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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

Temperature rise at the wetting front during spontaneous imbibition




Abstract

Spontaneous imbibition is a process when a wetting viscous fluid of a particular surface tension (e.g. water) that is mainly driven by capillary forces invades into the micro-structure of a porous medium displacing a non-wetting less viscous fluid (e.g. air) of different surface tension. Here we show experimentally, that in the absence of evaporation, and even if the temperatures of the imbibed and the host fluids are the same, the fluid displacement process causes a heat release increasing locally the temperatures at the advance wetting front (interface of wet and non-wet surface). Thermal and optical images were simultaneously acquired providing quantitative visualization of the temperature and flow fields during spontaneous imbibition of various fluids inside paper microstructures. Due to the fact the imbibition dynamics is significantly determined by the geometry of the porous host, paper is an appropriate mean for spontaneous imbibition research purposes, since fibres are usually randomly oriented resulting in a medium with non-uniformities in the micro-structural network. A large variation of different liquids have been performed including urea-water solutions, saltwater and variable oils aiming to determine the reason of heat release at the wetting front. The results indicated temperature rises varying from 0.25K to 4.5K depending on the invaded liquid and the imbibition stage.

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