A review of wetted media with potential application in the pre-cooling of natural draft dry cooling towers

There is no dearth of published data concerning direct evaporative cooling, especially concerning the wetted media used in this technique. In spite of the data abundance, the lack of a comprehensive review of wetted media with potential use for inlet air pre-cooling of Natural Draft Dry Cooling Towers (NDDCTs) triggered the motivation of this paper. This paper reviews the wetted media with potentiality in the pre-cooling application of NDDCTs in terms of wetted medium types, mathematical models, performance studies and empirical relations. A method to compare wetted media in terms of the balance between cooling potential and pressure drop is proposed and validated. This method should be useful for comparative evaluation of wetted medium types or at least to differentiate between good and bad medium types. The medium cost, the service life, the type of process to be cooled, environmental conditions, water quality, space availability, locations and economic requirements are essential considerations, and some significant trade-offs have to be made during medium selection. A framework for medium selection is presented and the advantages and disadvantages of different medium types are summarized to provide a starting point for such selection. The empirical correlations appeared in the literature are synthesized to better correlate and compare the test data of wetted media and subsequently to provide prerequisite information for performance prediction. Controversies concerning wetted medium studies are discussed, and finally the gaps related to wetted medium studies are articulated.