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Scalar transport in milli-scale reaction systems with integrated static mixing elements

English title Scalar transport in milli-scale reaction systems with integrated static mixing elements
Applicant Rudolf von Rohr Philipp
Number 132552
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 01.01.2011 - 30.09.2014
Approved amount 278'857.00
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Keywords (11)

milli-scale reaction system; metal foams; mass transfer; heat transfer; LIF; PIV; structured porous reactor; flow characterization; mixing in porous media; two phase flow; complex flow

Lay Summary (English)

Lead
Lay summary
The growing need of energy saving and sustainable production leads to a demand for small scale continuous devices as the recuperation of energy is more efficient and mass and heat transfer is strongly enhanced. The preferences of different scales lead to the conclusion that a favorable range for economical and sustainable large-scale production is found in between micro and macro reactors. We use highly porous micro structured inserts for plug flow reactors in the millimeter range.To exploit such milli reaction systems using porous structures a thorough investigation of the transport mechanisms, i.e. their mixing and heat transfer characteristics with respect to their describing parameters (i.e. pore size, porosity, ligament shape, etc.) is needed. Another open question is the amount of turbulence or flow separation which is induced by these porous materials. Therefore we propose to investigate the momentum and scalar transport in a milli-scale system using different structured inserts by optical measurements inside the structure. Simultaneous PIV and LIF measurements is applied to investigate scalar transport in complex flow situations. This technique will be used now to the milli-scale system and enable quantitative measurements inside the porous structure. In a first step we will address grid-structured mixing elements and thus the influence of the macroscopic geometry of the mixing elements on the induced turbulence and momentum exchange. We will perform PIV measurements between the different grid-planes and therefore inside the mixing element. In addition we will investigate the concentration field of a tracer dye injected in front of the mixing element by LIF. This is followed by the second step, where we increase the complexity of the mixing elements and focus on porous structures and the influence of their microscopic structure (pore size, pore geometry, ligament shape) on the transport properties. In a third step we propose to investigate the mixing performance of these inserts in a two-phase flow situation. Hereby we restrict ourselves in the beginning to liquid-liquid systems. Simultaneous velocity and concentration measurements will lead to a characterization of transport processes in porous structures when advancing to two-phase flows. The present project addresses the fundamental turbulent transport phenomena in milli-scale reaction systems employing porous static mixing elements. The findings allow to describe the mechanisms of simultaneous momentum and mass transport in milliscale systems relevant for industry and its correlation to turbulence production processes and turbulence structures inside mixing elements.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Investigation of emulsification in static mixers by optical measurement techniques using refractive index matching
Häfeli Richard, Rüegg Oliver, Altheimer Marco, Rudolf von Rohr Philipp (2016), Investigation of emulsification in static mixers by optical measurement techniques using refractive index matching, in Chemical Engineering Science, 143, 86-98.
PIV study of flow through porous structure using refractive index matching
Häfeli Richard, Altheimer Marco, Butscher Denis, Rudolf von Rohr Philipp (2014), PIV study of flow through porous structure using refractive index matching, in Exp Fluids, 55, 1717.
Dispersion in fully developed flow through regular porous structures: Experiments with wire-mesh sensors
Häfeli Richard, Hutter Cédric, Damsohn Manuel, Prasser Horst-Michael, Rudolf von Rohr Philipp (2013), Dispersion in fully developed flow through regular porous structures: Experiments with wire-mesh sensors, in Chem Eng Proc, 69, 104-111.

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
International conference on heat transfer and fluid flow Talk given at a conference Total thermal diffusivity in a porous structure measured by full field liquid crysta thermography 11.08.2014 Prag, Czech Republic Häfeli Richard;
9th world congress of chemical engineering Talk given at a conference Dependence of mass transport on the length of a tubular reactor with a porous structure. 18.08.2013 Seoul, Korean Republic (South Korea) Rudolf von Rohr Philipp; Häfeli Richard;
Characterisation of porous solids (COPS IX) Poster Flow characterisation in designed porous structures 05.06.2011 Dresden, Germany Häfeli Richard;


Abstract

In the industry large scale equipment, predominantly dis- or semicontinuous batch processes, are still used due to the economy of scale. For chemical plants the investment costs are in general proportional to the capacity to the power of 0.5 to 0.7. The growing need of energy saving and sustainable production leads to a demand for small scale continuous devices as the recuperation of energy is more efficient and mass and heat transfer is strongly enhanced. In micro reaction systems the scale up is mostly realized by numbering up individual micro reactors, which is not an economical solution for large-scale production. In spite of the huge pressure drop and the predominant laminar flow within microsystems the small scales offer many advantages. The preferences of different scales lead to the conclusion that a favorable range for economical and sustainable large-scale production is found in between micro and macro. Our approach is to use high porous micro structured inserts for plug flow reactors in the millimeter range. The system offers the possibility of high throughput (liquid flow rate up to 2.5 l/min) at a comparable small pressure drop. A huge potential arises from open cell metal foams due to their high specific surface area combined with a high porosity which is typically larger than 85%. The induced turbulence in this micro-structured geometry leads to an enhanced heat and mass transfer which was observed in preliminary experiments at our laboratory. The study compared three metal foams with different pore sizes and showed an influence of the dimension and the shape of the ligaments. However, no measurements inside the foam have been possible to further investigate the influence of the pore geometry. To exploit such mini reaction systems using porous structures a thorough investigation of the transport mechanisms, i.e. their mixing and heat transfer characteristics with respect to their describing parameters (i.e.~pore size, porosity, ligament shape, etc.) is needed. The amount of turbulence or flow separation which is induced by these porous materials is an additional and open question. Therefore we propose to investigate the momentum and scalar transport by optical measurements inside milli-scale systems with different inner structures. To manufacture these geometries we apply Stereolithography respectively Selective Laser Sintering which allows to design highly reproducible milli-reactors with fully integrated static mixing elements. In a past study (SNF project 109560) we applied simultaneous PIV and LIF measurements to investigate scalar transport in complex flow situations. The obtained results revealed the suitability of these non--intrusive methods to fully characterize transport mechanisms and to relate them to identified turbulence structures. Thus we propose to apply these measurement techniques to the milli-scale system and to extend it to enable quantitative measurements inside the porous structure. In a first step we will address grid-structured mixing elements and thus the influence of the macroscopic geometry of the mixing elements on the induced turbulence and momentum exchange. We will perform PIV measurements between the different grid-planes and therefore inside the mixing element. In addition we will investigate the concentration field of a tracer dye injected in front of the mixing element by LIF. This is followed by the second step, where we increase the complexity of the mixing elements and focus on porous structures and the influence of their microscopic structure (pore size, pore geometry, ligament shape) on the transport properties. Therefore we propose simultaneous velocity and concentration measurements using PIV and LIF with different foam-like inserts. In a third step we propose to investigate the mixing performance of these inserts in a two-phase flow situation. Hereby we restrict ourselves in the beginning to liquid-liquid systems. Simultaneous velocity and concentration measurements will lead to a characterization of transport processes in porous structures when advancing to two-phase flows. The present project advances the existing knowledge in a defined step and addresses the fundamental turbulent transport phenomena in milli-scale reaction systems employing porous static mixing elements. The findings allow to describe the mechanisms of simultaneous momentum and mass transport in milli-scale systems relevant for industry and its correlation to turbulence production processes and turbulence structures inside the mixing elements.
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