Cooling towers mechanical draft tower

Performance, 387 Ground Area vs. Height, 391 Pressure Losses, 393 Fan Horsepower for Mechanical Draft Tower, 392 Water Rates and Distribution, 393 Blow-Down and Continuation Build-Up, 394 Example 915 Determining Approximate Blow-Down for Cooling Tower, 395 Pre-... 

Evaporation losses are 1 % of the circulation for every 100 F of cooling range. Windage or drift losses of mechanical draft towers are 0.1-0.3%. Blowdown of 2.5-3.0% of the circulation is necessary to prevent excessive salt buildup. 

The magnitude of the heat rejection of large modern power generating plants is so great that the problem of potential environmental effects due to dry cooling systems must be studied. The plumes from both natural-draft and mechanical-draft towers designed for 1000-MW plants of several representative types are examined with respect to... 

Mechanical draft towers are always used for cooling systems requiring a low approach and typically have an L/G (liquid/gas) ratio within the range of 1 0.75 to 1 1. 

Evaporation losses are 1% of the circulation for every 10°F of cooling range. Windage or drift losses of mechanical draft towers... 

The thermal design of cooling towers follows the same general procedures already presented. Integration of equation 35 is usually done numerically using the appropriate software, mass-transfer coefficients, saturation enthalpies, etc. In mechanical-draft towers the air and water dows are both suppHed by machines, and hence dow rates are fixed. Under these conditions the design procedure is straightforward. 

Cooling-Tower Plumes. An important consideration in the acceptabiHty of either a mechanical-draft or a natural-draft tower cooling system is the effect on the environment. The plume emitted by a cooling tower is seen by the surrounding community and can lead to trouble if it is a source of severe ground fog under some atmospheric conditions. The natural-draft tower is much less likely to produce fogging than is the mechanical-draft tower. Nonetheless, it is desirable to devise techniques for predicting plume trajectory and attenuation. 

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

Mechanics-draft cooling towers normally are designed for L/Q ratios ranging from 0.75 to 1.50 accordingly, the vSues of KaV/L vaiy from 0.50 to 2.50. With these ranges in mind, an example of the use of the nomograph will readily explain the effecd of changing variables. 

Cooling towers are broadly classified on the basis of the type of draft natural draft (natural convection), mechanical draft (forced convection) and mechanical and natural. Further distinction is made based on (1) the type of flow i.e. - crossflow, counterflow, cocurrent flow (2) the type of heat dissipation-wet (evaporative cooling), dry, wet-dry and (3) the type of application-industrial or power plant. Each of the major types of cooling towers has a distinct configuration. The major designs are summarized in Figures 1 through 8 and a brief description of each follows. 

Lichtenstein, J. "Performance and Selection of Mechanical Draft Cooling Towers, " ASME Trans. (1943). 

Mechanical-draft cooling towers are normally supplied with either central baffles or inlet louvers. This depends on the tower dimensions. On these towers the wind or spray blowout is generally confined to relatively small singlecell units where an inlet may be provided on all four faces. In this case the major remedy is to provide internal diagonal baffles to prevent crossflow of air through the air inlets. 

Perhaps the most common environmental requirement in modem cooling tower installations is that of noise. The fan equipment and the falling water generate cooling tower noise. In large mechanical- or natural-draft cooling... 

Acceptance test procedure for water cooling towers of mechanical draft industrial type... 

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