Tower deflection

They are used with metal and plastic packings to prevent the bed lifting, or the entrainment of individual pieces of packing from being carried out of the tower. These packings usually do not break, and as long as the bed temperature is below the softening or deflection point... 

Recirculation the portion of exit or outlet air from the tower that recirculates back to the inlet of the fresh air to the tower. To keep this low it is important to space towers away from each other as well as from any structures which can deflect the exit moist air back to the inlet. Due to recirculation the wet bulb temperature at the tower inlet may be different from that at a point 100 yards away. The recirculation of induced draft towers is usually less than forced draft due to the upward velocity of discharge of the air. 

Tang, S. S. (1968) Hyd. Proc. 47 (Nov.) 230. Shortcut methods for calculating tower deflections. 

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. 

The sway of the tower will produce a maximum velocity as the tower passes through vertical center. Also, the maximum velocity of sway will be at the top of the column with zero velocity at the base. As the column reaches the limit of its deflection, the kinetic energy of motion is transferred to strain enei of the shell, causing reversal of direction. The column will sway back and forth until the energy is dissipated. The total strain energy stored in a tall vertical tower at its point of maximum deflection during sway is given by the equation... 

High efficiency trays and new tower packing materials may limit the tower deflection and make the static deflection an important design factor. 

If the deflection estimated by this method exceeds the maximum permissible deflection for the tower height, it will be necessary to increase the shell thicknesses. The deflection will be recalculated with the new shell thicknesses until it falls within the specification. In general, vertical columns are designed to deflect no more than 7 inches on either side of center per 100 feet of height under full design wind pressure. Thus, the allowable deflection for the tower shown in Figure 4-6 is (7/100) (116.75) = 8.16 inches. 

Tang, S.S. Shortcut Method for Calculating Tower Deflections. Hydrocarbon Processing, November 1968, p. 230. 

Youness, A. New Approach to Tower Deflection. Hydrocarbon Processing, June 1970, p. 121. 

Wall wipers (or "rosette ) redistributors (Fig. 3.86) This is a collection ring equipped with short projections extending toward the tower center. Liquid removed from the wall is deflected into the projections ("fingers ), which transport it to a desired location in the bed. Wall wipers effectively remove liquid from the wall, but they are only partially effective for counteracting composition pinches. Their ability to counteract composition pinches diminishes as column diameter increases. Therefore, they are only suitable for small columns [< 2 to 3 ft in diameter (74, 305)], where deflection of liquid and vapor by packing particles is sufficient to counteract pinching effects, and where wall flow formation is the main problem. 

Antijump baffles deflect the jumping liquid into the downcomer, as does the tower shell when the flow is toward the side downcomer. Antijump baffles also assist in breaking up the froth. The following guidelines have been recommended for antijump baffles ... 

This procedure calculates the static deflection of tall towers due to various loading and accounts for the following ... 

Tall cylindrical stacks and towers may be susceptible to wind-induced oscillations as a result of vortex shedding. This phenomenon, often referred to as dynamic instability, has resulted in severe oscillations, excessive deflections, structural damage, and even failure. Once it has been determined that a vessel is dynamically unstable, either the vessel must be redesigned to withstand the effects of wind-induced oscillations or external spoilers must be added to ensure that vortex shedding does not occur. 

Figure 10.16 IRT image showcasing the maximum thermal increase of the backside of an impacted PC/PET hehnet-grade material. An injection-molded plaque of 3.2 mm thickness was impacted with an instrumented drop tower at 3.0 m/s with a drop mass assembly of 5.0 kg that contained a rounded steel dart. No anvil was beneath the plaque therefore, deflection of the plaque was allowed to occur.

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