A. Control measurements

Control measurements on erected cooling towers are usually executed by the manufacturer, in order to compare the performance data of bigger cooling towers with the data of experimental investigations or with the performance of small size cooling towers.

The characteristic of the packing is not directly dependent on the volume of the packing and hence the specific performance of the cooling tower should also be independent of cooling tower size. Provided that the performance data are evaluated with an even distribution of air and water, in the test unit as well as in the larger types of cooling towers, the same specific performance will be achieved. This ideal case does hardly ever occurs, as shown in Figure 1. There are only more or less useful approximate values. The deviation from ideal test data can be considered with a reduction factor, which must be specifically determined for the constructed unit.

Figure 1 Air-to-water mass flow ratio distribution inside cooling towers (graphically) with typical distribution as for existing cooling lowers and even distribution for ideal cooling tower

The performance of the packing close to the cooling tower wall is different from the packing far away from it. This so-called wall-effect results from different mechanisms, such low air velocity close to the wall, and poor water distribution pattern. The nozzles close to the wall may spray a part of the water directly to the wall, while another part is guided by slanting channels out of the packing, where it is withdrawn from the effective cooling.