Experimental Characterization of the Wettability of Coated and Uncoated Plates for Indirect Evaporative Cooling Systems

Abstract

Indirect Evaporative Cooling (IEC) is a very promising technology to substitute and/or integrate traditional air conditioning systems, due to its ability to provide cooling capacity with limited power consumption. Literature studies proved that a higher wettability of the IEC plates corresponds to better performance of the system. In this work, wettability of three different surfaces used for IEC systems plates—uncoated aluminum alloy (AL), standard epoxy coating (STD), and a hydrophilic lacquer (HPHI)—is studied and characterized in terms of static and dynamic contact angles. The static contact angle resulted to be the lowest for the HPHI surface (average 69°), intermediate for the STD surface (average 75°), and the highest for the AL surface (average 89°). The analysis of the dynamic contact angles showed that their transient behavior is similar for all the surfaces, and the advancing and receding contact angles obtained are consistent with the results of the static analysis. These results will be useful as input parameters in models aimed at predicting the IEC system performance, also using computational fluid dynamics.

Experimental Analysis of the Effect of Limescale on the Wettability of Indirect Evaporative Cooling System Plates

“…Furthermore, as for the clean surfaces [10], the static contact angle obtained with the samples in parallel orientation is always lower than the one obtained in a perpendicular orientation. This effect, which is due to the fact that the drops tend to stretch along the grooves, is not reduced by the presence of limescale, but is, instead, accentuated.…”

“…Many versions of the ADSA technique have been developed over the years [28], but the method used in this analysis is the one thoroughly described in previous works of the same authors [10,29], which led to a measurement error within 1.5 • . In short, according to this approach, an objective function, to be minimized, is formulated as the summation of the squared distances between the theoretical and experimental points representing the drop profile.…”

“…Figure 9 shows a comparison between the overall results for the contact angles of the clean surfaces [10] and the limescale ones. From this comparison, it is possible to observe that for two surfaces (HPHI and AL), the contact angle decreases in the presence of limescale, while for the other surface (STD), the contact angle slightly increases.…”

“…In a previous study by the same research group [10], the wettability of three surfaces used for IEC systems plates was analyzed. In particular, the three surfaces were as follows: an aluminum uncoated surface (AL), the same surface covered with a standard epoxy coating (STD), and the surface commercially known as BBlue, which is the same aluminum surface, but covered with a hydrophilic lacquer (HPHI).…”

“…As a consequence, the purpose of this work is to experimentally investigate the effects of limescale on the wettability of the three surfaces previously analyzed [10], evaluating the new static contact angles, spreading factors, and the reversible work of adhesion. The results of this analysis will be useful both to understand if and how the wetting behavior of these surfaces will change due to aging, thus positively or negatively affecting the performance of IEC systems, and to obtain new values of the contact angles to be used in models which aim to take into account the real wettability of the plates after some operating cycles.…”