The Development of a Mechanical-Draught Water-Cooling Tower *

Abstract

The paper describes the development of a mechanical-draught water-cooling tower containing a number of novel features. The packing is composed of serrated timber laths down which the water flow is film-wise to avoid splash formation. An earlier paper (Carey and Williamson 1950)§ gave the results of small-scale tests which indicated the theoretical advantage of grid film-flow packings in that the ratio of heat transfer to pressure drop is greater in this type of packing than in any other. A non-splash multi-trough water distributor is used to avoid the carry-over of splash droplets and hence to prevent a local deposition nuisance. Special attention has been given to the even distribution of water and air. Induced draught effects this better than forced draught and, since the fans exhaust heated air, there is no danger of ice formation upon them in frosty weather. The fans are large slow-running and aerofoil bladed, designed to give the highest possible static efficiency and to reduce the loss of velocity head at exit. The main design variables of air velocity and air/water ratio are determined from a balance of capital charges, packing, and power cost.

Several examples, showing the methods of construction, are given of these towers. The main structure and shell is usually in reinforced concrete because of its rigidity in supporting the fans and drives and its permanence and fire resistance, but timber is quite satisfactory and cheaper. The pond is in concrete in all large towers. Timber is the usual material for the packing and distribution troughs, and the water flow is controlled by orifice tubes now made in glass. Methods have been developed for supporting the laths and troughs so that they remain level and in proper relation to each other after wetting. The packing is usually built on reinforced concrete beams across the main structure.

Running experience obtained during six years is given together with the results of a comprehensive programme of tests. The good small-scale packing performance has been confirmed on the large scale. The tests have shown deficiencies in gear-driven fan installations, established the harmful effect on cooling efficiency of recirculation of the warm exit air and, in general, put on record performance details for critical assessment of this new development.