ga. 

Passive fire protection for cooling towers involves increasing spacing distances and using noncombustible materials of construction. For cooling towers of totally noncombustible materials of construction, there are no fire protection requirements. Noncombustible means that the cooling tower s structure, fan and distribution decks, louvers, and fill materials must all be noncombustible materials. 

Some HTU data for cooling tower packing have been published, for example, those summarized on Figure 9.16. Other data appear in the additional literature cited for this chapter. Several kinds of tower fill made of redwood slats are illustrated in Figure 9.17. The numbers N of such decks corresponding to particular NTUs and (L/C)s are given by the equation... 

Figure 9.17. Kinds of fill made of redwood slats for cooling towers, and factors for determining the required number of decks with inlet water at 120°F (Cheremisinoff and Cheremisinoff, 1981).

The following equation can be used to estimate the number of decks of fill required and the height of the packed portion of the tower ... 

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