Hydrodynamics and mass transfer of gas–liquid flow in a falling film microreactor
TL;DR: In this paper, the authors investigated the flow pattern of liquid film and flooding phenomena of a falling film microreactor (FFMR) using high-speed CCD camera, and the experimental results indicate that kL is in the range of 5.83 to 13.4 � 10 � 5 ms � 1 and an empirical correlation was proposed to predict kL in FFMR.
Abstract: In this article, flow pattern of liquid film and flooding phenomena of a falling film microreactor (FFMR) were investigated using high-speed CCD camera. Three flow regimes were identified as ‘‘corner rivulet flow,’’ ‘‘falling film flow with dry patches,’’ and ‘‘complete falling film flow’’ when liquid flow rate increased gradually. Besides liquid film flow in microchannels, a flooding presented as the flow of liquid along the side wall of gas chamber in FFMR was found at high liquid flow rate. Moreover, the flooding could be initiated at lower flow rate with the reduction of the depth of the gas chamber. CO2 absorption was then investigated under the complete falling flow regime in FFMR, where the effects of liquid viscosity and surface tension on mass transfer were demonstrated. The experimental results indicate that kL is in the range of 5.83 to 13.4 � 10 � 5 ms � 1 and an empirical correlation was proposed to predict kL in FFMR.
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TL;DR: In this paper, a comprehensive overview of gas-liquid and liquid-liquid mass transfer in microstructured ReReactors (MSR) is presented, where different dimensionless parameters used to analyze mass transfer are discussed.
334 citations
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TL;DR: In this paper, a review of recent studies of hydrodynamics and mass transfer in gas-liquid microreactors with closed and open microchannels, e.g., falling-film micro reactors, is presented.
Abstract: Over the last ten to fifteen years, microreaction echnology has become of increased interest to both academics and industrialists for intensification of multiphase processes. Amongst the vast application possibilities, fast, highly exothermic and/or mass transfer-limited gas-liquid reactions benefit from process miniaturization. Recent studies of hydrodynamics and mass transfer in gas-liquid microreactors with closed and open microchannels, e.g., falling-film microreactors, are reviewed and compared. Special attention is paid to Taylor or slug flow in closed channels, as this regime seems to be most adapted for practical engineering applications.
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TL;DR: Rotating biological contactors (RBCs) for wastewater treatment began in the 1970s as discussed by the authors and have been applied with only limited success for enhanced biological phosphorus removal and attained up to 70% total phosphorus removal.
123 citations
Cites background from "Hydrodynamics and mass transfer of ..."
...659 The majority of film renewal is thought to occur when the surface tension resistance is broken under 660 the effect of gravity after the so called ‘falling film’ theory (Zhang et al. 2009)....
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TL;DR: In this article, an artificial neural network model was proposed for predicting α, revealing only an average absolute relative error of <5% for the interfacial area, α, in a tube-in-tube microchannel reactor (MTMCR).
Abstract: High-throughput microporous tube-in-tube microchannel reactor (MTMCR) was first designed and developed as a novel gas–liquid contactor. Experimentally measured kLα in MTMCR is at least one or two orders of magnitude higher than those in the conventional gas–liquid contactors. A high throughput of 500 L/h for gas and 43.31 L/h for liquid is over 60 times higher than that of T-type microchannel. An increase of the gas or liquid flow rate, as well as a reduction of the micropore size and annular channel width of MTMCR, could greatly intensify the gas–liquid mass transfer. The interfacial area, α, in MTMCR was measured to be as high as 2.2 × 105 m2/m3, which is much higher than those of microchannels (3400–9000 m2/m3) and traditional contactors (50–2050 m2/m3). The artificial neural network model was proposed for predicting α, revealing only an average absolute relative error of <5%. © 2010 American Institute of Chemical Engineers AIChE J, 2011
60 citations
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...The empirical correlations were proposed to predict mass transfer characters of microchannel reactors.(8,15) However, it seems very difficult to adopt the currently available correlation on the interfacial area in gas– liquid flow in MTMCR owing to its complex microporous structures from special manufacture mode, and a new modeling approach of MTMCR needs to be developed....
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References
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TL;DR: In this paper, hydrodynamics and mass transfer characteristics in cocurrent gas-liquid flow through a horizontal rectangular microchannel with a hydraulic diameter of 667 μ m have been investigated experimentally.
418 citations
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TL;DR: Any method by which one can vary the contact angle can be used to switch the length of the filament, as is demonstrated in the context of electrowetting.
Abstract: The wetting of microstructured surfaces is studied both experimentally and theoretically. Even relatively simple surface topographies such as grooves with rectangular cross section exhibit a large variety of different wetting morphologies as observed by atomic force microscopy. This polymorphism arises from liquid wedge formation along the groove corners and from contact line pinning along the groove edges. A global morphology diagram is derived that depends only on two system parameters: (i) the aspect ratio of the groove geometry and (ii) The contact angle of the underlying substrate material. For microfluidics, the most interesting shape regimes involve extended liquid filaments, which can grow and shrink in length while their cross section stays essentially constant. Thus, any method by which one can vary the contact angle can be used to switch the length of the filament, as is demonstrated in the context of electrowetting.
374 citations
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TL;DR: In this article, the flow of immiscible fluids in a PMMA microchannel 300 mu m wide and 600 pm deep was investigated experimentally Dyed de-ionized water and kerosene were selected as the test fluids Flow patterns were observed by using a CCD camera and were identified by examining the video images.
Abstract: In this work, the flow of immiscible fluids in a PMMA microchannel 300 mu m wide and 600 pm deep was investigated experimentally Dyed de-ionized water and kerosene were selected as the test fluids Flow patterns were observed by using a CCD camera and were identified by examining the video images Flow patterns obtained at the T-junction and in the microchannel are presented Superficial velocities varied between 926 x 10(-4) similar to 185 m/s for water and 926 x 10(-4) similar to 278 m/s for kerosene The formation mechanism of slug, monodispersed droplet and droplet populations at the T-junction was studied Weber numbers of water and kerosene, We(KS) and We(WS), were used to predict the flow regime transition and the flow patterns map The experimental data of volume of dispersed phase were successfully correlated as a function of We(KS), We(WS), and hold-up fraction Considering the uncertainty associated with experimental quantification of the process, the results are in satisfactory agreement over the wide range of 190 x 10(-3) < We(WS) < 3043 and 590 x 10(-6) < We(KS) < 013 with average absolute deviation of only 1618% (c) 2006 American Institute of Chemical Engineers
307 citations
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TL;DR: In this paper, a falling film microreactor and a micro bubble column were used for direct fluorination of toluene, pure or dissolved in either acetonitrile or methanol, using elemental fluorine in gas/liquid microreactors.
289 citations
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TL;DR: A variety of gas-liquid microchannel reactions have been developed so far, using different contacting principles as discussed by the authors, such as segmented (Taylor) flow in a single microchannel or numbered-up versions such as the microbubble column; other flow patterns such as annular flow may be achieved as well.
Abstract: A variety of gas-liquid microchannel reactors have been developed so far, using different contacting principles. Some devices utilize continuous-phase contacting (i.e., nondispersed separate phases with large specific interfaces). Among these are microstructured falling film, overlapping channel, and mesh reactors. Dispersed-phase contacting is obtained when one of the phases is interdispersed into the other phase. Regular flow patterns are provided by the segmented (Taylor) flow in a single microchannel or numbered-up versions such as the microbubble column; other flow patterns such as annular flow may be achieved as well. Foam microreactors utilize a moving rigid 3-D bubble network at high gas content. Miniaturized packed-bed microreactors follow the paths of classical engineering by enabling trickle-bed operation. Because of the often highly regular flow pattern, not obtained in conventional gas-liquid contactors, an understanding of the underlying hydrodynamics and heat and mass transfer is crucial for optimal performance of all types of gas-liquid microstructural reactors. Several examples are given, including film-thickness measurements, flow-pattern maps, determination of mass-transfer coefficients, residence-time distributions, scale-out issues, etc. Numerous applications demonstrate the improved performance of gas-liquid microreactors. Among these are fluorinations, chlorinations, hydrogenations, sulfonations, photo-oxidations, etc. Recently, the scope of reactions has been widened, since there is now the possibility to carry out gas-liquid-solid processes in the same microreactors as used for noncatalytic reactions because of the development of catalyst washcoats and other materials deposited onto microchannels. Some relevant examples are given for illustration.
283 citations