Shell, cooling towers

Evaporative condensers (Fig. 11-88) are widely used due to lower condensing temperatures than in the air-cooled condensers and also lower than the water-cooled condenser combined with the cooling tower. Water demands are far lower than for water-cooled condensers. The chemical industry uses shell-and-tube condensers widely, although the use of air-cooled condensing equipment and evaporative condensers is on the increase. 

Water flows inside the tubes, and vapors eondense on the shell side. Cooling water is normally chilled, as in a cooling tower, and reused. Air-eooled surfaee eondensers and some water-cooled units eondense inside the tubes. Air-cooled condensers are usually construeted with extended surfaee fins. 

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. 

Shell and tube heat exchangers evolved because of the need to prevent contamination of the hot fluid by the cold fluid in many heat transfer operations. In the case of a water cooling tower, where one of the fluids is a gas and the other a liquid, an impervious surface or separation is not necessary because the gas and liquid are. readily separable after mixing and exchanging heat. 

If possible, locate combustible cooling towers at a safe distance from ignition sources such as incinerators or stacks. Towers that must be near such hazards should be constructed entirely of noncombustible material, or at least the shell should be made from noncombustible materials. Fan openings should be protected with-i-in corrosion-proof wire mesh. 

The shells of the cooling towers shown in Figure 8.1 are constructed of polyethylene. Table 8.3 summarizes some of the properties of high-impact polyethylene. This plastic is also employed in constructing fill packing. Table 8.4 also gives chemical resistance information on various plastic resins. 

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. 

Stability of Hyperbolic Cooling Tower Shells Under Wind Load)... 

In designing axi-symmetric shell structures such as large-type cooling towers, it is necessary to predict the vibration responses to various external forces. The authors describe the linear vibration response analysis of axi-symmetric shell structures by the finite element method. They also analyze geometric nonlinear (large deflection) vibration which poses a problem in thin shell structures causes dynamic buckling in cooling towers. They present examples of numerical calculation and study the validity of this method. 11 refs, cited. 

Basic elastic and geometric stiffness properties of the individual supporting columns are synthesized into a stiffness matrix compatible with an axisymmetrical shell element by a series of transformations. These are to be used in conjunction with a finite element representation of the cooling tower, where the displacements are decomposed into Fourier... 

Spray Cooling An Alternative to Cooling Towers Shell, Gerry L. Wendt, Ronald C. 

Buckling of Cooling-Tower Shells Bifurcation Results Cole, Peter P. Abel, John F. Billington, David P. 

Thermal Loading of Thin-Shell Concrete Cooling Towers... 

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 periodic response of a linear viscoelastic cooling tower to a prescribed recurring sequence of pressure fluctuations and earth accelerations are analyzed. An approximate analysis, based on the bending theory of shells, is presented. The problem is reduced to a double sequence of boundary-value problems of linear ordinary differential equations. 19 refs, cited. 

Observations showed that the wind direction is not perpendicular to the cooling tower axis when a cooling tower is standing on a slope. To analyze pressure distributions on the inside and the outside face of the shell, tests were carried out at the Institut fuer Massivbau of the Technical University of Hannover to conduct the measurements of the inside and outside pressure distributions of an idealized cooling tower model in a wind tunnel and of perpendicular and nonperpendicular air stream to the model axis. 

Shell or stack. Hyperbolic structure of natural draft cooling tower, designed to induce air flow through the entire tower. 

---