FIGURES 1 Cooling tower operation

In normal operations, continuously recirculating water picks up waste heat from a refrigeration compressor or process heat exchanger, and the hot water is pumped to the top of the tower and dropped over the cooling tower. Evaporative action removes the heat from the water and adds it to the air. The hot, moist air is ejected from the fan stack, and the cooled water returns to the compressor or exchanger to pick up more heat. Figure 1.1 illustrates the cooling tower operation. 

The cooling tower operation is illustrated in Figure 5.5. Absolute humidities for incoming and exiting air streams can be obtained from the psychrometric chart (Figure 2.5) ... 

Let us now develop material and energy balances directly applicable to cooling towers. The idealized cooling tower operation is illustrated in Figure 5.6. The cooling tower operates with some type of heat source (a con-... 

Figure 5.12 Important design parameters for the countercurrent cooling tower operation.

A cooling tower operates in the countercurrent mode as illustrated by Figure 5.13. Entering air has a 5% wet-bulb temperature of 65°F. Hot process water enters the tower at 118°F and cold water leaves at a 15° approach to the wet-bulb (i.e., at 80°F). The cross-sectional area of the tower is 676 ft2. Determine the number of transfer units (Ntu ) required to meet the process requirements. Air is supplied to the tower by a blower having a capacity of 250,000 cfm and the water loading is 1500 lb/(hr)(ft2). 

A once-through cooling tower operation (i.e., no recycle) is schematically shown in Figure 5.16. Moist air is supplied to the cooling tower by a blower having a capacity of 9.0 X 106 ft3/hr. The dry- and wet-bulb temperatures of the incoming air are 75°F and 60°F, respectively. The air exits the tower at a dry-bulb temperature of 90° and a wet-bulb temperature of 85°F. The hot process water enters the tower at 130°F. The return water to the process operation must be at a temperature of 90°F. Determine how much water (gal/hr) can be cooled with this operation. 

Figure 9.1 Illustrates the danger of freezing for normal cooling tower operation (based on data of Cooper and Vodicka [ 1J).

FIGURE 3.26 Cooling tower operation. Diamonds, triangles, and squares represent interphase points, air temperature profile, and operating line, respectively. 

FIGURE 4.21 Water cooling in a cooling tower, which operates according to the parallel flow principle in other words, the water spray turns in the direction of the air flow. 

Figure 4.11 Power plant installation where multiple tower arrangement is utilized (towers ate operated in parallel). Cooling towers are placed in a row at right angles to the prevailing winds (courtesy of The Marley Company, Mission, KS).

Figure 4.20 Cooling tower design developed by Baltimore Aircoil Co. The system is designed to operate without fill packing.

Under certain conditions, such as high water temperatures, insufficient water supplies and problems of blowdown disposal, systems that depend on convection and use air as the transport medium may be preferable. The two types of dry cooling towers are the direct and indirect systems. Figures 4.21 and 4.22 show these systems in operation for nuclear station cooling. Indirect units use a surface or jet condenser at the turbine to condense exhaust steam. Water from the condenser is pumped to the dry tower for cooling and recirculation back to the condenser. In the direct system, steam is condensed in cooling coils without interfacing with a condenser. 

The use of these relationships in constructing and applying humidity charts is best illustrated by examining a simplified case, that of adiabatic cooling or humidification. Figure 5.4 illustrates this process between air and water that is recycled through the cooling tower. In this operation air is both cooled and... 

Figure 5.7 General operating diagram for a cooling tower.

When a zone is within the comfort gap, its reheat coil is turned off and its VAV box is closed to the minimum flow required for air refreshment (Figure 2.6). When all the zones are inside the ZEB, HW (hot water), CHW (chilled water), and STM supplies to the airhandler are all closed and the fan is operated at minimum flow. When all other airhandlers are also within the ZEB, the pumping stations, chillers, cooling towers, and HW generators are also turned off. 

The cost of fan operation can be reduced by allowing the cooling tower water temperature (Tctws in Figures 2.11 and 2.16) to rise, thereby increasing the approach (Tctws-Twb) at which the tower operates. As shown in Figure 2.16, as the approach, and therefore Tctws, rises, the temperature difference (Tctwr -Tctws) across the chiller condenser is reduced. This will cause an increase in water flow, and consequently the pumping costs (M2) will rise. 

Figure 9.16, the enthalpy-temperature diagram, shows the relationship between the water and air as they exist in a counterflow cooling tower. The vertical difference at any given water temperature between the water operating line and the air operating line is the enthalpy driving force. 

Figure 12-8f shows a typical plot of outlet water temperatures when a cooling tower is operated (1) in the fan-off position, (2) with the fan... 

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