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Transport mechanisms and large-scale structures in narrow channels

English title Transport mechanisms and large-scale structures in narrow channels
Applicant Rudolf von Rohr Philipp
Number 121562
Funding scheme Project funding (Div. I-III)
Research institution Institut für Verfahrenstechnik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Fluid Dynamics
Start/End 01.02.2009 - 31.01.2012
Approved amount 276'225.00
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Keywords (6)

narrow channel; complex surfaces; mass transfer; heat transfer; LIF; PIV

Lay Summary (English)

Lead
Lay summary
The state of the art reaction system used for fast and exothermic reactions by the chemical and pharmaceutical industry for medium throughput (i.e. fine chemicals) is the batch reactor. Despite all advantages,like the flexibility and the easy handling of such systems, disadvantages such as the difficult temperature control during the reaction and dead zones inside the reactor with less mixing efficiency are evident. Thus it is desirable to develop continuous mini reaction systems in the millimeter scale, which combine the advantages of micro-reactors, i.e. faster mixing, enhanced heat transfer, and a narrow residence time distribution, with the throughput of batch reactor systems. In addition, these processes are further characterized by the simultaneous transport of heat and mass as a result of combined buoyancy effects of thermal diffusion and diffusion of species (active scalar transport).To exploit these mini reaction systems a thorough investigation of the transport mechanisms, i.e. their mixing and heat transfer characteristics with respect to their geometry is needed. We propose to investigate the mixing properties of two soluble liquids, and the heat transfer of narrow channels with complex bottom surfaces. Reynolds numbers up to 40000 are considered, defined with the height of the channel and the bulk velocity. Previous studies revealed the correlation between the existence of large-scale structures in a channel flow between a flat top and a complex bottom wall and the transport of heat and species. For these studies two different well-defined bottom surfaces are considered, in order to achieve a homogeneous and inhomogeneous reference flow situation.The results suggest that transport mechanisms important in complex flow conditions are governed by large-scale structures, which means that ‘controlling’ these large-scale structures provides possibilities to influence the transport properties. In addition, these coherent structures appear to be sensitive to alterations in the structure of the wavy surfaces, i.e. to the geometry of the considered flow domain.Thus we propose to start from this configuration and investigate the role of the channel height with large aspect ratio (width to height ratio) as the first step. In a second step, we propose to investigate a rectangular channel geometry with reduced channel height, i.e. we investigate the influence of the side walls on the spatial organization, the meandering and the stability of large-scale structures. In addition and as a third step we propose to compare the scalar transport mechanisms of such narrow channels (with complex bottom surface) with a rectangular channel with inserted static mixing elements. As mixing elements we propose to investigate metal foams, which are characterized by a certain porosity (number of pores per inch: ppi), which are used in industry due to their heat transfer characteristics. We apply non-intrusive measurement techniques to simultaneously assess the two-dimensional fluid velocity and scalar fields by using a combined particle image velocimetry (PIV) and high-resolving planar laser-induced fluorescence (PLIF) technique. Spatio-temporal information on the interacting scalar fluxes and other important turbulence statistics can be addressed. A proper orthogonal decomposition (POD) of the velocity and scalar fields is expected to reveal dominant scales. The findings allow to describe the mechanisms of simultaneous momentum, heat and mass transport in industrial relevant flow situations and its correlation to turbulence production processes and turbulence structures.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Axial dispersion in metal foams and streamwise-periodic porous media
Hutter Cédric, Zenklusen Adrian, Lang Rolf, Rudolf von Rohr (2011), Axial dispersion in metal foams and streamwise-periodic porous media, in Chemical Engineering Science,, 66(6), 1132-1141.
Large eddy simulation of flow through a streamwise periodic structure
Hutter Cédric, Zenklusen Adrian, Kuhn Simon, Rudolf von Rohr Philipp (2011), Large eddy simulation of flow through a streamwise periodic structure, in Chemical Engineering Science, 66(3), 519-529.

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
European Congress of Chemical Engineering 12 25.09.2011 Berlin, Deutschland
CHISA 28.09.2010 Prag, Tschechien
Leonhard Euler annual meeting 06.11.2009 Lausanne, CH


Communication with the public

Communication Title Media Place Year
Other activities ETH-Industrie Besuchstag German-speaking Switzerland 11.09.2010

Associated projects

Number Title Start Funding scheme
109560 Transport mechanisms in mixed convective flow over complex surfaces 01.10.2005 Project funding (Div. I-III)

Abstract

The state of the art reaction system used for fast and exothermic reactions by the chemical and pharmaceuticalindustry for medium throughput (i.e. fine chemicals) is the batch reactor. Despite all advantages,like the flexibility and the easy handling of such systems, disadvantages such as the difficulttemperature control during the reaction and dead zones inside the reactor with less mixing efficiency areevident. Thus it is desirable to develop continuous mini reaction systems in the millimeter scale, whichcombine the advantages of micro-reactors, i.e. faster mixing, enhanced heat transfer, and a narrow residencetime distribution, with the throughput of batch reactor systems. In addition, these processes arefurther characterized by the simultaneous transport of heat and mass as a result of combined buoyancyeffects of thermal diffusion and diffusion of species (active scalar transport).To exploit these mini reaction systems a thorough investigation of the transport mechanisms, i.e. theirmixing and heat transfer characteristics with respect to their geometry is needed. We propose toinvestigate the mixing properties (e.g. mixing efficiency, concentration fluctuation intensity)of two soluble liquids, and the heat transfer (e.g. Nusselt numbers, turbulent heat flux) of narrowchannels with complex bottom surfaces. Reynolds numbers up to 40000 are considered, defined withthe height of the channel and the bulk velocity. An ongoing study (SNF project 109560) revealed thecorrelation between the existence of large-scale structures in a channel flow between a flat top and acomplex bottom wall and the transport of heat and species. For these studies two different well-definedbottom surfaces are considered, (i) a wavy wall with an amplitude-to-wavelength ratio alpha = 2a/Lambda = 0.1(Lambda = 30 mm), and (ii) a profile consisting of two superimposed waves, in order to achieve a homogeneousand inhomogeneous reference flow situation.The results suggest that transport mechanisms important in complex flow conditions are governed bylarge-scale structures, which means that ‘controlling’ these large-scale structures provides possibilitiesto influence the transport properties. In addition, these coherent structures appear to be sensitive toalterations in the structure of the wavy surfaces, i.e. to the geometry of the considered flow domain.Thus we propose to start from this configuration and investigate the role of the channel height withlarge aspect ratio (width to height ratio) as the first step. In a second step, we propose to investigate arectangular channel geometry with reduced channel height, i.e. we investigate the influence of the sidewalls on the spatial organization, the meandering and the stability of large-scale structures. In additionand as a third step we propose to compare the scalar transport mechanisms of such narrow channels(with complex bottom surface) with a rectangular channel with inserted static mixing elements. Asmixing elements we propose to investigate metal foams, which are characterized by a certain porosity(number of pores per inch: ppi), which are used in industry due to their heat transfer characteristics.The present project advances the existing knowledge in a defined step and addresses the fundamentalturbulent transport phenomena in industrial relevant narrow channels with complex surfaces andmixing elements. We apply non-intrusive measurement techniques to simultaneously assess the two-dimensional fluid velocity and scalar fields by using a combined particle image velocimetry (PIV) andhigh-resolving planar laser-induced fluorescence (PLIF) technique. Spatio-temporal information onthe interacting scalar fluxes, u'T', and u'c', and other important turbulence statistics can be addressed.A proper orthogonal decomposition (POD) of the velocity and scalar fields is expected to reveal dominantscales. The findings allow to describe the mechanisms of simultaneous momentum, heat and masstransport in industrial relevant flow situations and its correlation to turbulence production processesand turbulence structures.
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