23-23: New Method for Drift Rate Measurements – Drop Hunter Isokinetic Probe

The paper focuses on development and verification measurements of a Drop hunter probe isokinetic. The escape of the liquid phase from the cooling tower has adverse economic effects for the operator and at the same time represents a real danger to the surroundings. Eliminators are installed in cooling towers to prevent water leakage into the surroundings, whose efficiency currently reaches values of minimum 99.993%, however, even the remaining thousandths of a percent represent a significant amount of water in absolute terms. In addition to the loss of water itself, it is the cause of corrosion of the tower (and fan) structure, because the leaking water contains various organic and inorganic substances used for its treatment. In the warm environment of the tower, last but not least, bacteria of legionella can linger, causing serious diseases, which, especially in the case of smaller towers installed in dense urban areas, pose a real danger to residents. The size spectrum of droplets escaping from the tower is 5-200 micrometers, while legionella bacteria is maintained on smaller droplets up to 30 micrometers, which the human body cannot naturally get rid of by coughing. The danger is so serious that there are already countries that have introduced the maximum permissible drift value into legislation (in Europe, for example, Spain and France) and other countries are already preparing this legislation. Manufacturers of eliminators do declare the effectiveness value of their products, but that means measuring it in some demonstrable way. The only method using the Heated Glass Beads Isokinetic probe is used for the certified measurement of drift, which, moreover, can only be applied by two certified laboratories in the world. This method is costly and time-consuming, moreover, it is often difficult to apply for measurements on a cooling tower. First, it requires expensive instrumentation, and second, it is followed by expensive chemical analysis. In addition to this certified method, there are a number of mostly instrumentation-intensive ways to measure the drift, but they cannot be applied directly in the operation of the cooling tower. Their use is limited to the laboratory, which represents, among other things, additional costs for cooling tower operators who would like to verify the drift from their tower in operation. This paper presents the development of a new drift measurement method based on a principle known for decades, but which has not yet been put into practice. It is an isokinetic probe equipped with heated elements, which will allow to capture the drift droplets in the environment of a real cooling tower during operation and immediately evaluate energy needed for their evaporation, i.e. to determine the volume of water captured in this way. The development of this probe was preceded by a large number of verification measurements, where various methods were applied. The Particle Image Velocimetry method supplemented with the calculation of the droplet paths in the probe was used to optimize the shape of the probe. The Interferometric Particle Imaging method, performed on the probe model, determined the size spectrum of the droplets entering the probe. The probe used for certified Heated Glass Beads Isokinetic drift measurement was used to verify the new probe in laboratory conditions.