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Author(s): Adélio S. Cavadas
Fernando T. Pinho
João B. L. M. Campos
Title: Flow field of non-Newtonian fluids in impinging jets confined by slopping plane walls
Issue Date: 2008
Abstract: An experimental investigation was carried out to characterize the flow field in a liquid impingingjet confined by slopping plane walls and emanating from a rectangular duct for various non-Newtonianfluids. These jets are frequently found in processes within the food and pharmaceutical industries, and theyare formed when a high velocity fluid impinges a solid surface leading to intense levels of heat and masstransfer. The experimental work is complemented by results from a numerical investigation for purelyviscous fluids. This work continues previous research, Cavadas et al (2006), on the same flow geometry forNewtonian fluids in laminar and turbulent flow regimes. Here detailed measurements of mean flow fieldswere carried out by laser-Doppler anemometry at inlet duct Reynolds numbers of Kozicki (1966) (Re*) of200 pertaining to the laminar flow regime. The two non-Newtonian fluids were aqueous solutions of xanthangum (XG) and polyacrylamide (PAA) at weight concentrations of 0.2% and 0.125%, respectively. ForNewtonian fluids, Cavadas et al (2006) found a characteristic three-dimensional helical flow inside therecirculation, starting at the symmetry plane and evolving towards the flat side walls. This helical floweliminates the separated flow region near the side walls and was also visualized in the non-Newtonian cases.Before reaching the flat side walls, the fluid in helical motion exits the recirculation and joins the main flowstream creating a near-wall jet which can be seen as velocity peaks near the walls in the spanwise profiles ofstreamwise velocity. The numerical simulations investigated the roles of shear-thinning and inertia on themain flow characteristics for purely viscous fluids at Reynolds numbers between 10 and 800. The length ofthe recirculation (XR) is constant in the central portion of the channel and decays to zero before reaching theflat side walls. At high Reynolds numbers a slight increase in XR at the edge of the core of the flow isapparent. As expected, inertia increases the length of the recirculation as for Newtonian fluids, but somewhatsurprisingly it also increases the three-dimensional nature of the flow by reducing the size of the central core.Shear-thinning enhances the role of inertia especially at high Reynolds numbers, whereas at low Reynoldsnumbers the behavior is quite similar for all fluids. All flow fields were found to be symmetric relative to x-zand x-y centre planes
Subject: Engenharia mecânica, Engenharia química
Mechanical engineering, Chemical engineering
Source: 14th International Symposium on Applications of Laser Techniques to Fluid Mechanics
Document Type: Artigo em Livro de Atas de Conferência Internacional
Rights: openAccess
Appears in Collections:FEUP - Artigo em Livro de Atas de Conferência Internacional

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