Cooling towers heat load

Natural-draft cooling towers are extremely sensitive to air-inlet conditions owing to the effects on draft. It can rapidly be estabUshed from these approximate equations that as the air-inlet temperature approaches the water-inlet temperature, the allowable heat load decreases rapidly. For this reason, natural-draft towers are unsuitable in many regions of the United States. Figure 10 shows the effect of air-inlet temperature on the allowable heat load of a natural-draft tower for some arbitrary numerical values and inlet rh of 50%. The trend is typical. 

In operating a coohng tower in the thermocycle or free-cooling mode, some precautions are necessary to minimize icing problems. These include fan reversals to circulate air down through the tower inlet louvers, proper water distribution, constant water flow over the tower, heat tracing of lines such as makeup lines as required, and maximum loading per tower cell. 

A temporary extra heat load was placed on an olefin plant cooling tower one winter. The operations people asked the question, Will the cooling tower make it next summer with the extra load Of course the tower would deliver the heat removal, so the real question was, What will the cold water temperature be next summer ... 

Heat Load Amount of heat (in Btu) dissipated in a cooling tower. It is equal to the weight of water circulated per unit of time multiplied by the cooling range. 

Wood or plastic filled towers for cooling water by using air are quite economical for certain heat loads and geo-... 

Range the temperature difference between the warm water into the tower and the cold water out. The range determines the heat load on the tower, which in turn reflects the requirements of the cooling water service. The... 

Changes in circumstances will frequently require modifications to an existing cooling tower. Additional heat loads may be needed, and changes in the end process may cause the return temperature to increase, necessitating a new thermal load on the tower. Most frequently it is a requirement for an increase in hydraulics. 

Alternatively, air-cooled heat exchangers can be installed within the cooling water network to replace cooling water coolers. This has the effect of reducing the cooling load on the cooling tower and, in principle, allows the flowrate of cooling water to be decreased. 

Situations are often encountered when cooling water networks need to increase the heat load of individual coolers, which requires investment in new cooling tower capacity. Such situations demand a more complete analysis of the whole cooling water system. 

It should be noted that Lewis number, Le, is only a prediction. In reality, Le is closer to 0.9. The manner in which Equation 5.29 was derived produces an error only in the convective heat transfer coefficient. In normal cooling tower operation, convective heat transfer is generally less than 20% of the total heat load. For now, Equation 5.29 represents the centerpiece of our... 

Before applying our generalized equations to sizing cooling towers, we need to review some of the criteria for specifying operating conditions. The critical conditions that must be established before the design is initiated are the heat load, wet-bulb temperature, hot and cold water temperature and water rate. 

The determination of the heat to be dissipated by a cooling tower is an essential factor that not only affects the tower size, but also its effectiveness. If the heat load. determination is not accurate, either too high or too low, a larger or smaller size tower than is needed for a particular job could be selected. 

Theoretically, a cooling tower will cool water to the entering wet-bulb temperature when operating without a heat load however, a thermal potential is required in all heat rejection processes, so it is not possible to cool water to the entering wet-bulb temperature when a heat load is applied. The wet-bulb temperature has a direct impact on the operating temperature of the plant and influences operating conditions, plant efficiencies and operating cost. 

The approach has a significant effect on the tower size, as shown in Figure 5.11. For a given heat load, gpm and wet-bulb temperature, the cooling tower size increases as the approach decreases, and the closer the cold water temperature approaches the wet-bulb temperature, the greater the increase in the cooling tower size. 

Cooling towers are capable of operating over a wide range of water rates, air rates and heat loads. Variations are reflected in the approach of the cold water to the wet-bulb temperature. The available tower coefficient is not a constant but varies with operating conditions. 

The water consumption of a cooling tower depends not only on the heat load but also on the ratio of the amounts of heat carried off by increasing the temperature of the air through evaporation of the water. The amount of... 

A cooling tower has a cross-sectional area of 25 X 25 ft. The total heat load to the unit is 27,500,000 Btu/hr. The locality has a 5% wet-bulb temperature of 75°F. Water exits the tower with a 12° approach to the wet-bulb temperature (i.e., 87°F).The hot process water enters the tower at a temperature of 125°F, and the water equivalent to this range is 1800 gpm. The systems fan capacity is 150,000 cfm (a) Determine the number of diffusion units that the tower must be capable of performing to meet process requirements (b) the tower manufacturer provided the following data for overload and underload conditions for the tower ... 

Power consumption is computed on total hours of heat load operation. Total cost may be less, considering actual BHP used and cold weather operation during which the cooling tower will function with blower motor off. 

There are many applications in which it is important to maintain an average basin water temperature at an optimum value. One example is a utility cooling tower application in which an optimum average basin water temperature is required to ensure efficient turbine operation. In this example, the optimum temperature falls between 60° and 75°F. Ice prevention systems should be designed to provide sufficient flexibility to control the basin water temperature between specified limits without significant ice formation for a wide range of heat load and ambient environmental conditions. 

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