Cooling towers temperature data

In order that hot condenser water may be re-used in a plant, it is normally cooled by contact with an air stream. The equipment usually takes the form of a tower in which the hot water is run in at the top and allowed to flow downwards over a packing against a countercurrent flow of air which enters at the bottom of the cooling tower. The design of such towers forms an important part of the present chapter, though at the outset it is necessary to consider basic definitions of the various quantities involved in humidification, in particular wet-bulb and adiabatic saturation temperatures, and the way in which humidity data are presented on charts and graphs. While the present discussion is devoted to the very important air-water system, which is in some ways unique, the same principles may be applied to other liquids and gases, and this topic is covered in a final section. 

Climatic data. Winter and summer temperature extrema, cooling tower drybulb temperature, air cooler design temperature, strength and direction of prevailing winds, rain and snowfall maxima in 1 hr and in 12 hr, earthquake provision. 

For economic reasons, equilibrium conditions cannot be approached closely. In a cooling tower, for instance, the effluent air is not quite saturated, and the water temperature is not quite at the wet bulb temperature. Percent saturation in the vicinity of 90% often is feasible. Approach is the difference between the temperatures of the water and the wet bulb. It is a significant determinant of cooling tower sizfe as these selected data indicate ... 

Over the limited ranges of temperature that normally prevail in cooling towers a quadratic fit to the data,... 

Under some wind conditions, a portion of the warm moist air leaving the tower may recirculate back through tire tower inlet and thus degrade performance. Forced-draft towers have recirculation rates that are about double those of induced-draft towers. Both water loading and tower height play the dominant role in- recirculation. Correlations exist in the literature for defining the effects of these parameters, and corrections can be applied to the wet-bulb temperature [2,3], Cooling tower fabricators can supply data to estimate the severity of the problem. 

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 ... 

A direct-contact gas cooler system operates as follows Approximately 35,000 lb/hr of bone-dry air is passed over hot trays. The air is heated from 150°F to 325°F as it passes over the trays. It exits from the unit with a due point of 105°F. The hot air is sent to a direct-contact cooler, where its temperature is reduced back to 150°F. During the cooling stage, the air is dehumidified with water that is heated frpm 75°F to 105°F. The unit is rated at 3.5 inches of water pressure drop (a) Determine the number of diffusion units needed for this operation and (b) Establish the required dimensions for the direct-contact cooling tower (Hint Use standard low-pressure-drop data from the literature. Some of the older literature give pressure drop data for simple fill. See Sherwood, T. K. and C. E. Reed [6]. 

Extraction of potable water from saline waters by means of immiscible solvents has been shown to be theoretically possible, experimentally feasible, and economically attractive. Data presented show the process to be especially adaptable to the conversion of feed water in the range of 5000 to 10,000 p.p.m. It is adaptable to use of low-quality heat such as hot water from cooling towers or low pressure waste steam. By use of mixed solvent systems, the process can be optimized to take advantage of seasonal changes in temperature and sources of cold feed water and low-level heat sources. The process, in general, is somewhat more economical when a cold source of feed water is available. 

Cooling water is available between 85 and 105°F, so we can condense Propylene at 130°F. Since the mythical plant is stated to be in Odessa, Texas, we use a 72°F wet bulb temperature as our starting point. See the Temperature Data subsection in Section 10, Cooling Towers for the wet bulb USA map. Since a cooling tower can have recirculation from outlet to inlet, we will use a conservative 75 °F for the wet bulb temperature to the tower. Then a 10°F approach is common, so the cold water temperature becomes 85°F. A 20°F temperature rise across heat exchangers is reasonable, so therefore we have used 85 to 105°F. 

Small pressure drop (less than 4,000 Pa) on the secondary side of the heat exchanger is compatible with a system based on natural convection. Secondary system temperatures are compatible with a heat sink made of either the immerged heat exchangers or a cooling tower. System performance data are therefore compatible with an entirely passive decay heat removal. 

The temperature of the steam and noncondensible materials leaving the top of the tower is determined by setting a 50 to 75 degree F approach to the minimum practical cool oil temperature in the top pumparound system. This latter temperature is a function of the viscosity properties of the oil in question, and this data can usually be predicted from the crude assay. Normally, a cool oil temperature of 150 to 200 degrees F will not require excessive pump horsepower. This, in turn, allows an overhead temperature of 200 to 275 degrees F. 

Calculations of this sort are only of importance to the tower designer. Manufacturers application data will give the cooling range or capacity in terms of wet bulb, inlet water temperature and mass flow [16, 19]. 

It is supposed that water is to be cooled at a mass rate L per unit area from a temperature 0L2 to Ql - The air will be assumed to have a temperature 6G, a humidity Jf ], and an enthalpy Hoi (which can be calculated from the temperature and humidity), at the inlet point at the bottom of the tower, and its mass flow per unit area will be taken as G. The change in the condition of the liquid and gas phases will now be followed on an enthalpy-temperature diagram (Figure 13.16). The enthalpy-temperature curve PQ for saturated air is plotted either using calculated data or from the humidity chart (Figure 13.4). The region below this line relates to unsaturated air and the region above it to supersaturated air. If it is assumed that the air in contact with the liquid surface... 

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