Transport Phenomena in Microscale Reacting Flows

Kaisare, Niket S.; Stefanidis, Georgios D.; Vlachos, Dionisios G.

doi:10.1002/9783527631445.ch10

Cited by 3 publications

(4 citation statements)

References 27 publications

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“…Norton et al showed that a given system may be mass-transfer- or diffusion-limited, depending on the operating conditions. Similarly, a catalytic monolith system is kinetically controlled prior to light-off and becomes mass-transfer-controlled after light-off. , In nonadiabatic propane combustion, Kaisare et al found that wall thermal conductivity had a profound effect: low conductivity walls led to mass-transfer-limited operation, whereas highly conducting walls resulted in a Da value on the order of 1. Hence, we study the effect of kinetic/mass-transfer control for various fractal structuring by varying the Da value, keeping all other parameters constant.…”

Section: Resultsmentioning

confidence: 99%

“…Depending on the operating conditions, microreactors may be reactionlimited, diffusion-limited, or both may be equally important. 11 Moreover, Kaisare et al 20 showed that propane catalytic combustion shifts from diffusion-limited conditions to reaction-limited conditions, based on the thermal conductivity of the reactor wall material. We analyze fractal structuring for confined channels of microreactors (or individual channel of catalytic monolith) with a circular cross section.…”

Section: ' Introductionmentioning

confidence: 99%

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Numerical Analysis of Fractal Catalyst Structuring in Microreactors

Regatte

Kaisare

2011

Ind. Eng. Chem. Res.

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The objective of this work is to verify the feasibility of implementing fractal structuring to reduce the amount of active catalyst surface required in microreactors. This work follows up on the work by Phillips et al. [Chem. Eng. Sci., 2003, 58, 2403–2408], where the authors reported the use of Cantor triads to reduce the total amount of active catalyst in a mass-transfer-limited system. They considered flat-plate geometry with infinitely fast reactions. This work is extended to realistic microreactors with finite rate chemistry to study the effect of catalyst structuring in the presence of flow confinement. Fractal and periodic patterns are formed by removing the catalyst from various sections along the reactor wall, resulting in alternating catalytic and noncatalytic segments. Two-dimensional computational fluid dynamics (CFD) simulations of tubular microreactor channel with catalyst structuring are performed. Our results show that the role of catalyst structuring confined geometry is rather modest, compared to the open (flat-plate) geometries considered so far. We also show that singularities (boundary of noncatalytic and catalytic segments) formed with catalyst structuring, and not the fractal pattern itself, are responsible for improved conversion from the microreactor. Large gradients at singularities result in enhanced mass transfer, which is analyzed using Sherwood number correlations. The effect of various operating parameters is investigated.

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Section: Resultsmentioning

confidence: 99%

Section: ' Introductionmentioning

confidence: 99%

Numerical Analysis of Fractal Catalyst Structuring in Microreactors

Regatte

Kaisare

2011

Ind. Eng. Chem. Res.

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“…The residence time as well as the energy input into the system were determined by the bulk flow of reacting gases [161,162]. Reactants diffuse from the bulk gas to the wash coat, going into the porous support (catalyst layer) next.…”

Section: Combustion Characteristicsmentioning

confidence: 99%

Effect of Different Technologies on Performance Enhancement of the Micro-Combustor for the Micro Thermophotovoltaic Application: A Review

et al. 2021

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With the improvement and development of micro-mechanical manufacturing technology, people can produce an increasing variety of micro-electromechanical systems in recent years, such as micro-satellite thrusters, micro-sensors, micro-aircrafts, micro-medical devices, micro-pumps, and micro-motors. At present, these micro-mechatronic systems are driven by traditional energy power systems, but these traditional energy power systems have such disadvantages as short endurance time, large size, and low energy density. Therefore, efforts were made to study micro-energy dynamical systems with small size, light gravity, high density and energy, and long duration so as to provide continuous and reliable power for these systems. In general, the micro-thermal photoelectric system not only has a simple structure, but also no moving parts. The micro-thermal photoelectric system is a micro-energy power system with good application prospects at present. However, as one of the most important structural components of micro-thermal photoelectric systems, the microburner, is the key to realize the conversion of fuel chemical energy to electric energy in micro-thermal photoelectric system. The studies of how to improve the flame stability and combustion efficiency are very necessary and interesting. Thus, some methods to improve the performance of micro-burners were introduced and summarized systematically, hoping to bring some convenience to researchers in the field.

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“…The thermodynamic and transport properties are obtained from the CHEMKIN database. , Transverse heat and mass transfer coefficients are computed assuming constant values of Nusselt ( Nu = 4.0) and Sherwood ( Sh = 3.8) numbers as was found in ref . The transverse transport rates vary along the reactor axis on the basis of the local temperature and composition, according to eq T-6 shown in Table .…”

Section: Mathematical Modelmentioning

confidence: 99%

Millisecond Production of Hydrogen from Alternative, High Hydrogen Density Fuels in a Cocurrent Multifunctional Microreactor

Kaisare

Stefanidis

Vlachos

2009

Ind. Eng. Chem. Res.

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A pseudo-2-dimensional model is used for modeling a multifunctional microreactor for hydrogen generation by coupling catalytic ammonia decomposition on ruthenium with catalytic propane combustion on platinum. The two reactions are carried out in adjacent parallel plate channels in a cocurrent flow mode. Operating lines defining the attainable region are computed. The high temperatures and fast heat transfer ensure that both reactions go to completion in as low as submillisecond contact times and enable compact hydrogen production for portable and distributed power generation. The ammonia decomposition reaction tends to be limited by the intrinsic rate of reaction, whereas catalytic combustion is also affected by mass and heat diffusion. We have found that moderate and high conductivity materials are preferable because they support a rather wide attainable region. We show that one such device could enable variable hydrogen supply for variable power needs. A simple operating strategy to dial in the desirable power is proposed, which ensures high thermal efficiency (∼75% once-through efficiency of the integrated device and ∼85% reformer efficiency, both without any heat recuperation), wall isothermicity, and high conversions.

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Transport Phenomena in Microscale Reacting Flows

Cited by 3 publications

References 27 publications

Numerical Analysis of Fractal Catalyst Structuring in Microreactors

Numerical Analysis of Fractal Catalyst Structuring in Microreactors

Effect of Different Technologies on Performance Enhancement of the Micro-Combustor for the Micro Thermophotovoltaic Application: A Review

Millisecond Production of Hydrogen from Alternative, High Hydrogen Density Fuels in a Cocurrent Multifunctional Microreactor

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