Browsing by Author "Martinez-Agirre, Manex"
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Item Contact angle measurement for LiBr aqueous solutions on different surface materials used in absorption systems(2018-11) Martinez-Urrutia, Asier; Fernández de Arroiabe, Peru; Ramirez, Miguel; Martinez-Agirre, Manex; Mounir Bou-Ali, M.; Tecnalia Research & Innovation; SISTEMAS TÉRMICOS EFICIENTESWetting surface is a very important issue for the design of absorption applications and heat exchangers. The contact angle is deemed essential in wettability studies; However, LiBr aqueous solution contact angle studies are limited. This work analyses the contact angle of LiBr aqueous solution in the range of 0–55% mass fraction on different material surfaces: copper, aluminum, stainless-steel and polytetrafluoroethylene (PTFE) under atmospheric conditions. A sessile drop technique was used for measuring the contact angles, and a linear relation between solution surface tension and contact angle is observed in the tested materials. The study of three metals show hydrophilic performance (θ < 90°), whereas the PTFE shows hydrophobic performance. Additionally, the effect of the selection of the material, and consequent effect on the contact angle, on the minimum wetting rate and film thicknesses is presented under the working conditions of the absorption technologies. From the wettability point of view, the results show that using stainless-steel and aluminum leads to a slightly better performance than a copper made heat exchanger.Item Influence of the contact angle on the wettability of horizontal-tube falling films in the droplet and jet flow modes(2018-06) Fernández de Arroiabe, Peru; Martinez-Urrutia, Asier; Peña, Xabier; Martinez-Agirre, Manex; Bou-Ali, M. Mounir; Tecnalia Research & Innovation; SISTEMAS TÉRMICOS EFICIENTESWettability has a key impact on the performance of LiBr-H2O horizontal-tube falling film absorbers working under typical operating conditions. Therefore, it is necessary to study the influence of the wettability properties on the film hydrodynamics and wetted area. This work analyses the influence of the contact angle (0° – 120°) on the transient film hydrodynamics and the wetted area in the droplet and jet flow modes (7 ≤ Re ≤ 53). The comparison between two-dimensional and three-dimensional models evidences that three-dimensional models are needed for incomplete wetting conditions. The influence of the contact angle on both the film hydrodynamics and wetted area is demonstrated using 3D unsteady CFD model. Furthermore, the results indicate that each Reynolds number has a maximum contact angle to wet the whole tube steadily. When the value of the contact angle is lower than this maximum value, the contact angle has not influence on the wetting ratio. In contrast, at higher values, the wetting ratio decreases as the contact angle increases.