Natural draft cooling tower

Fig. 9. Natural-draft cooling tower (a) general tower drawing for countercurrent air—water dow arrangement (b) sectional drawing showing arrangement...

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. 

J. R. Singham, The Thermal Peformance of Natural Draft Cooling Towers, Imperial CoUege of Science and Technology, Department of Mechanical Engineering, London, 1967. 

FIG. 12-22 Universal performance chart for natural-draft cooling towers. (Risk and Steel, ASCE Symposium on Thermal Power Plants, October 1958. )... 

A large natural-draft cooling tower collapsed in a 70-mph (110-km/hr) v/ind, probably due to imperfections in the shape of the tower, which led to stresses greater than those it was designed to take and caused bending collapse [10]. 

Natural draft. Natural draft cooling towers consist of an empty shell, usually constructed in concrete. The upper, empty portion of the shell merely serves to increase the draft. The lower portion is fitted with the packing. The draft is created by the difference in density between the warm humid air within the tower and the denser ambient air. 

The fill material in natural draft cooling towers is frequently asbestos cement. Erosion of this fill material may result in the discharge of asbestos in cooling water blowdown. In a testing program for detection of asbestos fibers in the waters of 18 cooling systems, seven of the 18 sites... 

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. 

Natural-draft cooling towers with a hyperbolic configuration are usually constructed of concrete, have a large dimension and, consequently, large capacities. They are generally used in power plants. Figure 4.3 also illustrates this design. 

Natural-draft cooling towers evolved from spray ponds. The simplest and earliest design consisted of a small water spray pond surrounded with walls having inwardly sloping louvers. Figure 4.9 shows a cross section of a simple cooling tower formed by enclosing a spray pond with louvered walls. 

Table 4.1 Comparison Between Characteristics of Mechanical- and Natural-Draft Cooling Towers...

This paper discusses the impact of wind action on natural-draft cooling towers. The structure of the wind load may be divided into a static, a quasistatic, and a resonant part. The effect of surface roughness of the shell and of wind profile on the static load is discussed. The quasistatic load may be described by the variance of the pressure fluctuations and their circumferential and meridional correlations. The high-frequency end of the pressure spectra and of the coherence functions are used for the analysis of the resonant response. It is shown that the resonant response is small even for very high towers, however, it increases linearly with wind velocity. Equivalent static loads may be defined using appropriate gust-response factors. These loads produce an approximation of the behavior of the structure and in general are accurate. 11 refs, cited. 

Growing Role of Natural Draft Cooling Towers in U.S. Power Plants... 

Initial Investigations of the Effects of Heat and Moisture Dissipation from a Large Natural-Draft Cooling Tower... 

The paper examines the behavior of natural draft cooling tower wind pressure. Buckling loads of the towers of different meridional curvatures and shell thicknesses are computed and compared. The results show that an increase in stiffness of the structure with an increase in meridional curvature and changes of buckling load caused by changes in shdll thickness is approximately proportional. 10 refs, cited. 

The design of large natural draft cooling towers and analysis of their performance are complicated by the effects of variations in ambient air humidity. Often the effluent air from the tower is assumed to be at 100% relative humidity, to simplify calculations for design parameters. This study avoids the simplification, and proposes a procedure for determining the major design parameters for a natural draft tower. The theoretical and empirical relationships applicable to heat balance, heat transfer and transport, and tower draft and air resistance are given. 13 refs, cited. 

Model of Natural Draft Cooling Tower Performance Winiarski, L. D. Tichenor, B. A. 

The Nation s First Natural-Draft Cooling Tower Using Sea Water for Condenser Cooling)... 

Performance Testing of Large Natural Draft Cooling Towers Morgenweck, F. E. 

Natural Draft Cooling Tower, Maximum Liquid Loading Furzer, I. A. 

Natural Draft Cooling Towers and How They Fit Into the Thermal Pollution Picture... 

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