Abstract
Wetting 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.
Highlights
Absorption technologies have recently become more and more attractive, e.g. absorption chillers, absorption heat transformers and liquid desiccant systems (Rivera et al, 2015)
The linear relation between the contact angle cos θ and surface tension is observed by combination of the results in both works, and the linear function was adjusted in the range of the surface tension, A critical surface tension of 39.5 mN · m−1 was calculated
The contact angle of the aqueous LiBr solutions with different concentrations up to 55% on copper, aluminum, stainless-steel and PTFE have been measured by sessile drop tests
Summary
Absorption technologies have recently become more and more attractive, e.g. absorption chillers, absorption heat transformers and liquid desiccant systems (Rivera et al, 2015). One of the most critical component in these technologies is the absorber, where the refrigerant is directly absorbed by a hygroscopic solution (Garimella, 1999). The falling film configuration is usually used for water–LiBr heat exchangers, due to the large vapor-absorbent interface that optimizes both heat and mass transfer. A. Martinez-Urrutia et al / International Journal of Refrigeration 95 (2018) 182–188 Nomenclature Symbols T. — acceleration of gravity / m · s−2 Greek Symbols. — dimensionless mass flow-rate per unit length γ
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